rocksdb/table/block_based/block_based_table_reader.cc

//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include "table/block_based/block_based_table_reader.h"

#include <algorithm>
#include <array>
#include <limits>
#include <string>
#include <utility>
#include <vector>

#include "cache/cache_entry_roles.h"
#include "cache/sharded_cache.h"
#include "db/compaction/compaction_picker.h"
#include "db/dbformat.h"
#include "db/pinned_iterators_manager.h"
#include "file/file_prefetch_buffer.h"
#include "file/file_util.h"
#include "file/random_access_file_reader.h"
#include "logging/logging.h"
#include "monitoring/perf_context_imp.h"
#include "port/lang.h"
#include "rocksdb/cache.h"
#include "rocksdb/comparator.h"
#include "rocksdb/convenience.h"
#include "rocksdb/env.h"
#include "rocksdb/file_system.h"
#include "rocksdb/filter_policy.h"
#include "rocksdb/iterator.h"
#include "rocksdb/options.h"
#include "rocksdb/snapshot.h"
#include "rocksdb/statistics.h"
#include "rocksdb/system_clock.h"
#include "rocksdb/table.h"
#include "rocksdb/table_properties.h"
#include "rocksdb/trace_record.h"
#include "table/block_based/binary_search_index_reader.h"
#include "table/block_based/block.h"
#include "table/block_based/block_based_filter_block.h"
#include "table/block_based/block_based_table_factory.h"
#include "table/block_based/block_based_table_iterator.h"
#include "table/block_based/block_like_traits.h"
#include "table/block_based/block_prefix_index.h"
#include "table/block_based/block_type.h"
#include "table/block_based/filter_block.h"
#include "table/block_based/full_filter_block.h"
#include "table/block_based/hash_index_reader.h"
#include "table/block_based/partitioned_filter_block.h"
#include "table/block_based/partitioned_index_reader.h"
#include "table/block_fetcher.h"
#include "table/format.h"
#include "table/get_context.h"
#include "table/internal_iterator.h"
#include "table/meta_blocks.h"
#include "table/multiget_context.h"
#include "table/persistent_cache_helper.h"
#include "table/persistent_cache_options.h"
#include "table/sst_file_writer_collectors.h"
#include "table/two_level_iterator.h"
#include "test_util/sync_point.h"
#include "util/coding.h"
#include "util/crc32c.h"
#include "util/stop_watch.h"
#include "util/string_util.h"

namespace ROCKSDB_NAMESPACE {

extern const uint64_t kBlockBasedTableMagicNumber;
extern const std::string kHashIndexPrefixesBlock;
extern const std::string kHashIndexPrefixesMetadataBlock;

BlockBasedTable::~BlockBasedTable() {
  delete rep_;
}

std::atomic<uint64_t> BlockBasedTable::next_cache_key_id_(0);

namespace {
// Read the block identified by "handle" from "file".
// The only relevant option is options.verify_checksums for now.
// On failure return non-OK.
// On success fill *result and return OK - caller owns *result
// @param uncompression_dict Data for presetting the compression library's
//    dictionary.
template <typename TBlocklike>
Status ReadBlockFromFile(
    RandomAccessFileReader* file, FilePrefetchBuffer* prefetch_buffer,
    const Footer& footer, const ReadOptions& options, const BlockHandle& handle,
    std::unique_ptr<TBlocklike>* result, const ImmutableOptions& ioptions,
    bool do_uncompress, bool maybe_compressed, BlockType block_type,
    const UncompressionDict& uncompression_dict,
    const PersistentCacheOptions& cache_options, size_t read_amp_bytes_per_bit,
    MemoryAllocator* memory_allocator, bool for_compaction, bool using_zstd,
    const FilterPolicy* filter_policy) {
  assert(result);

  BlockContents contents;
  BlockFetcher block_fetcher(
      file, prefetch_buffer, footer, options, handle, &contents, ioptions,
      do_uncompress, maybe_compressed, block_type, uncompression_dict,
      cache_options, memory_allocator, nullptr, for_compaction);
  Status s = block_fetcher.ReadBlockContents();
  if (s.ok()) {
    result->reset(BlocklikeTraits<TBlocklike>::Create(
        std::move(contents), read_amp_bytes_per_bit, ioptions.stats, using_zstd,
        filter_policy));
  }

  return s;
}

// Release the cached entry and decrement its ref count.
// Do not force erase
void ReleaseCachedEntry(void* arg, void* h) {
  Cache* cache = reinterpret_cast<Cache*>(arg);
  Cache::Handle* handle = reinterpret_cast<Cache::Handle*>(h);
  cache->Release(handle, false /* force_erase */);
}

// For hash based index, return true if prefix_extractor and
// prefix_extractor_block mismatch, false otherwise. This flag will be used
// as total_order_seek via NewIndexIterator
bool PrefixExtractorChanged(const TableProperties* table_properties,
                            const SliceTransform* prefix_extractor) {
  // BlockBasedTableOptions::kHashSearch requires prefix_extractor to be set.
  // Turn off hash index in prefix_extractor is not set; if  prefix_extractor
  // is set but prefix_extractor_block is not set, also disable hash index
  if (prefix_extractor == nullptr || table_properties == nullptr ||
      table_properties->prefix_extractor_name.empty()) {
    return true;
  }

  // prefix_extractor and prefix_extractor_block are both non-empty
  if (table_properties->prefix_extractor_name != prefix_extractor->AsString()) {
    return true;
  } else {
    return false;
  }
}

CacheAllocationPtr CopyBufferToHeap(MemoryAllocator* allocator, Slice& buf) {
  CacheAllocationPtr heap_buf;
  heap_buf = AllocateBlock(buf.size(), allocator);
  memcpy(heap_buf.get(), buf.data(), buf.size());
  return heap_buf;
}
}  // namespace

void BlockBasedTable::UpdateCacheHitMetrics(BlockType block_type,
                                            GetContext* get_context,
                                            size_t usage) const {
  Statistics* const statistics = rep_->ioptions.stats;

  PERF_COUNTER_ADD(block_cache_hit_count, 1);
  PERF_COUNTER_BY_LEVEL_ADD(block_cache_hit_count, 1,
                            static_cast<uint32_t>(rep_->level));

  if (get_context) {
    ++get_context->get_context_stats_.num_cache_hit;
    get_context->get_context_stats_.num_cache_bytes_read += usage;
  } else {
    RecordTick(statistics, BLOCK_CACHE_HIT);
    RecordTick(statistics, BLOCK_CACHE_BYTES_READ, usage);
  }

  switch (block_type) {
    case BlockType::kFilter:
      PERF_COUNTER_ADD(block_cache_filter_hit_count, 1);

      if (get_context) {
        ++get_context->get_context_stats_.num_cache_filter_hit;
      } else {
        RecordTick(statistics, BLOCK_CACHE_FILTER_HIT);
      }
      break;

    case BlockType::kCompressionDictionary:
      // TODO: introduce perf counter for compression dictionary hit count
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_compression_dict_hit;
      } else {
        RecordTick(statistics, BLOCK_CACHE_COMPRESSION_DICT_HIT);
      }
      break;

    case BlockType::kIndex:
      PERF_COUNTER_ADD(block_cache_index_hit_count, 1);

      if (get_context) {
        ++get_context->get_context_stats_.num_cache_index_hit;
      } else {
        RecordTick(statistics, BLOCK_CACHE_INDEX_HIT);
      }
      break;

    default:
      // TODO: introduce dedicated tickers/statistics/counters
      // for range tombstones
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_data_hit;
      } else {
        RecordTick(statistics, BLOCK_CACHE_DATA_HIT);
      }
      break;
  }
}

void BlockBasedTable::UpdateCacheMissMetrics(BlockType block_type,
                                             GetContext* get_context) const {
  Statistics* const statistics = rep_->ioptions.stats;

  // TODO: introduce aggregate (not per-level) block cache miss count
  PERF_COUNTER_BY_LEVEL_ADD(block_cache_miss_count, 1,
                            static_cast<uint32_t>(rep_->level));

  if (get_context) {
    ++get_context->get_context_stats_.num_cache_miss;
  } else {
    RecordTick(statistics, BLOCK_CACHE_MISS);
  }

  // TODO: introduce perf counters for misses per block type
  switch (block_type) {
    case BlockType::kFilter:
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_filter_miss;
      } else {
        RecordTick(statistics, BLOCK_CACHE_FILTER_MISS);
      }
      break;

    case BlockType::kCompressionDictionary:
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_compression_dict_miss;
      } else {
        RecordTick(statistics, BLOCK_CACHE_COMPRESSION_DICT_MISS);
      }
      break;

    case BlockType::kIndex:
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_index_miss;
      } else {
        RecordTick(statistics, BLOCK_CACHE_INDEX_MISS);
      }
      break;

    default:
      // TODO: introduce dedicated tickers/statistics/counters
      // for range tombstones
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_data_miss;
      } else {
        RecordTick(statistics, BLOCK_CACHE_DATA_MISS);
      }
      break;
  }
}

void BlockBasedTable::UpdateCacheInsertionMetrics(
    BlockType block_type, GetContext* get_context, size_t usage, bool redundant,
    Statistics* const statistics) {
  // TODO: introduce perf counters for block cache insertions
  if (get_context) {
    ++get_context->get_context_stats_.num_cache_add;
    if (redundant) {
      ++get_context->get_context_stats_.num_cache_add_redundant;
    }
    get_context->get_context_stats_.num_cache_bytes_write += usage;
  } else {
    RecordTick(statistics, BLOCK_CACHE_ADD);
    if (redundant) {
      RecordTick(statistics, BLOCK_CACHE_ADD_REDUNDANT);
    }
    RecordTick(statistics, BLOCK_CACHE_BYTES_WRITE, usage);
  }

  switch (block_type) {
    case BlockType::kFilter:
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_filter_add;
        if (redundant) {
          ++get_context->get_context_stats_.num_cache_filter_add_redundant;
        }
        get_context->get_context_stats_.num_cache_filter_bytes_insert += usage;
      } else {
        RecordTick(statistics, BLOCK_CACHE_FILTER_ADD);
        if (redundant) {
          RecordTick(statistics, BLOCK_CACHE_FILTER_ADD_REDUNDANT);
        }
        RecordTick(statistics, BLOCK_CACHE_FILTER_BYTES_INSERT, usage);
      }
      break;

    case BlockType::kCompressionDictionary:
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_compression_dict_add;
        if (redundant) {
          ++get_context->get_context_stats_
                .num_cache_compression_dict_add_redundant;
        }
        get_context->get_context_stats_
            .num_cache_compression_dict_bytes_insert += usage;
      } else {
        RecordTick(statistics, BLOCK_CACHE_COMPRESSION_DICT_ADD);
        if (redundant) {
          RecordTick(statistics, BLOCK_CACHE_COMPRESSION_DICT_ADD_REDUNDANT);
        }
        RecordTick(statistics, BLOCK_CACHE_COMPRESSION_DICT_BYTES_INSERT,
                   usage);
      }
      break;

    case BlockType::kIndex:
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_index_add;
        if (redundant) {
          ++get_context->get_context_stats_.num_cache_index_add_redundant;
        }
        get_context->get_context_stats_.num_cache_index_bytes_insert += usage;
      } else {
        RecordTick(statistics, BLOCK_CACHE_INDEX_ADD);
        if (redundant) {
          RecordTick(statistics, BLOCK_CACHE_INDEX_ADD_REDUNDANT);
        }
        RecordTick(statistics, BLOCK_CACHE_INDEX_BYTES_INSERT, usage);
      }
      break;

    default:
      // TODO: introduce dedicated tickers/statistics/counters
      // for range tombstones
      if (get_context) {
        ++get_context->get_context_stats_.num_cache_data_add;
        if (redundant) {
          ++get_context->get_context_stats_.num_cache_data_add_redundant;
        }
        get_context->get_context_stats_.num_cache_data_bytes_insert += usage;
      } else {
        RecordTick(statistics, BLOCK_CACHE_DATA_ADD);
        if (redundant) {
          RecordTick(statistics, BLOCK_CACHE_DATA_ADD_REDUNDANT);
        }
        RecordTick(statistics, BLOCK_CACHE_DATA_BYTES_INSERT, usage);
      }
      break;
  }
}

Cache::Handle* BlockBasedTable::GetEntryFromCache(
    const CacheTier& cache_tier, Cache* block_cache, const Slice& key,
    BlockType block_type, const bool wait, GetContext* get_context,
    const Cache::CacheItemHelper* cache_helper,
    const Cache::CreateCallback& create_cb, Cache::Priority priority) const {
  Cache::Handle* cache_handle = nullptr;
  if (cache_tier == CacheTier::kNonVolatileBlockTier) {
    cache_handle = block_cache->Lookup(key, cache_helper, create_cb, priority,
                                       wait, rep_->ioptions.statistics.get());
  } else {
    cache_handle = block_cache->Lookup(key, rep_->ioptions.statistics.get());
  }

  if (cache_handle != nullptr) {
    UpdateCacheHitMetrics(block_type, get_context,
                          block_cache->GetUsage(cache_handle));
  } else {
    UpdateCacheMissMetrics(block_type, get_context);
  }

  return cache_handle;
}

template <typename TBlocklike>
Status BlockBasedTable::InsertEntryToCache(
    const CacheTier& cache_tier, Cache* block_cache, const Slice& key,
    const Cache::CacheItemHelper* cache_helper,
    std::unique_ptr<TBlocklike>& block_holder, size_t charge,
    Cache::Handle** cache_handle, Cache::Priority priority) const {
  Status s = Status::OK();
  if (cache_tier == CacheTier::kNonVolatileBlockTier) {
    s = block_cache->Insert(key, block_holder.get(), cache_helper, charge,
                            cache_handle, priority);
  } else {
    s = block_cache->Insert(key, block_holder.get(), charge,
                            cache_helper->del_cb, cache_handle, priority);
  }
  return s;
}

// Helper function to setup the cache key's prefix for the Table.
void BlockBasedTable::SetupCacheKeyPrefix(Rep* rep,
                                          const std::string& db_session_id,
                                          uint64_t file_num) {
  assert(kMaxCacheKeyPrefixSize >= 10);
  rep->cache_key_prefix_size = 0;
  rep->compressed_cache_key_prefix_size = 0;
  if (rep->table_options.block_cache != nullptr) {
    GenerateCachePrefix<Cache, FSRandomAccessFile>(
        rep->table_options.block_cache.get(), rep->file->file(),
        &rep->cache_key_prefix[0], &rep->cache_key_prefix_size, db_session_id,
        file_num);
  }
  if (rep->table_options.block_cache_compressed != nullptr) {
    GenerateCachePrefix<Cache, FSRandomAccessFile>(
        rep->table_options.block_cache_compressed.get(), rep->file->file(),
        &rep->compressed_cache_key_prefix[0],
        &rep->compressed_cache_key_prefix_size, db_session_id, file_num);
  }
  if (rep->table_options.persistent_cache != nullptr) {
    char persistent_cache_key_prefix[kMaxCacheKeyPrefixSize];
    size_t persistent_cache_key_prefix_size = 0;

    GenerateCachePrefix<PersistentCache, FSRandomAccessFile>(
        rep->table_options.persistent_cache.get(), rep->file->file(),
        &persistent_cache_key_prefix[0], &persistent_cache_key_prefix_size,
        db_session_id, file_num);

    rep->persistent_cache_options =
        PersistentCacheOptions(rep->table_options.persistent_cache,
                               std::string(persistent_cache_key_prefix,
                                           persistent_cache_key_prefix_size),
                               rep->ioptions.stats);
  }
}

namespace {
// Return True if table_properties has `user_prop_name` has a `true` value
// or it doesn't contain this property (for backward compatible).
bool IsFeatureSupported(const TableProperties& table_properties,
                        const std::string& user_prop_name, Logger* info_log) {
  auto& props = table_properties.user_collected_properties;
  auto pos = props.find(user_prop_name);
  // Older version doesn't have this value set. Skip this check.
  if (pos != props.end()) {
    if (pos->second == kPropFalse) {
      return false;
    } else if (pos->second != kPropTrue) {
      ROCKS_LOG_WARN(info_log, "Property %s has invalidate value %s",
                     user_prop_name.c_str(), pos->second.c_str());
    }
  }
  return true;
}

// Caller has to ensure seqno is not nullptr.
Status GetGlobalSequenceNumber(const TableProperties& table_properties,
                               SequenceNumber largest_seqno,
                               SequenceNumber* seqno) {
  const auto& props = table_properties.user_collected_properties;
  const auto version_pos = props.find(ExternalSstFilePropertyNames::kVersion);
  const auto seqno_pos = props.find(ExternalSstFilePropertyNames::kGlobalSeqno);

  *seqno = kDisableGlobalSequenceNumber;
  if (version_pos == props.end()) {
    if (seqno_pos != props.end()) {
      std::array<char, 200> msg_buf;
      // This is not an external sst file, global_seqno is not supported.
      snprintf(
          msg_buf.data(), msg_buf.max_size(),
          "A non-external sst file have global seqno property with value %s",
          seqno_pos->second.c_str());
      return Status::Corruption(msg_buf.data());
    }
    return Status::OK();
  }

  uint32_t version = DecodeFixed32(version_pos->second.c_str());
  if (version < 2) {
    if (seqno_pos != props.end() || version != 1) {
      std::array<char, 200> msg_buf;
      // This is a v1 external sst file, global_seqno is not supported.
      snprintf(msg_buf.data(), msg_buf.max_size(),
               "An external sst file with version %u have global seqno "
               "property with value %s",
               version, seqno_pos->second.c_str());
      return Status::Corruption(msg_buf.data());
    }
    return Status::OK();
  }

