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[lhc/web/wiklou.git] / includes / db / loadbalancer / LoadBalancer.php
1 <?php
2 /**
3 * Database load balancing.
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 * Database load balancing object
26 *
27 * @todo document
28 * @ingroup Database
29 */
30 class LoadBalancer {
31 /** @var array[] Map of (server index => server config array) */
32 private $mServers;
33 /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
34 private $mConns;
35 /** @var array Map of (server index => weight) */
36 private $mLoads;
37 /** @var array[] Map of (group => server index => weight) */
38 private $mGroupLoads;
39 /** @var bool Whether to disregard slave lag as a factor in slave selection */
40 private $mAllowLagged;
41 /** @var integer Seconds to spend waiting on slave lag to resolve */
42 private $mWaitTimeout;
43 /** @var array LBFactory information */
44 private $mParentInfo;
45
46 /** @var string The LoadMonitor subclass name */
47 private $mLoadMonitorClass;
48 /** @var LoadMonitor */
49 private $mLoadMonitor;
50 /** @var BagOStuff */
51 private $srvCache;
52 /** @var WANObjectCache */
53 private $wanCache;
54
55 /** @var bool|DatabaseBase Database connection that caused a problem */
56 private $mErrorConnection;
57 /** @var integer The generic (not query grouped) slave index (of $mServers) */
58 private $mReadIndex;
59 /** @var bool|DBMasterPos False if not set */
60 private $mWaitForPos;
61 /** @var bool Whether the generic reader fell back to a lagged slave */
62 private $laggedSlaveMode = false;
63 /** @var bool Whether the generic reader fell back to a lagged slave */
64 private $slavesDownMode = false;
65 /** @var string The last DB selection or connection error */
66 private $mLastError = 'Unknown error';
67 /** @var string|bool Reason the LB is read-only or false if not */
68 private $readOnlyReason = false;
69 /** @var integer Total connections opened */
70 private $connsOpened = 0;
71
72 /** @var TransactionProfiler */
73 protected $trxProfiler;
74
75 /** @var integer Warn when this many connection are held */
76 const CONN_HELD_WARN_THRESHOLD = 10;
77 /** @var integer Default 'max lag' when unspecified */
78 const MAX_LAG = 10;
79 /** @var integer Max time to wait for a slave to catch up (e.g. ChronologyProtector) */
80 const POS_WAIT_TIMEOUT = 10;
81 /** @var integer Seconds to cache master server read-only status */
82 const TTL_CACHE_READONLY = 5;
83
84 /**
85 * @var boolean
86 */
87 private $disabled = false;
88
89 /**
90 * @param array $params Array with keys:
91 * - servers : Required. Array of server info structures.
92 * - loadMonitor : Name of a class used to fetch server lag and load.
93 * - readOnlyReason : Reason the master DB is read-only if so [optional]
94 * @throws MWException
95 */
96 public function __construct( array $params ) {
97 if ( !isset( $params['servers'] ) ) {
98 throw new MWException( __CLASS__ . ': missing servers parameter' );
99 }
100 $this->mServers = $params['servers'];
101 $this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
102
103 $this->mReadIndex = -1;
104 $this->mWriteIndex = -1;
105 $this->mConns = [
106 'local' => [],
107 'foreignUsed' => [],
108 'foreignFree' => [] ];
109 $this->mLoads = [];
110 $this->mWaitForPos = false;
111 $this->mErrorConnection = false;
112 $this->mAllowLagged = false;
113
114 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
115 $this->readOnlyReason = $params['readOnlyReason'];
116 }
117
118 if ( isset( $params['loadMonitor'] ) ) {
119 $this->mLoadMonitorClass = $params['loadMonitor'];
120 } else {
121 $master = reset( $params['servers'] );
122 if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
123 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
124 } else {
125 $this->mLoadMonitorClass = 'LoadMonitorNull';
126 }
127 }
128
129 foreach ( $params['servers'] as $i => $server ) {
130 $this->mLoads[$i] = $server['load'];
131 if ( isset( $server['groupLoads'] ) ) {
132 foreach ( $server['groupLoads'] as $group => $ratio ) {
133 if ( !isset( $this->mGroupLoads[$group] ) ) {
134 $this->mGroupLoads[$group] = [];
135 }
136 $this->mGroupLoads[$group][$i] = $ratio;
137 }
138 }
139 }
140
141 // Use APC/memcached style caching, but avoids loops with CACHE_DB (T141804)
142 // @TODO: inject these in via LBFactory at some point
143 $cache = ObjectCache::getLocalServerInstance();
144 if ( $cache->getQoS( $cache::ATTR_EMULATION ) > $cache::QOS_EMULATION_SQL ) {
145 $this->srvCache = $cache;
146 } else {
147 $this->srvCache = new EmptyBagOStuff();
148 }
149 $wCache = ObjectCache::getMainWANInstance();
150 if ( $wCache->getQoS( $wCache::ATTR_EMULATION ) > $wCache::QOS_EMULATION_SQL ) {
151 $this->wanCache = $wCache;
152 } else {
153 $this->wanCache = WANObjectCache::newEmpty();
154 }
155
156 if ( isset( $params['trxProfiler'] ) ) {
157 $this->trxProfiler = $params['trxProfiler'];
158 } else {
159 $this->trxProfiler = new TransactionProfiler();
160 }
161 }
162
163 /**
164 * Get a LoadMonitor instance
165 *
166 * @return LoadMonitor
167 */
168 private function getLoadMonitor() {
169 if ( !isset( $this->mLoadMonitor ) ) {
170 $class = $this->mLoadMonitorClass;
171 $this->mLoadMonitor = new $class( $this );
172 }
173
174 return $this->mLoadMonitor;
175 }
176
177 /**
178 * Get or set arbitrary data used by the parent object, usually an LBFactory
179 * @param mixed $x
180 * @return mixed
181 */
182 public function parentInfo( $x = null ) {
183 return wfSetVar( $this->mParentInfo, $x );
184 }
185
186 /**
187 * @param array $loads
188 * @param bool|string $wiki Wiki to get non-lagged for
189 * @param int $maxLag Restrict the maximum allowed lag to this many seconds
190 * @return bool|int|string
191 */
192 private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
193 $lags = $this->getLagTimes( $wiki );
194
195 # Unset excessively lagged servers
196 foreach ( $lags as $i => $lag ) {
197 if ( $i != 0 ) {
198 $maxServerLag = $maxLag;
199 if ( isset( $this->mServers[$i]['max lag'] ) ) {
200 $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
201 }
202
203 $host = $this->getServerName( $i );
204 if ( $lag === false ) {
205 wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
206 unset( $loads[$i] );
207 } elseif ( $lag > $maxServerLag ) {
208 wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
209 unset( $loads[$i] );
210 }
211 }
212 }
213
214 # Find out if all the slaves with non-zero load are lagged
215 $sum = 0;
216 foreach ( $loads as $load ) {
217 $sum += $load;
218 }
219 if ( $sum == 0 ) {
220 # No appropriate DB servers except maybe the master and some slaves with zero load
221 # Do NOT use the master
222 # Instead, this function will return false, triggering read-only mode,
223 # and a lagged slave will be used instead.
