ChronologyProtector::shutdownLB() - Code Metrics - Inspection of "Daily Inspection: Merge "mw.special.movePage: Don'..." - wikimedia/mediawiki - Measure and Improve Code Quality continuously with Scrutinizer

Completed

Branch — master (4cbefc)

unknown

created 2016-09-12 17:53 UTC

ChronologyProtector::shutdownLB() A

↳ Parent: ChronologyProtector

Complexity

Conditions	4
Paths	4

Size

Total Lines	18
Code Lines	13

Duplication

Lines	0
Ratio	0 %

Importance

Changes

Metric	Value
cc	4
eloc	13
nc	4
nop	1
dl	0
loc	18
rs	9.2
c	0
b	0
f	0

<?php
/**
 * Generator of database load balancing objects.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Database
 */

/**
 * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
 * Kind of like Hawking's [[Chronology Protection Agency]].
 */
class ChronologyProtector {
	/** @var BagOStuff */
	protected $store;

	/** @var string Storage key name */
	protected $key;
	/** @var string Hash of client parameters */
	protected $clientId;
	/** @var bool Whether to no-op all method calls */
	protected $enabled = true;
	/** @var bool Whether to check and wait on positions */
	protected $wait = true;

	/** @var bool Whether the client data was loaded */
	protected $initialized = false;
	/** @var DBMasterPos[] Map of (DB master name => position) */
	protected $startupPositions = [];
	/** @var DBMasterPos[] Map of (DB master name => position) */
	protected $shutdownPositions = [];
	/** @var float[] Map of (DB master name => 1) */
	protected $shutdownTouchDBs = [];

	/**
	 * @param BagOStuff $store
	 * @param array $client Map of (ip: <IP>, agent: <user-agent>)
	 * @since 1.27
	 */
	public function __construct( BagOStuff $store, array $client ) {
		$this->store = $store;
		$this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
		$this->key = $store->makeGlobalKey( __CLASS__, $this->clientId );
	}

	/**
	 * @param bool $enabled Whether to no-op all method calls
	 * @since 1.27
	 */
	public function setEnabled( $enabled ) {
		$this->enabled = $enabled;
	}

	/**
	 * @param bool $enabled Whether to check and wait on positions
	 * @since 1.27
	 */
	public function setWaitEnabled( $enabled ) {
		$this->wait = $enabled;
	}

	/**
	 * Initialise a LoadBalancer to give it appropriate chronology protection.
	 *
	 * If the stash has a previous master position recorded, this will try to
	 * make sure that the next query to a replica DB of that master will see changes up
	 * to that position by delaying execution. The delay may timeout and allow stale
	 * data if no non-lagged replica DBs are available.
	 *
	 * @param LoadBalancer $lb
	 * @return void
	 */
	public function initLB( LoadBalancer $lb ) {
		if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
			return; // non-replicated setup or disabled
		}

		$this->initPositions();

		$masterName = $lb->getServerName( $lb->getWriterIndex() );
		if ( !empty( $this->startupPositions[$masterName] ) ) {
			$pos = $this->startupPositions[$masterName];
			wfDebugLog( 'replication', __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
			$lb->waitFor( $pos );
		}
	}

	/**
	 * Notify the ChronologyProtector that the LoadBalancer is about to shut
	 * down. Saves replication positions.
	 *
	 * @param LoadBalancer $lb
	 * @return void
	 */
	public function shutdownLB( LoadBalancer $lb ) {
		if ( !$this->enabled ) {
			return; // not enabled
		} elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
			// Only save the position if writes have been done on the connection
			return;
		}

		$masterName = $lb->getServerName( $lb->getWriterIndex() );
		if ( $lb->getServerCount() > 1 ) {
			$pos = $lb->getMasterPos();
			wfDebugLog( 'replication', __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
			$this->shutdownPositions[$masterName] = $pos;
		} else {
			wfDebugLog( 'replication', __METHOD__ . ": DB '$masterName' touched\n" );
		}
		$this->shutdownTouchDBs[$masterName] = 1;
	}

	/**
	 * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
	 * May commit chronology data to persistent storage.
	 *
	 * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
	 */
	public function shutdown() {
		if ( !$this->enabled ) {
			return [];
		}

		// Some callers might want to know if a user recently touched a DB.
		// These writes do not need to block on all datacenters receiving them.
		foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
			$this->store->set(
				$this->getTouchedKey( $this->store, $dbName ),
				microtime( true ),
				BagOStuff::TTL_DAY
			);
		}

		if ( !count( $this->shutdownPositions ) ) {
			return []; // nothing to save
		}

		wfDebugLog( 'replication',
			__METHOD__ . ": saving master pos for " .
			implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
		);

		// CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
		// lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
		// makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
		if ( $this->store->lock( $this->key, 3 ) ) {
			$ok = $this->store->set(
				$this->key,
				self::mergePositions( $this->store->get( $this->key ), $this->shutdownPositions ),
				BagOStuff::TTL_MINUTE,
				BagOStuff::WRITE_SYNC
			);
			$this->store->unlock( $this->key );
		} else {
			$ok = false;
		}

		if ( !$ok ) {
			// Raced out too many times or stash is down
			wfDebugLog( 'replication',
				__METHOD__ . ": failed to save master pos for " .
				implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
			);

			return $this->shutdownPositions;
		}

		return [];
	}

	/**
	 * @param string $dbName DB master name (e.g. "db1052")
	 * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
	 * @since 1.28
	 */
	public function getTouched( $dbName ) {
		return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
	}

	/**
	 * @param BagOStuff $store
	 * @param string $dbName
	 * @return string
	 */
	private function getTouchedKey( BagOStuff $store, $dbName ) {
		return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
	}

	/**
	 * Load in previous master positions for the client
	 */
	protected function initPositions() {
		if ( $this->initialized ) {
			return;
		}

		$this->initialized = true;
		if ( $this->wait ) {
			$data = $this->store->get( $this->key );
			$this->startupPositions = $data ? $data['positions'] : [];
			wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (read)\n" );
		} else {
			$this->startupPositions = [];
			wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (unread)\n" );
		}
	}

	/**
	 * @param array|bool $curValue
	 * @param DBMasterPos[] $shutdownPositions
	 * @return array
	 */
	private static function mergePositions( $curValue, array $shutdownPositions ) {
		/** @var $curPositions DBMasterPos[] */
		if ( $curValue === false ) {
			$curPositions = $shutdownPositions;
		} else {
			$curPositions = $curValue['positions'];
			// Use the newest positions for each DB master
			foreach ( $shutdownPositions as $db => $pos ) {
				if ( !isset( $curPositions[$db] )
					|| $pos->asOfTime() > $curPositions[$db]->asOfTime()
				) {
					$curPositions[$db] = $pos;
				}
			}
		}

