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b82e57d425
Summary: We carry compression type and "cachable" variables for every block in the block cache, while they take well-known values. 8-byte is wasted for each block (2-byte for useful information but it takes 8 bytes because of padding). With this change, these two variables are removed. The cachable information is only useful in the process of reading the block. We use other information to infer from it. For compressed blocks, the compression type is a part of the block content itself so we can get it from there. Some code is slightly refactored so that the cachable information can flow better. Another change is to only use class BlockContents for compressed block, and narrow the class Block to only be used for uncompressed blocks, including blocks in compressed block cache. This can make the Block class less confusing. It also saves tens of bytes for each block in compressed block cache. Pull Request resolved: https://github.com/facebook/rocksdb/pull/4650 Differential Revision: D12969070 Pulled By: siying fbshipit-source-id: 548b62724e9eb66993026429fd9c7c3acd1f95ed
81 lines
2.9 KiB
C++
81 lines
2.9 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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#pragma once
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#include "table/block.h"
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#include "table/format.h"
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#include "util/memory_allocator.h"
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namespace rocksdb {
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class BlockFetcher {
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public:
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// Read the block identified by "handle" from "file".
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// The only relevant option is options.verify_checksums for now.
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// On failure return non-OK.
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// On success fill *result and return OK - caller owns *result
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// @param compression_dict Data for presetting the compression library's
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// dictionary.
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BlockFetcher(RandomAccessFileReader* file,
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FilePrefetchBuffer* prefetch_buffer, const Footer& footer,
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const ReadOptions& read_options, const BlockHandle& handle,
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BlockContents* contents, const ImmutableCFOptions& ioptions,
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bool do_uncompress, const Slice& compression_dict,
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const PersistentCacheOptions& cache_options,
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MemoryAllocator* allocator = nullptr)
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: file_(file),
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prefetch_buffer_(prefetch_buffer),
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footer_(footer),
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read_options_(read_options),
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handle_(handle),
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contents_(contents),
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ioptions_(ioptions),
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do_uncompress_(do_uncompress),
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compression_dict_(compression_dict),
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cache_options_(cache_options),
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allocator_(allocator) {}
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Status ReadBlockContents();
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CompressionType get_compression_type() const { return compression_type_; }
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private:
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static const uint32_t kDefaultStackBufferSize = 5000;
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RandomAccessFileReader* file_;
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FilePrefetchBuffer* prefetch_buffer_;
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const Footer& footer_;
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const ReadOptions read_options_;
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const BlockHandle& handle_;
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BlockContents* contents_;
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const ImmutableCFOptions& ioptions_;
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bool do_uncompress_;
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const Slice& compression_dict_;
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const PersistentCacheOptions& cache_options_;
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MemoryAllocator* allocator_;
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Status status_;
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Slice slice_;
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char* used_buf_ = nullptr;
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size_t block_size_;
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CacheAllocationPtr heap_buf_;
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char stack_buf_[kDefaultStackBufferSize];
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bool got_from_prefetch_buffer_ = false;
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rocksdb::CompressionType compression_type_;
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// return true if found
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bool TryGetUncompressBlockFromPersistentCache();
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// return true if found
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bool TryGetFromPrefetchBuffer();
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bool TryGetCompressedBlockFromPersistentCache();
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void PrepareBufferForBlockFromFile();
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void GetBlockContents();
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void InsertCompressedBlockToPersistentCacheIfNeeded();
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void InsertUncompressedBlockToPersistentCacheIfNeeded();
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void CheckBlockChecksum();
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};
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} // namespace rocksdb
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