ChronologyProtector::minPosTime() - Code Metrics - Inspection of "Daily Inspection: Merge "Fix some PhpStorm warning..." - wikimedia/mediawiki - Measure and Improve Code Quality continuously with Scrutinizer

Completed

Branch — master (8d5465)

unknown

created 2016-09-13 17:53 UTC

ChronologyProtector::minPosTime() A

↳ Parent: ChronologyProtector

Complexity

Conditions	4
Paths	4

Size

Total Lines	13
Code Lines	7

Duplication

Lines	0
Ratio	0 %

Importance

Changes

Metric	Value
cc	4
eloc	7
nc	4
nop	1
dl	0
loc	13
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 float|null Minimum UNIX timestamp of 1+ expected startup positions */
	protected $waitForPosTime;
	/** @var int Max seconds to wait on positions to appear */
	protected $waitForPosTimeout = self::POS_WAIT_TIMEOUT;
	/** @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 = [];

	/** @var integer Seconds to store positions */
	const POSITION_TTL = 60;
	/** @var integer Max time to wait for positions to appear */
	const POS_WAIT_TIMEOUT = 5;

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

	/**
	 * @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.
	 *
	 * @param callable|null $workCallback Work to do instead of waiting on syncing positions
	 * @param string $mode One of (sync, async); whether to wait on remote datacenters
	 * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
	 */
	public function shutdown( callable $workCallback = null, $mode = 'sync' ) {
		if ( !$this->enabled ) {
			return [];
		}

		$store = $this->store;
		// 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 ) {
			$store->set(
				$this->getTouchedKey( $this->store, $dbName ),
				microtime( true ),
				$store::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 ( $store->lock( $this->key, 3 ) ) {
			if ( $workCallback ) {
				// Let the store run the work before blocking on a replication sync barrier. By the
				// time it's done with the work, the barrier should be fast if replication caught up.
				$store->addBusyCallback( $workCallback );
			}
			$ok = $store->set(
				$this->key,
				self::mergePositions( $store->get( $this->key ), $this->shutdownPositions ),
				self::POSITION_TTL,
				( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
			);
			$store->unlock( $this->key );
		} else {
			$ok = false;
		}

		if ( !$ok ) {
			$bouncedPositions = $this->shutdownPositions;
			// Raced out too many times or stash is down
			wfDebugLog( 'replication',
				__METHOD__ . ": failed to save master pos for " .
				implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
			);
		} elseif ( $mode === 'sync' &&
			$store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
		) {
			// Positions may not be in all datacenters, force LBFactory to play it safe
			wfDebugLog( 'replication',
				__METHOD__ . ": store does not report ability to sync replicas. " );
			$bouncedPositions = $this->shutdownPositions;
		} else {
			$bouncedPositions = [];
		}

		return $bouncedPositions;
	}

	/**
	 * @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 ) {
			// If there is an expectation to see master positions with a certain min
			// timestamp, then block until they appear, or until a timeout is reached.
			if ( $this->waitForPosTime ) {
				$data = null;
				$loop = new WaitConditionLoop(
					function () use ( &$data ) {
						$data = $this->store->get( $this->key );

						return ( self::minPosTime( $data ) >= $this->waitForPosTime )
							? WaitConditionLoop::CONDITION_REACHED
							: WaitConditionLoop::CONDITION_CONTINUE;
					},
					$this->waitForPosTimeout
				);
				$result = $loop->invoke();
				$waitedMs = $loop->getLastWaitTime() * 1e3;

				if ( $result == $loop::CONDITION_REACHED ) {
					$msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
				} else {
					$msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
				}
				wfDebugLog( 'replication', $msg );
			} else {
				$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 $data
	 * @return float|null
	 */
	private static function minPosTime( $data ) {
		if ( !isset( $data['positions'] ) ) {
			return null;
		}

		$min = null;
		foreach ( $data['positions'] as $pos ) {
			/** @var DBMasterPos $pos */
			$min = $min ? min( $pos->asOfTime(), $min ) : $pos->asOfTime();
		}

