1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
|
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/base/disallow_copying.h"
#include "mongo/util/concurrency/notification.h"
namespace mongo {
/**
* Implements the critical section logic for particular collection or database in the sharding
* subsystem. It supports two phases - catch-up and commit. During the catch-up phase, only writes
* are disallowed, but reads can still proceed. In the commit phase, both reads and writes are
* disallowed.
*
* Currently, only collections stay in the catch-up phase while the last batch of mods is
* transferred to the recipient shard. Databases effectively only support the commit phase.
*/
class ShardingMigrationCriticalSection {
MONGO_DISALLOW_COPYING(ShardingMigrationCriticalSection);
public:
ShardingMigrationCriticalSection();
~ShardingMigrationCriticalSection();
/**
* Enters the critical section in a mode, which still allows reads.
*
* NOTE: Must be called under the appropriate X lock (collection or database).
*/
void enterCriticalSectionCatchUpPhase();
/**
* Sets the critical section in a mode, which disallows reads.
*/
void enterCriticalSectionCommitPhase();
/**
* Leaves the critical section.
*/
void exitCriticalSection();
/**
* Retrieves a critical section notification to wait on. Will return nullptr if the migration is
* not yet in the critical section or if the caller is a reader and the migration is not yet in
* the commit phase.
*/
enum Operation { kRead, kWrite };
std::shared_ptr<Notification<void>> getSignal(Operation op) const;
private:
// Whether the migration source is in a critical section. Tracked as a shared pointer so that
// callers don't have to hold metadata locks in order to wait on it.
std::shared_ptr<Notification<void>> _critSecSignal;
// Used to delay blocking reads up until the commit of the metadata on the config server needs
// to happen. This allows the shard to serve reads up until the config server metadata update
// needs to be committed.
//
// The transition from false to true is protected by the database or collection X-lock, which
// happens just before the config server metadata commit is scheduled.
bool _readsShouldWaitOnCritSec{false};
};
} // namespace mongo
|
