1// Copyright (c) 2011 The LevelDB Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. See the AUTHORS file for names of contributors. 4 5#ifndef STORAGE_LEVELDB_TABLE_FORMAT_H_ 6#define STORAGE_LEVELDB_TABLE_FORMAT_H_ 7 8#include <string> 9#include <stdint.h> 10#include "leveldb/slice.h" 11#include "leveldb/status.h" 12#include "leveldb/table_builder.h" 13 14namespace leveldb { 15 16class Block; 17class RandomAccessFile; 18struct ReadOptions; 19 20// BlockHandle is a pointer to the extent of a file that stores a data 21// block or a meta block. 22class BlockHandle { 23 public: 24 BlockHandle(); 25 26 // The offset of the block in the file. 27 uint64_t offset() const { return offset_; } 28 void set_offset(uint64_t offset) { offset_ = offset; } 29 30 // The size of the stored block 31 uint64_t size() const { return size_; } 32 void set_size(uint64_t size) { size_ = size; } 33 34 void EncodeTo(std::string* dst) const; 35 Status DecodeFrom(Slice* input); 36 37 // Maximum encoding length of a BlockHandle 38 enum { kMaxEncodedLength = 10 + 10 }; 39 40 private: 41 uint64_t offset_; 42 uint64_t size_; 43}; 44 45// Footer encapsulates the fixed information stored at the tail 46// end of every table file. 47class Footer { 48 public: 49 Footer() { } 50 51 // The block handle for the metaindex block of the table 52 const BlockHandle& metaindex_handle() const { return metaindex_handle_; } 53 void set_metaindex_handle(const BlockHandle& h) { metaindex_handle_ = h; } 54 55 // The block handle for the index block of the table 56 const BlockHandle& index_handle() const { 57 return index_handle_; 58 } 59 void set_index_handle(const BlockHandle& h) { 60 index_handle_ = h; 61 } 62 63 void EncodeTo(std::string* dst) const; 64 Status DecodeFrom(Slice* input); 65 66 // Encoded length of a Footer. Note that the serialization of a 67 // Footer will always occupy exactly this many bytes. It consists 68 // of two block handles and a magic number. 69 enum { 70 kEncodedLength = 2*BlockHandle::kMaxEncodedLength + 8 71 }; 72 73 private: 74 BlockHandle metaindex_handle_; 75 BlockHandle index_handle_; 76}; 77 78// kTableMagicNumber was picked by running 79// echo http://code.google.com/p/leveldb/ | sha1sum 80// and taking the leading 64 bits. 81static const uint64_t kTableMagicNumber = 0xdb4775248b80fb57ull; 82 83// 1-byte type + 32-bit crc 84static const size_t kBlockTrailerSize = 5; 85 86struct BlockContents { 87 Slice data; // Actual contents of data 88 bool cachable; // True iff data can be cached 89 bool heap_allocated; // True iff caller should delete[] data.data() 90}; 91 92// Read the block identified by "handle" from "file". On failure 93// return non-OK. On success fill *result and return OK. 94extern Status ReadBlock(RandomAccessFile* file, 95 const ReadOptions& options, 96 const BlockHandle& handle, 97 BlockContents* result); 98 99// Implementation details follow. Clients should ignore, 100 101inline BlockHandle::BlockHandle() 102 : offset_(~static_cast<uint64_t>(0)), 103 size_(~static_cast<uint64_t>(0)) { 104} 105 106} // namespace leveldb 107 108#endif // STORAGE_LEVELDB_TABLE_FORMAT_H_ 109