3 * Database load balancing.
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
25 * Database load balancing object
31 /** @var array[] Map of (server index => server config array) */
33 /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
35 /** @var array Map of (server index => weight) */
37 /** @var array[] Map of (group => server index => weight) */
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 */
46 /** @var string The LoadMonitor subclass name */
47 private $mLoadMonitorClass;
48 /** @var LoadMonitor */
49 private $mLoadMonitor;
52 /** @var WANObjectCache */
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) */
59 /** @var bool|DBMasterPos False if not set */
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;
72 /** @var TransactionProfiler */
73 protected $trxProfiler;
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 */
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;
87 private $disabled = false;
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]
96 public function __construct( array $params ) {
97 if ( !isset( $params['servers'] ) ) {
98 throw new MWException( __CLASS__
. ': missing servers parameter' );
100 $this->mServers
= $params['servers'];
101 $this->mWaitTimeout
= self
::POS_WAIT_TIMEOUT
;
103 $this->mReadIndex
= -1;
104 $this->mWriteIndex
= -1;
108 'foreignFree' => [] ];
110 $this->mWaitForPos
= false;
111 $this->mErrorConnection
= false;
112 $this->mAllowLagged
= false;
114 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
115 $this->readOnlyReason
= $params['readOnlyReason'];
118 if ( isset( $params['loadMonitor'] ) ) {
119 $this->mLoadMonitorClass
= $params['loadMonitor'];
121 $master = reset( $params['servers'] );
122 if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
123 $this->mLoadMonitorClass
= 'LoadMonitorMySQL';
125 $this->mLoadMonitorClass
= 'LoadMonitorNull';
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] = [];
136 $this->mGroupLoads
[$group][$i] = $ratio;
141 $this->srvCache
= ObjectCache
::getLocalServerInstance();
142 $this->wanCache
= ObjectCache
::getMainWANInstance();
144 if ( isset( $params['trxProfiler'] ) ) {
145 $this->trxProfiler
= $params['trxProfiler'];
147 $this->trxProfiler
= new TransactionProfiler();
152 * Get a LoadMonitor instance
154 * @return LoadMonitor
156 private function getLoadMonitor() {
157 if ( !isset( $this->mLoadMonitor
) ) {
158 $class = $this->mLoadMonitorClass
;
159 $this->mLoadMonitor
= new $class( $this );
162 return $this->mLoadMonitor
;
166 * Get or set arbitrary data used by the parent object, usually an LBFactory
170 public function parentInfo( $x = null ) {
171 return wfSetVar( $this->mParentInfo
, $x );
175 * @param array $loads
176 * @param bool|string $wiki Wiki to get non-lagged for
177 * @param int $maxLag Restrict the maximum allowed lag to this many seconds
178 * @return bool|int|string
180 private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self
::MAX_LAG
) {
181 $lags = $this->getLagTimes( $wiki );
183 # Unset excessively lagged servers
184 foreach ( $lags as $i => $lag ) {
186 $maxServerLag = $maxLag;
187 if ( isset( $this->mServers
[$i]['max lag'] ) ) {
188 $maxServerLag = min( $maxServerLag, $this->mServers
[$i]['max lag'] );
191 $host = $this->getServerName( $i );
192 if ( $lag === false ) {
193 wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
195 } elseif ( $lag > $maxServerLag ) {
196 wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
202 # Find out if all the slaves with non-zero load are lagged
204 foreach ( $loads as $load ) {
208 # No appropriate DB servers except maybe the master and some slaves with zero load
209 # Do NOT use the master
210 # Instead, this function will return false, triggering read-only mode,
211 # and a lagged slave will be used instead.