  // Since we have a plan to deprecate global_seqno, we do not return failure
  // if seqno_pos == props.end(). We rely on version_pos to detect whether the
  // SST is external.
  SequenceNumber global_seqno(0);
  if (seqno_pos != props.end()) {
    global_seqno = DecodeFixed64(seqno_pos->second.c_str());
  }
  // SstTableReader open table reader with kMaxSequenceNumber as largest_seqno
  // to denote it is unknown.
  if (largest_seqno < kMaxSequenceNumber) {
    if (global_seqno == 0) {
      global_seqno = largest_seqno;
    }
    if (global_seqno != largest_seqno) {
      std::array<char, 200> msg_buf;
      snprintf(
          msg_buf.data(), msg_buf.max_size(),
          "An external sst file with version %u have global seqno property "
          "with value %s, while largest seqno in the file is %llu",
          version, seqno_pos->second.c_str(),
          static_cast<unsigned long long>(largest_seqno));
      return Status::Corruption(msg_buf.data());
    }
  }
  *seqno = global_seqno;

  if (global_seqno > kMaxSequenceNumber) {
    std::array<char, 200> msg_buf;
    snprintf(msg_buf.data(), msg_buf.max_size(),
             "An external sst file with version %u have global seqno property "
             "with value %llu, which is greater than kMaxSequenceNumber",
             version, static_cast<unsigned long long>(global_seqno));
    return Status::Corruption(msg_buf.data());
  }

  return Status::OK();
}
}  // namespace

Slice BlockBasedTable::GetCacheKey(const char* cache_key_prefix,
                                   size_t cache_key_prefix_size,
                                   const BlockHandle& handle, char* cache_key) {
  assert(cache_key != nullptr);
  assert(cache_key_prefix_size != 0);
  assert(cache_key_prefix_size <= kMaxCacheKeyPrefixSize);
  memcpy(cache_key, cache_key_prefix, cache_key_prefix_size);
  char* end =
      EncodeVarint64(cache_key + cache_key_prefix_size, handle.offset());
  return Slice(cache_key, static_cast<size_t>(end - cache_key));
}

Status BlockBasedTable::Open(
    const ReadOptions& read_options, const ImmutableOptions& ioptions,
    const EnvOptions& env_options, const BlockBasedTableOptions& table_options,
    const InternalKeyComparator& internal_comparator,
    std::unique_ptr<RandomAccessFileReader>&& file, uint64_t file_size,
    std::unique_ptr<TableReader>* table_reader,
    const SliceTransform* prefix_extractor,
    const bool prefetch_index_and_filter_in_cache, const bool skip_filters,
    const int level, const bool immortal_table,
    const SequenceNumber largest_seqno, const bool force_direct_prefetch,
    TailPrefetchStats* tail_prefetch_stats,
    BlockCacheTracer* const block_cache_tracer,
    size_t max_file_size_for_l0_meta_pin, const std::string& cur_db_session_id,
    uint64_t cur_file_num) {
  table_reader->reset();

  Status s;
  Footer footer;
  std::unique_ptr<FilePrefetchBuffer> prefetch_buffer;

  // Only retain read_options.deadline and read_options.io_timeout.
  // In future, we may retain more
  // options. Specifically, w ignore verify_checksums and default to
  // checksum verification anyway when creating the index and filter
  // readers.
  ReadOptions ro;
  ro.deadline = read_options.deadline;
  ro.io_timeout = read_options.io_timeout;

  // prefetch both index and filters, down to all partitions
  const bool prefetch_all = prefetch_index_and_filter_in_cache || level == 0;
  const bool preload_all = !table_options.cache_index_and_filter_blocks;

  if (!ioptions.allow_mmap_reads) {
    s = PrefetchTail(ro, file.get(), file_size, force_direct_prefetch,
                     tail_prefetch_stats, prefetch_all, preload_all,
                     &prefetch_buffer);
    // Return error in prefetch path to users.
    if (!s.ok()) {
      return s;
    }
  } else {
    // Should not prefetch for mmap mode.
    prefetch_buffer.reset(new FilePrefetchBuffer(
        nullptr, 0, 0, false /* enable */, true /* track_min_offset */));
  }

  // Read in the following order:
  //    1. Footer
  //    2. [metaindex block]
  //    3. [meta block: properties]
  //    4. [meta block: range deletion tombstone]
  //    5. [meta block: compression dictionary]
  //    6. [meta block: index]
  //    7. [meta block: filter]
  IOOptions opts;
  s = file->PrepareIOOptions(ro, opts);
  if (s.ok()) {
    s = ReadFooterFromFile(opts, file.get(), prefetch_buffer.get(), file_size,
                           &footer, kBlockBasedTableMagicNumber);
  }
  if (!s.ok()) {
    return s;
  }
  if (!BlockBasedTableSupportedVersion(footer.version())) {
    return Status::Corruption(
        "Unknown Footer version. Maybe this file was created with newer "
        "version of RocksDB?");
  }

  // We've successfully read the footer. We are ready to serve requests.
  // Better not mutate rep_ after the creation. eg. internal_prefix_transform
  // raw pointer will be used to create HashIndexReader, whose reset may
  // access a dangling pointer.
  BlockCacheLookupContext lookup_context{TableReaderCaller::kPrefetch};
  Rep* rep = new BlockBasedTable::Rep(ioptions, env_options, table_options,
                                      internal_comparator, skip_filters,
                                      file_size, level, immortal_table);
  rep->file = std::move(file);
  rep->footer = footer;
  rep->hash_index_allow_collision = table_options.hash_index_allow_collision;
  // We need to wrap data with internal_prefix_transform to make sure it can
  // handle prefix correctly.
  if (prefix_extractor != nullptr) {
    rep->internal_prefix_transform.reset(
        new InternalKeySliceTransform(prefix_extractor));
  }

  // For fully portable/stable cache keys, we need to read the properties
  // block before setting up cache keys. TODO: consider setting up a bootstrap
  // cache key for PersistentCache to use for metaindex and properties blocks.
  rep->persistent_cache_options = PersistentCacheOptions();

  // Meta-blocks are not dictionary compressed. Explicitly set the dictionary
  // handle to null, otherwise it may be seen as uninitialized during the below
  // meta-block reads.
  rep->compression_dict_handle = BlockHandle::NullBlockHandle();

  // Read metaindex
  std::unique_ptr<BlockBasedTable> new_table(
      new BlockBasedTable(rep, block_cache_tracer));
  std::unique_ptr<Block> metaindex;
  std::unique_ptr<InternalIterator> metaindex_iter;
  s = new_table->ReadMetaIndexBlock(ro, prefetch_buffer.get(), &metaindex,
                                    &metaindex_iter);
  if (!s.ok()) {
    return s;
  }

  // Populates table_properties and some fields that depend on it,
  // such as index_type.
  s = new_table->ReadPropertiesBlock(ro, prefetch_buffer.get(),
                                     metaindex_iter.get(), largest_seqno);
  if (!s.ok()) {
    return s;
  }

  // With properties loaded, we can set up portable/stable cache keys if
  // necessary info is available
  std::string db_session_id;
  uint64_t file_num;
  if (rep->table_properties && !rep->table_properties->db_session_id.empty() &&
      rep->table_properties->orig_file_number > 0) {
    // We must have both properties to get a stable unique id because
    // CreateColumnFamilyWithImport or IngestExternalFiles can change the
    // file numbers on a file.
    db_session_id = rep->table_properties->db_session_id;
    file_num = rep->table_properties->orig_file_number;
  } else {
    // We have to use transient (but unique) cache keys based on current
    // identifiers.
    db_session_id = cur_db_session_id;
    file_num = cur_file_num;
  }
  SetupCacheKeyPrefix(rep, db_session_id, file_num);

  s = new_table->ReadRangeDelBlock(ro, prefetch_buffer.get(),
                                   metaindex_iter.get(), internal_comparator,
                                   &lookup_context);
  if (!s.ok()) {
    return s;
  }
  s = new_table->PrefetchIndexAndFilterBlocks(
      ro, prefetch_buffer.get(), metaindex_iter.get(), new_table.get(),
      prefetch_all, table_options, level, file_size,
      max_file_size_for_l0_meta_pin, &lookup_context);

  if (s.ok()) {
    // Update tail prefetch stats
    assert(prefetch_buffer.get() != nullptr);
    if (tail_prefetch_stats != nullptr) {
      assert(prefetch_buffer->min_offset_read() < file_size);
      tail_prefetch_stats->RecordEffectiveSize(
          static_cast<size_t>(file_size) - prefetch_buffer->min_offset_read());
    }

    *table_reader = std::move(new_table);
  }

  return s;
}

Status BlockBasedTable::PrefetchTail(
    const ReadOptions& ro, RandomAccessFileReader* file, uint64_t file_size,
    bool force_direct_prefetch, TailPrefetchStats* tail_prefetch_stats,
    const bool prefetch_all, const bool preload_all,
    std::unique_ptr<FilePrefetchBuffer>* prefetch_buffer) {
  size_t tail_prefetch_size = 0;
  if (tail_prefetch_stats != nullptr) {
    // Multiple threads may get a 0 (no history) when running in parallel,
    // but it will get cleared after the first of them finishes.
    tail_prefetch_size = tail_prefetch_stats->GetSuggestedPrefetchSize();
  }
  if (tail_prefetch_size == 0) {
    // Before read footer, readahead backwards to prefetch data. Do more
    // readahead if we're going to read index/filter.
    // TODO: This may incorrectly select small readahead in case partitioned
    // index/filter is enabled and top-level partition pinning is enabled.
    // That's because we need to issue readahead before we read the properties,
    // at which point we don't yet know the index type.
    tail_prefetch_size = prefetch_all || preload_all ? 512 * 1024 : 4 * 1024;
  }
  size_t prefetch_off;
  size_t prefetch_len;
  if (file_size < tail_prefetch_size) {
    prefetch_off = 0;
    prefetch_len = static_cast<size_t>(file_size);
  } else {
    prefetch_off = static_cast<size_t>(file_size - tail_prefetch_size);
    prefetch_len = tail_prefetch_size;
  }
  TEST_SYNC_POINT_CALLBACK("BlockBasedTable::Open::TailPrefetchLen",
                           &tail_prefetch_size);

  // Try file system prefetch
  if (!file->use_direct_io() && !force_direct_prefetch) {
    if (!file->Prefetch(prefetch_off, prefetch_len).IsNotSupported()) {
      prefetch_buffer->reset(
          new FilePrefetchBuffer(nullptr, 0, 0, false, true));
      return Status::OK();
    }
  }

  // Use `FilePrefetchBuffer`
  prefetch_buffer->reset(new FilePrefetchBuffer(nullptr, 0, 0, true, true));
  IOOptions opts;
  Status s = file->PrepareIOOptions(ro, opts);
  if (s.ok()) {
    s = (*prefetch_buffer)->Prefetch(opts, file, prefetch_off, prefetch_len);
  }
  return s;
}

Status BlockBasedTable::ReadPropertiesBlock(
    const ReadOptions& ro, FilePrefetchBuffer* prefetch_buffer,
    InternalIterator* meta_iter, const SequenceNumber largest_seqno) {
  Status s;
  BlockHandle handle;
  s = FindOptionalMetaBlock(meta_iter, kPropertiesBlock, &handle);

  if (!s.ok()) {
    ROCKS_LOG_WARN(rep_->ioptions.logger,
                   "Error when seeking to properties block from file: %s",
                   s.ToString().c_str());
  } else if (!handle.IsNull()) {
    s = meta_iter->status();
    std::unique_ptr<TableProperties> table_properties;
    if (s.ok()) {
      s = ReadTablePropertiesHelper(
          ro, handle, rep_->file.get(), prefetch_buffer, rep_->footer,
          rep_->ioptions, &table_properties, nullptr /* memory_allocator */);
    }
    IGNORE_STATUS_IF_ERROR(s);

    if (!s.ok()) {
      ROCKS_LOG_WARN(rep_->ioptions.logger,
                     "Encountered error while reading data from properties "
                     "block %s",
                     s.ToString().c_str());
    } else {
      assert(table_properties != nullptr);
      rep_->table_properties = std::move(table_properties);
      rep_->blocks_maybe_compressed =
          rep_->table_properties->compression_name !=
          CompressionTypeToString(kNoCompression);
      rep_->blocks_definitely_zstd_compressed =
          (rep_->table_properties->compression_name ==
               CompressionTypeToString(kZSTD) ||
           rep_->table_properties->compression_name ==
               CompressionTypeToString(kZSTDNotFinalCompression));
    }
  } else {
    ROCKS_LOG_ERROR(rep_->ioptions.logger,
                    "Cannot find Properties block from file.");
  }
#ifndef ROCKSDB_LITE
  if (rep_->table_properties) {
    //**TODO: If/When the DBOptions has a registry in it, the ConfigOptions
    // will need to use it
    ConfigOptions config_options;
    Status st = SliceTransform::CreateFromString(
        config_options, rep_->table_properties->prefix_extractor_name,
        &(rep_->table_prefix_extractor));
    if (!st.ok()) {
      //**TODO: Should this be error be returned or swallowed?
      ROCKS_LOG_ERROR(rep_->ioptions.logger,
                      "Failed to create prefix extractor[%s]: %s",
                      rep_->table_properties->prefix_extractor_name.c_str(),
                      st.ToString().c_str());
    }
  }
#endif  // ROCKSDB_LITE

  // Read the table properties, if provided.
  if (rep_->table_properties) {
    rep_->whole_key_filtering &=
        IsFeatureSupported(*(rep_->table_properties),
                           BlockBasedTablePropertyNames::kWholeKeyFiltering,
                           rep_->ioptions.logger);
    rep_->prefix_filtering &= IsFeatureSupported(
        *(rep_->table_properties),
        BlockBasedTablePropertyNames::kPrefixFiltering, rep_->ioptions.logger);

    rep_->index_key_includes_seq =
        rep_->table_properties->index_key_is_user_key == 0;
    rep_->index_value_is_full =
        rep_->table_properties->index_value_is_delta_encoded == 0;

    // Update index_type with the true type.
    // If table properties don't contain index type, we assume that the table
    // is in very old format and has kBinarySearch index type.
    auto& props = rep_->table_properties->user_collected_properties;
    auto pos = props.find(BlockBasedTablePropertyNames::kIndexType);
    if (pos != props.end()) {
      rep_->index_type = static_cast<BlockBasedTableOptions::IndexType>(
          DecodeFixed32(pos->second.c_str()));
    }

    rep_->index_has_first_key =
        rep_->index_type == BlockBasedTableOptions::kBinarySearchWithFirstKey;

    s = GetGlobalSequenceNumber(*(rep_->table_properties), largest_seqno,
                                &(rep_->global_seqno));
    if (!s.ok()) {
      ROCKS_LOG_ERROR(rep_->ioptions.logger, "%s", s.ToString().c_str());
    }
  }
  return s;
}

Status BlockBasedTable::ReadRangeDelBlock(
    const ReadOptions& read_options, FilePrefetchBuffer* prefetch_buffer,
    InternalIterator* meta_iter,
    const InternalKeyComparator& internal_comparator,
    BlockCacheLookupContext* lookup_context) {
  Status s;
  BlockHandle range_del_handle;
  s = FindOptionalMetaBlock(meta_iter, kRangeDelBlock, &range_del_handle);
  if (!s.ok()) {
    ROCKS_LOG_WARN(
        rep_->ioptions.logger,
        "Error when seeking to range delete tombstones block from file: %s",
        s.ToString().c_str());
  } else if (!range_del_handle.IsNull()) {
    std::unique_ptr<InternalIterator> iter(NewDataBlockIterator<DataBlockIter>(
        read_options, range_del_handle,
        /*input_iter=*/nullptr, BlockType::kRangeDeletion,
        /*get_context=*/nullptr, lookup_context, Status(), prefetch_buffer));
    assert(iter != nullptr);
    s = iter->status();
    if (!s.ok()) {
      ROCKS_LOG_WARN(
          rep_->ioptions.logger,
          "Encountered error while reading data from range del block %s",
          s.ToString().c_str());
      IGNORE_STATUS_IF_ERROR(s);
    } else {
      rep_->fragmented_range_dels =
          std::make_shared<FragmentedRangeTombstoneList>(std::move(iter),
                                                         internal_comparator);
    }
  }
  return s;
}

Status BlockBasedTable::PrefetchIndexAndFilterBlocks(
    const ReadOptions& ro, FilePrefetchBuffer* prefetch_buffer,
    InternalIterator* meta_iter, BlockBasedTable* new_table, bool prefetch_all,
    const BlockBasedTableOptions& table_options, const int level,
    size_t file_size, size_t max_file_size_for_l0_meta_pin,
    BlockCacheLookupContext* lookup_context) {
  Status s;

  // Find filter handle and filter type
  if (rep_->filter_policy) {
    for (auto filter_type :
         {Rep::FilterType::kFullFilter, Rep::FilterType::kPartitionedFilter,
          Rep::FilterType::kBlockFilter}) {
      std::string prefix;
      switch (filter_type) {
        case Rep::FilterType::kFullFilter:
          prefix = kFullFilterBlockPrefix;
          break;
        case Rep::FilterType::kPartitionedFilter:
          prefix = kPartitionedFilterBlockPrefix;
          break;
        case Rep::FilterType::kBlockFilter:
          prefix = kFilterBlockPrefix;
          break;
        default:
          assert(0);
      }
      std::string filter_block_key = prefix;
      filter_block_key.append(rep_->filter_policy->Name());
      if (FindMetaBlock(meta_iter, filter_block_key, &rep_->filter_handle)
              .ok()) {
        rep_->filter_type = filter_type;
        break;
      }
    }
  }
  // Partition filters cannot be enabled without partition indexes
  assert(rep_->filter_type != Rep::FilterType::kPartitionedFilter ||
         rep_->index_type == BlockBasedTableOptions::kTwoLevelIndexSearch);

