64324e329e
Summary: As you know, almost all compilers support "pragma once" keyword instead of using include guards. To be keep consistency between header files, all header files are edited. Besides this, try to fix some warnings about loss of data. Pull Request resolved: https://github.com/facebook/rocksdb/pull/4339 Differential Revision: D9654990 Pulled By: ajkr fbshipit-source-id: c2cf3d2d03a599847684bed81378c401920ca848
102 lines
4.3 KiB
C++
102 lines
4.3 KiB
C++
// 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.
|
|
//
|
|
// Class for specifying user-defined functions which perform a
|
|
// transformation on a slice. It is not required that every slice
|
|
// belong to the domain and/or range of a function. Subclasses should
|
|
// define InDomain and InRange to determine which slices are in either
|
|
// of these sets respectively.
|
|
|
|
#pragma once
|
|
|
|
#include <string>
|
|
|
|
namespace rocksdb {
|
|
|
|
class Slice;
|
|
|
|
/*
|
|
* A SliceTransform is a generic pluggable way of transforming one string
|
|
* to another. Its primary use-case is in configuring rocksdb
|
|
* to store prefix blooms by setting prefix_extractor in
|
|
* ColumnFamilyOptions.
|
|
*/
|
|
class SliceTransform {
|
|
public:
|
|
virtual ~SliceTransform() {};
|
|
|
|
// Return the name of this transformation.
|
|
virtual const char* Name() const = 0;
|
|
|
|
// Extract a prefix from a specified key. This method is called when
|
|
// a key is inserted into the db, and the returned slice is used to
|
|
// create a bloom filter.
|
|
virtual Slice Transform(const Slice& key) const = 0;
|
|
|
|
// Determine whether the specified key is compatible with the logic
|
|
// specified in the Transform method. This method is invoked for every
|
|
// key that is inserted into the db. If this method returns true,
|
|
// then Transform is called to translate the key to its prefix and
|
|
// that returned prefix is inserted into the bloom filter. If this
|
|
// method returns false, then the call to Transform is skipped and
|
|
// no prefix is inserted into the bloom filters.
|
|
//
|
|
// For example, if the Transform method operates on a fixed length
|
|
// prefix of size 4, then an invocation to InDomain("abc") returns
|
|
// false because the specified key length(3) is shorter than the
|
|
// prefix size of 4.
|
|
//
|
|
// Wiki documentation here:
|
|
// https://github.com/facebook/rocksdb/wiki/Prefix-Seek-API-Changes
|
|
//
|
|
virtual bool InDomain(const Slice& key) const = 0;
|
|
|
|
// This is currently not used and remains here for backward compatibility.
|
|
virtual bool InRange(const Slice& /*dst*/) const { return false; }
|
|
|
|
// Some SliceTransform will have a full length which can be used to
|
|
// determine if two keys are consecuitive. Can be disabled by always
|
|
// returning 0
|
|
virtual bool FullLengthEnabled(size_t* /*len*/) const { return false; }
|
|
|
|
// Transform(s)=Transform(`prefix`) for any s with `prefix` as a prefix.
|
|
//
|
|
// This function is not used by RocksDB, but for users. If users pass
|
|
// Options by string to RocksDB, they might not know what prefix extractor
|
|
// they are using. This function is to help users can determine:
|
|
// if they want to iterate all keys prefixing `prefix`, whether it is
|
|
// safe to use prefix bloom filter and seek to key `prefix`.
|
|
// If this function returns true, this means a user can Seek() to a prefix
|
|
// using the bloom filter. Otherwise, user needs to skip the bloom filter
|
|
// by setting ReadOptions.total_order_seek = true.
|
|
//
|
|
// Here is an example: Suppose we implement a slice transform that returns
|
|
// the first part of the string after splitting it using delimiter ",":
|
|
// 1. SameResultWhenAppended("abc,") should return true. If applying prefix
|
|
// bloom filter using it, all slices matching "abc:.*" will be extracted
|
|
// to "abc,", so any SST file or memtable containing any of those key
|
|
// will not be filtered out.
|
|
// 2. SameResultWhenAppended("abc") should return false. A user will not
|
|
// guaranteed to see all the keys matching "abc.*" if a user seek to "abc"
|
|
// against a DB with the same setting. If one SST file only contains
|
|
// "abcd,e", the file can be filtered out and the key will be invisible.
|
|
//
|
|
// i.e., an implementation always returning false is safe.
|
|
virtual bool SameResultWhenAppended(const Slice& /*prefix*/) const {
|
|
return false;
|
|
}
|
|
};
|
|
|
|
extern const SliceTransform* NewFixedPrefixTransform(size_t prefix_len);
|
|
|
|
extern const SliceTransform* NewCappedPrefixTransform(size_t cap_len);
|
|
|
|
extern const SliceTransform* NewNoopTransform();
|
|
|
|
}
|