3 * Database load balancing manager
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.
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.
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
22 namespace Wikimedia\Rdbms
;
24 use Psr\Log\LoggerInterface
;
25 use Psr\Log\NullLogger
;
26 use Wikimedia\ScopedCallback
;
31 use UnexpectedValueException
;
32 use InvalidArgumentException
;
37 * Database connection, tracking, load balancing, and transaction manager for a cluster
41 class LoadBalancer
implements ILoadBalancer
{
42 /** @var ILoadMonitor */
44 /** @var callable|null Callback to run before the first connection attempt */
45 private $chronologyCallback;
48 /** @var WANObjectCache */
50 /** @var mixed Class name or object With profileIn/profileOut methods */
52 /** @var TransactionProfiler */
54 /** @var LoggerInterface */
56 /** @var LoggerInterface */
58 /** @var LoggerInterface */
60 /** @var LoggerInterface */
62 /** @var callable Exception logger */
64 /** @var callable Deprecation logger */
65 private $deprecationLogger;
67 /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
70 /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
73 /** @var array[] Map of (server index => server config array) */
75 /** @var float[] Map of (server index => weight) */
77 /** @var array[] Map of (group => server index => weight) */
79 /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
81 /** @var int Seconds to spend waiting on replica DB lag to resolve */
83 /** @var array The LoadMonitor configuration */
84 private $loadMonitorConfig;
85 /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
86 private $localDomainIdAlias;
90 /** @var string Current server name */
92 /** @var bool Whether this PHP instance is for a CLI script */
94 /** @var string Agent name for query profiling */
97 /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
98 private $tableAliases = [];
99 /** @var string[] Map of (index alias => index) */
100 private $indexAliases = [];
101 /** @var array[] Map of (name => callable) */
102 private $trxRecurringCallbacks = [];
104 /** @var Database DB connection object that caused a problem */
105 private $errorConnection;
106 /** @var int The generic (not query grouped) replica DB index (of $mServers) */
108 /** @var bool|DBMasterPos False if not set */
110 /** @var bool Whether the generic reader fell back to a lagged replica DB */
111 private $laggedReplicaMode = false;
112 /** @var bool Whether the generic reader fell back to a lagged replica DB */
113 private $allReplicasDownMode = false;
114 /** @var string The last DB selection or connection error */
115 private $lastError = 'Unknown error';
116 /** @var string|bool Reason the LB is read-only or false if not */
117 private $readOnlyReason = false;
118 /** @var int Total connections opened */
119 private $connsOpened = 0;
121 private $disabled = false;
122 /** @var bool Whether any connection has been attempted yet */
123 private $connectionAttempted = false;
125 /** @var string|bool String if a requested DBO_TRX transaction round is active */
126 private $trxRoundId = false;
127 /** @var string Stage of the current transaction round in the transaction round life-cycle */
128 private $trxRoundStage = self
::ROUND_CURSORY
;
130 /** @var string|null */
131 private $defaultGroup = null;
133 /** @var int Warn when this many connection are held */
134 const CONN_HELD_WARN_THRESHOLD
= 10;
136 /** @var int Default 'maxLag' when unspecified */
137 const MAX_LAG_DEFAULT
= 6;
138 /** @var int Default 'waitTimeout' when unspecified */
139 const MAX_WAIT_DEFAULT
= 10;
140 /** @var int Seconds to cache master server read-only status */
141 const TTL_CACHE_READONLY
= 5;
143 const KEY_LOCAL
= 'local';
144 const KEY_FOREIGN_FREE
= 'foreignFree';
145 const KEY_FOREIGN_INUSE
= 'foreignInUse';
147 const KEY_LOCAL_NOROUND
= 'localAutoCommit';
148 const KEY_FOREIGN_FREE_NOROUND
= 'foreignFreeAutoCommit';
149 const KEY_FOREIGN_INUSE_NOROUND
= 'foreignInUseAutoCommit';
151 /** @var string Transaction round, explicit or implicit, has not finished writing */
152 const ROUND_CURSORY
= 'cursory';
153 /** @var string Transaction round writes are complete and ready for pre-commit checks */
154 const ROUND_FINALIZED
= 'finalized';
155 /** @var string Transaction round passed final pre-commit checks */
156 const ROUND_APPROVED
= 'approved';
157 /** @var string Transaction round was committed and post-commit callbacks must be run */
158 const ROUND_COMMIT_CALLBACKS
= 'commit-callbacks';
159 /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
160 const ROUND_ROLLBACK_CALLBACKS
= 'rollback-callbacks';
161 /** @var string Transaction round encountered an error */
162 const ROUND_ERROR
= 'error';
164 public function __construct( array $params ) {
165 if ( !isset( $params['servers'] ) ) {
166 throw new InvalidArgumentException( __CLASS__
. ': missing servers parameter' );
168 $this->servers
= $params['servers'];
169 foreach ( $this->servers
as $i => $server ) {
171 $this->servers
[$i]['master'] = true;
173 $this->servers
[$i]['replica'] = true;
177 $localDomain = isset( $params['localDomain'] )
178 ? DatabaseDomain
::newFromId( $params['localDomain'] )
179 : DatabaseDomain
::newUnspecified();
180 $this->setLocalDomain( $localDomain );
182 $this->waitTimeout
= $params['waitTimeout'] ?? self
::MAX_WAIT_DEFAULT
;
184 $this->readIndex
= -1;
186 // Connection were transaction rounds may be applied
187 self
::KEY_LOCAL
=> [],
188 self
::KEY_FOREIGN_INUSE
=> [],
189 self
::KEY_FOREIGN_FREE
=> [],
190 // Auto-committing counterpart connections that ignore transaction rounds
191 self
::KEY_LOCAL_NOROUND
=> [],
192 self
::KEY_FOREIGN_INUSE_NOROUND
=> [],
193 self
::KEY_FOREIGN_FREE_NOROUND
=> []
196 $this->waitForPos
= false;
197 $this->allowLagged
= false;
199 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
200 $this->readOnlyReason
= $params['readOnlyReason'];
203 $this->maxLag
= $params['maxLag'] ?? self
::MAX_LAG_DEFAULT
;
205 $this->loadMonitorConfig
= $params['loadMonitor'] ??
[ 'class' => 'LoadMonitorNull' ];
206 $this->loadMonitorConfig +
= [ 'lagWarnThreshold' => $this->maxLag
];
208 foreach ( $params['servers'] as $i => $server ) {
209 $this->loads
[$i] = $server['load'];
210 if ( isset( $server['groupLoads'] ) ) {
211 foreach ( $server['groupLoads'] as $group => $ratio ) {
212 if ( !isset( $this->groupLoads
[$group] ) ) {
213 $this->groupLoads
[$group] = [];
215 $this->groupLoads
[$group][$i] = $ratio;
220 $this->srvCache
= $params['srvCache'] ??
new EmptyBagOStuff();
221 $this->wanCache
= $params['wanCache'] ?? WANObjectCache
::newEmpty();
222 $this->profiler
= $params['profiler'] ??
null;
223 $this->trxProfiler
= $params['trxProfiler'] ??
new TransactionProfiler();
225 $this->errorLogger
= $params['errorLogger'] ??
function ( Exception
$e ) {
226 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING
);
228 $this->deprecationLogger
= $params['deprecationLogger'] ??
function ( $msg ) {
229 trigger_error( $msg, E_USER_DEPRECATED
);
232 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
233 $this->$key = $params[$key] ??
new NullLogger();
236 $this->hostname
= $params['hostname'] ??
( gethostname() ?
: 'unknown' );
237 $this->cliMode
= $params['cliMode'] ??
( PHP_SAPI
=== 'cli' || PHP_SAPI
=== 'phpdbg' );
238 $this->agent
= $params['agent'] ??