		return [ 'positions' => $curPositions ];
	}
}


1			<?php
2			/**
3			* Generator of database load balancing objects.
4			*
5			* This program is free software; you can redistribute it and/or modify
6			* it under the terms of the GNU General Public License as published by
7			* the Free Software Foundation; either version 2 of the License, or
8			* (at your option) any later version.
9			*
10			* This program is distributed in the hope that it will be useful,
11			* but WITHOUT ANY WARRANTY; without even the implied warranty of
12			* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13			* GNU General Public License for more details.
14			*
15			* You should have received a copy of the GNU General Public License along
16			* with this program; if not, write to the Free Software Foundation, Inc.,
17			* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
18			* http://www.gnu.org/copyleft/gpl.html
19			*
20			* @file
21			* @ingroup Database
22			*/
23
24			/**
25			* Class for ensuring a consistent ordering of events as seen by the user, despite replication.
26			* Kind of like Hawking's [[Chronology Protection Agency]].
27			*/
28			class ChronologyProtector {
29			/** @var BagOStuff */
30			protected $store;
31
32			/** @var string Storage key name */
33			protected $key;
34			/** @var string Hash of client parameters */
35			protected $clientId;
36			/** @var bool Whether to no-op all method calls */
37			protected $enabled = true;
38			/** @var bool Whether to check and wait on positions */
39			protected $wait = true;
40
41			/** @var bool Whether the client data was loaded */
42			protected $initialized = false;
43			/** @var DBMasterPos[] Map of (DB master name => position) */
44			protected $startupPositions = [];
45			/** @var DBMasterPos[] Map of (DB master name => position) */
46			protected $shutdownPositions = [];
47			/** @var float[] Map of (DB master name => 1) */
48			protected $shutdownTouchDBs = [];
49
50			/**
51			* @param BagOStuff $store
52			* @param array $client Map of (ip: <IP>, agent: <user-agent>)
53			* @since 1.27
54			*/
55			public function __construct( BagOStuff $store, array $client ) {
56			$this->store = $store;
57			$this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
58			$this->key = $store->makeGlobalKey( __CLASS__, $this->clientId );
59			}
60
61			/**
62			* @param bool $enabled Whether to no-op all method calls
63			* @since 1.27
64			*/
65			public function setEnabled( $enabled ) {
66			$this->enabled = $enabled;
67			}
68
69			/**
70			* @param bool $enabled Whether to check and wait on positions
71			* @since 1.27
72			*/
73			public function setWaitEnabled( $enabled ) {
74			$this->wait = $enabled;
75			}
76
77			/**
78			* Initialise a LoadBalancer to give it appropriate chronology protection.
79			*
80			* If the stash has a previous master position recorded, this will try to
81			* make sure that the next query to a replica DB of that master will see changes up
82			* to that position by delaying execution. The delay may timeout and allow stale
83			* data if no non-lagged replica DBs are available.
84			*
85			* @param LoadBalancer $lb
86			* @return void
87			*/
88			public function initLB( LoadBalancer $lb ) {
89			if ( !$this->enabled \|\| $lb->getServerCount() <= 1 ) {
90			return; // non-replicated setup or disabled
91			}
92
93			$this->initPositions();
94
95			$masterName = $lb->getServerName( $lb->getWriterIndex() );
96			if ( !empty( $this->startupPositions[$masterName] ) ) {
97			$pos = $this->startupPositions[$masterName];
98			wfDebugLog( 'replication', __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
99			$lb->waitFor( $pos );
100			}
101			}
102
103			/**
104			* Notify the ChronologyProtector that the LoadBalancer is about to shut
105			* down. Saves replication positions.
106			*
107			* @param LoadBalancer $lb
108			* @return void
109			*/
110			public function shutdownLB( LoadBalancer $lb ) {
111			if ( !$this->enabled ) {
112			return; // not enabled
113			} elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
114			// Only save the position if writes have been done on the connection
115			return;
116			}
117
118			$masterName = $lb->getServerName( $lb->getWriterIndex() );
119			if ( $lb->getServerCount() > 1 ) {
120			$pos = $lb->getMasterPos();
121			wfDebugLog( 'replication', __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
122			$this->shutdownPositions[$masterName] = $pos;
123			} else {
124			wfDebugLog( 'replication', __METHOD__ . ": DB '$masterName' touched\n" );
125			}
126			$this->shutdownTouchDBs[$masterName] = 1;
127			}
128
129			/**
130			* Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
131			* May commit chronology data to persistent storage.
132			*
133			* @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
134			*/
135			public function shutdown() {
136			if ( !$this->enabled ) {
137			return [];
138			}
139
140			// Some callers might want to know if a user recently touched a DB.
141			// These writes do not need to block on all datacenters receiving them.
142			foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
143			$this->store->set(
144			$this->getTouchedKey( $this->store, $dbName ),
145			microtime( true ),
146			BagOStuff::TTL_DAY
147			);
148			}
149
150			if ( !count( $this->shutdownPositions ) ) {
151			return []; // nothing to save
152			}
153
154			wfDebugLog( 'replication',
155			__METHOD__ . ": saving master pos for " .
156			implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
157			);
158
159			// CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
160			// lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
161			// makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
162			if ( $this->store->lock( $this->key, 3 ) ) {
163			$ok = $this->store->set(
164			$this->key,
165			self::mergePositions( $this->store->get( $this->key ), $this->shutdownPositions ),
166			BagOStuff::TTL_MINUTE,
167			BagOStuff::WRITE_SYNC
168			);
169			$this->store->unlock( $this->key );
170			} else {
171			$ok = false;
172			}
173
174			if ( !$ok ) {
175			// Raced out too many times or stash is down
176			wfDebugLog( 'replication',
177			__METHOD__ . ": failed to save master pos for " .
178			implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
179			);
180
181			return $this->shutdownPositions;
182			}
183
184			return [];
185			}
186
187			/**
188			* @param string $dbName DB master name (e.g. "db1052")
189			* @return float\|bool UNIX timestamp when client last touched the DB; false if not on record
190			* @since 1.28
191			*/
192			public function getTouched( $dbName ) {
193			return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
194			}
195
196			/**
197			* @param BagOStuff $store
198			* @param string $dbName
199			* @return string
200			*/
201			private function getTouchedKey( BagOStuff $store, $dbName ) {
202			return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
203			}
204
205			/**
206			* Load in previous master positions for the client
207			*/
208			protected function initPositions() {
209			if ( $this->initialized ) {
210			return;
211			}
212
213			$this->initialized = true;
214			if ( $this->wait ) {
215			$data = $this->store->get( $this->key );
216			$this->startupPositions = $data ? $data['positions'] : [];
217			wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (read)\n" );
218			} else {
219			$this->startupPositions = [];
220			wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (unread)\n" );
221			}
222			}
223
224			/**
225			* @param array\|bool $curValue
226			* @param DBMasterPos[] $shutdownPositions
227			* @return array
228			*/
229			private static function mergePositions( $curValue, array $shutdownPositions ) {
230			/** @var $curPositions DBMasterPos[] */
231			if ( $curValue === false ) {
232			$curPositions = $shutdownPositions;
233			} else {
234			$curPositions = $curValue['positions'];
235			// Use the newest positions for each DB master
236			foreach ( $shutdownPositions as $db => $pos ) {
237			if ( !isset( $curPositions[$db] )
238			\|\| $pos->asOfTime() > $curPositions[$db]->asOfTime()
239			) {
240			$curPositions[$db] = $pos;
241			}
242			}
243			}
244
245			return [ 'positions' => $curPositions ];
246			}
247			}
248

wikimedia / mediawiki

Branch — master (4cbefc)

ChronologyProtector::shutdownLB() A

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