  // Find compression dictionary handle
  s = FindOptionalMetaBlock(meta_iter, kCompressionDictBlock,
                            &rep_->compression_dict_handle);
  if (!s.ok()) {
    return s;
  }

  BlockBasedTableOptions::IndexType index_type = rep_->index_type;

  const bool use_cache = table_options.cache_index_and_filter_blocks;

  const bool maybe_flushed =
      level == 0 && file_size <= max_file_size_for_l0_meta_pin;
  std::function<bool(PinningTier, PinningTier)> is_pinned =
      [maybe_flushed, &is_pinned](PinningTier pinning_tier,
                                  PinningTier fallback_pinning_tier) {
        // Fallback to fallback would lead to infinite recursion. Disallow it.
        assert(fallback_pinning_tier != PinningTier::kFallback);

        switch (pinning_tier) {
          case PinningTier::kFallback:
            return is_pinned(fallback_pinning_tier,
                             PinningTier::kNone /* fallback_pinning_tier */);
          case PinningTier::kNone:
            return false;
          case PinningTier::kFlushedAndSimilar:
            return maybe_flushed;
          case PinningTier::kAll:
            return true;
        };

        // In GCC, this is needed to suppress `control reaches end of non-void
        // function [-Werror=return-type]`.
        assert(false);
        return false;
      };
  const bool pin_top_level_index = is_pinned(
      table_options.metadata_cache_options.top_level_index_pinning,
      table_options.pin_top_level_index_and_filter ? PinningTier::kAll
                                                   : PinningTier::kNone);
  const bool pin_partition =
      is_pinned(table_options.metadata_cache_options.partition_pinning,
                table_options.pin_l0_filter_and_index_blocks_in_cache
                    ? PinningTier::kFlushedAndSimilar
                    : PinningTier::kNone);
  const bool pin_unpartitioned =
      is_pinned(table_options.metadata_cache_options.unpartitioned_pinning,
                table_options.pin_l0_filter_and_index_blocks_in_cache
                    ? PinningTier::kFlushedAndSimilar
                    : PinningTier::kNone);

  // pin the first level of index
  const bool pin_index =
      index_type == BlockBasedTableOptions::kTwoLevelIndexSearch
          ? pin_top_level_index
          : pin_unpartitioned;
  // prefetch the first level of index
  // WART: this might be redundant (unnecessary cache hit) if !pin_index,
  // depending on prepopulate_block_cache option
  const bool prefetch_index = prefetch_all || pin_index;

  std::unique_ptr<IndexReader> index_reader;
  s = new_table->CreateIndexReader(ro, prefetch_buffer, meta_iter, use_cache,
                                   prefetch_index, pin_index, lookup_context,
                                   &index_reader);
  if (!s.ok()) {
    return s;
  }

  rep_->index_reader = std::move(index_reader);

  // The partitions of partitioned index are always stored in cache. They
  // are hence follow the configuration for pin and prefetch regardless of
  // the value of cache_index_and_filter_blocks
  if (prefetch_all || pin_partition) {
    s = rep_->index_reader->CacheDependencies(ro, pin_partition);
  }
  if (!s.ok()) {
    return s;
  }

  // pin the first level of filter
  const bool pin_filter =
      rep_->filter_type == Rep::FilterType::kPartitionedFilter
          ? pin_top_level_index
          : pin_unpartitioned;
  // prefetch the first level of filter
  // WART: this might be redundant (unnecessary cache hit) if !pin_filter,
  // depending on prepopulate_block_cache option
  const bool prefetch_filter = prefetch_all || pin_filter;

  if (rep_->filter_policy) {
    auto filter = new_table->CreateFilterBlockReader(
        ro, prefetch_buffer, use_cache, prefetch_filter, pin_filter,
        lookup_context);

    if (filter) {
      // Refer to the comment above about paritioned indexes always being cached
      if (prefetch_all || pin_partition) {
        s = filter->CacheDependencies(ro, pin_partition);
        if (!s.ok()) {
          return s;
        }
      }
      rep_->filter = std::move(filter);
    }
  }

  if (!rep_->compression_dict_handle.IsNull()) {
    std::unique_ptr<UncompressionDictReader> uncompression_dict_reader;
    s = UncompressionDictReader::Create(
        this, ro, prefetch_buffer, use_cache, prefetch_all || pin_unpartitioned,
        pin_unpartitioned, lookup_context, &uncompression_dict_reader);
    if (!s.ok()) {
      return s;
    }

    rep_->uncompression_dict_reader = std::move(uncompression_dict_reader);
  }

  assert(s.ok());
  return s;
}

void BlockBasedTable::SetupForCompaction() {
  switch (rep_->ioptions.access_hint_on_compaction_start) {
    case Options::NONE:
      break;
    case Options::NORMAL:
      rep_->file->file()->Hint(FSRandomAccessFile::kNormal);
      break;
    case Options::SEQUENTIAL:
      rep_->file->file()->Hint(FSRandomAccessFile::kSequential);
      break;
    case Options::WILLNEED:
      rep_->file->file()->Hint(FSRandomAccessFile::kWillNeed);
      break;
    default:
      assert(false);
  }
}

std::shared_ptr<const TableProperties> BlockBasedTable::GetTableProperties()
    const {
  return rep_->table_properties;
}

size_t BlockBasedTable::ApproximateMemoryUsage() const {
  size_t usage = 0;
  if (rep_->filter) {
    usage += rep_->filter->ApproximateMemoryUsage();
  }
  if (rep_->index_reader) {
    usage += rep_->index_reader->ApproximateMemoryUsage();
  }
  if (rep_->uncompression_dict_reader) {
    usage += rep_->uncompression_dict_reader->ApproximateMemoryUsage();
  }
  return usage;
}

// Load the meta-index-block from the file. On success, return the loaded
// metaindex
// block and its iterator.
Status BlockBasedTable::ReadMetaIndexBlock(
    const ReadOptions& ro, FilePrefetchBuffer* prefetch_buffer,
    std::unique_ptr<Block>* metaindex_block,
    std::unique_ptr<InternalIterator>* iter) {
  // TODO(sanjay): Skip this if footer.metaindex_handle() size indicates
  // it is an empty block.
  std::unique_ptr<Block> metaindex;
  Status s = ReadBlockFromFile(
      rep_->file.get(), prefetch_buffer, rep_->footer, ro,
      rep_->footer.metaindex_handle(), &metaindex, rep_->ioptions,
      true /* decompress */, true /*maybe_compressed*/, BlockType::kMetaIndex,
      UncompressionDict::GetEmptyDict(), rep_->persistent_cache_options,
      0 /* read_amp_bytes_per_bit */, GetMemoryAllocator(rep_->table_options),
      false /* for_compaction */, rep_->blocks_definitely_zstd_compressed,
      nullptr /* filter_policy */);

  if (!s.ok()) {
    ROCKS_LOG_ERROR(rep_->ioptions.logger,
                    "Encountered error while reading data from properties"
                    " block %s",
                    s.ToString().c_str());
    return s;
  }

  *metaindex_block = std::move(metaindex);
  // meta block uses bytewise comparator.
  iter->reset(metaindex_block->get()->NewDataIterator(
      BytewiseComparator(), kDisableGlobalSequenceNumber));
  return Status::OK();
}

template <typename TBlocklike>
Status BlockBasedTable::GetDataBlockFromCache(
    const Slice& block_cache_key, const Slice& compressed_block_cache_key,
    Cache* block_cache, Cache* block_cache_compressed,
    const ReadOptions& read_options, CachableEntry<TBlocklike>* block,
    const UncompressionDict& uncompression_dict, BlockType block_type,
    const bool wait, GetContext* get_context) const {
  const size_t read_amp_bytes_per_bit =
      block_type == BlockType::kData
          ? rep_->table_options.read_amp_bytes_per_bit
          : 0;
  assert(block);
  assert(block->IsEmpty());
  const Cache::Priority priority =
      rep_->table_options.cache_index_and_filter_blocks_with_high_priority &&
              (block_type == BlockType::kFilter ||
               block_type == BlockType::kCompressionDictionary ||
               block_type == BlockType::kIndex)
          ? Cache::Priority::HIGH
          : Cache::Priority::LOW;

  Status s;
  BlockContents* compressed_block = nullptr;
  Cache::Handle* block_cache_compressed_handle = nullptr;
  Statistics* statistics = rep_->ioptions.statistics.get();
  bool using_zstd = rep_->blocks_definitely_zstd_compressed;
  const FilterPolicy* filter_policy = rep_->filter_policy;
  Cache::CreateCallback create_cb = GetCreateCallback<TBlocklike>(
      read_amp_bytes_per_bit, statistics, using_zstd, filter_policy);

  // Lookup uncompressed cache first
  if (block_cache != nullptr) {
    Cache::Handle* cache_handle = nullptr;
    cache_handle = GetEntryFromCache(
        rep_->ioptions.lowest_used_cache_tier, block_cache, block_cache_key,
        block_type, wait, get_context,
        BlocklikeTraits<TBlocklike>::GetCacheItemHelper(block_type), create_cb,
        priority);
    if (cache_handle != nullptr) {
      block->SetCachedValue(
          reinterpret_cast<TBlocklike*>(block_cache->Value(cache_handle)),
          block_cache, cache_handle);
      return s;
    }
  }

  // If not found, search from the compressed block cache.
  assert(block->IsEmpty());

  if (block_cache_compressed == nullptr) {
    return s;
  }

  assert(!compressed_block_cache_key.empty());
  BlockContents contents;
  if (rep_->ioptions.lowest_used_cache_tier ==
      CacheTier::kNonVolatileBlockTier) {
    Cache::CreateCallback create_cb_special = GetCreateCallback<BlockContents>(
        read_amp_bytes_per_bit, statistics, using_zstd, filter_policy);
    block_cache_compressed_handle = block_cache_compressed->Lookup(
        compressed_block_cache_key,
        BlocklikeTraits<BlockContents>::GetCacheItemHelper(block_type),
        create_cb_special, priority, true);
  } else {
    block_cache_compressed_handle =
        block_cache_compressed->Lookup(compressed_block_cache_key, statistics);
  }

  // if we found in the compressed cache, then uncompress and insert into
  // uncompressed cache
  if (block_cache_compressed_handle == nullptr) {
    RecordTick(statistics, BLOCK_CACHE_COMPRESSED_MISS);
    return s;
  }

  // found compressed block
  RecordTick(statistics, BLOCK_CACHE_COMPRESSED_HIT);
  compressed_block = reinterpret_cast<BlockContents*>(
      block_cache_compressed->Value(block_cache_compressed_handle));
  CompressionType compression_type = GetBlockCompressionType(*compressed_block);
  assert(compression_type != kNoCompression);

  // Retrieve the uncompressed contents into a new buffer
  UncompressionContext context(compression_type);
  UncompressionInfo info(context, uncompression_dict, compression_type);
  s = UncompressBlockContents(
      info, compressed_block->data.data(), compressed_block->data.size(),
      &contents, rep_->table_options.format_version, rep_->ioptions,
      GetMemoryAllocator(rep_->table_options));

  // Insert uncompressed block into block cache, the priority is based on the
  // data block type.
  if (s.ok()) {
    std::unique_ptr<TBlocklike> block_holder(
        BlocklikeTraits<TBlocklike>::Create(
            std::move(contents), read_amp_bytes_per_bit, statistics,
            rep_->blocks_definitely_zstd_compressed,
            rep_->table_options.filter_policy.get()));  // uncompressed block

    if (block_cache != nullptr && block_holder->own_bytes() &&
        read_options.fill_cache) {
      size_t charge = block_holder->ApproximateMemoryUsage();
      Cache::Handle* cache_handle = nullptr;
      s = InsertEntryToCache(
          rep_->ioptions.lowest_used_cache_tier, block_cache, block_cache_key,
          BlocklikeTraits<TBlocklike>::GetCacheItemHelper(block_type),
          block_holder, charge, &cache_handle, priority);
      if (s.ok()) {
        assert(cache_handle != nullptr);
        block->SetCachedValue(block_holder.release(), block_cache,
                              cache_handle);

        UpdateCacheInsertionMetrics(block_type, get_context, charge,
                                    s.IsOkOverwritten(), rep_->ioptions.stats);
      } else {
        RecordTick(statistics, BLOCK_CACHE_ADD_FAILURES);
      }
    } else {
      block->SetOwnedValue(block_holder.release());
    }
  }

  // Release hold on compressed cache entry
  block_cache_compressed->Release(block_cache_compressed_handle);
  return s;
}

template <typename TBlocklike>
Status BlockBasedTable::PutDataBlockToCache(
    const Slice& block_cache_key, const Slice& compressed_block_cache_key,
    Cache* block_cache, Cache* block_cache_compressed,
    CachableEntry<TBlocklike>* cached_block, BlockContents* raw_block_contents,
    CompressionType raw_block_comp_type,
    const UncompressionDict& uncompression_dict,
    MemoryAllocator* memory_allocator, BlockType block_type,
    GetContext* get_context) const {
  const ImmutableOptions& ioptions = rep_->ioptions;
  const uint32_t format_version = rep_->table_options.format_version;
  const size_t read_amp_bytes_per_bit =
      block_type == BlockType::kData
          ? rep_->table_options.read_amp_bytes_per_bit
          : 0;
  const Cache::Priority priority =
      rep_->table_options.cache_index_and_filter_blocks_with_high_priority &&
              (block_type == BlockType::kFilter ||
               block_type == BlockType::kCompressionDictionary ||
               block_type == BlockType::kIndex)
          ? Cache::Priority::HIGH
          : Cache::Priority::LOW;
  assert(cached_block);
  assert(cached_block->IsEmpty());

  Status s;
  Statistics* statistics = ioptions.stats;

  std::unique_ptr<TBlocklike> block_holder;
  if (raw_block_comp_type != kNoCompression) {
    // Retrieve the uncompressed contents into a new buffer
    BlockContents uncompressed_block_contents;
    UncompressionContext context(raw_block_comp_type);
    UncompressionInfo info(context, uncompression_dict, raw_block_comp_type);
    s = UncompressBlockContents(info, raw_block_contents->data.data(),
                                raw_block_contents->data.size(),
                                &uncompressed_block_contents, format_version,
                                ioptions, memory_allocator);
    if (!s.ok()) {
      return s;
    }

    block_holder.reset(BlocklikeTraits<TBlocklike>::Create(
        std::move(uncompressed_block_contents), read_amp_bytes_per_bit,
        statistics, rep_->blocks_definitely_zstd_compressed,
        rep_->table_options.filter_policy.get()));
  } else {
    block_holder.reset(BlocklikeTraits<TBlocklike>::Create(
        std::move(*raw_block_contents), read_amp_bytes_per_bit, statistics,
        rep_->blocks_definitely_zstd_compressed,
        rep_->table_options.filter_policy.get()));
  }

  // Insert compressed block into compressed block cache.
  // Release the hold on the compressed cache entry immediately.
  if (block_cache_compressed != nullptr &&
      raw_block_comp_type != kNoCompression && raw_block_contents != nullptr &&
      raw_block_contents->own_bytes()) {
#ifndef NDEBUG
    assert(raw_block_contents->is_raw_block);
#endif  // NDEBUG

    // We cannot directly put raw_block_contents because this could point to
    // an object in the stack.
    std::unique_ptr<BlockContents> block_cont_for_comp_cache(
        new BlockContents(std::move(*raw_block_contents)));
    s = InsertEntryToCache(
        rep_->ioptions.lowest_used_cache_tier, block_cache_compressed,
        compressed_block_cache_key,
        BlocklikeTraits<BlockContents>::GetCacheItemHelper(block_type),
        block_cont_for_comp_cache,
        block_cont_for_comp_cache->ApproximateMemoryUsage(), nullptr,
        Cache::Priority::LOW);

    BlockContents* block_cont_raw_ptr = block_cont_for_comp_cache.release();
    if (s.ok()) {
      // Avoid the following code to delete this cached block.
      RecordTick(statistics, BLOCK_CACHE_COMPRESSED_ADD);
    } else {
      RecordTick(statistics, BLOCK_CACHE_COMPRESSED_ADD_FAILURES);
      delete block_cont_raw_ptr;
    }
  }

  // insert into uncompressed block cache
  if (block_cache != nullptr && block_holder->own_bytes()) {
    size_t charge = block_holder->ApproximateMemoryUsage();
    Cache::Handle* cache_handle = nullptr;
    s = InsertEntryToCache(
        rep_->ioptions.lowest_used_cache_tier, block_cache, block_cache_key,
        BlocklikeTraits<TBlocklike>::GetCacheItemHelper(block_type),
        block_holder, charge, &cache_handle, priority);
    if (s.ok()) {
      assert(cache_handle != nullptr);
      cached_block->SetCachedValue(block_holder.release(), block_cache,
                                   cache_handle);

