mirror of https://github.com/facebook/rocksdb.git
103 lines
4.1 KiB
C++
103 lines
4.1 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_based/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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// Retrieves a single block of a given file. Utilizes the prefetch buffer and/or
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// persistent cache provided (if any) to try to avoid reading from the file
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// directly. Note that both the prefetch buffer and the persistent cache are
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// optional; also, note that the persistent cache may be configured to store either
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// compressed or uncompressed blocks.
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//
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// If the retrieved block is compressed and the do_uncompress flag is set,
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// BlockFetcher uncompresses the block (using the uncompression dictionary,
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// if provided, to prime the compression algorithm), and returns the resulting
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// uncompressed block data. Otherwise, it returns the original block.
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//
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// Two read options affect the behavior of BlockFetcher: if verify_checksums is
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// true, the checksum of the (original) block is checked; if fill_cache is true,
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// the block is added to the persistent cache if needed.
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//
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// Memory for uncompressed and compressed blocks is allocated as needed
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// using memory_allocator and memory_allocator_compressed, respectively
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// (if provided; otherwise, the default allocator is used).
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class BlockFetcher {
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public:
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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, bool maybe_compressed,
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const UncompressionDict& uncompression_dict,
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const PersistentCacheOptions& cache_options,
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MemoryAllocator* memory_allocator = nullptr,
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MemoryAllocator* memory_allocator_compressed = 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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maybe_compressed_(maybe_compressed),
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uncompression_dict_(uncompression_dict),
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cache_options_(cache_options),
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memory_allocator_(memory_allocator),
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memory_allocator_compressed_(memory_allocator_compressed) {}
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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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bool maybe_compressed_;
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const UncompressionDict& uncompression_dict_;
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const PersistentCacheOptions& cache_options_;
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MemoryAllocator* memory_allocator_;
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MemoryAllocator* memory_allocator_compressed_;
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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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CacheAllocationPtr compressed_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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// Copy content from used_buf_ to new heap buffer.
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void CopyBufferToHeap();
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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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