mirror of https://github.com/facebook/rocksdb.git
99 lines
3.7 KiB
C++
99 lines
3.7 KiB
C++
// 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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rep->CreateFilePrefetchBufferIfNotExists(compaction_readahead_size_,
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compaction_readahead_size_,
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&prefetch_buffer_, false);
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return;
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}
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// Explicit user requested readahead.
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if (readahead_size > 0) {
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rep->CreateFilePrefetchBufferIfNotExists(readahead_size, readahead_size,
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&prefetch_buffer_, false);
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return;
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}
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// Implicit readahead.
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// If max_auto_readahead_size is set to be 0 by user, no data will be
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// prefetched.
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size_t max_auto_readahead_size = rep->table_options.max_auto_readahead_size;
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if (max_auto_readahead_size == 0) {
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return;
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}
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size_t len = static_cast<size_t>(block_size(handle));
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size_t offset = handle.offset();
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// If FS supports prefetching (readahead_limit_ will be non zero in that case)
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// and current block exists in prefetch buffer then return.
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if (offset + len <= readahead_limit_) {
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UpdateReadPattern(offset, len);
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return;
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}
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if (!IsBlockSequential(offset)) {
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UpdateReadPattern(offset, len);
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ResetValues();
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return;
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}
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UpdateReadPattern(offset, len);
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// Implicit auto readahead, which will be enabled if the number of reads
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// reached `kMinNumFileReadsToStartAutoReadahead` (default: 2) and scans are
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// sequential.
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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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return;
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}
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size_t initial_auto_readahead_size = BlockBasedTable::kInitAutoReadaheadSize;
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if (initial_auto_readahead_size > max_auto_readahead_size) {
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initial_auto_readahead_size = max_auto_readahead_size;
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}
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if (rep->file->use_direct_io()) {
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rep->CreateFilePrefetchBufferIfNotExists(initial_auto_readahead_size,
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max_auto_readahead_size,
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&prefetch_buffer_, true);
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return;
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}
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if (readahead_size_ > max_auto_readahead_size) {
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readahead_size_ = max_auto_readahead_size;
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}
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// If prefetch is not supported, fall back to use internal prefetch buffer.
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// Discarding other 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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Status s = rep->file->Prefetch(handle.offset(),
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block_size(handle) + readahead_size_);
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if (s.IsNotSupported()) {
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rep->CreateFilePrefetchBufferIfNotExists(initial_auto_readahead_size,
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max_auto_readahead_size,
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&prefetch_buffer_, true);
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return;
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}
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readahead_limit_ = offset + len + readahead_size_;
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// Keep exponentially increasing readahead size until
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// max_auto_readahead_size.
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readahead_size_ = std::min(max_auto_readahead_size, readahead_size_ * 2);
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}
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} // namespace ROCKSDB_NAMESPACE
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