'';
240 if ( isset( $params['chronologyCallback'] ) ) {
241 $this->chronologyCallback
= $params['chronologyCallback'];
244 if ( isset( $params['roundStage'] ) ) {
245 if ( $params['roundStage'] === self
::STAGE_POSTCOMMIT_CALLBACKS
) {
246 $this->trxRoundStage
= self
::ROUND_COMMIT_CALLBACKS
;
247 } elseif ( $params['roundStage'] === self
::STAGE_POSTROLLBACK_CALLBACKS
) {
248 $this->trxRoundStage
= self
::ROUND_ROLLBACK_CALLBACKS
;
252 $this->defaultGroup
= $params['defaultGroup'] ??
null;
255 public function getLocalDomainID() {
256 return $this->localDomain
->getId();
259 public function resolveDomainID( $domain ) {
260 return ( $domain !== false ) ?
(string)$domain : $this->getLocalDomainID();
264 * Get a LoadMonitor instance
266 * @return ILoadMonitor
268 private function getLoadMonitor() {
269 if ( !isset( $this->loadMonitor
) ) {
271 'LoadMonitor' => LoadMonitor
::class,
272 'LoadMonitorNull' => LoadMonitorNull
::class,
273 'LoadMonitorMySQL' => LoadMonitorMySQL
::class,
276 $class = $this->loadMonitorConfig
['class'];
277 if ( isset( $compat[$class] ) ) {
278 $class = $compat[$class];
281 $this->loadMonitor
= new $class(
282 $this, $this->srvCache
, $this->wanCache
, $this->loadMonitorConfig
);
283 $this->loadMonitor
->setLogger( $this->replLogger
);
286 return $this->loadMonitor
;
290 * @param array $loads
291 * @param bool|string $domain Domain to get non-lagged for
292 * @param int $maxLag Restrict the maximum allowed lag to this many seconds
293 * @return bool|int|string
295 private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF
) {
296 $lags = $this->getLagTimes( $domain );
298 # Unset excessively lagged servers
299 foreach ( $lags as $i => $lag ) {
301 # How much lag this server nominally is allowed to have
302 $maxServerLag = $this->servers
[$i]['max lag'] ??
$this->maxLag
; // default
303 # Constrain that futher by $maxLag argument
304 $maxServerLag = min( $maxServerLag, $maxLag );
306 $host = $this->getServerName( $i );
307 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
308 $this->replLogger
->debug(
310 ": server {host} is not replicating?", [ 'host' => $host ] );
312 } elseif ( $lag > $maxServerLag ) {
313 $this->replLogger
->debug(
315 ": server {host} has {lag} seconds of lag (>= {maxlag})",
316 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
323 # Find out if all the replica DBs with non-zero load are lagged
325 foreach ( $loads as $load ) {
329 # No appropriate DB servers except maybe the master and some replica DBs with zero load
330 # Do NOT use the master
331 # Instead, this function will return false, triggering read-only mode,
332 # and a lagged replica DB will be used instead.
336 if ( count( $loads ) == 0 ) {
340 # Return a random representative of the remainder
341 return ArrayUtils
::pickRandom( $loads );
344 public function getReaderIndex( $group = false, $domain = false ) {
345 if ( count( $this->servers
) == 1 ) {
346 // Skip the load balancing if there's only one server
347 return $this->getWriterIndex();
348 } elseif ( $group === false && $this->readIndex
>= 0 ) {
349 // Shortcut if the generic reader index was already cached
350 return $this->readIndex
;
353 if ( $group !== false ) {
354 // Use the server weight array for this load group
355 if ( isset( $this->groupLoads
[$group] ) ) {
356 $loads = $this->groupLoads
[$group];
358 // No loads for this group, return false and the caller can use some other group
359 $this->connLogger
->info( __METHOD__
. ": no loads for group $group" );
364 // Use the generic load group
365 $loads = $this->loads
;
368 // Scale the configured load ratios according to each server's load and state
369 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
371 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
372 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
373 if ( $i === false ) {
374 // Replica DB connection unsuccessful
378 if ( $this->waitForPos
&& $i != $this->getWriterIndex() ) {
379 // Before any data queries are run, wait for the server to catch up to the
380 // specified position. This is used to improve session consistency. Note that
381 // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
382 // so update laggedReplicaMode as needed for consistency.
383 if ( !$this->doWait( $i ) ) {
384 $laggedReplicaMode = true;
388 if ( $this->readIndex
<= 0 && $this->loads
[$i] > 0 && $group === false ) {
389 // Cache the generic reader index for future ungrouped DB_REPLICA handles
390 $this->readIndex
= $i;
391 // Record if the generic reader index is in "lagged replica DB" mode
392 if ( $laggedReplicaMode ) {
393 $this->laggedReplicaMode
= true;
397 $serverName = $this->getServerName( $i );
398 $this->connLogger
->debug( __METHOD__
. ": using server $serverName for group '$group'" );
404 * @param array $loads List of server weights
405 * @param string|bool $domain
406 * @return array (reader index, lagged replica mode) or false on failure
408 private function pickReaderIndex( array $loads, $domain = false ) {
409 if ( $loads === [] ) {
410 throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
413 /** @var int|bool $i Index of selected server */
415 /** @var bool $laggedReplicaMode Whether server is considered lagged */
416 $laggedReplicaMode = false;
418 // Quickly look through the available servers for a server that meets criteria...
419 $currentLoads = $loads;
420 while ( count( $currentLoads ) ) {
421 if ( $this->allowLagged ||
$laggedReplicaMode ) {
422 $i = ArrayUtils
::pickRandom( $currentLoads );
425 if ( $this->waitForPos
&& $this->waitForPos
->asOfTime() ) {
426 // "chronologyCallback" sets "waitForPos" for session consistency.
427 // This triggers doWait() after connect, so it's especially good to
428 // avoid lagged servers so as to avoid excessive delay in that method.
429 $ago = microtime( true ) - $this->waitForPos
->asOfTime();
430 // Aim for <= 1 second of waiting (being too picky can backfire)
431 $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago +
1 );
433 if ( $i === false ) {
434 // Any server with less lag than it's 'max lag' param is preferable
435 $i = $this->getRandomNonLagged( $currentLoads, $domain );
437 if ( $i === false && count( $currentLoads ) != 0 ) {
438 // All replica DBs lagged. Switch to read-only mode
439 $this->replLogger
->error(
440 __METHOD__
. ": all replica DBs lagged. Switch to read-only mode" );
441 $i = ArrayUtils
::pickRandom( $currentLoads );
442 $laggedReplicaMode = true;
446 if ( $i === false ) {
447 // pickRandom() returned false.
448 // This is permanent and means the configuration or the load monitor
449 // wants us to return false.
450 $this->connLogger
->debug( __METHOD__
. ": pickRandom() returned false" );
452 return [ false, false ];
455 $serverName = $this->getServerName( $i );
456 $this->connLogger
->debug( __METHOD__
. ": Using reader #$i: $serverName..." );
458 $conn = $this->openConnection( $i, $domain );
460 $this->connLogger
->warning( __METHOD__
. ": Failed connecting to $i/$domain" );
461 unset( $currentLoads[$i] ); // avoid this server next iteration
466 // Decrement reference counter, we are finished with this connection.
467 // It will be incremented for the caller later.
