c2485f2d81
Summary: A new file interface `SupportPrefetch()` is added. When the user overrides it to `false`, an internal prefetch buffer will be used for readahead. Useful for non-directIO but FS doesn't have readahead support. Pull Request resolved: https://github.com/facebook/rocksdb/pull/7312 Reviewed By: anand1976 Differential Revision: D23329847 Pulled By: jay-zhuang fbshipit-source-id: 71cd4ce6f4a820840294e4e6aec111ab76175527
67 lines
2.6 KiB
C++
67 lines
2.6 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_);
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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_);
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return;
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}
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// Implicit auto readahead, which will be enabled if the number of reads
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// reached `kMinNumFileReadsToStartAutoReadahead` (default: 2).
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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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if (rep->file->use_direct_io()) {
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rep->CreateFilePrefetchBufferIfNotExists(
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BlockBasedTable::kInitAutoReadaheadSize,
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BlockBasedTable::kMaxAutoReadaheadSize, &prefetch_buffer_);
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return;
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}
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if (handle.offset() + static_cast<size_t>(block_size(handle)) <=
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readahead_limit_) {
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return;
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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(), readahead_size_);
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if (s.IsNotSupported()) {
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rep->CreateFilePrefetchBufferIfNotExists(
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BlockBasedTable::kInitAutoReadaheadSize,
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BlockBasedTable::kMaxAutoReadaheadSize, &prefetch_buffer_);
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return;
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}
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readahead_limit_ = 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_ =
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std::min(BlockBasedTable::kMaxAutoReadaheadSize, readahead_size_ * 2);
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}
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} // namespace ROCKSDB_NAMESPACE
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