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4da34b97ee
Summary: ### Context: Background compactions and flush generate large reads and writes, and can be long running, especially for universal compaction. In some cases, this can impact foreground reads and writes by users. ### Solution User, Flush, and Compaction reads share some code path. For this task, we update the rate_limiter_priority in ReadOptions for code paths (e.g. FindTable (mainly in BlockBasedTable::Open()) and various iterators), and eventually update the rate_limiter_priority in IOOptions for FSRandomAccessFile. **This PR is for the Read path.** The **Read:** dynamic priority for different state are listed as follows: | State | Normal | Delayed | Stalled | | ----- | ------ | ------- | ------- | | Flush (verification read in BuildTable()) | IO_USER | IO_USER | IO_USER | | Compaction | IO_LOW | IO_USER | IO_USER | | User | User provided | User provided | User provided | We will respect the read_options that the user provided and will not set it. The only sst read for Flush is the verification read in BuildTable(). It claims to be "regard as user read". **Details** 1. Set read_options.rate_limiter_priority dynamically: - User: Do not update the read_options. Use the read_options that the user provided. - Compaction: Update read_options in CompactionJob::ProcessKeyValueCompaction(). - Flush: Update read_options in BuildTable(). 2. Pass the rate limiter priority to FSRandomAccessFile functions: - After calling the FindTable(), read_options is passed through GetTableReader(table_cache.cc), BlockBasedTableFactory::NewTableReader(block_based_table_factory.cc), and BlockBasedTable::Open(). The Open() needs some updates for the ReadOptions variable and the updates are also needed for the called functions, including PrefetchTail(), PrepareIOOptions(), ReadFooterFromFile(), ReadMetaIndexblock(), ReadPropertiesBlock(), PrefetchIndexAndFilterBlocks(), and ReadRangeDelBlock(). - In RandomAccessFileReader, the functions to be updated include Read(), MultiRead(), ReadAsync(), and Prefetch(). - Update the downstream functions of NewIndexIterator(), NewDataBlockIterator(), and BlockBasedTableIterator(). ### Test Plans Add unit tests. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9996 Reviewed By: anand1976 Differential Revision: D36452483 Pulled By: gitbw95 fbshipit-source-id: 60978204a4f849bb9261cb78d9bc1cb56d6008cf
103 lines
3.7 KiB
C++
103 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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#include "rocksdb/file_system.h"
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#include "table/block_based/block_based_table_reader.h"
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namespace ROCKSDB_NAMESPACE {
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void BlockPrefetcher::PrefetchIfNeeded(
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const BlockBasedTable::Rep* rep, const BlockHandle& handle,
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const size_t readahead_size, bool is_for_compaction, const bool async_io,
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const Env::IOPriority rate_limiter_priority) {
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if (is_for_compaction) {
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rep->CreateFilePrefetchBufferIfNotExists(
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compaction_readahead_size_, compaction_readahead_size_,
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&prefetch_buffer_, false, async_io);
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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(
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readahead_size, readahead_size, &prefetch_buffer_, false, async_io);
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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 || initial_auto_readahead_size_ == 0) {
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return;
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}
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size_t len = BlockBasedTable::BlockSizeWithTrailer(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(rep->table_options.initial_auto_readahead_size);
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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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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, async_io);
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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(
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handle.offset(),
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BlockBasedTable::BlockSizeWithTrailer(handle) + readahead_size_,
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rate_limiter_priority);
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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, async_io);
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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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