ceph/src/rocksdb/table/block_based/block_prefetcher.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5 //
   6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   7 // Use of this source code is governed by a BSD-style license that can be
   8 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   9 #pragma once
  10 #include "table/block_based/block_based_table_reader.h"
  11
  12 namespace ROCKSDB_NAMESPACE {
  13 class BlockPrefetcher {
  14  public:
  15   explicit BlockPrefetcher(size_t compaction_readahead_size,
  16                            size_t initial_auto_readahead_size)
  17       : compaction_readahead_size_(compaction_readahead_size),
  18         readahead_size_(initial_auto_readahead_size),
  19         initial_auto_readahead_size_(initial_auto_readahead_size) {}
  20
  21   void PrefetchIfNeeded(const BlockBasedTable::Rep* rep,
  22                         const BlockHandle& handle, size_t readahead_size,
  23                         bool is_for_compaction,
  24                         const bool no_sequential_checking,
  25                         Env::IOPriority rate_limiter_priority);
  26   FilePrefetchBuffer* prefetch_buffer() { return prefetch_buffer_.get(); }
  27
  28   void UpdateReadPattern(const uint64_t& offset, const size_t& len) {
  29     prev_offset_ = offset;
  30     prev_len_ = len;
  31   }
  32
  33   bool IsBlockSequential(const uint64_t& offset) {
  34     return (prev_len_ == 0 || (prev_offset_ + prev_len_ == offset));
  35   }
  36
  37   void ResetValues(size_t initial_auto_readahead_size) {
  38     num_file_reads_ = 1;
  39     // Since initial_auto_readahead_size_ can be different from
  40     // the value passed to BlockBasedTableOptions.initial_auto_readahead_size in
  41     // case of adaptive_readahead, so fallback the readahead_size_ to that value
  42     // in case of reset.
  43     initial_auto_readahead_size_ = initial_auto_readahead_size;
  44     readahead_size_ = initial_auto_readahead_size_;
  45     readahead_limit_ = 0;
  46     return;
  47   }
  48
  49   void SetReadaheadState(ReadaheadFileInfo::ReadaheadInfo* readahead_info) {
  50     num_file_reads_ = readahead_info->num_file_reads;
  51     initial_auto_readahead_size_ = readahead_info->readahead_size;
  52     TEST_SYNC_POINT_CALLBACK("BlockPrefetcher::SetReadaheadState",
  53                              &initial_auto_readahead_size_);
  54   }
  55
  56  private:
  57   // Readahead size used in compaction, its value is used only if
  58   // lookup_context_.caller = kCompaction.
  59   size_t compaction_readahead_size_;
  60
  61   // readahead_size_ is used if underlying FS supports prefetching.
  62   size_t readahead_size_;
  63   size_t readahead_limit_ = 0;
  64   // initial_auto_readahead_size_ is used if RocksDB uses internal prefetch
  65   // buffer.
  66   uint64_t initial_auto_readahead_size_;
  67   uint64_t num_file_reads_ = 0;
  68   uint64_t prev_offset_ = 0;
  69   size_t prev_len_ = 0;
  70   std::unique_ptr<FilePrefetchBuffer> prefetch_buffer_;
  71 };
  72 }  // namespace ROCKSDB_NAMESPACE