rocksdb/table/block_fetcher.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_fetcher.h"

#include <cinttypes>
#include <string>

#include "logging/logging.h"
#include "memory/memory_allocator.h"
#include "monitoring/perf_context_imp.h"
#include "rocksdb/compression_type.h"
#include "rocksdb/env.h"
#include "table/block_based/block.h"
#include "table/block_based/block_based_table_reader.h"
#include "table/block_based/block_type.h"
#include "table/block_based/reader_common.h"
#include "table/format.h"
#include "table/persistent_cache_helper.h"
#include "util/compression.h"
#include "util/stop_watch.h"

namespace ROCKSDB_NAMESPACE {

inline void BlockFetcher::ProcessTrailerIfPresent() {
  if (footer_.GetBlockTrailerSize() > 0) {
    assert(footer_.GetBlockTrailerSize() == BlockBasedTable::kBlockTrailerSize);
    if (read_options_.verify_checksums) {
      io_status_ = status_to_io_status(VerifyBlockChecksum(
          footer_.checksum_type(), slice_.data(), block_size_,
          file_->file_name(), handle_.offset()));
      RecordTick(ioptions_.stats, BLOCK_CHECKSUM_COMPUTE_COUNT);
    }
    compression_type_ =
        BlockBasedTable::GetBlockCompressionType(slice_.data(), block_size_);
  } else {
    // E.g. plain table or cuckoo table
    compression_type_ = kNoCompression;
  }
}

inline bool BlockFetcher::TryGetUncompressBlockFromPersistentCache() {
  if (cache_options_.persistent_cache &&
      !cache_options_.persistent_cache->IsCompressed()) {
    Status status = PersistentCacheHelper::LookupUncompressedPage(
        cache_options_, handle_, contents_);
    if (status.ok()) {
      // uncompressed page is found for the block handle
      return true;
    } else {
      // uncompressed page is not found
      if (ioptions_.logger && !status.IsNotFound()) {
        assert(!status.ok());
        ROCKS_LOG_INFO(ioptions_.logger,
                       "Error reading from persistent cache. %s",
                       status.ToString().c_str());
      }
    }
  }
  return false;
}

inline bool BlockFetcher::TryGetFromPrefetchBuffer() {
  if (prefetch_buffer_ != nullptr) {
    IOOptions opts;
    IOStatus io_s = file_->PrepareIOOptions(read_options_, opts);
    if (io_s.ok()) {
      bool read_from_prefetch_buffer = false;
      if (read_options_.async_io) {
        read_from_prefetch_buffer = prefetch_buffer_->TryReadFromCacheAsync(
            opts, file_, handle_.offset(), block_size_with_trailer_, &slice_,
            &io_s, read_options_.rate_limiter_priority, for_compaction_);
      } else {
        read_from_prefetch_buffer = prefetch_buffer_->TryReadFromCache(
            opts, file_, handle_.offset(), block_size_with_trailer_, &slice_,
            &io_s, read_options_.rate_limiter_priority, for_compaction_);
      }
      if (read_from_prefetch_buffer) {
        ProcessTrailerIfPresent();
        if (!io_status_.ok()) {
          return true;
        }
        got_from_prefetch_buffer_ = true;
        used_buf_ = const_cast<char*>(slice_.data());
      }
    }
    if (!io_s.ok()) {
      io_status_ = io_s;
      return true;
    }
  }
  return got_from_prefetch_buffer_;
}

inline bool BlockFetcher::TryGetCompressedBlockFromPersistentCache() {
  if (cache_options_.persistent_cache &&
      cache_options_.persistent_cache->IsCompressed()) {
    // lookup uncompressed cache mode p-cache
    std::unique_ptr<char[]> raw_data;
    io_status_ = status_to_io_status(PersistentCacheHelper::LookupRawPage(
        cache_options_, handle_, &raw_data, block_size_with_trailer_));
    if (io_status_.ok()) {
      heap_buf_ = CacheAllocationPtr(raw_data.release());
      used_buf_ = heap_buf_.get();
      slice_ = Slice(heap_buf_.get(), block_size_);
      ProcessTrailerIfPresent();
      return true;
    } else if (!io_status_.IsNotFound() && ioptions_.logger) {
      assert(!io_status_.ok());
      ROCKS_LOG_INFO(ioptions_.logger,
                     "Error reading from persistent cache. %s",
                     io_status_.ToString().c_str());
    }
  }
  return false;
}