468 if ( $domain !== false ) {
469 $this->reuseConnection( $conn );
472 // Return this server
476 // If all servers were down, quit now
477 if ( $currentLoads === [] ) {
478 $this->connLogger
->error( __METHOD__
. ": all servers down" );
481 return [ $i, $laggedReplicaMode ];
484 public function waitFor( $pos ) {
485 $oldPos = $this->waitForPos
;
487 $this->waitForPos
= $pos;
488 // If a generic reader connection was already established, then wait now
489 $i = $this->readIndex
;
490 if ( ( $i > 0 ) && !$this->doWait( $i ) ) {
491 $this->laggedReplicaMode
= true;
494 // Restore the older position if it was higher since this is used for lag-protection
495 $this->setWaitForPositionIfHigher( $oldPos );
499 public function waitForOne( $pos, $timeout = null ) {
500 $oldPos = $this->waitForPos
;
502 $this->waitForPos
= $pos;
504 $i = $this->readIndex
;
506 // Pick a generic replica DB if there isn't one yet
507 $readLoads = $this->loads
;
508 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
509 $readLoads = array_filter( $readLoads ); // with non-zero load
510 $i = ArrayUtils
::pickRandom( $readLoads );
514 $ok = $this->doWait( $i, true, $timeout );
516 $ok = true; // no applicable loads
519 # Restore the old position, as this is not used for lag-protection but for throttling
520 $this->waitForPos
= $oldPos;
526 public function waitForAll( $pos, $timeout = null ) {
527 $timeout = $timeout ?
: $this->waitTimeout
;
529 $oldPos = $this->waitForPos
;
531 $this->waitForPos
= $pos;
532 $serverCount = count( $this->servers
);
535 for ( $i = 1; $i < $serverCount; $i++
) {
536 if ( $this->loads
[$i] > 0 ) {
537 $start = microtime( true );
538 $ok = $this->doWait( $i, true, $timeout ) && $ok;
539 $timeout -= intval( microtime( true ) - $start );
540 if ( $timeout <= 0 ) {
541 break; // timeout reached
546 # Restore the old position, as this is not used for lag-protection but for throttling
547 $this->waitForPos
= $oldPos;
554 * @param DBMasterPos|bool $pos
556 private function setWaitForPositionIfHigher( $pos ) {
561 if ( !$this->waitForPos ||
$pos->hasReached( $this->waitForPos
) ) {
562 $this->waitForPos
= $pos;
566 public function getAnyOpenConnection( $i, $flags = 0 ) {
567 $i = ( $i === self
::DB_MASTER
) ?
$this->getWriterIndex() : $i;
568 $autocommit = ( ( $flags & self
::CONN_TRX_AUTOCOMMIT
) == self
::CONN_TRX_AUTOCOMMIT
);
570 foreach ( $this->conns
as $connsByServer ) {
571 if ( $i === self
::DB_REPLICA
) {
572 $indexes = array_keys( $connsByServer );
574 $indexes = isset( $connsByServer[$i] ) ?
[ $i ] : [];
577 foreach ( $indexes as $index ) {
578 foreach ( $connsByServer[$index] as $conn ) {
579 if ( !$conn->isOpen() ) {
580 continue; // some sort of error occured?
582 if ( !$autocommit ||
$conn->getLBInfo( 'autoCommitOnly' ) ) {
593 * Wait for a given replica DB to catch up to the master pos stored in $this
594 * @param int $index Server index
595 * @param bool $open Check the server even if a new connection has to be made
596 * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
599 protected function doWait( $index, $open = false, $timeout = null ) {
600 $timeout = max( 1, intval( $timeout ?
: $this->waitTimeout
) );
602 // Check if we already know that the DB has reached this point
603 $server = $this->getServerName( $index );
604 $key = $this->srvCache
->makeGlobalKey( __CLASS__
, 'last-known-pos', $server, 'v1' );
605 /** @var DBMasterPos $knownReachedPos */
606 $knownReachedPos = $this->srvCache
->get( $key );
608 $knownReachedPos instanceof DBMasterPos
&&
609 $knownReachedPos->hasReached( $this->waitForPos
)
611 $this->replLogger
->debug(
613 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
614 [ 'dbserver' => $server ]
619 // Find a connection to wait on, creating one if needed and allowed
620 $close = false; // close the connection afterwards
621 $conn = $this->getAnyOpenConnection( $index );
624 $this->replLogger
->debug(
625 __METHOD__
. ': no connection open for {dbserver}',
626 [ 'dbserver' => $server ]
631 $conn = $this->openConnection( $index, self
::DOMAIN_ANY
);
633 $this->replLogger
->warning(
634 __METHOD__
. ': failed to connect to {dbserver}',
635 [ 'dbserver' => $server ]
640 // Avoid connection spam in waitForAll() when connections
641 // are made just for the sake of doing this lag check.
646 $this->replLogger
->info(
648 ': waiting for replica DB {dbserver} to catch up...',
649 [ 'dbserver' => $server ]
652 $result = $conn->masterPosWait( $this->waitForPos
, $timeout );
654 if ( $result === null ) {
655 $this->replLogger
->warning(
656 __METHOD__
. ': Errored out waiting on {host} pos {pos}',
659 'pos' => $this->waitForPos
,
660 'trace' => ( new RuntimeException() )->getTraceAsString()
664 } elseif ( $result == -1 ) {
665 $this->replLogger
->warning(
666 __METHOD__
. ': Timed out waiting on {host} pos {pos}',
669 'pos' => $this->waitForPos
,
670 'trace' => ( new RuntimeException() )->getTraceAsString()
675 $this->replLogger
->debug( __METHOD__
. ": done waiting" );
677 // Remember that the DB reached this point
678 $this->srvCache
->set( $key, $this->waitForPos
, BagOStuff
::TTL_DAY
);
682 $this->closeConnection( $conn );
688 public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
689 if ( $i === null ||
$i === false ) {
690 throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__
.
691 ' with invalid server index' );
694 if ( $this->localDomain
->equals( $domain ) ||
$domain === $this->localDomainIdAlias
) {
695 $domain = false; // local connection requested
698 if ( ( $flags & self
::CONN_TRX_AUTOCOMMIT
) === self
::CONN_TRX_AUTOCOMMIT
) {
699 // Assuming all servers are of the same type (or similar), which is overwhelmingly
700 // the case, use the master server information to get the attributes. The information
701 // for $i cannot be used since it might be DB_REPLICA, which might require connection
702 // attempts in order to be resolved into a real server index.
703 $attributes = $this->getServerAttributes( $this->getWriterIndex() );
704 if ( $attributes[Database
::ATTR_DB_LEVEL_LOCKING
] ) {
705 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
706 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
707 // to reduce lock contention. None of these apply for sqlite and using separate
708 // connections just causes self-deadlocks.
709 $flags &= ~self
::CONN_TRX_AUTOCOMMIT
;
710 $this->connLogger
->info( __METHOD__
.
711 ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
715 // Check one "group" per default: the generic pool
716 $defaultGroups = $this->defaultGroup ?
[ $this->defaultGroup
] : [ false ];
718 $groups = ( $groups === false ||
$groups === [] )
722 $masterOnly = ( $i == self
::DB_MASTER ||
$i == $this->getWriterIndex() );
723 $oldConnsOpened = $this->connsOpened
; // connections open now
725 if ( $i == self
::DB_MASTER
) {
726 $i = $this->getWriterIndex();
727 } elseif ( $i == self
::DB_REPLICA
) {
728 # Try to find an available server in any the query groups (in order)
729 foreach ( $groups as $group ) {
730 $groupIndex = $this->getReaderIndex( $group, $domain );
731 if ( $groupIndex !== false ) {
738 # Operation-based index
739 if ( $i == self
::DB_REPLICA
) {
740 $this->lastError
= 'Unknown error'; // reset error string
741 # Try the general server pool if $groups are unavailable.
742 $i = ( $groups === [ false ] )
743 ?
false // don't bother with this if that is what was tried above
744 : $this->getReaderIndex( false, $domain );
745 # Couldn't find a working server in getReaderIndex()?