215 if ( count( $loads ) == 0 ) {
219 # Return a random representative of the remainder
220 return ArrayUtils
::pickRandom( $loads );
224 * Get the index of the reader connection, which may be a slave
225 * This takes into account load ratios and lag times. It should
226 * always return a consistent index during a given invocation
228 * Side effect: opens connections to databases
229 * @param string|bool $group Query group, or false for the generic reader
230 * @param string|bool $wiki Wiki ID, or false for the current wiki
231 * @throws MWException
232 * @return bool|int|string
234 public function getReaderIndex( $group = false, $wiki = false ) {
237 # @todo FIXME: For now, only go through all this for mysql databases
238 if ( $wgDBtype != 'mysql' ) {
239 return $this->getWriterIndex();
242 if ( count( $this->mServers
) == 1 ) {
243 # Skip the load balancing if there's only one server
245 } elseif ( $group === false && $this->mReadIndex
>= 0 ) {
246 # Shortcut if generic reader exists already
247 return $this->mReadIndex
;
250 # Find the relevant load array
251 if ( $group !== false ) {
252 if ( isset( $this->mGroupLoads
[$group] ) ) {
253 $nonErrorLoads = $this->mGroupLoads
[$group];
255 # No loads for this group, return false and the caller can use some other group
256 wfDebugLog( 'connect', __METHOD__
. ": no loads for group $group\n" );
261 $nonErrorLoads = $this->mLoads
;
264 if ( !count( $nonErrorLoads ) ) {
265 throw new MWException( "Empty server array given to LoadBalancer" );
268 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
269 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
271 $laggedSlaveMode = false;
273 # No server found yet
276 # First try quickly looking through the available servers for a server that
278 $currentLoads = $nonErrorLoads;
279 while ( count( $currentLoads ) ) {
280 if ( $this->mAllowLagged ||
$laggedSlaveMode ) {
281 $i = ArrayUtils
::pickRandom( $currentLoads );
284 if ( $this->mWaitForPos
&& $this->mWaitForPos
->asOfTime() ) {
285 # ChronologyProtecter causes mWaitForPos to be set via sessions.
286 # This triggers doWait() after connect, so it's especially good to
287 # avoid lagged servers so as to avoid just blocking in that method.
288 $ago = microtime( true ) - $this->mWaitForPos
->asOfTime();
289 # Aim for <= 1 second of waiting (being too picky can backfire)
290 $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago +
1 );
292 if ( $i === false ) {
293 # Any server with less lag than it's 'max lag' param is preferable
294 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
296 if ( $i === false && count( $currentLoads ) != 0 ) {
297 # All slaves lagged. Switch to read-only mode
298 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
299 $i = ArrayUtils
::pickRandom( $currentLoads );
300 $laggedSlaveMode = true;
304 if ( $i === false ) {
305 # pickRandom() returned false
306 # This is permanent and means the configuration or the load monitor
307 # wants us to return false.
308 wfDebugLog( 'connect', __METHOD__
. ": pickRandom() returned false" );
313 $serverName = $this->getServerName( $i );
314 wfDebugLog( 'connect', __METHOD__
. ": Using reader #$i: $serverName..." );
316 $conn = $this->openConnection( $i, $wiki );
318 wfDebugLog( 'connect', __METHOD__
. ": Failed connecting to $i/$wiki" );
319 unset( $nonErrorLoads[$i] );
320 unset( $currentLoads[$i] );
325 // Decrement reference counter, we are finished with this connection.
326 // It will be incremented for the caller later.
327 if ( $wiki !== false ) {
328 $this->reuseConnection( $conn );
335 # If all servers were down, quit now
336 if ( !count( $nonErrorLoads ) ) {
337 wfDebugLog( 'connect', "All servers down" );
340 if ( $i !== false ) {
341 # Slave connection successful
342 # Wait for the session master pos for a short time
343 if ( $this->mWaitForPos
&& $i > 0 ) {
344 if ( !$this->doWait( $i ) ) {
345 $this->mServers
[$i]['slave pos'] = $conn->getSlavePos();
348 if ( $this->mReadIndex
<= 0 && $this->mLoads
[$i] > 0 && $group === false ) {
349 $this->mReadIndex
= $i;
350 # Record if the generic reader index is in "lagged slave" mode
351 if ( $laggedSlaveMode ) {
352 $this->laggedSlaveMode
= true;
355 $serverName = $this->getServerName( $i );
356 wfDebugLog( 'connect', __METHOD__
.