224 return false;
225 }
226
227 if ( count( $loads ) == 0 ) {
228 return false;
229 }
230
231 # Return a random representative of the remainder
232 return ArrayUtils::pickRandom( $loads );
233 }
234
235 /**
236 * Get the index of the reader connection, which may be a slave
237 * This takes into account load ratios and lag times. It should
238 * always return a consistent index during a given invocation
239 *
240 * Side effect: opens connections to databases
241 * @param string|bool $group Query group, or false for the generic reader
242 * @param string|bool $wiki Wiki ID, or false for the current wiki
243 * @throws MWException
244 * @return bool|int|string
245 */
246 public function getReaderIndex( $group = false, $wiki = false ) {
247 global $wgDBtype;
248
249 # @todo FIXME: For now, only go through all this for mysql databases
250 if ( $wgDBtype != 'mysql' ) {
251 return $this->getWriterIndex();
252 }
253
254 if ( count( $this->mServers ) == 1 ) {
255 # Skip the load balancing if there's only one server
256 return 0;
257 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
258 # Shortcut if generic reader exists already
259 return $this->mReadIndex;
260 }
261
262 # Find the relevant load array
263 if ( $group !== false ) {
264 if ( isset( $this->mGroupLoads[$group] ) ) {
265 $nonErrorLoads = $this->mGroupLoads[$group];
266 } else {
267 # No loads for this group, return false and the caller can use some other group
268 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
269
270 return false;
271 }
272 } else {
273 $nonErrorLoads = $this->mLoads;
274 }
275
276 if ( !count( $nonErrorLoads ) ) {
277 throw new MWException( "Empty server array given to LoadBalancer" );
278 }
279
280 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
281 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
282
283 $laggedSlaveMode = false;
284
285 # No server found yet
286 $i = false;
287 $conn = false;
288 # First try quickly looking through the available servers for a server that
289 # meets our criteria
290 $currentLoads = $nonErrorLoads;
291 while ( count( $currentLoads ) ) {
292 if ( $this->mAllowLagged || $laggedSlaveMode ) {
293 $i = ArrayUtils::pickRandom( $currentLoads );
294 } else {
295 $i = false;
296 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
297 # ChronologyProtecter causes mWaitForPos to be set via sessions.
298 # This triggers doWait() after connect, so it's especially good to
299 # avoid lagged servers so as to avoid just blocking in that method.
300 $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
301 # Aim for <= 1 second of waiting (being too picky can backfire)
302 $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
303 }
304 if ( $i === false ) {
305 # Any server with less lag than it's 'max lag' param is preferable
306 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
307 }
308 if ( $i === false && count( $currentLoads ) != 0 ) {
309 # All slaves lagged. Switch to read-only mode
310 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
311 $i = ArrayUtils::pickRandom( $currentLoads );
312 $laggedSlaveMode = true;
313 }
314 }
315
316 if ( $i === false ) {
317 # pickRandom() returned false
318 # This is permanent and means the configuration or the load monitor
319 # wants us to return false.
320 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
321
322 return false;
323 }
324
325 $serverName = $this->getServerName( $i );
326 wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
327
328 $conn = $this->openConnection( $i, $wiki );
329 if ( !$conn ) {
330 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
331 unset( $nonErrorLoads[$i] );
332 unset( $currentLoads[$i] );
333 $i = false;
334 continue;
335 }
336
337 // Decrement reference counter, we are finished with this connection.
338 // It will be incremented for the caller later.
339 if ( $wiki !== false ) {
340 $this->reuseConnection( $conn );
341 }
342
343 # Return this server
344 break;
345 }
346
347 # If all servers were down, quit now
348 if ( !count( $nonErrorLoads ) ) {
349 wfDebugLog( 'connect', "All servers down" );
350 }
351
352 if ( $i !== false ) {
353 # Slave connection successful
354 # Wait for the session master pos for a short time
355 if ( $this->mWaitForPos && $i > 0 ) {
356 if ( !$this->doWait( $i ) ) {
357 $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
358 }
359 }
360 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
361 $this->mReadIndex = $i;
362 # Record if the generic reader index is in "lagged slave" mode
363 if ( $laggedSlaveMode ) {
364 $this->laggedSlaveMode = true;
365 }
366 }
367 $serverName = $this->getServerName( $i );
368 wfDebugLog( 'connect', __METHOD__ .