746 if ( $i === false ) {
747 $this->lastError
= 'No working replica DB server: ' . $this->lastError
;
748 // Throw an exception
749 $this->reportConnectionError();
750 return null; // not reached
754 # Now we have an explicit index into the servers array
755 $conn = $this->openConnection( $i, $domain, $flags );
757 // Throw an exception
758 $this->reportConnectionError();
759 return null; // not reached
762 # Profile any new connections that happen
763 if ( $this->connsOpened
> $oldConnsOpened ) {
764 $host = $conn->getServer();
765 $dbname = $conn->getDBname();
766 $this->trxProfiler
->recordConnection( $host, $dbname, $masterOnly );
770 # Make master-requested DB handles inherit any read-only mode setting
771 $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
777 public function reuseConnection( IDatabase
$conn ) {
778 $serverIndex = $conn->getLBInfo( 'serverIndex' );
779 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
780 if ( $serverIndex === null ||
$refCount === null ) {
782 * This can happen in code like:
783 * foreach ( $dbs as $db ) {
784 * $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
786 * $lb->reuseConnection( $conn );
788 * When a connection to the local DB is opened in this way, reuseConnection()
792 } elseif ( $conn instanceof DBConnRef
) {
793 // DBConnRef already handles calling reuseConnection() and only passes the live
794 // Database instance to this method. Any caller passing in a DBConnRef is broken.
795 $this->connLogger
->error(
796 __METHOD__
. ": got DBConnRef instance.\n" .
797 ( new RuntimeException() )->getTraceAsString() );
802 if ( $this->disabled
) {
803 return; // DBConnRef handle probably survived longer than the LoadBalancer
806 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
807 $connFreeKey = self
::KEY_FOREIGN_FREE_NOROUND
;
808 $connInUseKey = self
::KEY_FOREIGN_INUSE_NOROUND
;
810 $connFreeKey = self
::KEY_FOREIGN_FREE
;
811 $connInUseKey = self
::KEY_FOREIGN_INUSE
;
814 $domain = $conn->getDomainID();
815 if ( !isset( $this->conns
[$connInUseKey][$serverIndex][$domain] ) ) {
816 throw new InvalidArgumentException( __METHOD__
.
817 ": connection $serverIndex/$domain not found; it may have already been freed." );
818 } elseif ( $this->conns
[$connInUseKey][$serverIndex][$domain] !== $conn ) {
819 throw new InvalidArgumentException( __METHOD__
.
820 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
823 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
824 if ( $refCount <= 0 ) {
825 $this->conns
[$connFreeKey][$serverIndex][$domain] = $conn;
826 unset( $this->conns
[$connInUseKey][$serverIndex][$domain] );
827 if ( !$this->conns
[$connInUseKey][$serverIndex] ) {
828 unset( $this->conns
[$connInUseKey][$serverIndex] ); // clean up
830 $this->connLogger
->debug( __METHOD__
. ": freed connection $serverIndex/$domain" );
832 $this->connLogger
->debug( __METHOD__
.
833 ": reference count for $serverIndex/$domain reduced to $refCount" );
837 public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
838 $domain = $this->resolveDomainID( $domain );
839 $role = $this->getRoleFromIndex( $i );
841 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
844 public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
845 $domain = $this->resolveDomainID( $domain );
846 $role = $this->getRoleFromIndex( $i );
848 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
851 public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
852 $domain = $this->resolveDomainID( $domain );
853 $role = $this->getRoleFromIndex( $i );
855 return new MaintainableDBConnRef(
856 $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
860 * @param int $i Server index or DB_MASTER/DB_REPLICA
861 * @return int One of DB_MASTER/DB_REPLICA
863 private function getRoleFromIndex( $i ) {
864 return ( $i === self
::DB_MASTER ||
$i === $this->getWriterIndex() )
869 public function openConnection( $i, $domain = false, $flags = 0 ) {
870 if ( $this->localDomain
->equals( $domain ) ||
$domain === $this->localDomainIdAlias
) {
871 $domain = false; // local connection requested
874 if ( !$this->connectionAttempted
&& $this->chronologyCallback
) {
875 $this->connLogger
->debug( __METHOD__
. ': calling initLB() before first connection.' );
876 // Load any "waitFor" positions before connecting so that doWait() is triggered
877 $this->connectionAttempted
= true;
878 ( $this->chronologyCallback
)( $this );
881 // Check if an auto-commit connection is being requested. If so, it will not reuse the
882 // main set of DB connections but rather its own pool since:
883 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
884 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
885 $autoCommit = ( ( $flags & self
::CONN_TRX_AUTOCOMMIT
) == self
::CONN_TRX_AUTOCOMMIT
);
887 if ( $domain !== false ) {
888 // Connection is to a foreign domain
889 $conn = $this->openForeignConnection( $i, $domain, $flags );
891 // Connection is to the local domain
892 $conn = $this->openLocalConnection( $i, $flags );
895 if ( $conn instanceof IDatabase
&& !$conn->isOpen() ) {
896 // Connection was made but later unrecoverably lost for some reason.
897 // Do not return a handle that will just throw exceptions on use,
898 // but let the calling code (e.g. getReaderIndex) try another server.
899 // See DatabaseMyslBase::ping() for how this can happen.
900 $this->errorConnection
= $conn;
904 if ( $autoCommit && $conn instanceof IDatabase
) {
905 if ( $conn->trxLevel() ) { // sanity
906 throw new DBUnexpectedError(
908 __METHOD__
. ': CONN_TRX_AUTOCOMMIT handle has a transaction.'
912 $conn->clearFlag( $conn::DBO_TRX
); // auto-commit mode
919 * Open a connection to a local DB, or return one if it is already open.
921 * On error, returns false, and the connection which caused the
922 * error will be available via $this->errorConnection.
924 * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
926 * @param int $i Server index
927 * @param int $flags Class CONN_* constant bitfield
930 private function openLocalConnection( $i, $flags = 0 ) {
931 $autoCommit = ( ( $flags & self
::CONN_TRX_AUTOCOMMIT
) == self
::CONN_TRX_AUTOCOMMIT
);
933 $connKey = $autoCommit ? self
::KEY_LOCAL_NOROUND
: self
::KEY_LOCAL
;
934 if ( isset( $this->conns
[$connKey][$i][0] ) ) {
935 $conn = $this->conns
[$connKey][$i][0];
937 if ( !isset( $this->servers
[$i] ) ||
!is_array( $this->servers
[$i] ) ) {
938 throw new InvalidArgumentException( "No server with index '$i'." );
940 // Open a new connection
941 $server = $this->servers
[$i];
942 $server['serverIndex'] = $i;
943 $server['autoCommitOnly'] = $autoCommit;
944 $conn = $this->reallyOpenConnection( $server, $this->localDomain
);
945 $host = $this->getServerName( $i );
946 if ( $conn->isOpen() ) {
947 $this->connLogger
->debug(
948 __METHOD__
. ": connected to database $i at '$host'." );
949 $this->conns
[$connKey][$i][0] = $conn;
951 $this->connLogger
->warning(
952 __METHOD__
. ": failed to connect to database $i at '$host'." );
953 $this->errorConnection
= $conn;
958 // Final sanity check to make sure the right domain is selected
960 $conn instanceof IDatabase
&&
961 !$this->localDomain
->isCompatible( $conn->getDomainID() )
963 throw new UnexpectedValueException(
964 "Got connection to '{$conn->getDomainID()}', " .
965 "but expected local domain ('{$this->localDomain}')." );
972 * Open a connection to a foreign DB, or return one if it is already open.
974 * Increments a reference count on the returned connection which locks the
975 * connection to the requested domain. This reference count can be
976 * decremented by calling reuseConnection().
978 * If a connection is open to the appropriate server already, but with the wrong
979 * database, it will be switched to the right database and returned, as long as
980 * it has been freed first with reuseConnection().
982 * On error, returns false, and the connection which caused the
983 * error will be available via $this->errorConnection.