357 ": using server $serverName for group '$group'\n" );
364 * Set the master wait position
365 * If a DB_SLAVE connection has been opened already, waits
366 * Otherwise sets a variable telling it to wait if such a connection is opened
367 * @param DBMasterPos $pos
369 public function waitFor( $pos ) {
370 $this->mWaitForPos
= $pos;
371 $i = $this->mReadIndex
;
374 if ( !$this->doWait( $i ) ) {
375 $this->mServers
[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
376 $this->laggedSlaveMode
= true;
382 * Set the master wait position and wait for a "generic" slave to catch up to it
384 * This can be used a faster proxy for waitForAll()
386 * @param DBMasterPos $pos
387 * @param int $timeout Max seconds to wait; default is mWaitTimeout
388 * @return bool Success (able to connect and no timeouts reached)
391 public function waitForOne( $pos, $timeout = null ) {
392 $this->mWaitForPos
= $pos;
394 $i = $this->mReadIndex
;
396 // Pick a generic slave if there isn't one yet
397 $readLoads = $this->mLoads
;
398 unset( $readLoads[$this->getWriterIndex()] ); // slaves only
399 $readLoads = array_filter( $readLoads ); // with non-zero load
400 $i = ArrayUtils
::pickRandom( $readLoads );
404 $ok = $this->doWait( $i, true, $timeout );
406 $ok = true; // no applicable loads
413 * Set the master wait position and wait for ALL slaves to catch up to it
414 * @param DBMasterPos $pos
415 * @param int $timeout Max seconds to wait; default is mWaitTimeout
416 * @return bool Success (able to connect and no timeouts reached)
418 public function waitForAll( $pos, $timeout = null ) {
419 $this->mWaitForPos
= $pos;
420 $serverCount = count( $this->mServers
);
423 for ( $i = 1; $i < $serverCount; $i++
) {
424 if ( $this->mLoads
[$i] > 0 ) {
425 $ok = $this->doWait( $i, true, $timeout ) && $ok;
433 * Get any open connection to a given server index, local or foreign
434 * Returns false if there is no connection open
437 * @return DatabaseBase|bool False on failure
439 public function getAnyOpenConnection( $i ) {
440 foreach ( $this->mConns
as $conns ) {
441 if ( !empty( $conns[$i] ) ) {
442 return reset( $conns[$i] );
450 * Wait for a given slave to catch up to the master pos stored in $this
451 * @param int $index Server index
452 * @param bool $open Check the server even if a new connection has to be made
453 * @param int $timeout Max seconds to wait; default is mWaitTimeout
456 protected function doWait( $index, $open = false, $timeout = null ) {
457 $close = false; // close the connection afterwards
459 // Check if we already know that the DB has reached this point
460 $server = $this->getServerName( $index );
461 $key = $this->srvCache
->makeGlobalKey( __CLASS__
, 'last-known-pos', $server );
462 /** @var DBMasterPos $knownReachedPos */
463 $knownReachedPos = $this->srvCache
->get( $key );
464 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos
) ) {
465 wfDebugLog( 'replication', __METHOD__
.
466 ": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
470 // Find a connection to wait on, creating one if needed and allowed
471 $conn = $this->getAnyOpenConnection( $index );
474 wfDebugLog( 'replication', __METHOD__
. ": no connection open for $server\n" );
478 $conn = $this->openConnection( $index, '' );
480 wfDebugLog( 'replication', __METHOD__
. ": failed to connect to $server\n" );
484 // Avoid connection spam in waitForAll() when connections
485 // are made just for the sake of doing this lag check.
490 wfDebugLog( 'replication', __METHOD__
. ": Waiting for slave $server to catch up...\n" );
491 $timeout = $timeout ?
: $this->mWaitTimeout
;
492 $result = $conn->masterPosWait( $this->mWaitForPos
, $timeout );
494 if ( $result == -1 ||
is_null( $result ) ) {
495 // Timed out waiting for slave, use master instead
496 $msg = __METHOD__
. ": Timed out waiting on $server pos {$this->mWaitForPos}";
497 wfDebugLog( 'replication', "$msg\n" );
498 wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
501 wfDebugLog( 'replication', __METHOD__
. ": Done\n" );
503 // Remember that the DB reached this point
504 $this->srvCache
->set( $key, $this->mWaitForPos
, BagOStuff
::TTL_DAY
);
508 $this->closeConnection( $conn );
515 * Get a connection by index
516 * This is the main entry point for this class.
518 * @param int $i Server index
519 * @param array|string|bool $groups Query group(s), or false for the generic reader
520 * @param string|bool $wiki Wiki ID, or false for the current wiki
522 * @throws MWException
523 * @return DatabaseBase
525 public function getConnection( $i, $groups = [], $wiki = false ) {
526 if ( $i === null ||
$i === false ) {
527 throw new MWException( 'Attempt to call ' . __METHOD__
.