369 ": using server $serverName for group '$group'\n" );
370 }
371
372 return $i;
373 }
374
375 /**
376 * Set the master wait position
377 * If a DB_SLAVE connection has been opened already, waits
378 * Otherwise sets a variable telling it to wait if such a connection is opened
379 * @param DBMasterPos $pos
380 */
381 public function waitFor( $pos ) {
382 $this->mWaitForPos = $pos;
383 $i = $this->mReadIndex;
384
385 if ( $i > 0 ) {
386 if ( !$this->doWait( $i ) ) {
387 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
388 $this->laggedSlaveMode = true;
389 }
390 }
391 }
392
393 /**
394 * Set the master wait position and wait for a "generic" slave to catch up to it
395 *
396 * This can be used a faster proxy for waitForAll()
397 *
398 * @param DBMasterPos $pos
399 * @param int $timeout Max seconds to wait; default is mWaitTimeout
400 * @return bool Success (able to connect and no timeouts reached)
401 * @since 1.26
402 */
403 public function waitForOne( $pos, $timeout = null ) {
404 $this->mWaitForPos = $pos;
405
406 $i = $this->mReadIndex;
407 if ( $i <= 0 ) {
408 // Pick a generic slave if there isn't one yet
409 $readLoads = $this->mLoads;
410 unset( $readLoads[$this->getWriterIndex()] ); // slaves only
411 $readLoads = array_filter( $readLoads ); // with non-zero load
412 $i = ArrayUtils::pickRandom( $readLoads );
413 }
414
415 if ( $i > 0 ) {
416 $ok = $this->doWait( $i, true, $timeout );
417 } else {
418 $ok = true; // no applicable loads
419 }
420
421 return $ok;
422 }
423
424 /**
425 * Set the master wait position and wait for ALL slaves to catch up to it
426 * @param DBMasterPos $pos
427 * @param int $timeout Max seconds to wait; default is mWaitTimeout
428 * @return bool Success (able to connect and no timeouts reached)
429 */
430 public function waitForAll( $pos, $timeout = null ) {
431 $this->mWaitForPos = $pos;
432 $serverCount = count( $this->mServers );
433
434 $ok = true;
435 for ( $i = 1; $i < $serverCount; $i++ ) {
436 if ( $this->mLoads[$i] > 0 ) {
437 $ok = $this->doWait( $i, true, $timeout ) && $ok;
438 }
439 }
440
441 return $ok;
442 }
443
444 /**
445 * Get any open connection to a given server index, local or foreign
446 * Returns false if there is no connection open
447 *
448 * @param int $i
449 * @return DatabaseBase|bool False on failure
450 */
451 public function getAnyOpenConnection( $i ) {
452 foreach ( $this->mConns as $conns ) {
453 if ( !empty( $conns[$i] ) ) {
454 return reset( $conns[$i] );
455 }
456 }
457
458 return false;
459 }
460
461 /**
462 * Wait for a given slave to catch up to the master pos stored in $this
463 * @param int $index Server index
464 * @param bool $open Check the server even if a new connection has to be made
465 * @param int $timeout Max seconds to wait; default is mWaitTimeout
466 * @return bool
467 */
468 protected function doWait( $index, $open = false, $timeout = null ) {
469 $close = false; // close the connection afterwards
470
471 // Check if we already know that the DB has reached this point
472 $server = $this->getServerName( $index );
473 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
474 /** @var DBMasterPos $knownReachedPos */
475 $knownReachedPos = $this->srvCache->get( $key );
476 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
477 wfDebugLog( 'replication', __METHOD__ .
478 ": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
479 return true;
480 }
481
482 // Find a connection to wait on, creating one if needed and allowed
483 $conn = $this->getAnyOpenConnection( $index );
484 if ( !$conn ) {
485 if ( !$open ) {
486 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
487
488 return false;
489 } else {
490 $conn = $this->openConnection( $index, '' );
491 if ( !$conn ) {
492 wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
493
494 return false;
495 }
496 // Avoid connection spam in waitForAll() when connections
497 // are made just for the sake of doing this lag check.
498 $close = true;
499 }
500 }
501
502 wfDebugLog( 'replication', __METHOD__ . ": Waiting for slave $server to catch up...\n" );
503 $timeout = $timeout ?: $this->mWaitTimeout;
504 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
505
506 if ( $result == -1 || is_null( $result ) ) {
507 // Timed out waiting for slave, use master instead
508 $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
509 wfDebugLog( 'replication', "$msg\n" );
510 wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
511 $ok = false;
512 } else {
513 wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
514 $ok = true;
515 // Remember that the DB reached this point
516 $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
517 }
518
519 if ( $close ) {
520 $this->closeConnection( $conn );
521 }
522
523 return $ok;
524 }
525
526 /**
527 * Get a connection by index
528 * This is the main entry point for this class.
529 *
530 * @param int $i Server index
531 * @param array|string|bool $groups Query group(s), or false for the generic reader
532 * @param string|bool $wiki Wiki ID, or false for the current wiki
533 *
534 * @throws MWException
535 * @return DatabaseBase
536 */
537 public function getConnection( $i, $groups = [], $wiki = false ) {
538 if ( $i === null || $i === false ) {
539 throw new MWException( 'Attempt to call ' . __METHOD__ .
540 ' with invalid server index' );
541 }
542
543 if ( $wiki === wfWikiID() ) {
544 $wiki = false;
545 }
546
547 $groups = ( $groups === false || $groups === [] )
548 ? [ false ] // check one "group": the generic pool
549 : (array)$groups;
550
551 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
552 $oldConnsOpened = $this->connsOpened; // connections open now
553
554 if ( $i == DB_MASTER ) {
555 $i = $this->getWriterIndex();
556 } else {
557 # Try to find an available server in any the query groups (in order)
558 foreach ( $groups as $group ) {
559 $groupIndex = $this->getReaderIndex( $group, $wiki );
560 if ( $groupIndex !== false ) {
561 $i = $groupIndex;
562 break;
563 }
564 }
565 }
566
567 # Operation-based index
568 if ( $i == DB_SLAVE ) {
569 $this->mLastError = 'Unknown error'; // reset error string
570 # Try the general server pool if $groups are unavailable.
