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rocksdb/table/format.h

207 lines
7.4 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);
// Return a string that contains the copy of handle.
std::string ToString(bool hex = true) const;
// 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().
// Use this when you plan to load Footer with DecodeFrom(). Never use this
// when you plan to EncodeTo.
Footer() : Footer(kInvalidTableMagicNumber, 0) {}
// Use this constructor when you plan to write out the footer using
// EncodeTo(). Never use this constructor with DecodeFrom().
Footer(uint64_t table_magic_number, uint32_t version);
// The version of the footer in this file
uint32_t version() const { return version_; }
// The checksum type used in this file
ChecksumType checksum() const { return checksum_; }
void set_checksum(const ChecksumType c) { checksum_ = c; }
// 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.
//
// REQUIRES: table_magic_number_ is not set (i.e.,
// HasInitializedTableMagicNumber() is true). The function will initialize the
// magic number
Status DecodeFrom(Slice* input);
// Encoded length of a Footer. Note that the serialization of a Footer will
// always occupy at least kMinEncodedLength bytes. If fields are changed
// the version number should be incremented and kMaxEncodedLength should be
// increased accordingly.
enum {
// Footer version 0 (legacy) will always occupy exactly this many bytes.
// It consists of two block handles, padding, and a magic number.
kVersion0EncodedLength = 2 * BlockHandle::kMaxEncodedLength + 8,
// Footer of versions 1 and higher will always occupy exactly this many
// bytes. It consists of the checksum type, two block handles, padding,
// a version number (bigger than 1), and a magic number
kNewVersionsEncodedLength = 1 + 2 * BlockHandle::kMaxEncodedLength + 4 + 8,
kMinEncodedLength = kVersion0EncodedLength,
kMaxEncodedLength = kNewVersionsEncodedLength,
};
static const uint64_t kInvalidTableMagicNumber = 0;
// convert this object to a human readable form
std::string ToString() const;
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);
}
uint32_t version_;
ChecksumType checksum_;
BlockHandle metaindex_handle_;
BlockHandle index_handle_;
uint64_t table_magic_number_ = 0;
};
// Read the footer from file
// If enforce_table_magic_number != 0, ReadFooterFromFile() will return
// corruption if table_magic number is not equal to enforce_table_magic_number
Status ReadFooterFromFile(RandomAccessFile* file, uint64_t file_size,
Footer* footer,
uint64_t enforce_table_magic_number = 0);
// 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
CompressionType compression_type;
std::unique_ptr<char[]> allocation;
BlockContents() : cachable(false), compression_type(kNoCompression) {}
BlockContents(const Slice& _data, bool _cachable,
CompressionType _compression_type)
: data(_data), cachable(_cachable), compression_type(_compression_type) {}
BlockContents(std::unique_ptr<char[]>&& _data, size_t _size, bool _cachable,
CompressionType _compression_type)
: data(_data.get(), _size),
cachable(_cachable),
compression_type(_compression_type),
allocation(std::move(_data)) {}
};
// 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 Footer& footer,
const ReadOptions& options,
const BlockHandle& handle,
BlockContents* contents, 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* contents);
// 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