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 <string>
#include <inttypes.h>

#include "monitoring/perf_context_imp.h"
#include "monitoring/statistics.h"
#include "rocksdb/env.h"
#include "table/block.h"
#include "table/block_based_table_reader.h"
#include "table/persistent_cache_helper.h"
#include "table/format.h"
#include "util/coding.h"
#include "util/compression.h"
#include "util/crc32c.h"
#include "util/file_reader_writer.h"
#include "util/logging.h"
#include "util/stop_watch.h"
#include "util/string_util.h"
#include "util/xxhash.h"

namespace rocksdb {

inline
void BlockFetcher::CheckBlockChecksum() {
  // Check the crc of the type and the block contents
  if (read_options_.verify_checksums) {
    const char* data = slice_.data();  // Pointer to where Read put the data
    PERF_TIMER_GUARD(block_checksum_time);
    uint32_t value = DecodeFixed32(data + block_size_ + 1);
    uint32_t actual = 0;
    switch (footer_.checksum()) {
      case kNoChecksum:
        break;
      case kCRC32c:
        value = crc32c::Unmask(value);
        actual = crc32c::Value(data, block_size_ + 1);
        break;
      case kxxHash:
        actual = XXH32(data, static_cast<int>(block_size_) + 1, 0);
        break;
      default:
        status_ = Status::Corruption(
            "unknown checksum type " + ToString(footer_.checksum()) + " in " +
            file_->file_name() + " offset " + ToString(handle_.offset()) +
            " size " + ToString(block_size_));
    }
    if (status_.ok() && actual != value) {
      status_ = Status::Corruption(
          "block checksum mismatch: expected " + ToString(actual) + ", got " +
          ToString(value) + "  in " + file_->file_name() + " offset " +
          ToString(handle_.offset()) + " size " + ToString(block_size_));
    }
  }
}

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_.info_log && !status.IsNotFound()) {
        assert(!status.ok());
        ROCKS_LOG_INFO(ioptions_.info_log,
                       "Error reading from persistent cache. %s",
                       status.ToString().c_str());
      }
    }
  }
  return false;
}

inline
bool BlockFetcher::TryGetFromPrefetchBuffer() {
  if (prefetch_buffer_ != nullptr &&
      prefetch_buffer_->TryReadFromCache(
          handle_.offset(),
          static_cast<size_t>(handle_.size()) + kBlockTrailerSize, &slice_)) {
    block_size_ = static_cast<size_t>(handle_.size());
    CheckBlockChecksum();
    if (!status_.ok()) {
      return true;
    }
    got_from_prefetch_buffer_ = true;
    used_buf_ = const_cast<char*>(slice_.data());
  }
  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
    status_ = PersistentCacheHelper::LookupRawPage(
        cache_options_, handle_, &heap_buf_, block_size_ + kBlockTrailerSize);
    if (status_.ok()) {
      used_buf_ = heap_buf_.get();
      slice_ = Slice(heap_buf_.get(), block_size_);
      return true;
    } else if (!status_.IsNotFound() && ioptions_.info_log) {
      assert(!status_.ok());
      ROCKS_LOG_INFO(ioptions_.info_log,
                     "Error reading from persistent cache. %s",
                     status_.ToString().c_str());
    }
  }
  return false;
}

inline
void BlockFetcher::PrepareBufferForBlockFromFile() {
  // cache miss read from device
  if (do_uncompress_ &&
      block_size_ + kBlockTrailerSize < 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()
    used_buf_ = &stack_buf_[0];
  } else {
    heap_buf_.reset(new char[block_size_ + kBlockTrailerSize]);
    used_buf_ = heap_buf_.get();
  }
}

inline
void BlockFetcher::InsertCompressedBlockToPersistentCacheIfNeeded() {
  if (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_ + kBlockTrailerSize);
  }
}

inline
void BlockFetcher::InsertUncompressedBlockToPersistentCacheIfNeeded() {
  if (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::GetBlockContents() {
  if (slice_.data() != used_buf_) {
    // the slice content is not the buffer provided
    *contents_ = BlockContents(Slice(slice_.data(), block_size_), false,
                               compression_type);
  } else {
    // page is uncompressed, the buffer either stack or heap provided
    if (got_from_prefetch_buffer_ || used_buf_ == &stack_buf_[0]) {
      heap_buf_.reset(new char[block_size_]);
      memcpy(heap_buf_.get(), used_buf_, block_size_);
    }
    *contents_ = BlockContents(std::move(heap_buf_), block_size_, true,
                               compression_type);
  }
}

Status BlockFetcher::ReadBlockContents() {
  block_size_ = static_cast<size_t>(handle_.size());

  if (TryGetUncompressBlockFromPersistentCache()) {
    return Status::OK();
  }
  if (TryGetFromPrefetchBuffer()) {
    if (!status_.ok()) {
      return status_;
    }
  } else if (!TryGetCompressedBlockFromPersistentCache()) {
    PrepareBufferForBlockFromFile();
    Status s;

    {
      PERF_TIMER_GUARD(block_read_time);
      // Actual file read
      status_ = file_->Read(handle_.offset(), block_size_ + kBlockTrailerSize,
                            &slice_, used_buf_);
    }
    PERF_COUNTER_ADD(block_read_count, 1);
    PERF_COUNTER_ADD(block_read_byte, block_size_ + kBlockTrailerSize);
    if (!status_.ok()) {
      return status_;
    }

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

    CheckBlockChecksum();
    if (status_.ok()) {
      InsertCompressedBlockToPersistentCacheIfNeeded();
    } else {
      return status_;
    }
  }

  PERF_TIMER_GUARD(block_decompress_time);

  compression_type =
      static_cast<rocksdb::CompressionType>(slice_.data()[block_size_]);

  if (do_uncompress_ && compression_type != kNoCompression) {
    // compressed page, uncompress, update cache
    UncompressionContext uncompression_ctx(compression_type, compression_dict_);
    status_ = UncompressBlockContents(uncompression_ctx, 
                                      slice_.data(), block_size_, contents_,
                                      footer_.version(),
                                      ioptions_);
  } else {
    GetBlockContents();
  }

  InsertUncompressedBlockToPersistentCacheIfNeeded();

  return status_;
}

}  // namespace rocksdb