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rocksdb/include/rocksdb/slice_transform.h

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// 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.
//
// 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;
class SliceTransform {
public:
virtual ~SliceTransform() {};
// Return the name of this transformation.
virtual const char* Name() const = 0;
// transform a src in domain to a dst in the range
virtual Slice Transform(const Slice& src) const = 0;
// determine whether this is a valid src upon the function applies
virtual bool InDomain(const Slice& src) const = 0;
// determine whether dst=Transform(src) for some src
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_