d1be594636
Test Plan: make check Subscribers: leveldb, andrewkr, dhruba Differential Revision: https://reviews.facebook.net/D61875
100 lines
4.2 KiB
C++
100 lines
4.2 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.
|
|
//
|
|
// 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.
|
|
|
|
#ifndef STORAGE_ROCKSDB_INCLUDE_SLICE_TRANSFORM_H_
|
|
#define STORAGE_ROCKSDB_INCLUDE_SLICE_TRANSFORM_H_
|
|
|
|
#include <string>
|
|
|
|
namespace rocksdb {
|
|
|
|
class Slice;
|
|
|
|
/*
|
|
* A SliceTranform 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 = 0;
|
|
|
|
// 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`, whetherit 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 spliting it using deimiter ",":
|
|
// 1. SameResultWhenAppended("abc,") should return true. If aplying 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();
|
|
|
|
}
|
|
|
|
#endif // STORAGE_ROCKSDB_INCLUDE_SLICE_TRANSFORM_H_
|