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rocksdb/table/format.h

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5.8 KiB

// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include <string>
#include <stdint.h>
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
#include "rocksdb/options.h"
#include "rocksdb/table.h"
namespace rocksdb {
class Block;
class RandomAccessFile;
struct ReadOptions;
// the length of the magic number in bytes.
const int kMagicNumberLengthByte = 8;
// BlockHandle is a pointer to the extent of a file that stores a data
// block or a meta block.
class BlockHandle {
public:
BlockHandle();
BlockHandle(uint64_t offset, uint64_t size);
// The offset of the block in the file.
uint64_t offset() const { return offset_; }
void set_offset(uint64_t offset) { offset_ = offset; }
// The size of the stored block
uint64_t size() const { return size_; }
void set_size(uint64_t size) { size_ = size; }
void EncodeTo(std::string* dst) const;
Status DecodeFrom(Slice* input);
// if the block handle's offset and size are both "0", we will view it
// as a null block handle that points to no where.
bool IsNull() const {
return offset_ == 0 && size_ == 0;
}
static const BlockHandle& NullBlockHandle() {
return kNullBlockHandle;
}
// Maximum encoding length of a BlockHandle
enum { kMaxEncodedLength = 10 + 10 };
private:
uint64_t offset_ = 0;
uint64_t size_ = 0;
static const BlockHandle kNullBlockHandle;
};
// Footer encapsulates the fixed information stored at the tail
// end of every table file.
class Footer {
public:
// Constructs a footer without specifying its table magic number.
// In such case, the table magic number of such footer should be
// initialized via @ReadFooterFromFile().
Footer() : Footer(kInvalidTableMagicNumber) {}
// @table_magic_number serves two purposes:
// 1. Identify different types of the tables.
// 2. Help us to identify if a given file is a valid sst.
explicit Footer(uint64_t table_magic_number)
: table_magic_number_(table_magic_number) {}
// The block handle for the metaindex block of the table
const BlockHandle& metaindex_handle() const { return metaindex_handle_; }
void set_metaindex_handle(const BlockHandle& h) { metaindex_handle_ = h; }
// The block handle for the index block of the table
const BlockHandle& index_handle() const {
return index_handle_;
}
void set_index_handle(const BlockHandle& h) {
index_handle_ = h;
}
uint64_t table_magic_number() const { return table_magic_number_; }
void EncodeTo(std::string* dst) const;
// Set the current footer based on the input slice. If table_magic_number_
// is not set (i.e., HasInitializedTableMagicNumber() is true), then this
// function will also initialize table_magic_number_. Otherwise, this
// function will verify whether the magic number specified in the input
// slice matches table_magic_number_ and update the current footer only
// when the test passes.
Status DecodeFrom(Slice* input);
// Encoded length of a Footer. Note that the serialization of a
// Footer will always occupy exactly this many bytes. It consists
// of two block handles and a magic number.
enum {
kEncodedLength = 2 * BlockHandle::kMaxEncodedLength + 8
};
static const uint64_t kInvalidTableMagicNumber = 0;
private:
// REQUIRES: magic number wasn't initialized.
void set_table_magic_number(uint64_t magic_number) {
assert(!HasInitializedTableMagicNumber());
table_magic_number_ = magic_number;
}
// return true if @table_magic_number_ is set to a value different
// from @kInvalidTableMagicNumber.
bool HasInitializedTableMagicNumber() const {
return (table_magic_number_ != kInvalidTableMagicNumber);
}
BlockHandle metaindex_handle_;
BlockHandle index_handle_;
uint64_t table_magic_number_ = 0;
};
// Read the footer from file
Status ReadFooterFromFile(RandomAccessFile* file,
uint64_t file_size,
Footer* footer);
// 1-byte type + 32-bit crc
static const size_t kBlockTrailerSize = 5;
struct BlockContents {
Slice data; // Actual contents of data
bool cachable; // True iff data can be cached
bool heap_allocated; // True iff caller should delete[] data.data()
CompressionType compression_type;
};
// Read the block identified by "handle" from "file". On failure
// return non-OK. On success fill *result and return OK.
extern Status ReadBlockContents(RandomAccessFile* file,
const ReadOptions& options,
const BlockHandle& handle,
BlockContents* result,
Env* env,
bool do_uncompress);
// The 'data' points to the raw block contents read in from file.
// This method allocates a new heap buffer and the raw block
// contents are uncompresed into this buffer. This buffer is
// returned via 'result' and it is upto the caller to
// free this buffer.
extern Status UncompressBlockContents(const char* data,
size_t n,
BlockContents* result);
// Implementation details follow. Clients should ignore,
inline BlockHandle::BlockHandle()
: BlockHandle(~static_cast<uint64_t>(0),
~static_cast<uint64_t>(0)) {
}
inline BlockHandle::BlockHandle(uint64_t offset, uint64_t size)
: offset_(offset),
size_(size) {
}
} // namespace rocksdb