985 * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
987 * @param int $i Server index
988 * @param string $domain Domain ID to open
989 * @param int $flags Class CONN_* constant bitfield
990 * @return Database|bool Returns false on connection error
991 * @throws DBError When database selection fails
993 private function openForeignConnection( $i, $domain, $flags = 0 ) {
994 $domainInstance = DatabaseDomain
::newFromId( $domain );
995 $autoCommit = ( ( $flags & self
::CONN_TRX_AUTOCOMMIT
) == self
::CONN_TRX_AUTOCOMMIT
);
998 $connFreeKey = self
::KEY_FOREIGN_FREE_NOROUND
;
999 $connInUseKey = self
::KEY_FOREIGN_INUSE_NOROUND
;
1001 $connFreeKey = self
::KEY_FOREIGN_FREE
;
1002 $connInUseKey = self
::KEY_FOREIGN_INUSE
;
1005 /** @var Database $conn */
1008 if ( isset( $this->conns
[$connInUseKey][$i][$domain] ) ) {
1009 // Reuse an in-use connection for the same domain
1010 $conn = $this->conns
[$connInUseKey][$i][$domain];
1011 $this->connLogger
->debug( __METHOD__
. ": reusing connection $i/$domain" );
1012 } elseif ( isset( $this->conns
[$connFreeKey][$i][$domain] ) ) {
1013 // Reuse a free connection for the same domain
1014 $conn = $this->conns
[$connFreeKey][$i][$domain];
1015 unset( $this->conns
[$connFreeKey][$i][$domain] );
1016 $this->conns
[$connInUseKey][$i][$domain] = $conn;
1017 $this->connLogger
->debug( __METHOD__
. ": reusing free connection $i/$domain" );
1018 } elseif ( !empty( $this->conns
[$connFreeKey][$i] ) ) {
1019 // Reuse a free connection from another domain if possible
1020 foreach ( $this->conns
[$connFreeKey][$i] as $oldDomain => $conn ) {
1021 if ( $domainInstance->getDatabase() !== null ) {
1022 // Check if changing the database will require a new connection.
1023 // In that case, leave the connection handle alone and keep looking.
1024 // This prevents connections from being closed mid-transaction and can
1025 // also avoid overhead if the same database will later be requested.
1027 $conn->databasesAreIndependent() &&
1028 $conn->getDBname() !== $domainInstance->getDatabase()
1032 // Select the new database, schema, and prefix
1033 $conn->selectDomain( $domainInstance );
1035 // Stay on the current database, but update the schema/prefix
1036 $conn->dbSchema( $domainInstance->getSchema() );
1037 $conn->tablePrefix( $domainInstance->getTablePrefix() );
1039 unset( $this->conns
[$connFreeKey][$i][$oldDomain] );
1040 // Note that if $domain is an empty string, getDomainID() might not match it
1041 $this->conns
[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1042 $this->connLogger
->debug( __METHOD__
.
1043 ": reusing free connection from $oldDomain for $domain" );
1049 if ( !isset( $this->servers
[$i] ) ||
!is_array( $this->servers
[$i] ) ) {
1050 throw new InvalidArgumentException( "No server with index '$i'." );
1052 // Open a new connection
1053 $server = $this->servers
[$i];
1054 $server['serverIndex'] = $i;
1055 $server['foreignPoolRefCount'] = 0;
1056 $server['foreign'] = true;
1057 $server['autoCommitOnly'] = $autoCommit;
1058 $conn = $this->reallyOpenConnection( $server, $domainInstance );
1059 if ( !$conn->isOpen() ) {
1060 $this->connLogger
->warning( __METHOD__
. ": connection error for $i/$domain" );
1061 $this->errorConnection
= $conn;
1064 // Note that if $domain is an empty string, getDomainID() might not match it
1065 $this->conns
[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1066 $this->connLogger
->debug( __METHOD__
. ": opened new connection for $i/$domain" );
1070 if ( $conn instanceof IDatabase
) {
1071 // Final sanity check to make sure the right domain is selected
1072 if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1073 throw new UnexpectedValueException(
1074 "Got connection to '{$conn->getDomainID()}', but expected '$domain'." );
1076 // Increment reference count
1077 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1078 $conn->setLBInfo( 'foreignPoolRefCount', $refCount +
1 );
1084 public function getServerAttributes( $i ) {
1085 return Database
::attributesFromType(
1086 $this->getServerType( $i ),
1087 $this->servers
[$i]['driver'] ??
null
1092 * Test if the specified index represents an open connection
1094 * @param int $index Server index
1098 private function isOpen( $index ) {
1099 if ( !is_int( $index ) ) {
1103 return (bool)$this->getAnyOpenConnection( $index );
1107 * Open a new network connection to a server (uncached)
1109 * Returns a Database object whether or not the connection was successful.
1111 * @param array $server
1112 * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1114 * @throws DBAccessError
1115 * @throws InvalidArgumentException
1117 protected function reallyOpenConnection( array $server, DatabaseDomain
$domain ) {
1118 if ( $this->disabled
) {
1119 throw new DBAccessError();
1122 if ( $domain->getDatabase() === null ) {
1123 // The database domain does not specify a DB name and some database systems require a
1124 // valid DB specified on connection. The $server configuration array contains a default
1125 // DB name to use for connections in such cases.
1126 if ( $server['type'] === 'mysql' ) {
1127 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1128 // and the DB name in $server might not exist due to legacy reasons (the default
1129 // domain used to ignore the local LB domain, even when mismatched).
1130 $server['dbname'] = null;
1133 $server['dbname'] = $domain->getDatabase();
1136 if ( $domain->getSchema() !== null ) {
1137 $server['schema'] = $domain->getSchema();
1140 // It is always possible to connect with any prefix, even the empty string
1141 $server['tablePrefix'] = $domain->getTablePrefix();
1143 // Let the handle know what the cluster master is (e.g. "db1052")
1144 $masterName = $this->getServerName( $this->getWriterIndex() );
1145 $server['clusterMasterHost'] = $masterName;
1147 // Log when many connection are made on requests
1148 if ( ++
$this->connsOpened
>= self
::CONN_HELD_WARN_THRESHOLD
) {
1149 $this->perfLogger
->warning( __METHOD__
. ": " .
1150 "{$this->connsOpened}+ connections made (master=$masterName)" );
1153 $server['srvCache'] = $this->srvCache
;
1154 // Set loggers and profilers
1155 $server['connLogger'] = $this->connLogger
;
1156 $server['queryLogger'] = $this->queryLogger
;
1157 $server['errorLogger'] = $this->errorLogger
;
1158 $server['deprecationLogger'] = $this->deprecationLogger
;
1159 $server['profiler'] = $this->profiler
;
1160 $server['trxProfiler'] = $this->trxProfiler
;
1161 // Use the same agent and PHP mode for all DB handles
1162 $server['cliMode'] = $this->cliMode
;
1163 $server['agent'] = $this->agent
;
1164 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1165 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1166 $server['flags'] = $server['flags'] ?? IDatabase
::DBO_DEFAULT
;
1168 // Create a live connection object
1170 $db = Database
::factory( $server['type'], $server );
1171 } catch ( DBConnectionError
$e ) {
1172 // FIXME: This is probably the ugliest thing I have ever done to
1173 // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1177 $db->setLBInfo( $server );
1178 $db->setLazyMasterHandle(
1179 $this->getLazyConnectionRef( self
::DB_MASTER
, [], $db->getDomainID() )
1181 $db->setTableAliases( $this->tableAliases
);
1182 $db->setIndexAliases( $this->indexAliases
);
1184 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1185 if ( $this->trxRoundId
!== false ) {
1186 $this->applyTransactionRoundFlags( $db );
1188 foreach ( $this->trxRecurringCallbacks
as $name => $callback ) {
1189 $db->setTransactionListener( $name, $callback );
1197 * @throws DBConnectionError
1199 private function reportConnectionError() {
1200 $conn = $this->errorConnection
; // the connection which caused the error
1202 'method' => __METHOD__
,
1203 'last_error' => $this->lastError
,
1206 if ( $conn instanceof IDatabase
) {
1207 $context['db_server'] = $conn->getServer();
1208 $this->connLogger
->warning(
1209 __METHOD__
. ": connection error: {last_error} ({db_server})",
1213 throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1215 // No last connection, probably due to all servers being too busy
1216 $this->connLogger
->error(
1218 ": LB failure with no last connection. Connection error: {last_error}",
1222 // If all servers were busy, "lastError" will contain something sensible
1223 throw new DBConnectionError( null, $this->lastError
);
1227 public function getWriterIndex() {
1231 public function haveIndex( $i ) {
1232 return array_key_exists( $i, $this->servers
);
1235 public function isNonZeroLoad( $i ) {
1236 return array_key_exists( $i, $this->servers
) && $this->loads
[$i] != 0;
1239 public function getServerCount() {
1240 return count( $this->servers
);
1243 public function getServerName( $i ) {
1244 $name = $this->servers
[$i]['hostName'] ??