571 $i = in_array( false, $groups, true )
572 ? false // don't bother with this if that is what was tried above
573 : $this->getReaderIndex( false, $wiki );
574 # Couldn't find a working server in getReaderIndex()?
575 if ( $i === false ) {
576 $this->mLastError = 'No working slave server: ' . $this->mLastError;
577
578 return $this->reportConnectionError();
579 }
580 }
581
582 # Now we have an explicit index into the servers array
583 $conn = $this->openConnection( $i, $wiki );
584 if ( !$conn ) {
585 return $this->reportConnectionError();
586 }
587
588 # Profile any new connections that happen
589 if ( $this->connsOpened > $oldConnsOpened ) {
590 $host = $conn->getServer();
591 $dbname = $conn->getDBname();
592 $trxProf = Profiler::instance()->getTransactionProfiler();
593 $trxProf->recordConnection( $host, $dbname, $masterOnly );
594 }
595
596 if ( $masterOnly ) {
597 # Make master-requested DB handles inherit any read-only mode setting
598 $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
599 }
600
601 return $conn;
602 }
603
604 /**
605 * Mark a foreign connection as being available for reuse under a different
606 * DB name or prefix. This mechanism is reference-counted, and must be called
607 * the same number of times as getConnection() to work.
608 *
609 * @param DatabaseBase $conn
610 * @throws MWException
611 */
612 public function reuseConnection( $conn ) {
613 $serverIndex = $conn->getLBInfo( 'serverIndex' );
614 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
615 if ( $serverIndex === null || $refCount === null ) {
616 wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
617 /**
618 * This can happen in code like:
619 * foreach ( $dbs as $db ) {
620 * $conn = $lb->getConnection( DB_SLAVE, array(), $db );
621 * ...
622 * $lb->reuseConnection( $conn );
623 * }
624 * When a connection to the local DB is opened in this way, reuseConnection()
625 * should be ignored
626 */
627 return;
628 }
629
630 $dbName = $conn->getDBname();
631 $prefix = $conn->tablePrefix();
632 if ( strval( $prefix ) !== '' ) {
633 $wiki = "$dbName-$prefix";
634 } else {
635 $wiki = $dbName;
636 }
637 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
638 throw new MWException( __METHOD__ . ": connection not found, has " .
639 "the connection been freed already?" );
640 }
641 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
642 if ( $refCount <= 0 ) {
643 $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
644 unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
645 wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
646 } else {
647 wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
648 }
649 }
650
651 /**
652 * Get a database connection handle reference
653 *
654 * The handle's methods wrap simply wrap those of a DatabaseBase handle
655 *
656 * @see LoadBalancer::getConnection() for parameter information
657 *
658 * @param int $db
659 * @param array|string|bool $groups Query group(s), or false for the generic reader
660 * @param string|bool $wiki Wiki ID, or false for the current wiki
661 * @return DBConnRef
662 */
663 public function getConnectionRef( $db, $groups = [], $wiki = false ) {
664 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
665 }
666
667 /**
668 * Get a database connection handle reference without connecting yet
669 *
670 * The handle's methods wrap simply wrap those of a DatabaseBase handle
671 *
672 * @see LoadBalancer::getConnection() for parameter information
673 *
674 * @param int $db
675 * @param array|string|bool $groups Query group(s), or false for the generic reader
676 * @param string|bool $wiki Wiki ID, or false for the current wiki
677 * @return DBConnRef
678 */
679 public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
680 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
681 }
682
683 /**
684 * Open a connection to the server given by the specified index
685 * Index must be an actual index into the array.
686 * If the server is already open, returns it.
687 *
688 * On error, returns false, and the connection which caused the
689 * error will be available via $this->mErrorConnection.
690 *
691 * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
692 *
693 * @param int $i Server index
694 * @param string|bool $wiki Wiki ID, or false for the current wiki
695 * @return DatabaseBase|bool Returns false on errors
696 */
697 public function openConnection( $i, $wiki = false ) {
698 if ( $wiki !== false ) {
699 $conn = $this->openForeignConnection( $i, $wiki );
700 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
701 $conn = $this->mConns['local'][$i][0];
702 } else {
703 $server = $this->mServers[$i];
704 $server['serverIndex'] = $i;
705 $conn = $this->reallyOpenConnection( $server, false );
706 $serverName = $this->getServerName( $i );
707 if ( $conn->isOpen() ) {
708 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
709 $this->mConns['local'][$i][0] = $conn;
710 } else {
711 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
712 $this->mErrorConnection = $conn;
713 $conn = false;
714 }
715 }
716
717 if ( $conn && !$conn->isOpen() ) {
718 // Connection was made but later unrecoverably lost for some reason.
719 // Do not return a handle that will just throw exceptions on use,
720 // but let the calling code (e.g. getReaderIndex) try another server.
721 // See DatabaseMyslBase::ping() for how this can happen.
722 $this->mErrorConnection = $conn;
723 $conn = false;
724 }
725
726 return $conn;
727 }
728
729 /**
730 * Open a connection to a foreign DB, or return one if it is already open.
731 *
732 * Increments a reference count on the returned connection which locks the
733 * connection to the requested wiki. This reference count can be
734 * decremented by calling reuseConnection().
735 *
736 * If a connection is open to the appropriate server already, but with the wrong
737 * database, it will be switched to the right database and returned, as long as
738 * it has been freed first with reuseConnection().
