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rocksdb/table/filter_block.h

93 lines
3.2 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) 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.
#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 "util/hash.h"
namespace rocksdb {
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 AddKey*)* Finish
class FilterBlockBuilder {
public:
explicit FilterBlockBuilder(const Options& opt,
const Comparator* internal_comparator);
void StartBlock(uint64_t block_offset);
void AddKey(const Slice& key);
Slice Finish();
private:
bool SamePrefix(const Slice &key1, const Slice &key2) const;
void GenerateFilter();
// important: all of these might point to invalid addresses
// at the time of destruction of this filter block. destructor
// should NOT dereference them.
const FilterPolicy* policy_;
const SliceTransform* prefix_extractor_;
bool whole_key_filtering_;
const Comparator* comparator_;
std::string entries_; // Flattened entry contents
std::vector<size_t> start_; // Starting index in entries_ of each entry
std::string result_; // Filter data computed so far
std::vector<Slice> tmp_entries_; // policy_->CreateFilter() argument
std::vector<uint32_t> filter_offsets_;
// No copying allowed
FilterBlockBuilder(const FilterBlockBuilder&);
void operator=(const FilterBlockBuilder&);
};
class FilterBlockReader {
public:
// REQUIRES: "contents" and *policy must stay live while *this is live.
FilterBlockReader(
const Options& opt,
const Slice& contents,
bool delete_contents_after_use = false);
bool KeyMayMatch(uint64_t block_offset, const Slice& key);
bool PrefixMayMatch(uint64_t block_offset, const Slice& prefix);
size_t ApproximateMemoryUsage() const;
private:
const FilterPolicy* policy_;
const SliceTransform* prefix_extractor_;
bool whole_key_filtering_;
const char* data_; // Pointer to filter data (at block-start)
const char* offset_; // Pointer to beginning of offset array (at block-end)
size_t num_; // Number of entries in offset array
size_t base_lg_; // Encoding parameter (see kFilterBaseLg in .cc file)
std::unique_ptr<const char[]> filter_data;
bool MayMatch(uint64_t block_offset, const Slice& entry);
};
}