      UpdateCacheInsertionMetrics(block_type, get_context, charge,
                                  s.IsOkOverwritten(), rep_->ioptions.stats);
    } else {
      RecordTick(statistics, BLOCK_CACHE_ADD_FAILURES);
    }
  } else {
    cached_block->SetOwnedValue(block_holder.release());
  }

  return s;
}

std::unique_ptr<FilterBlockReader> BlockBasedTable::CreateFilterBlockReader(
    const ReadOptions& ro, FilePrefetchBuffer* prefetch_buffer, bool use_cache,
    bool prefetch, bool pin, BlockCacheLookupContext* lookup_context) {
  auto& rep = rep_;
  auto filter_type = rep->filter_type;
  if (filter_type == Rep::FilterType::kNoFilter) {
    return std::unique_ptr<FilterBlockReader>();
  }

  assert(rep->filter_policy);

  switch (filter_type) {
    case Rep::FilterType::kPartitionedFilter:
      return PartitionedFilterBlockReader::Create(
          this, ro, prefetch_buffer, use_cache, prefetch, pin, lookup_context);

    case Rep::FilterType::kBlockFilter:
      return BlockBasedFilterBlockReader::Create(
          this, ro, prefetch_buffer, use_cache, prefetch, pin, lookup_context);

    case Rep::FilterType::kFullFilter:
      return FullFilterBlockReader::Create(this, ro, prefetch_buffer, use_cache,
                                           prefetch, pin, lookup_context);

    default:
      // filter_type is either kNoFilter (exited the function at the first if),
      // or it must be covered in this switch block
      assert(false);
      return std::unique_ptr<FilterBlockReader>();
  }
}

// disable_prefix_seek should be set to true when prefix_extractor found in SST
// differs from the one in mutable_cf_options and index type is HashBasedIndex
InternalIteratorBase<IndexValue>* BlockBasedTable::NewIndexIterator(
    const ReadOptions& read_options, bool disable_prefix_seek,
    IndexBlockIter* input_iter, GetContext* get_context,
    BlockCacheLookupContext* lookup_context) const {
  assert(rep_ != nullptr);
  assert(rep_->index_reader != nullptr);

  // We don't return pinned data from index blocks, so no need
  // to set `block_contents_pinned`.
  return rep_->index_reader->NewIterator(read_options, disable_prefix_seek,
                                         input_iter, get_context,
                                         lookup_context);
}

template <>
DataBlockIter* BlockBasedTable::InitBlockIterator<DataBlockIter>(
    const Rep* rep, Block* block, BlockType block_type,
    DataBlockIter* input_iter, bool block_contents_pinned) {
  return block->NewDataIterator(rep->internal_comparator.user_comparator(),
                                rep->get_global_seqno(block_type), input_iter,
                                rep->ioptions.stats, block_contents_pinned);
}

template <>
IndexBlockIter* BlockBasedTable::InitBlockIterator<IndexBlockIter>(
    const Rep* rep, Block* block, BlockType block_type,
    IndexBlockIter* input_iter, bool block_contents_pinned) {
  return block->NewIndexIterator(
      rep->internal_comparator.user_comparator(),
      rep->get_global_seqno(block_type), input_iter, rep->ioptions.stats,
      /* total_order_seek */ true, rep->index_has_first_key,
      rep->index_key_includes_seq, rep->index_value_is_full,
      block_contents_pinned);
}

// If contents is nullptr, this function looks up the block caches for the
// data block referenced by handle, and read the block from disk if necessary.
// If contents is non-null, it skips the cache lookup and disk read, since
// the caller has already read it. In both cases, if ro.fill_cache is true,
// it inserts the block into the block cache.
template <typename TBlocklike>
Status BlockBasedTable::MaybeReadBlockAndLoadToCache(
    FilePrefetchBuffer* prefetch_buffer, const ReadOptions& ro,
    const BlockHandle& handle, const UncompressionDict& uncompression_dict,
    const bool wait, CachableEntry<TBlocklike>* block_entry,
    BlockType block_type, GetContext* get_context,
    BlockCacheLookupContext* lookup_context, BlockContents* contents) const {
  assert(block_entry != nullptr);
  const bool no_io = (ro.read_tier == kBlockCacheTier);
  Cache* block_cache = rep_->table_options.block_cache.get();
  Cache* block_cache_compressed =
      rep_->table_options.block_cache_compressed.get();

  // First, try to get the block from the cache
  //
  // If either block cache is enabled, we'll try to read from it.
  Status s;
  char cache_key[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
  char compressed_cache_key[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
  Slice key /* key to the block cache */;
  Slice ckey /* key to the compressed block cache */;
  bool is_cache_hit = false;
  if (block_cache != nullptr || block_cache_compressed != nullptr) {
    // create key for block cache
    if (block_cache != nullptr) {
      key = GetCacheKey(rep_->cache_key_prefix, rep_->cache_key_prefix_size,
                        handle, cache_key);
    }

    if (block_cache_compressed != nullptr) {
      ckey = GetCacheKey(rep_->compressed_cache_key_prefix,
                         rep_->compressed_cache_key_prefix_size, handle,
                         compressed_cache_key);
    }

    if (!contents) {
      s = GetDataBlockFromCache(key, ckey, block_cache, block_cache_compressed,
                                ro, block_entry, uncompression_dict, block_type,
                                wait, get_context);
      // Value could still be null at this point, so check the cache handle
      // and update the read pattern for prefetching
      if (block_entry->GetValue() || block_entry->GetCacheHandle()) {
        // TODO(haoyu): Differentiate cache hit on uncompressed block cache and
        // compressed block cache.
        is_cache_hit = true;
        if (prefetch_buffer) {
          // Update the block details so that PrefetchBuffer can use the read
          // pattern to determine if reads are sequential or not for
          // prefetching. It should also take in account blocks read from cache.
          prefetch_buffer->UpdateReadPattern(handle.offset(),
                                             BlockSizeWithTrailer(handle),
                                             ro.adaptive_readahead);
        }
      }
    }

    // Can't find the block from the cache. If I/O is allowed, read from the
    // file.
    if (block_entry->GetValue() == nullptr &&
        block_entry->GetCacheHandle() == nullptr && !no_io && ro.fill_cache) {
      Statistics* statistics = rep_->ioptions.stats;
      const bool maybe_compressed =
          block_type != BlockType::kFilter &&
          block_type != BlockType::kCompressionDictionary &&
          rep_->blocks_maybe_compressed;
      const bool do_uncompress = maybe_compressed && !block_cache_compressed;
      CompressionType raw_block_comp_type;
      BlockContents raw_block_contents;
      if (!contents) {
        StopWatch sw(rep_->ioptions.clock, statistics, READ_BLOCK_GET_MICROS);
        BlockFetcher block_fetcher(
            rep_->file.get(), prefetch_buffer, rep_->footer, ro, handle,
            &raw_block_contents, rep_->ioptions, do_uncompress,
            maybe_compressed, block_type, uncompression_dict,
            rep_->persistent_cache_options,
            GetMemoryAllocator(rep_->table_options),
            GetMemoryAllocatorForCompressedBlock(rep_->table_options));
        s = block_fetcher.ReadBlockContents();
        raw_block_comp_type = block_fetcher.get_compression_type();
        contents = &raw_block_contents;
        if (get_context) {
          switch (block_type) {
            case BlockType::kIndex:
              ++get_context->get_context_stats_.num_index_read;
              break;
            case BlockType::kFilter:
              ++get_context->get_context_stats_.num_filter_read;
              break;
            case BlockType::kData:
              ++get_context->get_context_stats_.num_data_read;
              break;
            default:
              break;
          }
        }
      } else {
        raw_block_comp_type = GetBlockCompressionType(*contents);
      }

      if (s.ok()) {
        // If filling cache is allowed and a cache is configured, try to put the
        // block to the cache.
        s = PutDataBlockToCache(
            key, ckey, block_cache, block_cache_compressed, block_entry,
            contents, raw_block_comp_type, uncompression_dict,
            GetMemoryAllocator(rep_->table_options), block_type, get_context);
      }
    }
  }

  // Fill lookup_context.
  if (block_cache_tracer_ && block_cache_tracer_->is_tracing_enabled() &&
      lookup_context) {
    size_t usage = 0;
    uint64_t nkeys = 0;
    if (block_entry->GetValue()) {
      // Approximate the number of keys in the block using restarts.
      nkeys =
          rep_->table_options.block_restart_interval *
          BlocklikeTraits<TBlocklike>::GetNumRestarts(*block_entry->GetValue());
      usage = block_entry->GetValue()->ApproximateMemoryUsage();
    }
    TraceType trace_block_type = TraceType::kTraceMax;
    switch (block_type) {
      case BlockType::kData:
        trace_block_type = TraceType::kBlockTraceDataBlock;
        break;
      case BlockType::kFilter:
        trace_block_type = TraceType::kBlockTraceFilterBlock;
        break;
      case BlockType::kCompressionDictionary:
        trace_block_type = TraceType::kBlockTraceUncompressionDictBlock;
        break;
      case BlockType::kRangeDeletion:
        trace_block_type = TraceType::kBlockTraceRangeDeletionBlock;
        break;
      case BlockType::kIndex:
        trace_block_type = TraceType::kBlockTraceIndexBlock;
        break;
      default:
        // This cannot happen.
        assert(false);
        break;
    }
    bool no_insert = no_io || !ro.fill_cache;
    if (BlockCacheTraceHelper::IsGetOrMultiGetOnDataBlock(
            trace_block_type, lookup_context->caller)) {
      // Defer logging the access to Get() and MultiGet() to trace additional
      // information, e.g., referenced_key_exist_in_block.

      // Make a copy of the block key here since it will be logged later.
      lookup_context->FillLookupContext(
          is_cache_hit, no_insert, trace_block_type,
          /*block_size=*/usage, /*block_key=*/key.ToString(), nkeys);
    } else {
      // Avoid making copy of block_key and cf_name when constructing the access
      // record.
      BlockCacheTraceRecord access_record(
          rep_->ioptions.clock->NowMicros(),
          /*block_key=*/"", trace_block_type,
          /*block_size=*/usage, rep_->cf_id_for_tracing(),
          /*cf_name=*/"", rep_->level_for_tracing(),
          rep_->sst_number_for_tracing(), lookup_context->caller, is_cache_hit,
          no_insert, lookup_context->get_id,
          lookup_context->get_from_user_specified_snapshot,
          /*referenced_key=*/"");
      // TODO: Should handle this error?
      block_cache_tracer_
          ->WriteBlockAccess(access_record, key, rep_->cf_name_for_tracing(),
                             lookup_context->referenced_key)
          .PermitUncheckedError();
    }
  }

  assert(s.ok() || block_entry->GetValue() == nullptr);
  return s;
}

// This function reads multiple data blocks from disk using Env::MultiRead()
// and optionally inserts them into the block cache. It uses the scratch
// buffer provided by the caller, which is contiguous. If scratch is a nullptr
// it allocates a separate buffer for each block. Typically, if the blocks
// need to be uncompressed and there is no compressed block cache, callers
// can allocate a temporary scratch buffer in order to minimize memory
// allocations.
// If options.fill_cache is true, it inserts the blocks into cache. If its
// false and scratch is non-null and the blocks are uncompressed, it copies
// the buffers to heap. In any case, the CachableEntry<Block> returned will
// own the data bytes.
// If compression is enabled and also there is no compressed block cache,
// the adjacent blocks are read out in one IO (combined read)
// batch - A MultiGetRange with only those keys with unique data blocks not
//         found in cache
// handles - A vector of block handles. Some of them me be NULL handles
// scratch - An optional contiguous buffer to read compressed blocks into
void BlockBasedTable::RetrieveMultipleBlocks(
    const ReadOptions& options, const MultiGetRange* batch,
    const autovector<BlockHandle, MultiGetContext::MAX_BATCH_SIZE>* handles,
    autovector<Status, MultiGetContext::MAX_BATCH_SIZE>* statuses,
    autovector<CachableEntry<Block>, MultiGetContext::MAX_BATCH_SIZE>* results,
    char* scratch, const UncompressionDict& uncompression_dict) const {
  RandomAccessFileReader* file = rep_->file.get();
  const Footer& footer = rep_->footer;
  const ImmutableOptions& ioptions = rep_->ioptions;
  size_t read_amp_bytes_per_bit = rep_->table_options.read_amp_bytes_per_bit;
  MemoryAllocator* memory_allocator = GetMemoryAllocator(rep_->table_options);

  if (ioptions.allow_mmap_reads) {
    size_t idx_in_batch = 0;
    for (auto mget_iter = batch->begin(); mget_iter != batch->end();
         ++mget_iter, ++idx_in_batch) {
      BlockCacheLookupContext lookup_data_block_context(
          TableReaderCaller::kUserMultiGet);
      const BlockHandle& handle = (*handles)[idx_in_batch];
      if (handle.IsNull()) {
        continue;
      }

      (*statuses)[idx_in_batch] =
          RetrieveBlock(nullptr, options, handle, uncompression_dict,
                        &(*results)[idx_in_batch], BlockType::kData,
                        mget_iter->get_context, &lookup_data_block_context,
                        /* for_compaction */ false, /* use_cache */ true,
                        /* wait_for_cache */ true);
    }
    return;
  }

  // In direct IO mode, blocks share the direct io buffer.
  // Otherwise, blocks share the scratch buffer.
  const bool use_shared_buffer = file->use_direct_io() || scratch != nullptr;

  autovector<FSReadRequest, MultiGetContext::MAX_BATCH_SIZE> read_reqs;
  size_t buf_offset = 0;
  size_t idx_in_batch = 0;

  uint64_t prev_offset = 0;
  size_t prev_len = 0;
  autovector<size_t, MultiGetContext::MAX_BATCH_SIZE> req_idx_for_block;
  autovector<size_t, MultiGetContext::MAX_BATCH_SIZE> req_offset_for_block;
  for (auto mget_iter = batch->begin(); mget_iter != batch->end();
       ++mget_iter, ++idx_in_batch) {
    const BlockHandle& handle = (*handles)[idx_in_batch];
    if (handle.IsNull()) {
      continue;
    }

    size_t prev_end = static_cast<size_t>(prev_offset) + prev_len;

    // If current block is adjacent to the previous one, at the same time,
    // compression is enabled and there is no compressed cache, we combine
    // the two block read as one.
    // We don't combine block reads here in direct IO mode, because when doing
    // direct IO read, the block requests will be realigned and merged when
    // necessary.
    if (use_shared_buffer && !file->use_direct_io() &&
        prev_end == handle.offset()) {
      req_offset_for_block.emplace_back(prev_len);
      prev_len += BlockSizeWithTrailer(handle);
    } else {
      // No compression or current block and previous one is not adjacent:
      // Step 1, create a new request for previous blocks
      if (prev_len != 0) {
        FSReadRequest req;
        req.offset = prev_offset;
        req.len = prev_len;
        if (file->use_direct_io()) {
          req.scratch = nullptr;
        } else if (use_shared_buffer) {
          req.scratch = scratch + buf_offset;
          buf_offset += req.len;
        } else {
          req.scratch = new char[req.len];
        }
        read_reqs.emplace_back(req);
      }

      // Step 2, remeber the previous block info
      prev_offset = handle.offset();
      prev_len = BlockSizeWithTrailer(handle);
      req_offset_for_block.emplace_back(0);
    }
    req_idx_for_block.emplace_back(read_reqs.size());

    PERF_COUNTER_ADD(block_read_count, 1);
    PERF_COUNTER_ADD(block_read_byte, BlockSizeWithTrailer(handle));
  }
  // Handle the last block and process the pending last request
  if (prev_len != 0) {
    FSReadRequest req;
    req.offset = prev_offset;
    req.len = prev_len;
    if (file->use_direct_io()) {
      req.scratch = nullptr;
    } else if (use_shared_buffer) {
      req.scratch = scratch + buf_offset;
    } else {
      req.scratch = new char[req.len];
    }
    read_reqs.emplace_back(req);
  }

  AlignedBuf direct_io_buf;
  {
    IOOptions opts;
    IOStatus s = file->PrepareIOOptions(options, opts);
    if (s.ok()) {
      s = file->MultiRead(opts, &read_reqs[0], read_reqs.size(),
                          &direct_io_buf);
    }
    if (!s.ok()) {
      // Discard all the results in this batch if there is any time out
      // or overall MultiRead error
      for (FSReadRequest& req : read_reqs) {
        req.status = s;
      }
    }
  }

  idx_in_batch = 0;
  size_t valid_batch_idx = 0;
  for (auto mget_iter = batch->begin(); mget_iter != batch->end();
       ++mget_iter, ++idx_in_batch) {
    const BlockHandle& handle = (*handles)[idx_in_batch];

    if (handle.IsNull()) {
      continue;
    }

    assert(valid_batch_idx < req_idx_for_block.size());
    assert(valid_batch_idx < req_offset_for_block.size());
    assert(req_idx_for_block[valid_batch_idx] < read_reqs.size());
    size_t& req_idx = req_idx_for_block[valid_batch_idx];
    size_t& req_offset = req_offset_for_block[valid_batch_idx];
    valid_batch_idx++;
    if (mget_iter->get_context) {
      ++(mget_iter->get_context->get_context_stats_.num_data_read);
    }
    FSReadRequest& req = read_reqs[req_idx];
    Status s = req.status;
    if (s.ok()) {
      if ((req.result.size() != req.len) ||
          (req_offset + BlockSizeWithTrailer(handle) > req.result.size())) {
        s = Status::Corruption(
            "truncated block read from " + rep_->file->file_name() +
            " offset " + ToString(handle.offset()) + ", expected " +
            ToString(req.len) + " bytes, got " + ToString(req.result.size()));
      }
    }