739 *
740 * On error, returns false, and the connection which caused the
741 * error will be available via $this->mErrorConnection.
742 *
743 * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
744 *
745 * @param int $i Server index
746 * @param string $wiki Wiki ID to open
747 * @return DatabaseBase
748 */
749 private function openForeignConnection( $i, $wiki ) {
750 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
751 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
752 // Reuse an already-used connection
753 $conn = $this->mConns['foreignUsed'][$i][$wiki];
754 wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
755 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
756 // Reuse a free connection for the same wiki
757 $conn = $this->mConns['foreignFree'][$i][$wiki];
758 unset( $this->mConns['foreignFree'][$i][$wiki] );
759 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
760 wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
761 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
762 // Reuse a connection from another wiki
763 $conn = reset( $this->mConns['foreignFree'][$i] );
764 $oldWiki = key( $this->mConns['foreignFree'][$i] );
765
766 // The empty string as a DB name means "don't care".
767 // DatabaseMysqlBase::open() already handle this on connection.
768 if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
769 $this->mLastError = "Error selecting database $dbName on server " .
770 $conn->getServer() . " from client host " . wfHostname() . "\n";
771 $this->mErrorConnection = $conn;
772 $conn = false;
773 } else {
774 $conn->tablePrefix( $prefix );
775 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
776 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
777 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
778 }
779 } else {
780 // Open a new connection
781 $server = $this->mServers[$i];
782 $server['serverIndex'] = $i;
783 $server['foreignPoolRefCount'] = 0;
784 $server['foreign'] = true;
785 $conn = $this->reallyOpenConnection( $server, $dbName );
786 if ( !$conn->isOpen() ) {
787 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
788 $this->mErrorConnection = $conn;
789 $conn = false;
790 } else {
791 $conn->tablePrefix( $prefix );
792 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
793 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
794 }
795 }
796
797 // Increment reference count
798 if ( $conn ) {
799 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
800 $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
801 }
802
803 return $conn;
804 }
805
806 /**
807 * Test if the specified index represents an open connection
808 *
809 * @param int $index Server index
810 * @access private
811 * @return bool
812 */
813 private function isOpen( $index ) {
814 if ( !is_integer( $index ) ) {
815 return false;
816 }
817
818 return (bool)$this->getAnyOpenConnection( $index );
819 }
820
821 /**
822 * Really opens a connection. Uncached.
823 * Returns a Database object whether or not the connection was successful.
824 * @access private
825 *
826 * @param array $server
827 * @param bool $dbNameOverride
828 * @throws MWException
829 * @return DatabaseBase
830 */
831 protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
832 if ( $this->disabled ) {
833 throw new DBAccessError();
834 }
835
836 if ( !is_array( $server ) ) {
837 throw new MWException( 'You must update your load-balancing configuration. ' .
838 'See DefaultSettings.php entry for $wgDBservers.' );
839 }
840
841 if ( $dbNameOverride !== false ) {
842 $server['dbname'] = $dbNameOverride;
843 }
844
845 // Let the handle know what the cluster master is (e.g. "db1052")
846 $masterName = $this->getServerName( 0 );
847 $server['clusterMasterHost'] = $masterName;
848
849 // Log when many connection are made on requests
850 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
851 wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
852 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
853 wfBacktrace( true ) );
854 }
855
856 # Create object
857 try {
858 $db = DatabaseBase::factory( $server['type'], $server );
859 } catch ( DBConnectionError $e ) {
860 // FIXME: This is probably the ugliest thing I have ever done to
861 // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
862 $db = $e->db;
863 }
864
865 $db->setLBInfo( $server );
866 $db->setLazyMasterHandle(
867 $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
868 );
869 $db->setTransactionProfiler( $this->trxProfiler );
870
871 return $db;
872 }
873
874 /**
875 * @throws DBConnectionError
876 * @return bool
877 */
878 private function reportConnectionError() {
879 $conn = $this->mErrorConnection; // The connection which caused the error
880 $context = [
881 'method' => __METHOD__,
882 'last_error' => $this->mLastError,
883 ];
884
885 if ( !is_object( $conn ) ) {
886 // No last connection, probably due to all servers being too busy
887 wfLogDBError(
888 "LB failure with no last connection. Connection error: {last_error}",
889 $context
890 );
891
892 // If all servers were busy, mLastError will contain something sensible
893 throw new DBConnectionError( null, $this->mLastError );
894 } else {
895 $context['db_server'] = $conn->getProperty( 'mServer' );
896 wfLogDBError(
897 "Connection error: {last_error} ({db_server})",
898 $context
899 );
900
901 // throws DBConnectionError
902 $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
903 }
904
905 return false; /* not reached */
906 }
907
908 /**
909 * @return int
910 * @since 1.26
911 */
912 public function getWriterIndex() {
913 return 0;
914 }
915
916 /**
917 * Returns true if the specified index is a valid server index
918 *
919 * @param string $i
920 * @return bool
921 */
922 public function haveIndex( $i ) {
923 return array_key_exists( $i, $this->mServers );
924 }
925
926 /**
927 * Returns true if the specified index is valid and has non-zero load
928 *
929 * @param string $i
930 * @return bool
931 */
932 public function isNonZeroLoad( $i ) {
933 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
934 }
935
936 /**
937 * Get the number of defined servers (not the number of open connections)
938 *
939 * @return int
940 */
941 public function getServerCount() {
942 return count( $this->mServers );
943 }
944
945 /**
946 * Get the host name or IP address of the server with the specified index
947 * Prefer a readable name if available.
948 * @param string $i
949 * @return string
950 */
951 public function getServerName( $i ) {
952 if ( isset( $this->mServers[$i]['hostName'] ) ) {
953 $name = $this->mServers[$i]['hostName'];
954 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
955 $name = $this->mServers[$i]['host'];
956 } else {
957 $name = '';
958 }
959
960 return ( $name != '' ) ? $name : 'localhost';
961 }
962
963 /**
964 * Return the server info structure for a given index, or false if the index is invalid.