$this->servers
[$i]['host'] ??
'';
1246 return ( $name != '' ) ?
$name : 'localhost';
1249 public function getServerInfo( $i ) {
1250 return $this->servers
[$i] ??
false;
1253 public function getServerType( $i ) {
1254 return $this->servers
[$i]['type'] ??
'unknown';
1257 public function getMasterPos() {
1258 # If this entire request was served from a replica DB without opening a connection to the
1259 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1260 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1261 if ( !$masterConn ) {
1262 $serverCount = count( $this->servers
);
1263 for ( $i = 1; $i < $serverCount; $i++
) {
1264 $conn = $this->getAnyOpenConnection( $i );
1266 return $conn->getReplicaPos();
1270 return $masterConn->getMasterPos();
1276 public function disable() {
1278 $this->disabled
= true;
1281 public function closeAll() {
1282 $fname = __METHOD__
;
1283 $this->forEachOpenConnection( function ( IDatabase
$conn ) use ( $fname ) {
1284 $host = $conn->getServer();
1285 $this->connLogger
->debug(
1286 $fname . ": closing connection to database '$host'." );
1291 self
::KEY_LOCAL
=> [],
1292 self
::KEY_FOREIGN_INUSE
=> [],
1293 self
::KEY_FOREIGN_FREE
=> [],
1294 self
::KEY_LOCAL_NOROUND
=> [],
1295 self
::KEY_FOREIGN_INUSE_NOROUND
=> [],
1296 self
::KEY_FOREIGN_FREE_NOROUND
=> []
1298 $this->connsOpened
= 0;
1301 public function closeConnection( IDatabase
$conn ) {
1302 if ( $conn instanceof DBConnRef
) {
1303 // Avoid calling close() but still leaving the handle in the pool
1304 throw new RuntimeException( __METHOD__
. ': got DBConnRef instance.' );
1307 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1308 foreach ( $this->conns
as $type => $connsByServer ) {
1309 if ( !isset( $connsByServer[$serverIndex] ) ) {
1313 foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1314 if ( $conn === $trackedConn ) {
1315 $host = $this->getServerName( $i );
1316 $this->connLogger
->debug(
1317 __METHOD__
. ": closing connection to database $i at '$host'." );
1318 unset( $this->conns
[$type][$serverIndex][$i] );
1319 --$this->connsOpened
;
1328 public function commitAll( $fname = __METHOD__
) {
1329 $this->commitMasterChanges( $fname );
1330 $this->flushMasterSnapshots( $fname );
1331 $this->flushReplicaSnapshots( $fname );
1334 public function finalizeMasterChanges() {
1335 $this->assertTransactionRoundStage( [ self
::ROUND_CURSORY
, self
::ROUND_FINALIZED
] );
1337 $this->trxRoundStage
= self
::ROUND_ERROR
; // "failed" until proven otherwise
1338 // Loop until callbacks stop adding callbacks on other connections
1341 $count = 0; // callbacks execution attempts
1342 $this->forEachOpenMasterConnection( function ( Database
$conn ) use ( &$count ) {
1343 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1344 // Any error should cause all (peer) transactions to be rolled back together.
1345 $count +
= $conn->runOnTransactionPreCommitCallbacks();
1348 } while ( $count > 0 );
1349 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1350 $this->forEachOpenMasterConnection( function ( Database
$conn ) {
1351 $conn->setTrxEndCallbackSuppression( true );
1353 $this->trxRoundStage
= self
::ROUND_FINALIZED
;
1358 public function approveMasterChanges( array $options ) {
1359 $this->assertTransactionRoundStage( self
::ROUND_FINALIZED
);
1361 $limit = $options['maxWriteDuration'] ??
0;
1363 $this->trxRoundStage
= self
::ROUND_ERROR
; // "failed" until proven otherwise
1364 $this->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( $limit ) {
1365 // If atomic sections or explicit transactions are still open, some caller must have
1366 // caught an exception but failed to properly rollback any changes. Detect that and
1367 // throw and error (causing rollback).
1368 $conn->assertNoOpenTransactions();
1369 // Assert that the time to replicate the transaction will be sane.
1370 // If this fails, then all DB transactions will be rollback back together.
1371 $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY
);
1372 if ( $limit > 0 && $time > $limit ) {
1373 throw new DBTransactionSizeError(
1375 "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1379 // If a connection sits idle while slow queries execute on another, that connection
1380 // may end up dropped before the commit round is reached. Ping servers to detect this.
1381 if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1382 throw new DBTransactionError(
1384 "A connection to the {$conn->getDBname()} database was lost before commit."
1388 $this->trxRoundStage
= self
::ROUND_APPROVED
;
1391 public function beginMasterChanges( $fname = __METHOD__
) {
1392 if ( $this->trxRoundId
!== false ) {
1393 throw new DBTransactionError(
1395 "$fname: Transaction round '{$this->trxRoundId}' already started."
1398 $this->assertTransactionRoundStage( self
::ROUND_CURSORY
);
1400 // Clear any empty transactions (no writes/callbacks) from the implicit round
1401 $this->flushMasterSnapshots( $fname );
1403 $this->trxRoundId
= $fname;
1404 $this->trxRoundStage
= self
::ROUND_ERROR
; // "failed" until proven otherwise
1405 // Mark applicable handles as participating in this explicit transaction round.
1406 // For each of these handles, any writes and callbacks will be tied to a single
1407 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1408 // are part of an en masse commit or an en masse rollback.
1409 $this->forEachOpenMasterConnection( function ( Database
$conn ) {
1410 $this->applyTransactionRoundFlags( $conn );
1412 $this->trxRoundStage
= self
::ROUND_CURSORY
;
1415 public function commitMasterChanges( $fname = __METHOD__
) {
1416 $this->assertTransactionRoundStage( self
::ROUND_APPROVED
);
1420 /** @noinspection PhpUnusedLocalVariableInspection */
1421 $scope = ScopedCallback
::newScopedIgnoreUserAbort(); // try to ignore client aborts
1423 $restore = ( $this->trxRoundId
!== false );
1424 $this->trxRoundId
= false;
1425 $this->trxRoundStage
= self
::ROUND_ERROR
; // "failed" until proven otherwise
1426 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1427 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1428 $this->forEachOpenMasterConnection(
1429 function ( IDatabase
$conn ) use ( $fname, &$failures ) {
1431 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS
);
1432 } catch ( DBError
$e ) {
1433 ( $this->errorLogger
)( $e );
1434 $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1439 throw new DBTransactionError(
1441 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1445 // Unmark handles as participating in this explicit transaction round
1446 $this->forEachOpenMasterConnection( function ( Database
$conn ) {
1447 $this->undoTransactionRoundFlags( $conn );
1450 $this->trxRoundStage
= self
::ROUND_COMMIT_CALLBACKS
;
1453 public function runMasterTransactionIdleCallbacks() {
1454 if ( $this->trxRoundStage
=== self
::ROUND_COMMIT_CALLBACKS
) {
1455 $type = IDatabase
::TRIGGER_COMMIT
;
1456 } elseif ( $this->trxRoundStage
=== self
::ROUND_ROLLBACK_CALLBACKS
) {
1457 $type = IDatabase
::TRIGGER_ROLLBACK
;
1459 throw new DBTransactionError(
1461 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1465 $oldStage = $this->trxRoundStage
;
1466 $this->trxRoundStage
= self
::ROUND_ERROR
; // "failed" until proven otherwise
1468 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1469 $this->forEachOpenMasterConnection( function ( Database
$conn ) {
1470 $conn->setTrxEndCallbackSuppression( false );
1473 $e = null; // first exception
1474 $fname = __METHOD__
;
1475 // Loop until callbacks stop adding callbacks on other connections
1477 // Run any pending callbacks for each connection...