		return $min;
	}

	/**
	 * @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 float\|null Minimum UNIX timestamp of 1+ expected startup positions */
37			protected $waitForPosTime;
38			/** @var int Max seconds to wait on positions to appear */
39			protected $waitForPosTimeout = self::POS_WAIT_TIMEOUT;
40			/** @var bool Whether to no-op all method calls */
41			protected $enabled = true;
42			/** @var bool Whether to check and wait on positions */
43			protected $wait = true;
44
45			/** @var bool Whether the client data was loaded */
46			protected $initialized = false;
47			/** @var DBMasterPos[] Map of (DB master name => position) */
48			protected $startupPositions = [];
49			/** @var DBMasterPos[] Map of (DB master name => position) */
50			protected $shutdownPositions = [];
51			/** @var float[] Map of (DB master name => 1) */
52			protected $shutdownTouchDBs = [];
53
54			/** @var integer Seconds to store positions */
55			const POSITION_TTL = 60;
56			/** @var integer Max time to wait for positions to appear */
57			const POS_WAIT_TIMEOUT = 5;
58
59			/**
60			* @param BagOStuff $store
61			* @param array $client Map of (ip: <IP>, agent: <user-agent>)
62			* @param float $posTime UNIX timestamp
63			* @since 1.27
64			*/
65			public function __construct( BagOStuff $store, array $client, $posTime = null ) {
66			$this->store = $store;
67			$this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
68			$this->key = $store->makeGlobalKey( __CLASS__, $this->clientId );
69			$this->waitForPosTime = $posTime;
70			}
71
72			/**
73			* @param bool $enabled Whether to no-op all method calls
74			* @since 1.27
75			*/
76			public function setEnabled( $enabled ) {
77			$this->enabled = $enabled;
78			}
79
80			/**
81			* @param bool $enabled Whether to check and wait on positions
82			* @since 1.27
83			*/
84			public function setWaitEnabled( $enabled ) {
85			$this->wait = $enabled;
86			}
87
88			/**
89			* Initialise a LoadBalancer to give it appropriate chronology protection.
90			*
91			* If the stash has a previous master position recorded, this will try to
92			* make sure that the next query to a replica DB of that master will see changes up
93			* to that position by delaying execution. The delay may timeout and allow stale
94			* data if no non-lagged replica DBs are available.
95			*
96			* @param LoadBalancer $lb
97			* @return void
98			*/
99			public function initLB( LoadBalancer $lb ) {
100			if ( !$this->enabled \|\| $lb->getServerCount() <= 1 ) {
101			return; // non-replicated setup or disabled
102			}
103
104			$this->initPositions();
105
106			$masterName = $lb->getServerName( $lb->getWriterIndex() );
107			if ( !empty( $this->startupPositions[$masterName] ) ) {
108			$pos = $this->startupPositions[$masterName];
109			wfDebugLog( 'replication', __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
110			$lb->waitFor( $pos );
111			}
112			}
113
114			/**
115			* Notify the ChronologyProtector that the LoadBalancer is about to shut
116			* down. Saves replication positions.
117			*
118			* @param LoadBalancer $lb
119			* @return void
120			*/
121			public function shutdownLB( LoadBalancer $lb ) {
122			if ( !$this->enabled ) {
123			return; // not enabled
124			} elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
125			// Only save the position if writes have been done on the connection
126			return;
127			}
128
129			$masterName = $lb->getServerName( $lb->getWriterIndex() );
130			if ( $lb->getServerCount() > 1 ) {
131			$pos = $lb->getMasterPos();
132			wfDebugLog( 'replication', __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
133			$this->shutdownPositions[$masterName] = $pos;
134			} else {
135			wfDebugLog( 'replication', __METHOD__ . ": DB '$masterName' touched\n" );
136			}
137			$this->shutdownTouchDBs[$masterName] = 1;
138			}
139
140			/**
141			* Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
142			* May commit chronology data to persistent storage.
143			*
144			* @param callable\|null $workCallback Work to do instead of waiting on syncing positions
145			* @param string $mode One of (sync, async); whether to wait on remote datacenters
146			* @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
147			*/
148			public function shutdown( callable $workCallback = null, $mode = 'sync' ) {
149			if ( !$this->enabled ) {
150			return [];
151			}
152
153			$store = $this->store;
154			// Some callers might want to know if a user recently touched a DB.
155			// These writes do not need to block on all datacenters receiving them.
156			foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
157			$store->set(
158			$this->getTouchedKey( $this->store, $dbName ),
159			microtime( true ),
160			$store::TTL_DAY
161			);
162			}
163
164			if ( !count( $this->shutdownPositions ) ) {
165			return []; // nothing to save
166			}
167
168			wfDebugLog( 'replication',
169			__METHOD__ . ": saving master pos for " .
170			implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