    BlockContents raw_block_contents;
    if (s.ok()) {
      if (!use_shared_buffer) {
        // We allocated a buffer for this block. Give ownership of it to
        // BlockContents so it can free the memory
        assert(req.result.data() == req.scratch);
        assert(req.result.size() == BlockSizeWithTrailer(handle));
        assert(req_offset == 0);
        std::unique_ptr<char[]> raw_block(req.scratch);
        raw_block_contents = BlockContents(std::move(raw_block), handle.size());
      } else {
        // We used the scratch buffer or direct io buffer
        // which are shared by the blocks.
        // raw_block_contents does not have the ownership.
        raw_block_contents =
            BlockContents(Slice(req.result.data() + req_offset, handle.size()));
      }
#ifndef NDEBUG
      raw_block_contents.is_raw_block = true;
#endif

      if (options.verify_checksums) {
        PERF_TIMER_GUARD(block_checksum_time);
        const char* data = req.result.data();
        // Since the scratch might be shared, the offset of the data block in
        // the buffer might not be 0. req.result.data() only point to the
        // begin address of each read request, we need to add the offset
        // in each read request. Checksum is stored in the block trailer,
        // beyond the payload size.
        s = VerifyBlockChecksum(footer.checksum(), data + req_offset,
                                handle.size(), rep_->file->file_name(),
                                handle.offset());
        TEST_SYNC_POINT_CALLBACK("RetrieveMultipleBlocks:VerifyChecksum", &s);
      }
    } else if (!use_shared_buffer) {
      // Free the allocated scratch buffer.
      delete[] req.scratch;
    }

    if (s.ok()) {
      // When the blocks share the same underlying buffer (scratch or direct io
      // buffer), we may need to manually copy the block into heap if the raw
      // block has to be inserted into a cache. That falls into th following
      // cases -
      // 1. Raw block is not compressed, it needs to be inserted into the
      //    uncompressed block cache if there is one
      // 2. If the raw block is compressed, it needs to be inserted into the
      //    compressed block cache if there is one
      //
      // In all other cases, the raw block is either uncompressed into a heap
      // buffer or there is no cache at all.
      CompressionType compression_type =
          GetBlockCompressionType(raw_block_contents);
      if (use_shared_buffer && (compression_type == kNoCompression ||
                                (compression_type != kNoCompression &&
                                 rep_->table_options.block_cache_compressed))) {
        Slice raw =
            Slice(req.result.data() + req_offset, BlockSizeWithTrailer(handle));
        raw_block_contents = BlockContents(
            CopyBufferToHeap(GetMemoryAllocator(rep_->table_options), raw),
            handle.size());
#ifndef NDEBUG
        raw_block_contents.is_raw_block = true;
#endif
      }
    }

    if (s.ok()) {
      if (options.fill_cache) {
        BlockCacheLookupContext lookup_data_block_context(
            TableReaderCaller::kUserMultiGet);
        CachableEntry<Block>* block_entry = &(*results)[idx_in_batch];
        // MaybeReadBlockAndLoadToCache will insert into the block caches if
        // necessary. Since we're passing the raw block contents, it will
        // avoid looking up the block cache
        s = MaybeReadBlockAndLoadToCache(
            nullptr, options, handle, uncompression_dict, /*wait=*/true,
            block_entry, BlockType::kData, mget_iter->get_context,
            &lookup_data_block_context, &raw_block_contents);

        // block_entry value could be null if no block cache is present, i.e
        // BlockBasedTableOptions::no_block_cache is true and no compressed
        // block cache is configured. In that case, fall
        // through and set up the block explicitly
        if (block_entry->GetValue() != nullptr) {
          s.PermitUncheckedError();
          continue;
        }
      }

      CompressionType compression_type =
          GetBlockCompressionType(raw_block_contents);
      BlockContents contents;
      if (compression_type != kNoCompression) {
        UncompressionContext context(compression_type);
        UncompressionInfo info(context, uncompression_dict, compression_type);
        s = UncompressBlockContents(info, req.result.data() + req_offset,
                                    handle.size(), &contents, footer.version(),
                                    rep_->ioptions, memory_allocator);
      } else {
        // There are two cases here:
        // 1) caller uses the shared buffer (scratch or direct io buffer);
        // 2) we use the requst buffer.
        // If scratch buffer or direct io buffer is used, we ensure that
        // all raw blocks are copyed to the heap as single blocks. If scratch
        // buffer is not used, we also have no combined read, so the raw
        // block can be used directly.
        contents = std::move(raw_block_contents);
      }
      if (s.ok()) {
        (*results)[idx_in_batch].SetOwnedValue(new Block(
            std::move(contents), read_amp_bytes_per_bit, ioptions.stats));
      }
    }
    (*statuses)[idx_in_batch] = s;
  }
}

template <typename TBlocklike>
Status BlockBasedTable::RetrieveBlock(
    FilePrefetchBuffer* prefetch_buffer, const ReadOptions& ro,
    const BlockHandle& handle, const UncompressionDict& uncompression_dict,
    CachableEntry<TBlocklike>* block_entry, BlockType block_type,
    GetContext* get_context, BlockCacheLookupContext* lookup_context,
    bool for_compaction, bool use_cache, bool wait_for_cache) const {
  assert(block_entry);
  assert(block_entry->IsEmpty());

  Status s;
  if (use_cache) {
    s = MaybeReadBlockAndLoadToCache(
        prefetch_buffer, ro, handle, uncompression_dict, wait_for_cache,
        block_entry, block_type, get_context, lookup_context,
        /*contents=*/nullptr);

    if (!s.ok()) {
      return s;
    }

    if (block_entry->GetValue() != nullptr ||
        block_entry->GetCacheHandle() != nullptr) {
      assert(s.ok());
      return s;
    }
  }

  assert(block_entry->IsEmpty());

  const bool no_io = ro.read_tier == kBlockCacheTier;
  if (no_io) {
    return Status::Incomplete("no blocking io");
  }

  const bool maybe_compressed =
      block_type != BlockType::kFilter &&
      block_type != BlockType::kCompressionDictionary &&
      rep_->blocks_maybe_compressed;
  const bool do_uncompress = maybe_compressed;
  std::unique_ptr<TBlocklike> block;

  {
    StopWatch sw(rep_->ioptions.clock, rep_->ioptions.stats,
                 READ_BLOCK_GET_MICROS);
    s = ReadBlockFromFile(
        rep_->file.get(), prefetch_buffer, rep_->footer, ro, handle, &block,
        rep_->ioptions, do_uncompress, maybe_compressed, block_type,
        uncompression_dict, rep_->persistent_cache_options,
        block_type == BlockType::kData
            ? rep_->table_options.read_amp_bytes_per_bit
            : 0,
        GetMemoryAllocator(rep_->table_options), for_compaction,
        rep_->blocks_definitely_zstd_compressed,
        rep_->table_options.filter_policy.get());

    if (get_context) {
      switch (block_type) {
        case BlockType::kIndex:
          ++(get_context->get_context_stats_.num_index_read);
          break;
        case BlockType::kFilter:
          ++(get_context->get_context_stats_.num_filter_read);
          break;
        case BlockType::kData:
          ++(get_context->get_context_stats_.num_data_read);
          break;
        default:
          break;
      }
    }
  }

  if (!s.ok()) {
    return s;
  }

  block_entry->SetOwnedValue(block.release());

  assert(s.ok());
  return s;
}

// Explicitly instantiate templates for both "blocklike" types we use.
// This makes it possible to keep the template definitions in the .cc file.
template Status BlockBasedTable::RetrieveBlock<BlockContents>(
    FilePrefetchBuffer* prefetch_buffer, const ReadOptions& ro,
    const BlockHandle& handle, const UncompressionDict& uncompression_dict,
    CachableEntry<BlockContents>* block_entry, BlockType block_type,
    GetContext* get_context, BlockCacheLookupContext* lookup_context,
    bool for_compaction, bool use_cache, bool wait_for_cache) const;

template Status BlockBasedTable::RetrieveBlock<ParsedFullFilterBlock>(
    FilePrefetchBuffer* prefetch_buffer, const ReadOptions& ro,
    const BlockHandle& handle, const UncompressionDict& uncompression_dict,
    CachableEntry<ParsedFullFilterBlock>* block_entry, BlockType block_type,
    GetContext* get_context, BlockCacheLookupContext* lookup_context,
    bool for_compaction, bool use_cache, bool wait_for_cache) const;

template Status BlockBasedTable::RetrieveBlock<Block>(
    FilePrefetchBuffer* prefetch_buffer, const ReadOptions& ro,
    const BlockHandle& handle, const UncompressionDict& uncompression_dict,
    CachableEntry<Block>* block_entry, BlockType block_type,
    GetContext* get_context, BlockCacheLookupContext* lookup_context,
    bool for_compaction, bool use_cache, bool wait_for_cache) const;

template Status BlockBasedTable::RetrieveBlock<UncompressionDict>(
    FilePrefetchBuffer* prefetch_buffer, const ReadOptions& ro,
    const BlockHandle& handle, const UncompressionDict& uncompression_dict,
    CachableEntry<UncompressionDict>* block_entry, BlockType block_type,
    GetContext* get_context, BlockCacheLookupContext* lookup_context,
    bool for_compaction, bool use_cache, bool wait_for_cache) const;

BlockBasedTable::PartitionedIndexIteratorState::PartitionedIndexIteratorState(
    const BlockBasedTable* table,
    std::unordered_map<uint64_t, CachableEntry<Block>>* block_map)
    : table_(table), block_map_(block_map) {}

InternalIteratorBase<IndexValue>*
BlockBasedTable::PartitionedIndexIteratorState::NewSecondaryIterator(
    const BlockHandle& handle) {
  // Return a block iterator on the index partition
  auto block = block_map_->find(handle.offset());
  // block_map_ must be exhaustive
  if (block == block_map_->end()) {
    assert(false);
    // Signal problem to caller
    return nullptr;
  }
  const Rep* rep = table_->get_rep();
  assert(rep);

  Statistics* kNullStats = nullptr;
  // We don't return pinned data from index blocks, so no need
  // to set `block_contents_pinned`.
  return block->second.GetValue()->NewIndexIterator(
      rep->internal_comparator.user_comparator(),
      rep->get_global_seqno(BlockType::kIndex), nullptr, kNullStats, true,
      rep->index_has_first_key, rep->index_key_includes_seq,
      rep->index_value_is_full);
}

// This will be broken if the user specifies an unusual implementation
// of Options.comparator, or if the user specifies an unusual
// definition of prefixes in BlockBasedTableOptions.filter_policy.
// In particular, we require the following three properties:
//
// 1) key.starts_with(prefix(key))
// 2) Compare(prefix(key), key) <= 0.
// 3) If Compare(key1, key2) <= 0, then Compare(prefix(key1), prefix(key2)) <= 0
//
// If read_options.read_tier == kBlockCacheTier, this method will do no I/O and
// will return true if the filter block is not in memory and not found in block
// cache.
//
// REQUIRES: this method shouldn't be called while the DB lock is held.
bool BlockBasedTable::PrefixMayMatch(
    const Slice& internal_key, const ReadOptions& read_options,
    const SliceTransform* options_prefix_extractor,
    const bool need_upper_bound_check,
    BlockCacheLookupContext* lookup_context) const {
  if (!rep_->filter_policy) {
    return true;
  }

  const SliceTransform* prefix_extractor;

  if (rep_->table_prefix_extractor == nullptr) {
    if (need_upper_bound_check) {
      return true;
    }
    prefix_extractor = options_prefix_extractor;
  } else {
    prefix_extractor = rep_->table_prefix_extractor.get();
  }
  auto ts_sz = rep_->internal_comparator.user_comparator()->timestamp_size();
  auto user_key_without_ts =
      ExtractUserKeyAndStripTimestamp(internal_key, ts_sz);
  if (!prefix_extractor->InDomain(user_key_without_ts)) {
    return true;
  }

  bool may_match = true;

  // First, try check with full filter
  FilterBlockReader* const filter = rep_->filter.get();
  bool filter_checked = true;
  if (filter != nullptr) {
    const bool no_io = read_options.read_tier == kBlockCacheTier;

    if (!filter->IsBlockBased()) {
      const Slice* const const_ikey_ptr = &internal_key;
      may_match = filter->RangeMayExist(
          read_options.iterate_upper_bound, user_key_without_ts,
          prefix_extractor, rep_->internal_comparator.user_comparator(),
          const_ikey_ptr, &filter_checked, need_upper_bound_check, no_io,
          lookup_context);
    } else {
      // if prefix_extractor changed for block based filter, skip filter
      if (need_upper_bound_check) {
        return true;
      }
      auto prefix = prefix_extractor->Transform(user_key_without_ts);
      InternalKey internal_key_prefix(prefix, kMaxSequenceNumber, kTypeValue);
      auto internal_prefix = internal_key_prefix.Encode();

      // To prevent any io operation in this method, we set `read_tier` to make
      // sure we always read index or filter only when they have already been
      // loaded to memory.
      ReadOptions no_io_read_options;
      no_io_read_options.read_tier = kBlockCacheTier;

      // Then, try find it within each block
      // we already know prefix_extractor and prefix_extractor_name must match
      // because `CheckPrefixMayMatch` first checks `check_filter_ == true`
      std::unique_ptr<InternalIteratorBase<IndexValue>> iiter(NewIndexIterator(
          no_io_read_options,
          /*need_upper_bound_check=*/false, /*input_iter=*/nullptr,
          /*get_context=*/nullptr, lookup_context));
      iiter->Seek(internal_prefix);

      if (!iiter->Valid()) {
        // we're past end of file
        // if it's incomplete, it means that we avoided I/O
        // and we're not really sure that we're past the end
        // of the file
        may_match = iiter->status().IsIncomplete();
      } else if ((rep_->index_key_includes_seq ? ExtractUserKey(iiter->key())
                                               : iiter->key())
                     .starts_with(ExtractUserKey(internal_prefix))) {
        // we need to check for this subtle case because our only
        // guarantee is that "the key is a string >= last key in that data
        // block" according to the doc/table_format.txt spec.
        //
        // Suppose iiter->key() starts with the desired prefix; it is not
        // necessarily the case that the corresponding data block will
        // contain the prefix, since iiter->key() need not be in the
        // block.  However, the next data block may contain the prefix, so
        // we return true to play it safe.
        may_match = true;
      } else if (filter->IsBlockBased()) {
        // iiter->key() does NOT start with the desired prefix.  Because
        // Seek() finds the first key that is >= the seek target, this
        // means that iiter->key() > prefix.  Thus, any data blocks coming
        // after the data block corresponding to iiter->key() cannot
        // possibly contain the key.  Thus, the corresponding data block
        // is the only on could potentially contain the prefix.
        BlockHandle handle = iiter->value().handle;
        may_match = filter->PrefixMayMatch(
            prefix, prefix_extractor, handle.offset(), no_io,
            /*const_key_ptr=*/nullptr, /*get_context=*/nullptr, lookup_context);
      }
    }
  }

  if (filter_checked) {
    Statistics* statistics = rep_->ioptions.stats;
    RecordTick(statistics, BLOOM_FILTER_PREFIX_CHECKED);
    if (!may_match) {
      RecordTick(statistics, BLOOM_FILTER_PREFIX_USEFUL);
    }
  }

  return may_match;
}


InternalIterator* BlockBasedTable::NewIterator(
    const ReadOptions& read_options, const SliceTransform* prefix_extractor,
    Arena* arena, bool skip_filters, TableReaderCaller caller,
    size_t compaction_readahead_size, bool allow_unprepared_value) {
  BlockCacheLookupContext lookup_context{caller};
  bool need_upper_bound_check =
      read_options.auto_prefix_mode ||
      PrefixExtractorChanged(rep_->table_properties.get(), prefix_extractor);
  std::unique_ptr<InternalIteratorBase<IndexValue>> index_iter(NewIndexIterator(
      read_options,
      need_upper_bound_check &&
          rep_->index_type == BlockBasedTableOptions::kHashSearch,
      /*input_iter=*/nullptr, /*get_context=*/nullptr, &lookup_context));
  if (arena == nullptr) {
    return new BlockBasedTableIterator(
        this, read_options, rep_->internal_comparator, std::move(index_iter),
        !skip_filters && !read_options.total_order_seek &&
            prefix_extractor != nullptr,
        need_upper_bound_check, prefix_extractor, caller,
        compaction_readahead_size, allow_unprepared_value);
  } else {
    auto* mem = arena->AllocateAligned(sizeof(BlockBasedTableIterator));
    return new (mem) BlockBasedTableIterator(
        this, read_options, rep_->internal_comparator, std::move(index_iter),
        !skip_filters && !read_options.total_order_seek &&
            prefix_extractor != nullptr,
        need_upper_bound_check, prefix_extractor, caller,
        compaction_readahead_size, allow_unprepared_value);
  }
}