965 * @param int $i
966 * @return array|bool
967 */
968 public function getServerInfo( $i ) {
969 if ( isset( $this->mServers[$i] ) ) {
970 return $this->mServers[$i];
971 } else {
972 return false;
973 }
974 }
975
976 /**
977 * Sets the server info structure for the given index. Entry at index $i
978 * is created if it doesn't exist
979 * @param int $i
980 * @param array $serverInfo
981 */
982 public function setServerInfo( $i, array $serverInfo ) {
983 $this->mServers[$i] = $serverInfo;
984 }
985
986 /**
987 * Get the current master position for chronology control purposes
988 * @return mixed
989 */
990 public function getMasterPos() {
991 # If this entire request was served from a slave without opening a connection to the
992 # master (however unlikely that may be), then we can fetch the position from the slave.
993 $masterConn = $this->getAnyOpenConnection( 0 );
994 if ( !$masterConn ) {
995 $serverCount = count( $this->mServers );
996 for ( $i = 1; $i < $serverCount; $i++ ) {
997 $conn = $this->getAnyOpenConnection( $i );
998 if ( $conn ) {
999 return $conn->getSlavePos();
1000 }
1001 }
1002 } else {
1003 return $masterConn->getMasterPos();
1004 }
1005
1006 return false;
1007 }
1008
1009 /**
1010 * Disable this load balancer. All connections are closed, and any attempt to
1011 * open a new connection will result in a DBAccessError.
1012 *
1013 * @since 1.27
1014 */
1015 public function disable() {
1016 $this->closeAll();
1017 $this->disabled = true;
1018 }
1019
1020 /**
1021 * Close all open connections
1022 */
1023 public function closeAll() {
1024 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1025 $conn->close();
1026 } );
1027
1028 $this->mConns = [
1029 'local' => [],
1030 'foreignFree' => [],
1031 'foreignUsed' => [],
1032 ];
1033 $this->connsOpened = 0;
1034 }
1035
1036 /**
1037 * Close a connection
1038 * Using this function makes sure the LoadBalancer knows the connection is closed.
1039 * If you use $conn->close() directly, the load balancer won't update its state.
1040 * @param DatabaseBase $conn
1041 */
1042 public function closeConnection( $conn ) {
1043 $done = false;
1044 foreach ( $this->mConns as $i1 => $conns2 ) {
1045 foreach ( $conns2 as $i2 => $conns3 ) {
1046 foreach ( $conns3 as $i3 => $candidateConn ) {
1047 if ( $conn === $candidateConn ) {
1048 $conn->close();
1049 unset( $this->mConns[$i1][$i2][$i3] );
1050 --$this->connsOpened;
1051 $done = true;
1052 break;
1053 }
1054 }
1055 }
1056 }
1057 if ( !$done ) {
1058 $conn->close();
1059 }
1060 }
1061
1062 /**
1063 * Commit transactions on all open connections
1064 * @param string $fname Caller name
1065 */
1066 public function commitAll( $fname = __METHOD__ ) {
1067 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( $fname ) {
1068 $conn->commit( $fname, 'flush' );
1069 } );
1070 }
1071
1072 /**
1073 * Perform all pre-commit callbacks that remain part of the atomic transactions
1074 * and disable any post-commit callbacks until runMasterPostCommitCallbacks()
1075 * @since 1.28
1076 */
1077 public function runMasterPreCommitCallbacks() {
1078 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1079 // Any error will cause all DB transactions to be rolled back together.
1080 $conn->runOnTransactionPreCommitCallbacks();
1081 // Defer post-commit callbacks until COMMIT finishes for all DBs.
1082 $conn->setPostCommitCallbackSupression( true );
1083 } );
1084 }
1085
1086 /**
1087 * Perform all pre-commit checks for things like replication safety
1088 * @param array $options Includes:
1089 * - maxWriteDuration : max write query duration time in seconds
1090 * @throws DBTransactionError
1091 * @since 1.28
1092 */
1093 public function approveMasterChanges( array $options ) {
1094 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1095 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1096 // Assert that the time to replicate the transaction will be sane.
1097 // If this fails, then all DB transactions will be rollback back together.
1098 $time = $conn->pendingWriteQueryDuration();
1099 if ( $limit > 0 && $time > $limit ) {
1100 throw new DBTransactionError(
1101 $conn,
1102 wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1103 );
1104 }
1105 } );
1106 }
1107
1108 /**
1109 * Issue COMMIT on all master connections where writes where done
1110 * @param string $fname Caller name
1111 */
1112 public function commitMasterChanges( $fname = __METHOD__ ) {
1113 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $fname ) {
1114 if ( $conn->writesOrCallbacksPending() ) {
1115 $conn->commit( $fname, 'flush' );
1116 }
1117 } );
1118 }
1119
1120 /**
1121 * Issue all pending post-commit callbacks
1122 * @since 1.28
1123 */
1124 public function runMasterPostCommitCallbacks() {
1125 $this->forEachOpenMasterConnection( function ( DatabaseBase $db ) {
1126 $db->setPostCommitCallbackSupression( false );
1127 $db->runOnTransactionIdleCallbacks( IDatabase::TRIGGER_COMMIT );
1128 } );
1129 }
1130
1131 /**
1132 * Issue ROLLBACK only on master, only if queries were done on connection
1133 * @param string $fname Caller name
1134 * @throws DBExpectedError
1135 * @since 1.23
1136 */
1137 public function rollbackMasterChanges( $fname = __METHOD__ ) {
1138 $failedServers = [];
1139
1140 $masterIndex = $this->getWriterIndex();
1141 foreach ( $this->mConns as $conns2 ) {
1142 if ( empty( $conns2[$masterIndex] ) ) {
1143 continue;
1144 }
1145 /** @var DatabaseBase $conn */
1146 foreach ( $conns2[$masterIndex] as $conn ) {
1147 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1148 try {
1149 $conn->rollback( $fname, 'flush' );
1150 } catch ( DBError $e ) {
1151 MWExceptionHandler::logException( $e );
1152 $failedServers[] = $conn->getServer();
1153 }
1154 }
1155 }
1156 }
1157
1158 if ( $failedServers ) {
1159 throw new DBExpectedError( null, "Rollback failed on server(s) " .
