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1 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_CHANGES_VERSION_H_
6 #define CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_CHANGES_VERSION_H_
7 #pragma once
8 
9 namespace syncable {
10 
11 // For the most part, the sync engine treats version numbers as opaque values.
12 // However, there are parts of our code base that break this abstraction, and
13 // depend on the following two invariants:
14 //
15 //  1.  CHANGES_VERSION is less than 0.
16 //  2.  The server only issues positive version numbers.
17 //
18 // Breaking these abstractions makes some operations 10 times
19 // faster.  If either of these invariants change, then those queries
20 // must be revisited.
21 
22 enum {
23   CHANGES_VERSION = -1
24 };
25 
26 #define CHANGES_VERSION_STRING "-1"
27 
28 }  // namespace syncable
29 
30 #endif  // CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_CHANGES_VERSION_H_
31