FragmentedRangeTombstoneIterator* BlockBasedTable::NewRangeTombstoneIterator(
    const ReadOptions& read_options) {
  if (rep_->fragmented_range_dels == nullptr) {
    return nullptr;
  }
  SequenceNumber snapshot = kMaxSequenceNumber;
  if (read_options.snapshot != nullptr) {
    snapshot = read_options.snapshot->GetSequenceNumber();
  }
  return new FragmentedRangeTombstoneIterator(
      rep_->fragmented_range_dels, rep_->internal_comparator, snapshot);
}

bool BlockBasedTable::FullFilterKeyMayMatch(
    const ReadOptions& read_options, FilterBlockReader* filter,
    const Slice& internal_key, const bool no_io,
    const SliceTransform* prefix_extractor, GetContext* get_context,
    BlockCacheLookupContext* lookup_context) const {
  if (filter == nullptr || filter->IsBlockBased()) {
    return true;
  }
  Slice user_key = ExtractUserKey(internal_key);
  const Slice* const const_ikey_ptr = &internal_key;
  bool may_match = true;
  size_t ts_sz = rep_->internal_comparator.user_comparator()->timestamp_size();
  Slice user_key_without_ts = StripTimestampFromUserKey(user_key, ts_sz);
  if (rep_->whole_key_filtering) {
    may_match =
        filter->KeyMayMatch(user_key_without_ts, prefix_extractor, kNotValid,
                            no_io, const_ikey_ptr, get_context, lookup_context);
  } else if (!read_options.total_order_seek && prefix_extractor &&
             rep_->table_properties->prefix_extractor_name ==
                 prefix_extractor->AsString() &&
             prefix_extractor->InDomain(user_key_without_ts) &&
             !filter->PrefixMayMatch(
                 prefix_extractor->Transform(user_key_without_ts),
                 prefix_extractor, kNotValid, no_io, const_ikey_ptr,
                 get_context, lookup_context)) {
    may_match = false;
  }
  if (may_match) {
    RecordTick(rep_->ioptions.stats, BLOOM_FILTER_FULL_POSITIVE);
    PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_full_positive, 1, rep_->level);
  }
  return may_match;
}

void BlockBasedTable::FullFilterKeysMayMatch(
    const ReadOptions& read_options, FilterBlockReader* filter,
    MultiGetRange* range, const bool no_io,
    const SliceTransform* prefix_extractor,
    BlockCacheLookupContext* lookup_context) const {
  if (filter == nullptr || filter->IsBlockBased()) {
    return;
  }
  uint64_t before_keys = range->KeysLeft();
  assert(before_keys > 0);  // Caller should ensure
  if (rep_->whole_key_filtering) {
    filter->KeysMayMatch(range, prefix_extractor, kNotValid, no_io,
                         lookup_context);
    uint64_t after_keys = range->KeysLeft();
    if (after_keys) {
      RecordTick(rep_->ioptions.stats, BLOOM_FILTER_FULL_POSITIVE, after_keys);
      PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_full_positive, after_keys,
                                rep_->level);
    }
    uint64_t filtered_keys = before_keys - after_keys;
    if (filtered_keys) {
      RecordTick(rep_->ioptions.stats, BLOOM_FILTER_USEFUL, filtered_keys);
      PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_useful, filtered_keys,
                                rep_->level);
    }
  } else if (!read_options.total_order_seek && prefix_extractor &&
             rep_->table_properties->prefix_extractor_name ==
                 prefix_extractor->AsString()) {
    filter->PrefixesMayMatch(range, prefix_extractor, kNotValid, false,
                             lookup_context);
    RecordTick(rep_->ioptions.stats, BLOOM_FILTER_PREFIX_CHECKED, before_keys);
    uint64_t after_keys = range->KeysLeft();
    uint64_t filtered_keys = before_keys - after_keys;
    if (filtered_keys) {
      RecordTick(rep_->ioptions.stats, BLOOM_FILTER_PREFIX_USEFUL,
                 filtered_keys);
    }
  }
}

Status BlockBasedTable::Get(const ReadOptions& read_options, const Slice& key,
                            GetContext* get_context,
                            const SliceTransform* prefix_extractor,
                            bool skip_filters) {
  assert(key.size() >= 8);  // key must be internal key
  assert(get_context != nullptr);
  Status s;
  const bool no_io = read_options.read_tier == kBlockCacheTier;

  FilterBlockReader* const filter =
      !skip_filters ? rep_->filter.get() : nullptr;

  // First check the full filter
  // If full filter not useful, Then go into each block
  uint64_t tracing_get_id = get_context->get_tracing_get_id();
  BlockCacheLookupContext lookup_context{
      TableReaderCaller::kUserGet, tracing_get_id,
      /*get_from_user_specified_snapshot=*/read_options.snapshot != nullptr};
  if (block_cache_tracer_ && block_cache_tracer_->is_tracing_enabled()) {
    // Trace the key since it contains both user key and sequence number.
    lookup_context.referenced_key = key.ToString();
    lookup_context.get_from_user_specified_snapshot =
        read_options.snapshot != nullptr;
  }
  TEST_SYNC_POINT("BlockBasedTable::Get:BeforeFilterMatch");
  const bool may_match =
      FullFilterKeyMayMatch(read_options, filter, key, no_io, prefix_extractor,
                            get_context, &lookup_context);
  TEST_SYNC_POINT("BlockBasedTable::Get:AfterFilterMatch");
  if (!may_match) {
    RecordTick(rep_->ioptions.stats, BLOOM_FILTER_USEFUL);
    PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_useful, 1, rep_->level);
  } else {
    IndexBlockIter iiter_on_stack;
    // if prefix_extractor found in block differs from options, disable
    // BlockPrefixIndex. Only do this check when index_type is kHashSearch.
    bool need_upper_bound_check = false;
    if (rep_->index_type == BlockBasedTableOptions::kHashSearch) {
      need_upper_bound_check = PrefixExtractorChanged(
          rep_->table_properties.get(), prefix_extractor);
    }
    auto iiter =
        NewIndexIterator(read_options, need_upper_bound_check, &iiter_on_stack,
                         get_context, &lookup_context);
    std::unique_ptr<InternalIteratorBase<IndexValue>> iiter_unique_ptr;
    if (iiter != &iiter_on_stack) {
      iiter_unique_ptr.reset(iiter);
    }

    size_t ts_sz =
        rep_->internal_comparator.user_comparator()->timestamp_size();
    bool matched = false;  // if such user key matched a key in SST
    bool done = false;
    for (iiter->Seek(key); iiter->Valid() && !done; iiter->Next()) {
      IndexValue v = iiter->value();

      bool not_exist_in_filter =
          filter != nullptr && filter->IsBlockBased() == true &&
          !filter->KeyMayMatch(ExtractUserKeyAndStripTimestamp(key, ts_sz),
                               prefix_extractor, v.handle.offset(), no_io,
                               /*const_ikey_ptr=*/nullptr, get_context,
                               &lookup_context);

      if (not_exist_in_filter) {
        // Not found
        // TODO: think about interaction with Merge. If a user key cannot
        // cross one data block, we should be fine.
        RecordTick(rep_->ioptions.stats, BLOOM_FILTER_USEFUL);
        PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_useful, 1, rep_->level);
        break;
      }

      if (!v.first_internal_key.empty() && !skip_filters &&
          UserComparatorWrapper(rep_->internal_comparator.user_comparator())
                  .CompareWithoutTimestamp(
                      ExtractUserKey(key),
                      ExtractUserKey(v.first_internal_key)) < 0) {
        // The requested key falls between highest key in previous block and
        // lowest key in current block.
        break;
      }

      BlockCacheLookupContext lookup_data_block_context{
          TableReaderCaller::kUserGet, tracing_get_id,
          /*get_from_user_specified_snapshot=*/read_options.snapshot !=
              nullptr};
      bool does_referenced_key_exist = false;
      DataBlockIter biter;
      uint64_t referenced_data_size = 0;
      NewDataBlockIterator<DataBlockIter>(
          read_options, v.handle, &biter, BlockType::kData, get_context,
          &lookup_data_block_context,
          /*s=*/Status(), /*prefetch_buffer*/ nullptr);

      if (no_io && biter.status().IsIncomplete()) {
        // couldn't get block from block_cache
        // Update Saver.state to Found because we are only looking for
        // whether we can guarantee the key is not there when "no_io" is set
        get_context->MarkKeyMayExist();
        s = biter.status();
        break;
      }
      if (!biter.status().ok()) {
        s = biter.status();
        break;
      }

      bool may_exist = biter.SeekForGet(key);
      // If user-specified timestamp is supported, we cannot end the search
      // just because hash index lookup indicates the key+ts does not exist.
      if (!may_exist && ts_sz == 0) {
        // HashSeek cannot find the key this block and the the iter is not
        // the end of the block, i.e. cannot be in the following blocks
        // either. In this case, the seek_key cannot be found, so we break
        // from the top level for-loop.
        done = true;
      } else {
        // Call the *saver function on each entry/block until it returns false
        for (; biter.Valid(); biter.Next()) {
          ParsedInternalKey parsed_key;
          Status pik_status = ParseInternalKey(
              biter.key(), &parsed_key, false /* log_err_key */);  // TODO
          if (!pik_status.ok()) {
            s = pik_status;
          }

          if (!get_context->SaveValue(
                  parsed_key, biter.value(), &matched,
                  biter.IsValuePinned() ? &biter : nullptr)) {
            if (get_context->State() == GetContext::GetState::kFound) {
              does_referenced_key_exist = true;
              referenced_data_size = biter.key().size() + biter.value().size();
            }
            done = true;
            break;
          }
        }
        s = biter.status();
      }
      // Write the block cache access record.
      if (block_cache_tracer_ && block_cache_tracer_->is_tracing_enabled()) {
        // Avoid making copy of block_key, cf_name, and referenced_key when
        // constructing the access record.
        Slice referenced_key;
        if (does_referenced_key_exist) {
          referenced_key = biter.key();
        } else {
          referenced_key = key;
        }
        BlockCacheTraceRecord access_record(
            rep_->ioptions.clock->NowMicros(),
            /*block_key=*/"", lookup_data_block_context.block_type,
            lookup_data_block_context.block_size, rep_->cf_id_for_tracing(),
            /*cf_name=*/"", rep_->level_for_tracing(),
            rep_->sst_number_for_tracing(), lookup_data_block_context.caller,
            lookup_data_block_context.is_cache_hit,
            lookup_data_block_context.no_insert,
            lookup_data_block_context.get_id,
            lookup_data_block_context.get_from_user_specified_snapshot,
            /*referenced_key=*/"", referenced_data_size,
            lookup_data_block_context.num_keys_in_block,
            does_referenced_key_exist);
        // TODO: Should handle status here?
        block_cache_tracer_
            ->WriteBlockAccess(access_record,
                               lookup_data_block_context.block_key,
                               rep_->cf_name_for_tracing(), referenced_key)
            .PermitUncheckedError();
      }

      if (done) {
        // Avoid the extra Next which is expensive in two-level indexes
        break;
      }
    }
    if (matched && filter != nullptr && !filter->IsBlockBased()) {
      RecordTick(rep_->ioptions.stats, BLOOM_FILTER_FULL_TRUE_POSITIVE);
      PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_full_true_positive, 1,
                                rep_->level);
    }
    if (s.ok() && !iiter->status().IsNotFound()) {
      s = iiter->status();
    }
  }

  return s;
}

using MultiGetRange = MultiGetContext::Range;
void BlockBasedTable::MultiGet(const ReadOptions& read_options,
                               const MultiGetRange* mget_range,
                               const SliceTransform* prefix_extractor,
                               bool skip_filters) {
  if (mget_range->empty()) {
    // Caller should ensure non-empty (performance bug)
    assert(false);
    return;  // Nothing to do
  }

  FilterBlockReader* const filter =
      !skip_filters ? rep_->filter.get() : nullptr;
  MultiGetRange sst_file_range(*mget_range, mget_range->begin(),
                               mget_range->end());

  // First check the full filter
  // If full filter not useful, Then go into each block
  const bool no_io = read_options.read_tier == kBlockCacheTier;
  uint64_t tracing_mget_id = BlockCacheTraceHelper::kReservedGetId;
  if (sst_file_range.begin()->get_context) {
    tracing_mget_id = sst_file_range.begin()->get_context->get_tracing_get_id();
  }
  BlockCacheLookupContext lookup_context{
      TableReaderCaller::kUserMultiGet, tracing_mget_id,
      /*get_from_user_specified_snapshot=*/read_options.snapshot != nullptr};
  FullFilterKeysMayMatch(read_options, filter, &sst_file_range, no_io,
                         prefix_extractor, &lookup_context);

  if (!sst_file_range.empty()) {
    IndexBlockIter iiter_on_stack;
    // if prefix_extractor found in block differs from options, disable
    // BlockPrefixIndex. Only do this check when index_type is kHashSearch.
    bool need_upper_bound_check = false;
    if (rep_->index_type == BlockBasedTableOptions::kHashSearch) {
      need_upper_bound_check = PrefixExtractorChanged(
          rep_->table_properties.get(), prefix_extractor);
    }
    auto iiter =
        NewIndexIterator(read_options, need_upper_bound_check, &iiter_on_stack,
                         sst_file_range.begin()->get_context, &lookup_context);
    std::unique_ptr<InternalIteratorBase<IndexValue>> iiter_unique_ptr;
    if (iiter != &iiter_on_stack) {
      iiter_unique_ptr.reset(iiter);
    }

    uint64_t offset = std::numeric_limits<uint64_t>::max();
    autovector<BlockHandle, MultiGetContext::MAX_BATCH_SIZE> block_handles;
    autovector<CachableEntry<Block>, MultiGetContext::MAX_BATCH_SIZE> results;
    autovector<Status, MultiGetContext::MAX_BATCH_SIZE> statuses;
    char stack_buf[kMultiGetReadStackBufSize];
    std::unique_ptr<char[]> block_buf;
    {
      MultiGetRange data_block_range(sst_file_range, sst_file_range.begin(),
                                     sst_file_range.end());
      std::vector<Cache::Handle*> cache_handles;
      bool wait_for_cache_results = false;

      CachableEntry<UncompressionDict> uncompression_dict;
      Status uncompression_dict_status;
      uncompression_dict_status.PermitUncheckedError();
      bool uncompression_dict_inited = false;
      size_t total_len = 0;
      ReadOptions ro = read_options;
      ro.read_tier = kBlockCacheTier;

      for (auto miter = data_block_range.begin();
           miter != data_block_range.end(); ++miter) {
        const Slice& key = miter->ikey;
        iiter->Seek(miter->ikey);

        IndexValue v;
        if (iiter->Valid()) {
          v = iiter->value();
        }
        if (!iiter->Valid() ||
            (!v.first_internal_key.empty() && !skip_filters &&
             UserComparatorWrapper(rep_->internal_comparator.user_comparator())
                     .CompareWithoutTimestamp(
                         ExtractUserKey(key),
                         ExtractUserKey(v.first_internal_key)) < 0)) {
          // The requested key falls between highest key in previous block and
          // lowest key in current block.
          if (!iiter->status().IsNotFound()) {
            *(miter->s) = iiter->status();
          }
          data_block_range.SkipKey(miter);
          sst_file_range.SkipKey(miter);
          continue;
        }

        if (!uncompression_dict_inited && rep_->uncompression_dict_reader) {
          uncompression_dict_status =
              rep_->uncompression_dict_reader->GetOrReadUncompressionDictionary(
                  nullptr /* prefetch_buffer */, no_io,
                  sst_file_range.begin()->get_context, &lookup_context,
                  &uncompression_dict);
          uncompression_dict_inited = true;
        }

        if (!uncompression_dict_status.ok()) {
          assert(!uncompression_dict_status.IsNotFound());
          *(miter->s) = uncompression_dict_status;
          data_block_range.SkipKey(miter);
          sst_file_range.SkipKey(miter);
          continue;
        }

        statuses.emplace_back();
        results.emplace_back();
        if (v.handle.offset() == offset) {
          // We're going to reuse the block for this key later on. No need to
          // look it up now. Place a null handle
          block_handles.emplace_back(BlockHandle::NullBlockHandle());
          continue;
        }
        // Lookup the cache for the given data block referenced by an index
        // iterator value (i.e BlockHandle). If it exists in the cache,
        // initialize block to the contents of the data block.
        offset = v.handle.offset();
        BlockHandle handle = v.handle;
        BlockCacheLookupContext lookup_data_block_context(
            TableReaderCaller::kUserMultiGet);
        const UncompressionDict& dict = uncompression_dict.GetValue()
                                            ? *uncompression_dict.GetValue()
                                            : UncompressionDict::GetEmptyDict();
        Status s = RetrieveBlock(
            nullptr, ro, handle, dict, &(results.back()), BlockType::kData,
            miter->get_context, &lookup_data_block_context,
            /* for_compaction */ false, /* use_cache */ true,
            /* wait_for_cache */ false);
        if (s.IsIncomplete()) {
          s = Status::OK();
        }
        if (s.ok() && !results.back().IsEmpty()) {
          // Since we have a valid handle, check the value. If its nullptr,
          // it means the cache is waiting for the final result and we're
          // supposed to call WaitAll() to wait for the result.
          if (results.back().GetValue() != nullptr) {
            // Found it in the cache. Add NULL handle to indicate there is
            // nothing to read from disk.
            if (results.back().GetCacheHandle()) {
              results.back().UpdateCachedValue();
            }
            block_handles.emplace_back(BlockHandle::NullBlockHandle());
          } else {
            // We have to wait for the cache lookup to finish in the
            // background, and then we may have to read the block from disk
            // anyway
            assert(results.back().GetCacheHandle());
            wait_for_cache_results = true;
            block_handles.emplace_back(handle);
            cache_handles.emplace_back(results.back().GetCacheHandle());
          }
        } else {
          block_handles.emplace_back(handle);
          total_len += BlockSizeWithTrailer(handle);
        }
      }

      if (wait_for_cache_results) {
        Cache* block_cache = rep_->table_options.block_cache.get();
        block_cache->WaitAll(cache_handles);
        for (size_t i = 0; i < block_handles.size(); ++i) {
          // If this block was a success or failure or not needed because
          // the corresponding key is in the same block as a prior key, skip
          if (block_handles[i] == BlockHandle::NullBlockHandle() ||
              results[i].IsEmpty()) {
            continue;
          }
          results[i].UpdateCachedValue();
          void* val = results[i].GetValue();
          if (!val) {
            // The async cache lookup failed - could be due to an error
            // or a false positive. We need to read the data block from
            // the SST file
            results[i].Reset();
            total_len += BlockSizeWithTrailer(block_handles[i]);
          } else {
            block_handles[i] = BlockHandle::NullBlockHandle();
          }
        }
      }

      if (total_len) {
        char* scratch = nullptr;
        const UncompressionDict& dict = uncompression_dict.GetValue()
                                            ? *uncompression_dict.GetValue()
                                            : UncompressionDict::GetEmptyDict();
        assert(uncompression_dict_inited || !rep_->uncompression_dict_reader);
        assert(uncompression_dict_status.ok());
        // If using direct IO, then scratch is not used, so keep it nullptr.
        // If the blocks need to be uncompressed and we don't need the
        // compressed blocks, then we can use a contiguous block of
        // memory to read in all the blocks as it will be temporary
        // storage
        // 1. If blocks are compressed and compressed block cache is there,
        //    alloc heap bufs
        // 2. If blocks are uncompressed, alloc heap bufs
        // 3. If blocks are compressed and no compressed block cache, use
        //    stack buf
        if (!rep_->file->use_direct_io() &&
            rep_->table_options.block_cache_compressed == nullptr &&
            rep_->blocks_maybe_compressed) {
          if (total_len <= kMultiGetReadStackBufSize) {
            scratch = stack_buf;
          } else {
            scratch = new char[total_len];
            block_buf.reset(scratch);
          }
        }
        RetrieveMultipleBlocks(read_options, &data_block_range, &block_handles,
                               &statuses, &results, scratch, dict);
        if (sst_file_range.begin()->get_context) {
          ++(sst_file_range.begin()
                 ->get_context->get_context_stats_.num_sst_read);
        }
      }
    }