inline void BlockFetcher::PrepareBufferForBlockFromFile() {
  // cache miss read from device
  if ((do_uncompress_ || ioptions_.allow_mmap_reads) &&
      block_size_with_trailer_ < kDefaultStackBufferSize) {
    // If we've got a small enough hunk of data, read it in to the
    // trivially allocated stack buffer instead of needing a full malloc()
    //
    // `GetBlockContents()` cannot return this data as its lifetime is tied to
    // this `BlockFetcher`'s lifetime. That is fine because this is only used
    // in cases where we do not expect the `GetBlockContents()` result to be the
    // same buffer we are assigning here. If we guess incorrectly, there will be
    // a heap allocation and memcpy in `GetBlockContents()` to obtain the final
    // result. Considering we are eliding a heap allocation here by using the
    // stack buffer, the cost of guessing incorrectly here is one extra memcpy.
    //
    // When `do_uncompress_` is true, we expect the uncompression step will
    // allocate heap memory for the final result. However this expectation will
    // be wrong if the block turns out to already be uncompressed, which we
    // won't know for sure until after reading it.
    //
    // When `ioptions_.allow_mmap_reads` is true, we do not expect the file
    // reader to use the scratch buffer at all, but instead return a pointer
    // into the mapped memory. This expectation will be wrong when using a
    // file reader that does not implement mmap reads properly.
    used_buf_ = &stack_buf_[0];
  } else if (maybe_compressed_ && !do_uncompress_) {
    compressed_buf_ = AllocateBlock(block_size_with_trailer_,
                                    memory_allocator_compressed_);
    used_buf_ = compressed_buf_.get();
  } else {
    heap_buf_ =
        AllocateBlock(block_size_with_trailer_, memory_allocator_);
    used_buf_ = heap_buf_.get();
  }
}

inline void BlockFetcher::InsertCompressedBlockToPersistentCacheIfNeeded() {
  if (io_status_.ok() && read_options_.fill_cache &&
      cache_options_.persistent_cache &&
      cache_options_.persistent_cache->IsCompressed()) {
    // insert to raw cache
    PersistentCacheHelper::InsertRawPage(cache_options_, handle_, used_buf_,
                                         block_size_with_trailer_);
  }
}

inline void BlockFetcher::InsertUncompressedBlockToPersistentCacheIfNeeded() {
  if (io_status_.ok() && !got_from_prefetch_buffer_ &&
      read_options_.fill_cache && cache_options_.persistent_cache &&
      !cache_options_.persistent_cache->IsCompressed()) {
    // insert to uncompressed cache
    PersistentCacheHelper::InsertUncompressedPage(cache_options_, handle_,
                                                  *contents_);
  }
}

inline void BlockFetcher::CopyBufferToHeapBuf() {
  assert(used_buf_ != heap_buf_.get());
  heap_buf_ = AllocateBlock(block_size_with_trailer_, memory_allocator_);
  memcpy(heap_buf_.get(), used_buf_, block_size_with_trailer_);
#ifndef NDEBUG
  num_heap_buf_memcpy_++;
#endif
}

inline void BlockFetcher::CopyBufferToCompressedBuf() {
  assert(used_buf_ != compressed_buf_.get());
  compressed_buf_ = AllocateBlock(block_size_with_trailer_,
                                  memory_allocator_compressed_);
  memcpy(compressed_buf_.get(), used_buf_, block_size_with_trailer_);
#ifndef NDEBUG
  num_compressed_buf_memcpy_++;
#endif
}

// Entering this method means the block is not compressed or do not need to be
// uncompressed. The block can be in one of the following buffers:
// 1. prefetch buffer if prefetch is enabled and the block is prefetched before
// 2. stack_buf_ if block size is smaller than the stack_buf_ size and block
//    is not compressed
// 3. heap_buf_ if the block is not compressed
// 4. compressed_buf_ if the block is compressed
// 5. direct_io_buf_ if direct IO is enabled
// After this method, if the block is compressed, it should be in
// compressed_buf_, otherwise should be in heap_buf_.
inline void BlockFetcher::GetBlockContents() {
  if (slice_.data() != used_buf_) {
    // the slice content is not the buffer provided
    *contents_ = BlockContents(Slice(slice_.data(), block_size_));
  } else {
    // page can be either uncompressed or compressed, the buffer either stack
    // or heap provided. Refer to https://github.com/facebook/rocksdb/pull/4096
    if (got_from_prefetch_buffer_ || used_buf_ == &stack_buf_[0]) {
      CopyBufferToHeapBuf();
    } else if (used_buf_ == compressed_buf_.get()) {
      if (compression_type_ == kNoCompression &&
          memory_allocator_ != memory_allocator_compressed_) {
        CopyBufferToHeapBuf();
      } else {
        heap_buf_ = std::move(compressed_buf_);
      }
    } else if (direct_io_buf_.get() != nullptr) {
      if (compression_type_ == kNoCompression) {
        CopyBufferToHeapBuf();
      } else {
        CopyBufferToCompressedBuf();
        heap_buf_ = std::move(compressed_buf_);
      }
    }
    *contents_ = BlockContents(std::move(heap_buf_), block_size_);
  }
#ifndef NDEBUG
  contents_->is_raw_block = true;
#endif
}

