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