    DataBlockIter first_biter;
    DataBlockIter next_biter;
    size_t idx_in_batch = 0;
    for (auto miter = sst_file_range.begin(); miter != sst_file_range.end();
         ++miter) {
      Status s;
      GetContext* get_context = miter->get_context;
      const Slice& key = miter->ikey;
      bool matched = false;  // if such user key matched a key in SST
      bool done = false;
      bool first_block = true;
      do {
        DataBlockIter* biter = nullptr;
        bool reusing_block = true;
        uint64_t referenced_data_size = 0;
        bool does_referenced_key_exist = false;
        BlockCacheLookupContext lookup_data_block_context(
            TableReaderCaller::kUserMultiGet, tracing_mget_id,
            /*get_from_user_specified_snapshot=*/read_options.snapshot !=
                nullptr);
        if (first_block) {
          if (!block_handles[idx_in_batch].IsNull() ||
              !results[idx_in_batch].IsEmpty()) {
            first_biter.Invalidate(Status::OK());
            NewDataBlockIterator<DataBlockIter>(
                read_options, results[idx_in_batch], &first_biter,
                statuses[idx_in_batch]);
            reusing_block = false;
          } else {
            // If handler is null and result is empty, then the status is never
            // set, which should be the initial value: ok().
            assert(statuses[idx_in_batch].ok());
          }
          biter = &first_biter;
          idx_in_batch++;
        } else {
          IndexValue v = iiter->value();
          if (!v.first_internal_key.empty() && !skip_filters &&
              UserComparatorWrapper(rep_->internal_comparator.user_comparator())
                      .CompareWithoutTimestamp(
                          ExtractUserKey(key),
                          ExtractUserKey(v.first_internal_key)) < 0) {
            // The requested key falls between highest key in previous block and
            // lowest key in current block.
            break;
          }

          next_biter.Invalidate(Status::OK());
          NewDataBlockIterator<DataBlockIter>(
              read_options, iiter->value().handle, &next_biter,
              BlockType::kData, get_context, &lookup_data_block_context,
              Status(), nullptr);
          biter = &next_biter;
          reusing_block = false;
        }

        if (read_options.read_tier == kBlockCacheTier &&
            biter->status().IsIncomplete()) {
          // couldn't get block from block_cache
          // Update Saver.state to Found because we are only looking for
          // whether we can guarantee the key is not there when "no_io" is set
          get_context->MarkKeyMayExist();
          break;
        }
        if (!biter->status().ok()) {
          s = biter->status();
          break;
        }

        bool may_exist = biter->SeekForGet(key);
        if (!may_exist) {
          // HashSeek cannot find the key this block and the the iter is not
          // the end of the block, i.e. cannot be in the following blocks
          // either. In this case, the seek_key cannot be found, so we break
          // from the top level for-loop.
          break;
        }

        // Call the *saver function on each entry/block until it returns false
        for (; biter->Valid(); biter->Next()) {
          ParsedInternalKey parsed_key;
          Cleanable dummy;
          Cleanable* value_pinner = nullptr;
          Status pik_status = ParseInternalKey(
              biter->key(), &parsed_key, false /* log_err_key */);  // TODO
          if (!pik_status.ok()) {
            s = pik_status;
          }
          if (biter->IsValuePinned()) {
            if (reusing_block) {
              Cache* block_cache = rep_->table_options.block_cache.get();
              assert(biter->cache_handle() != nullptr);
              block_cache->Ref(biter->cache_handle());
              dummy.RegisterCleanup(&ReleaseCachedEntry, block_cache,
                                    biter->cache_handle());
              value_pinner = &dummy;
            } else {
              value_pinner = biter;
            }
          }
          if (!get_context->SaveValue(parsed_key, biter->value(), &matched,
                                      value_pinner)) {
            if (get_context->State() == GetContext::GetState::kFound) {
              does_referenced_key_exist = true;
              referenced_data_size =
                  biter->key().size() + biter->value().size();
            }
            done = true;
            break;
          }
          s = biter->status();
        }
        // Write the block cache access.
        if (block_cache_tracer_ && block_cache_tracer_->is_tracing_enabled()) {
          // Avoid making copy of block_key, cf_name, and referenced_key when
          // constructing the access record.
          Slice referenced_key;
          if (does_referenced_key_exist) {
            referenced_key = biter->key();
          } else {
            referenced_key = key;
          }
          BlockCacheTraceRecord access_record(
              rep_->ioptions.clock->NowMicros(),
              /*block_key=*/"", lookup_data_block_context.block_type,
              lookup_data_block_context.block_size, rep_->cf_id_for_tracing(),
              /*cf_name=*/"", rep_->level_for_tracing(),
              rep_->sst_number_for_tracing(), lookup_data_block_context.caller,
              lookup_data_block_context.is_cache_hit,
              lookup_data_block_context.no_insert,
              lookup_data_block_context.get_id,
              lookup_data_block_context.get_from_user_specified_snapshot,
              /*referenced_key=*/"", referenced_data_size,
              lookup_data_block_context.num_keys_in_block,
              does_referenced_key_exist);
          // TODO: Should handle status here?
          block_cache_tracer_
              ->WriteBlockAccess(access_record,
                                 lookup_data_block_context.block_key,
                                 rep_->cf_name_for_tracing(), referenced_key)
              .PermitUncheckedError();
        }
        s = biter->status();
        if (done) {
          // Avoid the extra Next which is expensive in two-level indexes
          break;
        }
        if (first_block) {
          iiter->Seek(key);
        }
        first_block = false;
        iiter->Next();
      } while (iiter->Valid());

      if (matched && filter != nullptr && !filter->IsBlockBased()) {
        RecordTick(rep_->ioptions.stats, BLOOM_FILTER_FULL_TRUE_POSITIVE);
        PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_full_true_positive, 1,
                                  rep_->level);
      }
      if (s.ok() && !iiter->status().IsNotFound()) {
        s = iiter->status();
      }
      *(miter->s) = s;
    }
#ifdef ROCKSDB_ASSERT_STATUS_CHECKED
    // Not sure why we need to do it. Should investigate more.
    for (auto& st : statuses) {
      st.PermitUncheckedError();
    }
#endif  // ROCKSDB_ASSERT_STATUS_CHECKED
  }
}

Status BlockBasedTable::Prefetch(const Slice* const begin,
                                 const Slice* const end) {
  auto& comparator = rep_->internal_comparator;
  UserComparatorWrapper user_comparator(comparator.user_comparator());
  // pre-condition
  if (begin && end && comparator.Compare(*begin, *end) > 0) {
    return Status::InvalidArgument(*begin, *end);
  }
  BlockCacheLookupContext lookup_context{TableReaderCaller::kPrefetch};
  IndexBlockIter iiter_on_stack;
  auto iiter = NewIndexIterator(ReadOptions(), /*need_upper_bound_check=*/false,
                                &iiter_on_stack, /*get_context=*/nullptr,
                                &lookup_context);
  std::unique_ptr<InternalIteratorBase<IndexValue>> iiter_unique_ptr;
  if (iiter != &iiter_on_stack) {
    iiter_unique_ptr = std::unique_ptr<InternalIteratorBase<IndexValue>>(iiter);
  }

  if (!iiter->status().ok()) {
    // error opening index iterator
    return iiter->status();
  }

  // indicates if we are on the last page that need to be pre-fetched
  bool prefetching_boundary_page = false;

  for (begin ? iiter->Seek(*begin) : iiter->SeekToFirst(); iiter->Valid();
       iiter->Next()) {
    BlockHandle block_handle = iiter->value().handle;
    const bool is_user_key = !rep_->index_key_includes_seq;
    if (end &&
        ((!is_user_key && comparator.Compare(iiter->key(), *end) >= 0) ||
         (is_user_key &&
          user_comparator.Compare(iiter->key(), ExtractUserKey(*end)) >= 0))) {
      if (prefetching_boundary_page) {
        break;
      }

      // The index entry represents the last key in the data block.
      // We should load this page into memory as well, but no more
      prefetching_boundary_page = true;
    }

    // Load the block specified by the block_handle into the block cache
    DataBlockIter biter;

    NewDataBlockIterator<DataBlockIter>(
        ReadOptions(), block_handle, &biter, /*type=*/BlockType::kData,
        /*get_context=*/nullptr, &lookup_context, Status(),
        /*prefetch_buffer=*/nullptr);

    if (!biter.status().ok()) {
      // there was an unexpected error while pre-fetching
      return biter.status();
    }
  }

  return Status::OK();
}

Status BlockBasedTable::VerifyChecksum(const ReadOptions& read_options,
                                       TableReaderCaller caller) {
  Status s;
  // Check Meta blocks
  std::unique_ptr<Block> metaindex;
  std::unique_ptr<InternalIterator> metaindex_iter;
  ReadOptions ro;
  s = ReadMetaIndexBlock(ro, nullptr /* prefetch buffer */, &metaindex,
                         &metaindex_iter);
  if (s.ok()) {
    s = VerifyChecksumInMetaBlocks(metaindex_iter.get());
    if (!s.ok()) {
      return s;
    }
  } else {
    return s;
  }
  // Check Data blocks
  IndexBlockIter iiter_on_stack;
  BlockCacheLookupContext context{caller};
  InternalIteratorBase<IndexValue>* iiter = NewIndexIterator(
      read_options, /*disable_prefix_seek=*/false, &iiter_on_stack,
      /*get_context=*/nullptr, &context);
  std::unique_ptr<InternalIteratorBase<IndexValue>> iiter_unique_ptr;
  if (iiter != &iiter_on_stack) {
    iiter_unique_ptr = std::unique_ptr<InternalIteratorBase<IndexValue>>(iiter);
  }
  if (!iiter->status().ok()) {
    // error opening index iterator
    return iiter->status();
  }
  s = VerifyChecksumInBlocks(read_options, iiter);
  return s;
}

Status BlockBasedTable::VerifyChecksumInBlocks(
    const ReadOptions& read_options,
    InternalIteratorBase<IndexValue>* index_iter) {
  Status s;
  // We are scanning the whole file, so no need to do exponential
  // increasing of the buffer size.
  size_t readahead_size = (read_options.readahead_size != 0)
                              ? read_options.readahead_size
                              : rep_->table_options.max_auto_readahead_size;
  // FilePrefetchBuffer doesn't work in mmap mode and readahead is not
  // needed there.
  FilePrefetchBuffer prefetch_buffer(
      rep_->file.get(), readahead_size /* readahead_size */,
      readahead_size /* max_readahead_size */,
      !rep_->ioptions.allow_mmap_reads /* enable */);

  for (index_iter->SeekToFirst(); index_iter->Valid(); index_iter->Next()) {
    s = index_iter->status();
    if (!s.ok()) {
      break;
    }
    BlockHandle handle = index_iter->value().handle;
    BlockContents contents;
    BlockFetcher block_fetcher(
        rep_->file.get(), &prefetch_buffer, rep_->footer, ReadOptions(), handle,
        &contents, rep_->ioptions, false /* decompress */,
        false /*maybe_compressed*/, BlockType::kData,
        UncompressionDict::GetEmptyDict(), rep_->persistent_cache_options);
    s = block_fetcher.ReadBlockContents();
    if (!s.ok()) {
      break;
    }
  }
  if (s.ok()) {
    // In the case of two level indexes, we would have exited the above loop
    // by checking index_iter->Valid(), but Valid() might have returned false
    // due to an IO error. So check the index_iter status
    s = index_iter->status();
  }
  return s;
}

BlockType BlockBasedTable::GetBlockTypeForMetaBlockByName(
    const Slice& meta_block_name) {
  if (meta_block_name.starts_with(kFilterBlockPrefix) ||
      meta_block_name.starts_with(kFullFilterBlockPrefix) ||
      meta_block_name.starts_with(kPartitionedFilterBlockPrefix)) {
    return BlockType::kFilter;
  }

  if (meta_block_name == kPropertiesBlock) {
    return BlockType::kProperties;
  }

  if (meta_block_name == kCompressionDictBlock) {
    return BlockType::kCompressionDictionary;
  }

  if (meta_block_name == kRangeDelBlock) {
    return BlockType::kRangeDeletion;
  }

  if (meta_block_name == kHashIndexPrefixesBlock) {
    return BlockType::kHashIndexPrefixes;
  }

  if (meta_block_name == kHashIndexPrefixesMetadataBlock) {
    return BlockType::kHashIndexMetadata;
  }

  assert(false);
  return BlockType::kInvalid;
}

Status BlockBasedTable::VerifyChecksumInMetaBlocks(
    InternalIteratorBase<Slice>* index_iter) {
  Status s;
  for (index_iter->SeekToFirst(); index_iter->Valid(); index_iter->Next()) {
    s = index_iter->status();
    if (!s.ok()) {
      break;
    }
    BlockHandle handle;
    Slice input = index_iter->value();
    s = handle.DecodeFrom(&input);
    BlockContents contents;
    const Slice meta_block_name = index_iter->key();
    if (meta_block_name == kPropertiesBlock) {
      // Unfortunate special handling for properties block checksum w/
      // global seqno
      std::unique_ptr<TableProperties> table_properties;
      s = ReadTablePropertiesHelper(ReadOptions(), handle, rep_->file.get(),
                                    nullptr /* prefetch_buffer */, rep_->footer,
                                    rep_->ioptions, &table_properties,
                                    nullptr /* memory_allocator */);
    } else {
      s = BlockFetcher(
              rep_->file.get(), nullptr /* prefetch buffer */, rep_->footer,
              ReadOptions(), handle, &contents, rep_->ioptions,
              false /* decompress */, false /*maybe_compressed*/,
              GetBlockTypeForMetaBlockByName(meta_block_name),
              UncompressionDict::GetEmptyDict(), rep_->persistent_cache_options)
              .ReadBlockContents();
    }
    if (!s.ok()) {
      break;
    }
  }
  return s;
}

bool BlockBasedTable::TEST_BlockInCache(const BlockHandle& handle) const {
  assert(rep_ != nullptr);

  Cache* const cache = rep_->table_options.block_cache.get();
  if (cache == nullptr) {
    return false;
  }

  char cache_key_storage[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
  Slice cache_key =
      GetCacheKey(rep_->cache_key_prefix, rep_->cache_key_prefix_size, handle,
                  cache_key_storage);