171			);
172
173			// CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
174			// lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
175			// makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
176			if ( $store->lock( $this->key, 3 ) ) {
177			if ( $workCallback ) {
178			// Let the store run the work before blocking on a replication sync barrier. By the
179			// time it's done with the work, the barrier should be fast if replication caught up.
180			$store->addBusyCallback( $workCallback );
181			}
182			$ok = $store->set(
183			$this->key,
184			self::mergePositions( $store->get( $this->key ), $this->shutdownPositions ),
185			self::POSITION_TTL,
186			( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
187			);
188			$store->unlock( $this->key );
189			} else {
190			$ok = false;
191			}
192
193			if ( !$ok ) {
194			$bouncedPositions = $this->shutdownPositions;
195			// Raced out too many times or stash is down
196			wfDebugLog( 'replication',
197			__METHOD__ . ": failed to save master pos for " .
198			implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
199			);
200			} elseif ( $mode === 'sync' &&
201			$store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
202			) {
203			// Positions may not be in all datacenters, force LBFactory to play it safe
204			wfDebugLog( 'replication',
205			__METHOD__ . ": store does not report ability to sync replicas. " );
206			$bouncedPositions = $this->shutdownPositions;
207			} else {
208			$bouncedPositions = [];
209			}
210
211			return $bouncedPositions;
212			}
213
214			/**
215			* @param string $dbName DB master name (e.g. "db1052")
216			* @return float\|bool UNIX timestamp when client last touched the DB; false if not on record
217			* @since 1.28
218			*/
219			public function getTouched( $dbName ) {
220			return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
221			}
222
223			/**
224			* @param BagOStuff $store
225			* @param string $dbName
226			* @return string
227			*/
228			private function getTouchedKey( BagOStuff $store, $dbName ) {
229			return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
230			}
231
232			/**
233			* Load in previous master positions for the client
234			*/
235			protected function initPositions() {
236			if ( $this->initialized ) {
237			return;
238			}
239
240			$this->initialized = true;
241			if ( $this->wait ) {
242			// If there is an expectation to see master positions with a certain min
243			// timestamp, then block until they appear, or until a timeout is reached.
244			if ( $this->waitForPosTime ) {
245			$data = null;
246			$loop = new WaitConditionLoop(
247			function () use ( &$data ) {
248			$data = $this->store->get( $this->key );
249
250			return ( self::minPosTime( $data ) >= $this->waitForPosTime )
251			? WaitConditionLoop::CONDITION_REACHED
252			: WaitConditionLoop::CONDITION_CONTINUE;
253			},
254			$this->waitForPosTimeout
255			);
256			$result = $loop->invoke();
257			$waitedMs = $loop->getLastWaitTime() * 1e3;
258
259			if ( $result == $loop::CONDITION_REACHED ) {
260			$msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
261			} else {
262			$msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
263			}
264			wfDebugLog( 'replication', $msg );
265			} else {
266			$data = $this->store->get( $this->key );
267			}
268
269			$this->startupPositions = $data ? $data['positions'] : [];
270			wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (read)\n" );
271			} else {
272			$this->startupPositions = [];
273			wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (unread)\n" );
274			}
275			}
276
277			/**
278			* @param array\|bool $data
279			* @return float\|null
280			*/
281			private static function minPosTime( $data ) {
282			if ( !isset( $data['positions'] ) ) {
283			return null;
284			}
285
286			$min = null;
287			foreach ( $data['positions'] as $pos ) {
288			/** @var DBMasterPos $pos */
289			$min = $min ? min( $pos->asOfTime(), $min ) : $pos->asOfTime();
290			}
291
292			return $min;
293			}
294
295			/**
296			* @param array\|bool $curValue
297			* @param DBMasterPos[] $shutdownPositions
298			* @return array
299			*/
300			private static function mergePositions( $curValue, array $shutdownPositions ) {
301			/** @var $curPositions DBMasterPos[] */
302			if ( $curValue === false ) {
303			$curPositions = $shutdownPositions;
304			} else {
305			$curPositions = $curValue['positions'];
306			// Use the newest positions for each DB master
307			foreach ( $shutdownPositions as $db => $pos ) {
308			if ( !isset( $curPositions[$db] )
309			\|\| $pos->asOfTime() > $curPositions[$db]->asOfTime()
310			) {
311			$curPositions[$db] = $pos;
312			}
313			}
314			}
315
316			return [ 'positions' => $curPositions ];
317			}
318			}
319

wikimedia / mediawiki

Branch — master (8d5465)

ChronologyProtector::minPosTime() A

Complexity

Size

Duplication

Importance

Duplication Side-by-Side

Filter issues like