IOStatus BlockFetcher::ReadBlockContents() {
  if (TryGetUncompressBlockFromPersistentCache()) {
    compression_type_ = kNoCompression;
#ifndef NDEBUG
    contents_->is_raw_block = true;
#endif  // NDEBUG
    return IOStatus::OK();
  }
  if (TryGetFromPrefetchBuffer()) {
    if (!io_status_.ok()) {
      return io_status_;
    }
  } else if (!TryGetCompressedBlockFromPersistentCache()) {
    IOOptions opts;
    io_status_ = file_->PrepareIOOptions(read_options_, opts);
    // Actual file read
    if (io_status_.ok()) {
      if (file_->use_direct_io()) {
        PERF_TIMER_GUARD(block_read_time);
        io_status_ = file_->Read(
            opts, handle_.offset(), block_size_with_trailer_, &slice_, nullptr,
            &direct_io_buf_, read_options_.rate_limiter_priority);
        PERF_COUNTER_ADD(block_read_count, 1);
        used_buf_ = const_cast<char*>(slice_.data());
      } else {
        PrepareBufferForBlockFromFile();
        PERF_TIMER_GUARD(block_read_time);
        io_status_ = file_->Read(opts, handle_.offset(),
                                 block_size_with_trailer_, &slice_, used_buf_,
                                 nullptr, read_options_.rate_limiter_priority);
        PERF_COUNTER_ADD(block_read_count, 1);
#ifndef NDEBUG
        if (slice_.data() == &stack_buf_[0]) {
          num_stack_buf_memcpy_++;
        } else if (slice_.data() == heap_buf_.get()) {
          num_heap_buf_memcpy_++;
        } else if (slice_.data() == compressed_buf_.get()) {
          num_compressed_buf_memcpy_++;
        }
#endif
      }
    }

    // TODO: introduce dedicated perf counter for range tombstones
    switch (block_type_) {
      case BlockType::kFilter:
        PERF_COUNTER_ADD(filter_block_read_count, 1);
        break;

      case BlockType::kCompressionDictionary:
        PERF_COUNTER_ADD(compression_dict_block_read_count, 1);
        break;

      case BlockType::kIndex:
        PERF_COUNTER_ADD(index_block_read_count, 1);
        break;

      // Nothing to do here as we don't have counters for the other types.
      default:
        break;
    }

    PERF_COUNTER_ADD(block_read_byte, block_size_with_trailer_);
    if (!io_status_.ok()) {
      return io_status_;
    }

    if (slice_.size() != block_size_with_trailer_) {
      return IOStatus::Corruption("truncated block read from " +
                                  file_->file_name() + " offset " +
                                  ToString(handle_.offset()) + ", expected " +
                                  ToString(block_size_with_trailer_) +
                                  " bytes, got " + ToString(slice_.size()));
    }

    ProcessTrailerIfPresent();
    if (io_status_.ok()) {
      InsertCompressedBlockToPersistentCacheIfNeeded();
    } else {
      return io_status_;
    }
  }

  if (do_uncompress_ && compression_type_ != kNoCompression) {
    PERF_TIMER_GUARD(block_decompress_time);
    // compressed page, uncompress, update cache
    UncompressionContext context(compression_type_);
    UncompressionInfo info(context, uncompression_dict_, compression_type_);
    io_status_ = status_to_io_status(UncompressBlockContents(
        info, slice_.data(), block_size_, contents_, footer_.format_version(),
        ioptions_, memory_allocator_));
#ifndef NDEBUG
    num_heap_buf_memcpy_++;
#endif
    compression_type_ = kNoCompression;
  } else {
    GetBlockContents();
  }

  InsertUncompressedBlockToPersistentCacheIfNeeded();

  return io_status_;
}

}  // namespace ROCKSDB_NAMESPACE