1478 $count = 0; // callback execution attempts
1479 $this->forEachOpenMasterConnection(
1480 function ( Database
$conn ) use ( $type, &$e, &$count ) {
1481 if ( $conn->trxLevel() ) {
1482 return; // retry in the next iteration, after commit() is called
1485 $count +
= $conn->runOnTransactionIdleCallbacks( $type );
1486 } catch ( Exception
$ex ) {
1491 // Clear out any active transactions left over from callbacks...
1492 $this->forEachOpenMasterConnection( function ( Database
$conn ) use ( &$e, $fname ) {
1493 if ( $conn->writesPending() ) {
1494 // A callback from another handle wrote to this one and DBO_TRX is set
1495 $this->queryLogger
->warning( $fname . ": found writes pending." );
1496 $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1497 $this->queryLogger
->warning(
1498 $fname . ": found writes pending ($fnames).",
1500 'db_server' => $conn->getServer(),
1501 'db_name' => $conn->getDBname()
1504 } elseif ( $conn->trxLevel() ) {
1505 // A callback from another handle read from this one and DBO_TRX is set,
1506 // which can easily happen if there is only one DB (no replicas)
1507 $this->queryLogger
->debug( $fname . ": found empty transaction." );
1510 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS
);
1511 } catch ( Exception
$ex ) {
1515 } while ( $count > 0 );
1517 $this->trxRoundStage
= $oldStage;
1522 public function runMasterTransactionListenerCallbacks() {
1523 if ( $this->trxRoundStage
=== self
::ROUND_COMMIT_CALLBACKS
) {
1524 $type = IDatabase
::TRIGGER_COMMIT
;
1525 } elseif ( $this->trxRoundStage
=== self
::ROUND_ROLLBACK_CALLBACKS
) {
1526 $type = IDatabase
::TRIGGER_ROLLBACK
;
1528 throw new DBTransactionError(
1530 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1536 $this->trxRoundStage
= self
::ROUND_ERROR
; // "failed" until proven otherwise
1537 $this->forEachOpenMasterConnection( function ( Database
$conn ) use ( $type, &$e ) {
1539 $conn->runTransactionListenerCallbacks( $type );
1540 } catch ( Exception
$ex ) {
1544 $this->trxRoundStage
= self
::ROUND_CURSORY
;
1549 public function rollbackMasterChanges( $fname = __METHOD__
) {
1550 $restore = ( $this->trxRoundId
!== false );
1551 $this->trxRoundId
= false;
1552 $this->trxRoundStage
= self
::ROUND_ERROR
; // "failed" until proven otherwise
1553 $this->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( $fname ) {
1554 $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS
);
1557 // Unmark handles as participating in this explicit transaction round
1558 $this->forEachOpenMasterConnection( function ( Database
$conn ) {
1559 $this->undoTransactionRoundFlags( $conn );
1562 $this->trxRoundStage
= self
::ROUND_ROLLBACK_CALLBACKS
;
1566 * @param string|string[] $stage
1568 private function assertTransactionRoundStage( $stage ) {
1569 $stages = (array)$stage;
1571 if ( !in_array( $this->trxRoundStage
, $stages, true ) ) {
1572 $stageList = implode(
1574 array_map( function ( $v ) {
1578 throw new DBTransactionError(
1580 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1586 * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1588 * Some servers may have neither flag enabled, meaning that they opt out of such
1589 * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1590 * when a DB server is used for something like simple key/value storage.
1592 * @param Database $conn
1594 private function applyTransactionRoundFlags( Database
$conn ) {
1595 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1596 return; // transaction rounds do not apply to these connections
1599 if ( $conn->getFlag( $conn::DBO_DEFAULT
) ) {
1600 // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1601 // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1602 $conn->setFlag( $conn::DBO_TRX
, $conn::REMEMBER_PRIOR
);
1605 if ( $conn->getFlag( $conn::DBO_TRX
) ) {
1606 $conn->setLBInfo( 'trxRoundId', $this->trxRoundId
);
1611 * @param Database $conn
1613 private function undoTransactionRoundFlags( Database
$conn ) {
1614 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1615 return; // transaction rounds do not apply to these connections
1618 if ( $conn->getFlag( $conn::DBO_TRX
) ) {
1619 $conn->setLBInfo( 'trxRoundId', false );
1622 if ( $conn->getFlag( $conn::DBO_DEFAULT
) ) {
1623 $conn->restoreFlags( $conn::RESTORE_PRIOR
);
1627 public function flushReplicaSnapshots( $fname = __METHOD__
) {
1628 $this->forEachOpenReplicaConnection( function ( IDatabase
$conn ) use ( $fname ) {
1629 $conn->flushSnapshot( $fname );
1633 public function flushMasterSnapshots( $fname = __METHOD__
) {
1634 $this->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( $fname ) {
1635 $conn->flushSnapshot( $fname );
1643 public function getTransactionRoundStage() {
1644 return $this->trxRoundStage
;
1647 public function hasMasterConnection() {
1648 return $this->isOpen( $this->getWriterIndex() );
1651 public function hasMasterChanges() {
1653 $this->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( &$pending ) {
1654 $pending |
= $conn->writesOrCallbacksPending();
1657 return (bool)$pending;
1660 public function lastMasterChangeTimestamp() {
1662 $this->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( &$lastTime ) {
1663 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1669 public function hasOrMadeRecentMasterChanges( $age = null ) {
1670 $age = ( $age === null ) ?
$this->waitTimeout
: $age;
1672 return ( $this->hasMasterChanges()
1673 ||
$this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1676 public function pendingMasterChangeCallers() {
1678 $this->forEachOpenMasterConnection( function ( IDatabase
$conn ) use ( &$fnames ) {
1679 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1685 public function getLaggedReplicaMode( $domain = false ) {
1686 // No-op if there is only one DB (also avoids recursion)
1687 if ( !$this->laggedReplicaMode
&& $this->getServerCount() > 1 ) {
1689 // See if laggedReplicaMode gets set
1690 $conn = $this->getConnection( self
::DB_REPLICA
, false, $domain );
1691 $this->reuseConnection( $conn );
1692 } catch ( DBConnectionError
$e ) {
1693 // Avoid expensive re-connect attempts and failures
1694 $this->allReplicasDownMode
= true;
1695 $this->laggedReplicaMode
= true;
1699 return $this->laggedReplicaMode
;
1702 public function laggedReplicaUsed() {
1703 return $this->laggedReplicaMode
;
1709 * @deprecated Since 1.28; use laggedReplicaUsed()
1711 public function laggedSlaveUsed() {
1712 return $this->laggedReplicaUsed();
1715 public function getReadOnlyReason( $domain = false, IDatabase
$conn = null ) {
1716 if ( $this->readOnlyReason
!== false ) {
1717 return $this->readOnlyReason
;
1718 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1719 if ( $this->allReplicasDownMode
) {
1720 return 'The database has been automatically locked ' .
1721 'until the replica database servers become available';
1723 return 'The database has been automatically locked ' .
