rocksdb/table/filter_block.h
2016-02-09 15:12:00 -08:00

91 lines
3.1 KiB
C++

// Copyright (c) 2011-present, 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) 2012 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.
//
// A filter block is stored near the end of a Table file. It contains
// filters (e.g., bloom filters) for all data blocks in the table combined
// into a single filter block.
//
// It is a base class for BlockBasedFilter and FullFilter.
// These two are both used in BlockBasedTable. The first one contain filter
// For a part of keys in sst file, the second contain filter for all keys
// in sst file.
#pragma once
#include <memory>
#include <stddef.h>
#include <stdint.h>
#include <string>
#include <vector>
#include "rocksdb/options.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
#include "rocksdb/table.h"
#include "util/hash.h"
#include "format.h"
namespace rocksdb {
const uint64_t kNotValid = ULLONG_MAX;
class FilterPolicy;
// A FilterBlockBuilder is used to construct all of the filters for a
// particular Table. It generates a single string which is stored as
// a special block in the Table.
//
// The sequence of calls to FilterBlockBuilder must match the regexp:
// (StartBlock Add*)* Finish
//
// BlockBased/Full FilterBlock would be called in the same way.
class FilterBlockBuilder {
public:
explicit FilterBlockBuilder() {}
virtual ~FilterBlockBuilder() {}
virtual bool IsBlockBased() = 0; // If is blockbased filter
virtual void StartBlock(uint64_t block_offset) = 0; // Start new block filter
virtual void Add(const Slice& key) = 0; // Add a key to current filter
virtual Slice Finish() = 0; // Generate Filter
private:
// No copying allowed
FilterBlockBuilder(const FilterBlockBuilder&);
void operator=(const FilterBlockBuilder&);
};
// A FilterBlockReader is used to parse filter from SST table.
// KeyMayMatch and PrefixMayMatch would trigger filter checking
//
// BlockBased/Full FilterBlock would be called in the same way.
class FilterBlockReader {
public:
explicit FilterBlockReader() {}
virtual ~FilterBlockReader() {}
virtual bool IsBlockBased() = 0; // If is blockbased filter
virtual bool KeyMayMatch(const Slice& key,
uint64_t block_offset = kNotValid) = 0;
virtual bool PrefixMayMatch(const Slice& prefix,
uint64_t block_offset = kNotValid) = 0;
virtual size_t ApproximateMemoryUsage() const = 0;
// convert this object to a human readable form
virtual std::string ToString() const {
std::string error_msg("Unsupported filter \n");
return error_msg;
}
private:
// No copying allowed
FilterBlockReader(const FilterBlockReader&);
void operator=(const FilterBlockReader&);
};
} // namespace rocksdb