mirror of
https://github.com/facebook/rocksdb.git
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57 lines
2.6 KiB
C++
57 lines
2.6 KiB
C++
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "table/block_based/block_prefetcher.h"
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namespace ROCKSDB_NAMESPACE {
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void BlockPrefetcher::PrefetchIfNeeded(const BlockBasedTable::Rep* rep,
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const BlockHandle& handle,
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size_t readahead_size,
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bool is_for_compaction) {
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if (!is_for_compaction) {
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if (readahead_size == 0) {
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// Implicit auto readahead
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num_file_reads_++;
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if (num_file_reads_ >
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BlockBasedTable::kMinNumFileReadsToStartAutoReadahead) {
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if (!rep->file->use_direct_io() &&
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(handle.offset() + static_cast<size_t>(block_size(handle)) >
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readahead_limit_)) {
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// Buffered I/O
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// Discarding the return status of Prefetch calls intentionally, as
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// we can fallback to reading from disk if Prefetch fails.
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rep->file->Prefetch(handle.offset(), readahead_size_);
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readahead_limit_ =
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static_cast<size_t>(handle.offset() + readahead_size_);
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// Keep exponentially increasing readahead size until
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// kMaxAutoReadaheadSize.
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readahead_size_ = std::min(BlockBasedTable::kMaxAutoReadaheadSize,
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readahead_size_ * 2);
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} else if (rep->file->use_direct_io() && !prefetch_buffer_) {
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// Direct I/O
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// Let FilePrefetchBuffer take care of the readahead.
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rep->CreateFilePrefetchBuffer(BlockBasedTable::kInitAutoReadaheadSize,
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BlockBasedTable::kMaxAutoReadaheadSize,
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&prefetch_buffer_);
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}
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}
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} else if (!prefetch_buffer_) {
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// Explicit user requested readahead
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// The actual condition is:
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// if (readahead_size != 0 && !prefetch_buffer_)
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rep->CreateFilePrefetchBuffer(readahead_size, readahead_size,
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&prefetch_buffer_);
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}
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} else if (!prefetch_buffer_) {
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rep->CreateFilePrefetchBuffer(compaction_readahead_size_,
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compaction_readahead_size_,
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&prefetch_buffer_);
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}
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}
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} // namespace ROCKSDB_NAMESPACE
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