63 lines
2.3 KiB
C++
63 lines
2.3 KiB
C++
// Copyright (c) 2011 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.
|
|
|
|
#ifndef STORAGE_LEVELDB_INCLUDE_COMPARATOR_H_
|
|
#define STORAGE_LEVELDB_INCLUDE_COMPARATOR_H_
|
|
|
|
#include <string>
|
|
|
|
namespace leveldb {
|
|
|
|
class Slice;
|
|
|
|
// A Comparator object provides a total order across slices that are
|
|
// used as keys in an sstable or a database. A Comparator implementation
|
|
// must be thread-safe since leveldb may invoke its methods concurrently
|
|
// from multiple threads.
|
|
class Comparator {
|
|
public:
|
|
virtual ~Comparator();
|
|
|
|
// Three-way comparison. Returns value:
|
|
// < 0 iff "a" < "b",
|
|
// == 0 iff "a" == "b",
|
|
// > 0 iff "a" > "b"
|
|
virtual int Compare(const Slice& a, const Slice& b) const = 0;
|
|
|
|
// The name of the comparator. Used to check for comparator
|
|
// mismatches (i.e., a DB created with one comparator is
|
|
// accessed using a different comparator.
|
|
//
|
|
// The client of this package should switch to a new name whenever
|
|
// the comparator implementation changes in a way that will cause
|
|
// the relative ordering of any two keys to change.
|
|
//
|
|
// Names starting with "leveldb." are reserved and should not be used
|
|
// by any clients of this package.
|
|
virtual const char* Name() const = 0;
|
|
|
|
// Advanced functions: these are used to reduce the space requirements
|
|
// for internal data structures like index blocks.
|
|
|
|
// If *start < limit, changes *start to a short string in [start,limit).
|
|
// Simple comparator implementations may return with *start unchanged,
|
|
// i.e., an implementation of this method that does nothing is correct.
|
|
virtual void FindShortestSeparator(
|
|
std::string* start,
|
|
const Slice& limit) const = 0;
|
|
|
|
// Changes *key to a short string >= *key.
|
|
// Simple comparator implementations may return with *key unchanged,
|
|
// i.e., an implementation of this method that does nothing is correct.
|
|
virtual void FindShortSuccessor(std::string* key) const = 0;
|
|
};
|
|
|
|
// Return a builtin comparator that uses lexicographic byte-wise
|
|
// ordering. The result remains the property of this module and
|
|
// must not be deleted.
|
|
extern const Comparator* BytewiseComparator();
|
|
|
|
} // namespace leveldb
|
|
|
|
#endif // STORAGE_LEVELDB_INCLUDE_COMPARATOR_H_
|