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100 строки
3.0 KiB
100 строки
3.0 KiB
// 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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#ifndef STORAGE_LEVELDB_TABLE_FORMAT_H_
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#define STORAGE_LEVELDB_TABLE_FORMAT_H_
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#include <stdint.h>
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#include <string>
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#include "leveldb/slice.h"
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#include "leveldb/status.h"
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#include "leveldb/table_builder.h"
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namespace leveldb {
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class Block;
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class RandomAccessFile;
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struct ReadOptions;
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// BlockHandle is a pointer to the extent of a file that stores a data
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// block or a meta block.
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class BlockHandle {
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public:
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// Maximum encoding length of a BlockHandle
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enum { kMaxEncodedLength = 10 + 10 };
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BlockHandle();
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// The offset of the block in the file.
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uint64_t offset() const { return offset_; }
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void set_offset(uint64_t offset) { offset_ = offset; }
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// The size of the stored block
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uint64_t size() const { return size_; }
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void set_size(uint64_t size) { size_ = size; }
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void EncodeTo(std::string* dst) const;
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Status DecodeFrom(Slice* input);
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private:
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uint64_t offset_;
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uint64_t size_;
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};
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// Footer encapsulates the fixed information stored at the tail
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// end of every table file.
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class Footer {
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public:
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// Encoded length of a Footer. Note that the serialization of a
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// Footer will always occupy exactly this many bytes. It consists
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// of two block handles and a magic number.
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enum { kEncodedLength = 2 * BlockHandle::kMaxEncodedLength + 8 };
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Footer() = default;
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// The block handle for the metaindex block of the table
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const BlockHandle& metaindex_handle() const { return metaindex_handle_; }
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void set_metaindex_handle(const BlockHandle& h) { metaindex_handle_ = h; }
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// The block handle for the index block of the table
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const BlockHandle& index_handle() const { return index_handle_; }
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void set_index_handle(const BlockHandle& h) { index_handle_ = h; }
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void EncodeTo(std::string* dst) const;
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Status DecodeFrom(Slice* input);
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private:
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BlockHandle metaindex_handle_;
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BlockHandle index_handle_;
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};
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// kTableMagicNumber was picked by running
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// echo http://code.google.com/p/leveldb/ | sha1sum
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// and taking the leading 64 bits.
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static const uint64_t kTableMagicNumber = 0xdb4775248b80fb57ull;
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// 1-byte type + 32-bit crc
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static const size_t kBlockTrailerSize = 5;
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struct BlockContents {
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Slice data; // Actual contents of data
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bool cachable; // True iff data can be cached
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bool heap_allocated; // True iff caller should delete[] data.data()
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};
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// Read the block identified by "handle" from "file". On failure
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// return non-OK. On success fill *result and return OK.
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Status ReadBlock(RandomAccessFile* file, const ReadOptions& options,
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const BlockHandle& handle, BlockContents* result);
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// Implementation details follow. Clients should ignore,
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inline BlockHandle::BlockHandle()
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: offset_(~static_cast<uint64_t>(0)), size_(~static_cast<uint64_t>(0)) {}
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_TABLE_FORMAT_H_
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