1160 implode( ', ', array_unique( $failedServers ) ) );
1161 }
1162 }
1163
1164 /**
1165 * @return bool Whether a master connection is already open
1166 * @since 1.24
1167 */
1168 public function hasMasterConnection() {
1169 return $this->isOpen( $this->getWriterIndex() );
1170 }
1171
1172 /**
1173 * Determine if there are pending changes in a transaction by this thread
1174 * @since 1.23
1175 * @return bool
1176 */
1177 public function hasMasterChanges() {
1178 $masterIndex = $this->getWriterIndex();
1179 foreach ( $this->mConns as $conns2 ) {
1180 if ( empty( $conns2[$masterIndex] ) ) {
1181 continue;
1182 }
1183 /** @var DatabaseBase $conn */
1184 foreach ( $conns2[$masterIndex] as $conn ) {
1185 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1186 return true;
1187 }
1188 }
1189 }
1190 return false;
1191 }
1192
1193 /**
1194 * Get the timestamp of the latest write query done by this thread
1195 * @since 1.25
1196 * @return float|bool UNIX timestamp or false
1197 */
1198 public function lastMasterChangeTimestamp() {
1199 $lastTime = false;
1200 $masterIndex = $this->getWriterIndex();
1201 foreach ( $this->mConns as $conns2 ) {
1202 if ( empty( $conns2[$masterIndex] ) ) {
1203 continue;
1204 }
1205 /** @var DatabaseBase $conn */
1206 foreach ( $conns2[$masterIndex] as $conn ) {
1207 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1208 }
1209 }
1210 return $lastTime;
1211 }
1212
1213 /**
1214 * Check if this load balancer object had any recent or still
1215 * pending writes issued against it by this PHP thread
1216 *
1217 * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1218 * @return bool
1219 * @since 1.25
1220 */
1221 public function hasOrMadeRecentMasterChanges( $age = null ) {
1222 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1223
1224 return ( $this->hasMasterChanges()
1225 || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1226 }
1227
1228 /**
1229 * Get the list of callers that have pending master changes
1230 *
1231 * @return array
1232 * @since 1.27
1233 */
1234 public function pendingMasterChangeCallers() {
1235 $fnames = [];
1236
1237 $masterIndex = $this->getWriterIndex();
1238 foreach ( $this->mConns as $conns2 ) {
1239 if ( empty( $conns2[$masterIndex] ) ) {
1240 continue;
1241 }
1242 /** @var DatabaseBase $conn */
1243 foreach ( $conns2[$masterIndex] as $conn ) {
1244 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1245 }
1246 }
1247
1248 return $fnames;
1249 }
1250
1251 /**
1252 * @param mixed $value
1253 * @return mixed
1254 */
1255 public function waitTimeout( $value = null ) {
1256 return wfSetVar( $this->mWaitTimeout, $value );
1257 }
1258
1259 /**
1260 * @note This method will trigger a DB connection if not yet done
1261 *
1262 * @param string|bool $wiki Wiki ID, or false for the current wiki
1263 * @return bool Whether the generic connection for reads is highly "lagged"
1264 */
1265 public function getLaggedSlaveMode( $wiki = false ) {
1266 // No-op if there is only one DB (also avoids recursion)
1267 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1268 try {
1269 // See if laggedSlaveMode gets set
1270 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1271 $this->reuseConnection( $conn );
1272 } catch ( DBConnectionError $e ) {
1273 // Avoid expensive re-connect attempts and failures
1274 $this->slavesDownMode = true;
1275 $this->laggedSlaveMode = true;
1276 }
1277 }
1278
1279 return $this->laggedSlaveMode;
1280 }
1281
1282 /**
1283 * @note This method will never cause a new DB connection
1284 * @return bool Whether any generic connection used for reads was highly "lagged"
1285 * @since 1.27
1286 */
1287 public function laggedSlaveUsed() {
1288 return $this->laggedSlaveMode;
1289 }
1290
1291 /**
1292 * @note This method may trigger a DB connection if not yet done
1293 * @param string|bool $wiki Wiki ID, or false for the current wiki
1294 * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1295 * @return string|bool Reason the master is read-only or false if it is not
1296 * @since 1.27
1297 */
1298 public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1299 if ( $this->readOnlyReason !== false ) {
1300 return $this->readOnlyReason;
1301 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1302 if ( $this->slavesDownMode ) {
1303 return 'The database has been automatically locked ' .
1304 'until the slave database servers become available';
1305 } else {
1306 return 'The database has been automatically locked ' .