1724 'while the replica database servers catch up to the master.';
1726 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1727 return 'The database master is running in read-only mode.';
1734 * @param string $domain Domain ID, or false for the current domain
1735 * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1738 private function masterRunningReadOnly( $domain, IDatabase
$conn = null ) {
1739 $cache = $this->wanCache
;
1740 $masterServer = $this->getServerName( $this->getWriterIndex() );
1742 return (bool)$cache->getWithSetCallback(
1743 $cache->makeGlobalKey( __CLASS__
, 'server-read-only', $masterServer ),
1744 self
::TTL_CACHE_READONLY
,
1745 function () use ( $domain, $conn ) {
1746 $old = $this->trxProfiler
->setSilenced( true );
1748 $dbw = $conn ?
: $this->getConnection( self
::DB_MASTER
, [], $domain );
1749 $readOnly = (int)$dbw->serverIsReadOnly();
1751 $this->reuseConnection( $dbw );
1753 } catch ( DBError
$e ) {
1756 $this->trxProfiler
->setSilenced( $old );
1759 [ 'pcTTL' => $cache::TTL_PROC_LONG
, 'busyValue' => 0 ]
1763 public function allowLagged( $mode = null ) {
1764 if ( $mode === null ) {
1765 return $this->allowLagged
;
1767 $this->allowLagged
= $mode;
1769 return $this->allowLagged
;
1772 public function pingAll() {
1774 $this->forEachOpenConnection( function ( IDatabase
$conn ) use ( &$success ) {
1775 if ( !$conn->ping() ) {
1783 public function forEachOpenConnection( $callback, array $params = [] ) {
1784 foreach ( $this->conns
as $connsByServer ) {
1785 foreach ( $connsByServer as $serverConns ) {
1786 foreach ( $serverConns as $conn ) {
1787 $callback( $conn, ...$params );
1793 public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1794 $masterIndex = $this->getWriterIndex();
1795 foreach ( $this->conns
as $connsByServer ) {
1796 if ( isset( $connsByServer[$masterIndex] ) ) {
1797 /** @var IDatabase $conn */
1798 foreach ( $connsByServer[$masterIndex] as $conn ) {
1799 $callback( $conn, ...$params );
1805 public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1806 foreach ( $this->conns
as $connsByServer ) {
1807 foreach ( $connsByServer as $i => $serverConns ) {
1808 if ( $i === $this->getWriterIndex() ) {
1809 continue; // skip master
1811 foreach ( $serverConns as $conn ) {
1812 $callback( $conn, ...$params );
1818 public function getMaxLag( $domain = false ) {
1823 if ( $this->getServerCount() <= 1 ) {
1824 return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1827 $lagTimes = $this->getLagTimes( $domain );
1828 foreach ( $lagTimes as $i => $lag ) {
1829 if ( $this->loads
[$i] > 0 && $lag > $maxLag ) {
1831 $host = $this->servers
[$i]['host'];
1836 return [ $host, $maxLag, $maxIndex ];
1839 public function getLagTimes( $domain = false ) {
1840 if ( $this->getServerCount() <= 1 ) {
1841 return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1844 $knownLagTimes = []; // map of (server index => 0 seconds)
1845 $indexesWithLag = [];
1846 foreach ( $this->servers
as $i => $server ) {
1847 if ( empty( $server['is static'] ) ) {
1848 $indexesWithLag[] = $i; // DB server might have replication lag
1850 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1854 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) +
$knownLagTimes;
1857 public function safeGetLag( IDatabase
$conn ) {
1858 if ( $this->getServerCount() <= 1 ) {
1861 return $conn->getLag();
1865 public function safeWaitForMasterPos( IDatabase
$conn, $pos = false, $timeout = null ) {
1866 $timeout = max( 1, $timeout ?
: $this->waitTimeout
);
1868 if ( $this->getServerCount() <= 1 ||
!$conn->getLBInfo( 'replica' ) ) {
1869 return true; // server is not a replica DB
1873 // Get the current master position, opening a connection if needed
1874 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1875 if ( $masterConn ) {
1876 $pos = $masterConn->getMasterPos();
1878 $masterConn = $this->openConnection( $this->getWriterIndex(), self
::DOMAIN_ANY
);
1879 if ( !$masterConn ) {
1880 throw new DBReplicationWaitError(
1882 "Could not obtain a master database connection to get the position"
1885 $pos = $masterConn->getMasterPos();
1886 $this->closeConnection( $masterConn );
1890 if ( $pos instanceof DBMasterPos
) {
1891 $result = $conn->masterPosWait( $pos, $timeout );
1892 if ( $result == -1 ||
is_null( $result ) ) {
1893 $msg = __METHOD__
. ': timed out waiting on {host} pos {pos}';
1894 $this->replLogger
->warning( $msg, [
1895 'host' => $conn->getServer(),
1897 'trace' => ( new RuntimeException() )->getTraceAsString()
1901 $this->replLogger
->debug( __METHOD__
. ': done waiting' );
1905 $ok = false; // something is misconfigured
1906 $this->replLogger
->error(
1907 __METHOD__
. ': could not get master pos for {host}',
1909 'host' => $conn->getServer(),
1910 'trace' => ( new RuntimeException() )->getTraceAsString()
1918 public function setTransactionListener( $name, callable
$callback = null ) {
1920 $this->trxRecurringCallbacks
[$name] = $callback;
1922 unset( $this->trxRecurringCallbacks
[$name] );
1924 $this->forEachOpenMasterConnection(
1925 function ( IDatabase
$conn ) use ( $name, $callback ) {
1926 $conn->setTransactionListener( $name, $callback );
1931 public function setTableAliases( array $aliases ) {
1932 $this->tableAliases
= $aliases;
1935 public function setIndexAliases( array $aliases ) {
1936 $this->indexAliases
= $aliases;
1940 * @param string $prefix
1941 * @deprecated Since 1.33
1943 public function setDomainPrefix( $prefix ) {
1944 $this->setLocalDomainPrefix( $prefix );
1947 public function setLocalDomainPrefix( $prefix ) {
1948 // Find connections to explicit foreign domains still marked as in-use...
1950 $this->forEachOpenConnection( function ( IDatabase
$conn ) use ( &$domainsInUse ) {
1951 // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1952 // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1953 if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1954 $domainsInUse[] = $conn->getDomainID();
1958 // Do not switch connections to explicit foreign domains unless marked as safe
1959 if ( $domainsInUse ) {
1960 $domains = implode( ', ', $domainsInUse );
1961 throw new DBUnexpectedError( null,
1962 "Foreign domain connections are still in use ($domains)." );
1965 $this->setLocalDomain( new DatabaseDomain(
1966 $this->localDomain
->getDatabase(),
1967 $this->localDomain
->getSchema(),
1971 // Update the prefix for all local connections...
1972 $this->forEachOpenConnection( function ( IDatabase
$db ) use ( $prefix ) {
1973 if ( !$db->getLBInfo( 'foreign' ) ) {
1974 $db->tablePrefix( $prefix );
1979 public function redefineLocalDomain( $domain ) {
1982 $this->setLocalDomain( DatabaseDomain
::newFromId( $domain ) );
1986 * @param DatabaseDomain $domain
1988 private function setLocalDomain( DatabaseDomain
$domain ) {
1989 $this->localDomain
= $domain;
1990 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1991 // always true, gracefully handle the case when they fail to account for escaping.
1992 if ( $this->localDomain
->getTablePrefix() != '' ) {
1993 $this->localDomainIdAlias
=
1994 $this->localDomain
->getDatabase() . '-' . $this->localDomain
->getTablePrefix();
1996 $this->localDomainIdAlias
= $this->localDomain
->getDatabase();
2000 function __destruct() {
2001 // Avoid connection leaks for sanity
2007 * @deprecated since 1.29
2009 class_alias( LoadBalancer
::class, 'LoadBalancer' );