  Cache::Handle* const cache_handle = cache->Lookup(cache_key);
  if (cache_handle == nullptr) {
    return false;
  }

  cache->Release(cache_handle);

  return true;
}

bool BlockBasedTable::TEST_KeyInCache(const ReadOptions& options,
                                      const Slice& key) {
  std::unique_ptr<InternalIteratorBase<IndexValue>> iiter(NewIndexIterator(
      options, /*need_upper_bound_check=*/false, /*input_iter=*/nullptr,
      /*get_context=*/nullptr, /*lookup_context=*/nullptr));
  iiter->Seek(key);
  assert(iiter->Valid());

  return TEST_BlockInCache(iiter->value().handle);
}

// REQUIRES: The following fields of rep_ should have already been populated:
//  1. file
//  2. index_handle,
//  3. options
//  4. internal_comparator
//  5. index_type
Status BlockBasedTable::CreateIndexReader(
    const ReadOptions& ro, FilePrefetchBuffer* prefetch_buffer,
    InternalIterator* preloaded_meta_index_iter, bool use_cache, bool prefetch,
    bool pin, BlockCacheLookupContext* lookup_context,
    std::unique_ptr<IndexReader>* index_reader) {
  // kHashSearch requires non-empty prefix_extractor but bypass checking
  // prefix_extractor here since we have no access to MutableCFOptions.
  // Add need_upper_bound_check flag in  BlockBasedTable::NewIndexIterator.
  // If prefix_extractor does not match prefix_extractor_name from table
  // properties, turn off Hash Index by setting total_order_seek to true

  switch (rep_->index_type) {
    case BlockBasedTableOptions::kTwoLevelIndexSearch: {
      return PartitionIndexReader::Create(this, ro, prefetch_buffer, use_cache,
                                          prefetch, pin, lookup_context,
                                          index_reader);
    }
    case BlockBasedTableOptions::kBinarySearch:
      FALLTHROUGH_INTENDED;
    case BlockBasedTableOptions::kBinarySearchWithFirstKey: {
      return BinarySearchIndexReader::Create(this, ro, prefetch_buffer,
                                             use_cache, prefetch, pin,
                                             lookup_context, index_reader);
    }
    case BlockBasedTableOptions::kHashSearch: {
      std::unique_ptr<Block> metaindex_guard;
      std::unique_ptr<InternalIterator> metaindex_iter_guard;
      auto meta_index_iter = preloaded_meta_index_iter;
      bool should_fallback = false;
      if (rep_->internal_prefix_transform.get() == nullptr) {
        ROCKS_LOG_WARN(rep_->ioptions.logger,
                       "No prefix extractor passed in. Fall back to binary"
                       " search index.");
        should_fallback = true;
      } else if (meta_index_iter == nullptr) {
        auto s = ReadMetaIndexBlock(ro, prefetch_buffer, &metaindex_guard,
                                    &metaindex_iter_guard);
        if (!s.ok()) {
          // we simply fall back to binary search in case there is any
          // problem with prefix hash index loading.
          ROCKS_LOG_WARN(rep_->ioptions.logger,
                         "Unable to read the metaindex block."
                         " Fall back to binary search index.");
          should_fallback = true;
        }
        meta_index_iter = metaindex_iter_guard.get();
      }

      if (should_fallback) {
        return BinarySearchIndexReader::Create(this, ro, prefetch_buffer,
                                               use_cache, prefetch, pin,
                                               lookup_context, index_reader);
      } else {
        return HashIndexReader::Create(this, ro, prefetch_buffer,
                                       meta_index_iter, use_cache, prefetch,
                                       pin, lookup_context, index_reader);
      }
    }
    default: {
      std::string error_message =
          "Unrecognized index type: " + ToString(rep_->index_type);
      return Status::InvalidArgument(error_message.c_str());
    }
  }
}

uint64_t BlockBasedTable::ApproximateDataOffsetOf(
    const InternalIteratorBase<IndexValue>& index_iter,
    uint64_t data_size) const {
  if (index_iter.Valid()) {
    BlockHandle handle = index_iter.value().handle;
    return handle.offset();
  } else {
    // The iterator is past the last key in the file.
    return data_size;
  }
}

uint64_t BlockBasedTable::GetApproximateDataSize() {
  // Should be in table properties unless super old version
  if (rep_->table_properties) {
    return rep_->table_properties->data_size;
  }
  // Fall back to rough estimate from footer
  return rep_->footer.metaindex_handle().offset();
}

uint64_t BlockBasedTable::ApproximateOffsetOf(const Slice& key,
                                              TableReaderCaller caller) {
  uint64_t data_size = GetApproximateDataSize();
  if (UNLIKELY(data_size == 0)) {
    // Hmm. Let's just split in half to avoid skewing one way or another,
    // since we don't know whether we're operating on lower bound or
    // upper bound.
    return rep_->file_size / 2;
  }

  BlockCacheLookupContext context(caller);
  IndexBlockIter iiter_on_stack;
  ReadOptions ro;
  ro.total_order_seek = true;
  auto index_iter =
      NewIndexIterator(ro, /*disable_prefix_seek=*/true,
                       /*input_iter=*/&iiter_on_stack, /*get_context=*/nullptr,
                       /*lookup_context=*/&context);
  std::unique_ptr<InternalIteratorBase<IndexValue>> iiter_unique_ptr;
  if (index_iter != &iiter_on_stack) {
    iiter_unique_ptr.reset(index_iter);
  }

  index_iter->Seek(key);

  uint64_t offset = ApproximateDataOffsetOf(*index_iter, data_size);
  // Pro-rate file metadata (incl filters) size-proportionally across data
  // blocks.
  double size_ratio =
      static_cast<double>(offset) / static_cast<double>(data_size);
  return static_cast<uint64_t>(size_ratio *
                               static_cast<double>(rep_->file_size));
}

uint64_t BlockBasedTable::ApproximateSize(const Slice& start, const Slice& end,
                                          TableReaderCaller caller) {
  assert(rep_->internal_comparator.Compare(start, end) <= 0);

  uint64_t data_size = GetApproximateDataSize();
  if (UNLIKELY(data_size == 0)) {
    // Hmm. Assume whole file is involved, since we have lower and upper
    // bound.
    return rep_->file_size;
  }

  BlockCacheLookupContext context(caller);
  IndexBlockIter iiter_on_stack;
  ReadOptions ro;
  ro.total_order_seek = true;
  auto index_iter =
      NewIndexIterator(ro, /*disable_prefix_seek=*/true,
                       /*input_iter=*/&iiter_on_stack, /*get_context=*/nullptr,
                       /*lookup_context=*/&context);
  std::unique_ptr<InternalIteratorBase<IndexValue>> iiter_unique_ptr;
  if (index_iter != &iiter_on_stack) {
    iiter_unique_ptr.reset(index_iter);
  }

  index_iter->Seek(start);
  uint64_t start_offset = ApproximateDataOffsetOf(*index_iter, data_size);
  index_iter->Seek(end);
  uint64_t end_offset = ApproximateDataOffsetOf(*index_iter, data_size);

  assert(end_offset >= start_offset);
  // Pro-rate file metadata (incl filters) size-proportionally across data
  // blocks.
  double size_ratio = static_cast<double>(end_offset - start_offset) /
                      static_cast<double>(data_size);
  return static_cast<uint64_t>(size_ratio *
                               static_cast<double>(rep_->file_size));
}

bool BlockBasedTable::TEST_FilterBlockInCache() const {
  assert(rep_ != nullptr);
  return TEST_BlockInCache(rep_->filter_handle);
}

bool BlockBasedTable::TEST_IndexBlockInCache() const {
  assert(rep_ != nullptr);

  return TEST_BlockInCache(rep_->footer.index_handle());
}

Status BlockBasedTable::GetKVPairsFromDataBlocks(
    std::vector<KVPairBlock>* kv_pair_blocks) {
  std::unique_ptr<InternalIteratorBase<IndexValue>> blockhandles_iter(
      NewIndexIterator(ReadOptions(), /*need_upper_bound_check=*/false,
                       /*input_iter=*/nullptr, /*get_context=*/nullptr,
                       /*lookup_contex=*/nullptr));

  Status s = blockhandles_iter->status();
  if (!s.ok()) {
    // Cannot read Index Block
    return s;
  }

  for (blockhandles_iter->SeekToFirst(); blockhandles_iter->Valid();
       blockhandles_iter->Next()) {
    s = blockhandles_iter->status();

    if (!s.ok()) {
      break;
    }

    std::unique_ptr<InternalIterator> datablock_iter;
    datablock_iter.reset(NewDataBlockIterator<DataBlockIter>(
        ReadOptions(), blockhandles_iter->value().handle,
        /*input_iter=*/nullptr, /*type=*/BlockType::kData,
        /*get_context=*/nullptr, /*lookup_context=*/nullptr, Status(),
        /*prefetch_buffer=*/nullptr));
    s = datablock_iter->status();

    if (!s.ok()) {
      // Error reading the block - Skipped
      continue;
    }

    KVPairBlock kv_pair_block;
    for (datablock_iter->SeekToFirst(); datablock_iter->Valid();
         datablock_iter->Next()) {
      s = datablock_iter->status();
      if (!s.ok()) {
        // Error reading the block - Skipped
        break;
      }
      const Slice& key = datablock_iter->key();
      const Slice& value = datablock_iter->value();
      std::string key_copy = std::string(key.data(), key.size());
      std::string value_copy = std::string(value.data(), value.size());

      kv_pair_block.push_back(
          std::make_pair(std::move(key_copy), std::move(value_copy)));
    }
    kv_pair_blocks->push_back(std::move(kv_pair_block));
  }
  return Status::OK();
}

Status BlockBasedTable::DumpTable(WritableFile* out_file) {
  WritableFileStringStreamAdapter out_file_wrapper(out_file);
  std::ostream out_stream(&out_file_wrapper);
  // Output Footer
  out_stream << "Footer Details:\n"
                "--------------------------------------\n";
  out_stream << "  " << rep_->footer.ToString() << "\n";

  // Output MetaIndex
  out_stream << "Metaindex Details:\n"
                "--------------------------------------\n";
  std::unique_ptr<Block> metaindex;
  std::unique_ptr<InternalIterator> metaindex_iter;
  ReadOptions ro;
  Status s = ReadMetaIndexBlock(ro, nullptr /* prefetch_buffer */, &metaindex,
                                &metaindex_iter);
  if (s.ok()) {
    for (metaindex_iter->SeekToFirst(); metaindex_iter->Valid();
         metaindex_iter->Next()) {
      s = metaindex_iter->status();
      if (!s.ok()) {
        return s;
      }
      if (metaindex_iter->key() == kPropertiesBlock) {
        out_stream << "  Properties block handle: "
                   << metaindex_iter->value().ToString(true) << "\n";
      } else if (metaindex_iter->key() == kCompressionDictBlock) {
        out_stream << "  Compression dictionary block handle: "
                   << metaindex_iter->value().ToString(true) << "\n";
      } else if (strstr(metaindex_iter->key().ToString().c_str(),
                        "filter.rocksdb.") != nullptr) {
        out_stream << "  Filter block handle: "
                   << metaindex_iter->value().ToString(true) << "\n";
      } else if (metaindex_iter->key() == kRangeDelBlock) {
        out_stream << "  Range deletion block handle: "
                   << metaindex_iter->value().ToString(true) << "\n";
      }
    }
    out_stream << "\n";
  } else {
    return s;
  }

  // Output TableProperties
  const ROCKSDB_NAMESPACE::TableProperties* table_properties;
  table_properties = rep_->table_properties.get();

  if (table_properties != nullptr) {
    out_stream << "Table Properties:\n"
                  "--------------------------------------\n";
    out_stream << "  " << table_properties->ToString("\n  ", ": ") << "\n";
  }

  if (rep_->filter) {
    out_stream << "Filter Details:\n"
                  "--------------------------------------\n";
    out_stream << "  " << rep_->filter->ToString() << "\n";
  }

  // Output Index block
  s = DumpIndexBlock(out_stream);
  if (!s.ok()) {
    return s;
  }

  // Output compression dictionary
  if (rep_->uncompression_dict_reader) {
    CachableEntry<UncompressionDict> uncompression_dict;
    s = rep_->uncompression_dict_reader->GetOrReadUncompressionDictionary(
        nullptr /* prefetch_buffer */, false /* no_io */,
        nullptr /* get_context */, nullptr /* lookup_context */,
        &uncompression_dict);
    if (!s.ok()) {
      return s;
    }

    assert(uncompression_dict.GetValue());

    const Slice& raw_dict = uncompression_dict.GetValue()->GetRawDict();
    out_stream << "Compression Dictionary:\n"
                  "--------------------------------------\n";
    out_stream << "  size (bytes): " << raw_dict.size() << "\n\n";
    out_stream << "  HEX    " << raw_dict.ToString(true) << "\n\n";
  }

  // Output range deletions block
  auto* range_del_iter = NewRangeTombstoneIterator(ReadOptions());
  if (range_del_iter != nullptr) {
    range_del_iter->SeekToFirst();
    if (range_del_iter->Valid()) {
      out_stream << "Range deletions:\n"
                    "--------------------------------------\n";
      for (; range_del_iter->Valid(); range_del_iter->Next()) {
        DumpKeyValue(range_del_iter->key(), range_del_iter->value(),
                     out_stream);
      }
      out_stream << "\n";
    }
    delete range_del_iter;
  }
  // Output Data blocks
  s = DumpDataBlocks(out_stream);

  if (!s.ok()) {
    return s;
  }

  if (!out_stream.good()) {
    return Status::IOError("Failed to write to output file");
  }
  return Status::OK();
}

Status BlockBasedTable::DumpIndexBlock(std::ostream& out_stream) {
  out_stream << "Index Details:\n"
                "--------------------------------------\n";
  std::unique_ptr<InternalIteratorBase<IndexValue>> blockhandles_iter(
      NewIndexIterator(ReadOptions(), /*need_upper_bound_check=*/false,
                       /*input_iter=*/nullptr, /*get_context=*/nullptr,
                       /*lookup_contex=*/nullptr));
  Status s = blockhandles_iter->status();
  if (!s.ok()) {
    out_stream << "Can not read Index Block \n\n";
    return s;
  }

  out_stream << "  Block key hex dump: Data block handle\n";
  out_stream << "  Block key ascii\n\n";
  for (blockhandles_iter->SeekToFirst(); blockhandles_iter->Valid();
       blockhandles_iter->Next()) {
    s = blockhandles_iter->status();
    if (!s.ok()) {
      break;
    }
    Slice key = blockhandles_iter->key();
    Slice user_key;
    InternalKey ikey;
    if (!rep_->index_key_includes_seq) {
      user_key = key;
    } else {
      ikey.DecodeFrom(key);
      user_key = ikey.user_key();
    }

    out_stream << "  HEX    " << user_key.ToString(true) << ": "
               << blockhandles_iter->value().ToString(true,
                                                      rep_->index_has_first_key)
               << "\n";

    std::string str_key = user_key.ToString();
    std::string res_key("");
    char cspace = ' ';
    for (size_t i = 0; i < str_key.size(); i++) {
      res_key.append(&str_key[i], 1);
      res_key.append(1, cspace);
    }
    out_stream << "  ASCII  " << res_key << "\n";
    out_stream << "  ------\n";
  }
  out_stream << "\n";
  return Status::OK();
}

Status BlockBasedTable::DumpDataBlocks(std::ostream& out_stream) {
  std::unique_ptr<InternalIteratorBase<IndexValue>> blockhandles_iter(
      NewIndexIterator(ReadOptions(), /*need_upper_bound_check=*/false,
                       /*input_iter=*/nullptr, /*get_context=*/nullptr,
                       /*lookup_contex=*/nullptr));
  Status s = blockhandles_iter->status();
  if (!s.ok()) {
    out_stream << "Can not read Index Block \n\n";
    return s;
  }

  uint64_t datablock_size_min = std::numeric_limits<uint64_t>::max();
  uint64_t datablock_size_max = 0;
  uint64_t datablock_size_sum = 0;

  size_t block_id = 1;
  for (blockhandles_iter->SeekToFirst(); blockhandles_iter->Valid();
       block_id++, blockhandles_iter->Next()) {
    s = blockhandles_iter->status();
    if (!s.ok()) {
      break;
    }

    BlockHandle bh = blockhandles_iter->value().handle;
    uint64_t datablock_size = bh.size();
    datablock_size_min = std::min(datablock_size_min, datablock_size);
    datablock_size_max = std::max(datablock_size_max, datablock_size);
    datablock_size_sum += datablock_size;

    out_stream << "Data Block # " << block_id << " @ "
               << blockhandles_iter->value().handle.ToString(true) << "\n";
    out_stream << "--------------------------------------\n";

    std::unique_ptr<InternalIterator> datablock_iter;
    datablock_iter.reset(NewDataBlockIterator<DataBlockIter>(
        ReadOptions(), blockhandles_iter->value().handle,
        /*input_iter=*/nullptr, /*type=*/BlockType::kData,
        /*get_context=*/nullptr, /*lookup_context=*/nullptr, Status(),
        /*prefetch_buffer=*/nullptr));
    s = datablock_iter->status();

    if (!s.ok()) {
      out_stream << "Error reading the block - Skipped \n\n";
      continue;
    }

    for (datablock_iter->SeekToFirst(); datablock_iter->Valid();
         datablock_iter->Next()) {
      s = datablock_iter->status();
      if (!s.ok()) {
        out_stream << "Error reading the block - Skipped \n";
        break;
      }
      DumpKeyValue(datablock_iter->key(), datablock_iter->value(), out_stream);
    }
    out_stream << "\n";
  }

  uint64_t num_datablocks = block_id - 1;
  if (num_datablocks) {
    double datablock_size_avg =
        static_cast<double>(datablock_size_sum) / num_datablocks;
    out_stream << "Data Block Summary:\n";
    out_stream << "--------------------------------------\n";
    out_stream << "  # data blocks: " << num_datablocks << "\n";
    out_stream << "  min data block size: " << datablock_size_min << "\n";
    out_stream << "  max data block size: " << datablock_size_max << "\n";
    out_stream << "  avg data block size: " << ToString(datablock_size_avg)
               << "\n";
  }

  return Status::OK();
}

void BlockBasedTable::DumpKeyValue(const Slice& key, const Slice& value,
                                   std::ostream& out_stream) {
  InternalKey ikey;
  ikey.DecodeFrom(key);

  out_stream << "  HEX    " << ikey.user_key().ToString(true) << ": "
             << value.ToString(true) << "\n";

  std::string str_key = ikey.user_key().ToString();
  std::string str_value = value.ToString();
  std::string res_key(""), res_value("");
  char cspace = ' ';
  for (size_t i = 0; i < str_key.size(); i++) {
    if (str_key[i] == '\0') {
      res_key.append("\\0", 2);
    } else {
      res_key.append(&str_key[i], 1);
    }
    res_key.append(1, cspace);
  }
  for (size_t i = 0; i < str_value.size(); i++) {
    if (str_value[i] == '\0') {
      res_value.append("\\0", 2);
    } else {
      res_value.append(&str_value[i], 1);
    }
    res_value.append(1, cspace);
  }

  out_stream << "  ASCII  " << res_key << ": " << res_value << "\n";
  out_stream << "  ------\n";
}

}  // namespace ROCKSDB_NAMESPACE