1307 'while the slave database servers catch up to the master.';
1308 }
1309 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1310 return 'The database master is running in read-only mode.';
1311 }
1312
1313 return false;
1314 }
1315
1316 /**
1317 * @param string $wiki Wiki ID, or false for the current wiki
1318 * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1319 * @return bool
1320 */
1321 private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1322 $cache = $this->wanCache;
1323 $masterServer = $this->getServerName( $this->getWriterIndex() );
1324
1325 return (bool)$cache->getWithSetCallback(
1326 $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1327 self::TTL_CACHE_READONLY,
1328 function () use ( $wiki, $conn ) {
1329 $this->trxProfiler->setSilenced( true );
1330 try {
1331 $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1332 $readOnly = (int)$dbw->serverIsReadOnly();
1333 } catch ( DBError $e ) {
1334 $readOnly = 0;
1335 }
1336 $this->trxProfiler->setSilenced( false );
1337 return $readOnly;
1338 },
1339 [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1340 );
1341 }
1342
1343 /**
1344 * Disables/enables lag checks
1345 * @param null|bool $mode
1346 * @return bool
1347 */
1348 public function allowLagged( $mode = null ) {
1349 if ( $mode === null ) {
1350 return $this->mAllowLagged;
1351 }
1352 $this->mAllowLagged = $mode;
1353
1354 return $this->mAllowLagged;
1355 }
1356
1357 /**
1358 * @return bool
1359 */
1360 public function pingAll() {
1361 $success = true;
1362 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1363 if ( !$conn->ping() ) {
1364 $success = false;
1365 }
1366 } );
1367
1368 return $success;
1369 }
1370
1371 /**
1372 * Call a function with each open connection object
1373 * @param callable $callback
1374 * @param array $params
1375 */
1376 public function forEachOpenConnection( $callback, array $params = [] ) {
1377 foreach ( $this->mConns as $connsByServer ) {
1378 foreach ( $connsByServer as $serverConns ) {
1379 foreach ( $serverConns as $conn ) {
1380 $mergedParams = array_merge( [ $conn ], $params );
1381 call_user_func_array( $callback, $mergedParams );
1382 }
1383 }
1384 }
1385 }
1386
1387 /**
1388 * Call a function with each open connection object to a master
1389 * @param callable $callback
1390 * @param array $params
1391 * @since 1.28
1392 */
1393 public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1394 $masterIndex = $this->getWriterIndex();
1395 foreach ( $this->mConns as $connsByServer ) {
1396 if ( isset( $connsByServer[$masterIndex] ) ) {
1397 /** @var DatabaseBase $conn */
1398 foreach ( $connsByServer[$masterIndex] as $conn ) {
1399 $mergedParams = array_merge( [ $conn ], $params );
1400 call_user_func_array( $callback, $mergedParams );
1401 }
1402 }
1403 }
1404 }
1405
1406 /**
1407 * Get the hostname and lag time of the most-lagged slave
1408 *
1409 * This is useful for maintenance scripts that need to throttle their updates.
1410 * May attempt to open connections to slaves on the default DB. If there is
1411 * no lag, the maximum lag will be reported as -1.
1412 *
1413 * @param bool|string $wiki Wiki ID, or false for the default database
1414 * @return array ( host, max lag, index of max lagged host )
1415 */
1416 public function getMaxLag( $wiki = false ) {
1417 $maxLag = -1;
1418 $host = '';
1419 $maxIndex = 0;
1420
1421 if ( $this->getServerCount() <= 1 ) {
1422 return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1423 }
1424
1425 $lagTimes = $this->getLagTimes( $wiki );
1426 foreach ( $lagTimes as $i => $lag ) {
1427 if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1428 $maxLag = $lag;
1429 $host = $this->mServers[$i]['host'];
1430 $maxIndex = $i;
1431 }
1432 }
1433
1434 return [ $host, $maxLag, $maxIndex ];
1435 }
1436
1437 /**
1438 * Get an estimate of replication lag (in seconds) for each server
1439 *
1440 * Results are cached for a short time in memcached/process cache
1441 *
1442 * Values may be "false" if replication is too broken to estimate
1443 *
1444 * @param string|bool $wiki
1445 * @return int[] Map of (server index => float|int|bool)
1446 */
1447 public function getLagTimes( $wiki = false ) {
1448 if ( $this->getServerCount() <= 1 ) {
1449 return [ 0 => 0 ]; // no replication = no lag
1450 }
1451
1452 # Send the request to the load monitor
1453 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1454 }
1455
1456 /**
1457 * Get the lag in seconds for a given connection, or zero if this load
1458 * balancer does not have replication enabled.
1459 *
1460 * This should be used in preference to Database::getLag() in cases where
1461 * replication may not be in use, since there is no way to determine if
1462 * replication is in use at the connection level without running
1463 * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1464 * function instead of Database::getLag() avoids a fatal error in this
1465 * case on many installations.
1466 *
1467 * @param IDatabase $conn
1468 * @return int|bool Returns false on error
1469 */
1470 public function safeGetLag( IDatabase $conn ) {
1471 if ( $this->getServerCount() == 1 ) {
1472 return 0;
1473 } else {
1474 return $conn->getLag();
1475 }
1476 }
1477
1478 /**
1479 * Wait for a slave DB to reach a specified master position
1480 *
1481 * This will connect to the master to get an accurate position if $pos is not given
1482 *
1483 * @param IDatabase $conn Slave DB
1484 * @param DBMasterPos|bool $pos Master position; default: current position
1485 * @param integer $timeout Timeout in seconds
1486 * @return bool Success
1487 * @since 1.27
1488 */
1489 public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1490 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1491 return true; // server is not a slave DB
1492 }
1493
1494 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1495 if ( !( $pos instanceof DBMasterPos ) ) {
1496 return false; // something is misconfigured
1497 }
1498
1499 $result = $conn->masterPosWait( $pos, $timeout );
1500 if ( $result == -1 || is_null( $result ) ) {
1501 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1502 wfDebugLog( 'replication', "$msg\n" );
1503 wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1504 $ok = false;
1505 } else {
1506 wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1507 $ok = true;
1508 }
1509
1510 return $ok;
1511 }
1512
1513 /**
1514 * Clear the cache for slag lag delay times
1515 *
1516 * This is only used for testing
1517 */
1518 public function clearLagTimeCache() {
1519 $this->getLoadMonitor()->clearCaches();
1520 }
1521 }
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