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rocksdb/table/filter_block.h

132 lines
4.7 KiB

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root 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 size_t NumAdded() const = 0; // Number of keys added
Slice Finish() { // Generate Filter
const BlockHandle empty_handle;
Status dont_care_status;
auto ret = Finish(empty_handle, &dont_care_status);
assert(dont_care_status.ok());
return ret;
}
virtual Slice Finish(const BlockHandle& tmp, Status* status) = 0;
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()
: whole_key_filtering_(true), size_(0), statistics_(nullptr) {}
explicit FilterBlockReader(size_t s, Statistics* stats,
bool _whole_key_filtering)
: whole_key_filtering_(_whole_key_filtering),
size_(s),
statistics_(stats) {}
virtual ~FilterBlockReader() {}
virtual bool IsBlockBased() = 0; // If is blockbased filter
/**
* If no_io is set, then it returns true if it cannot answer the query without
* reading data from disk. This is used in PartitionedFilterBlockReader to
* avoid reading partitions that are not in block cache already
*
* Normally filters are built on only the user keys and the InternalKey is not
* needed for a query. The index in PartitionedFilterBlockReader however is
* built upon InternalKey and must be provided via const_ikey_ptr when running
* queries.
*/
virtual bool KeyMayMatch(const Slice& key, uint64_t block_offset = kNotValid,
const bool no_io = false,
const Slice* const const_ikey_ptr = nullptr) = 0;
/**
* no_io and const_ikey_ptr here means the same as in KeyMayMatch
*/
virtual bool PrefixMayMatch(const Slice& prefix,
uint64_t block_offset = kNotValid,
const bool no_io = false,
const Slice* const const_ikey_ptr = nullptr) = 0;
virtual size_t ApproximateMemoryUsage() const = 0;
virtual size_t size() const { return size_; }
virtual Statistics* statistics() const { return statistics_; }
bool whole_key_filtering() const { return whole_key_filtering_; }
// convert this object to a human readable form
virtual std::string ToString() const {
std::string error_msg("Unsupported filter \n");
return error_msg;
}
virtual void CacheDependencies(bool /*pin*/) {}
protected:
bool whole_key_filtering_;
private:
// No copying allowed
FilterBlockReader(const FilterBlockReader&);
void operator=(const FilterBlockReader&);
size_t size_;
Statistics* statistics_;
int level_ = -1;
};
} // namespace rocksdb