528 ' with invalid server index' );
531 if ( $wiki === wfWikiID() ) {
535 $groups = ( $groups === false ||
$groups === [] )
536 ?
[ false ] // check one "group": the generic pool
539 $masterOnly = ( $i == DB_MASTER ||
$i == $this->getWriterIndex() );
540 $oldConnsOpened = $this->connsOpened
; // connections open now
542 if ( $i == DB_MASTER
) {
543 $i = $this->getWriterIndex();
545 # Try to find an available server in any the query groups (in order)
546 foreach ( $groups as $group ) {
547 $groupIndex = $this->getReaderIndex( $group, $wiki );
548 if ( $groupIndex !== false ) {
555 # Operation-based index
556 if ( $i == DB_SLAVE
) {
557 $this->mLastError
= 'Unknown error'; // reset error string
558 # Try the general server pool if $groups are unavailable.
559 $i = in_array( false, $groups, true )
560 ?
false // don't bother with this if that is what was tried above
561 : $this->getReaderIndex( false, $wiki );
562 # Couldn't find a working server in getReaderIndex()?
563 if ( $i === false ) {
564 $this->mLastError
= 'No working slave server: ' . $this->mLastError
;
566 return $this->reportConnectionError();
570 # Now we have an explicit index into the servers array
571 $conn = $this->openConnection( $i, $wiki );
573 return $this->reportConnectionError();
576 # Profile any new connections that happen
577 if ( $this->connsOpened
> $oldConnsOpened ) {
578 $host = $conn->getServer();
579 $dbname = $conn->getDBname();
580 $trxProf = Profiler
::instance()->getTransactionProfiler();
581 $trxProf->recordConnection( $host, $dbname, $masterOnly );
585 # Make master-requested DB handles inherit any read-only mode setting
586 $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
593 * Mark a foreign connection as being available for reuse under a different
594 * DB name or prefix. This mechanism is reference-counted, and must be called
595 * the same number of times as getConnection() to work.
597 * @param DatabaseBase $conn
598 * @throws MWException
600 public function reuseConnection( $conn ) {
601 $serverIndex = $conn->getLBInfo( 'serverIndex' );
602 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
603 if ( $serverIndex === null ||
$refCount === null ) {
604 wfDebug( __METHOD__
. ": this connection was not opened as a foreign connection\n" );
606 * This can happen in code like:
607 * foreach ( $dbs as $db ) {
608 * $conn = $lb->getConnection( DB_SLAVE, array(), $db );
610 * $lb->reuseConnection( $conn );
612 * When a connection to the local DB is opened in this way, reuseConnection()
618 $dbName = $conn->getDBname();
619 $prefix = $conn->tablePrefix();
620 if ( strval( $prefix ) !== '' ) {
621 $wiki = "$dbName-$prefix";
625 if ( $this->mConns
['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
626 throw new MWException( __METHOD__
. ": connection not found, has " .
627 "the connection been freed already?" );
629 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
630 if ( $refCount <= 0 ) {
631 $this->mConns
['foreignFree'][$serverIndex][$wiki] = $conn;
632 unset( $this->mConns
['foreignUsed'][$serverIndex][$wiki] );
633 wfDebug( __METHOD__
. ": freed connection $serverIndex/$wiki\n" );
635 wfDebug( __METHOD__
. ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
640 * Get a database connection handle reference
642 * The handle's methods wrap simply wrap those of a DatabaseBase handle
644 * @see LoadBalancer::getConnection() for parameter information
647 * @param array|string|bool $groups Query group(s), or false for the generic reader
648 * @param string|bool $wiki Wiki ID, or false for the current wiki
651 public function getConnectionRef( $db, $groups = [], $wiki = false ) {
652 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
656 * Get a database connection handle reference without connecting yet
658 * The handle's methods wrap simply wrap those of a DatabaseBase handle
660 * @see LoadBalancer::getConnection() for parameter information
663 * @param array|string|bool $groups Query group(s), or false for the generic reader
664 * @param string|bool $wiki Wiki ID, or false for the current wiki
667 public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
668 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
672 * Open a connection to the server given by the specified index
673 * Index must be an actual index into the array.
674 * If the server is already open, returns it.
676 * On error, returns false, and the connection which caused the
677 * error will be available via $this->mErrorConnection.
679 * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
681 * @param int $i Server index
682 * @param string|bool $wiki Wiki ID, or false for the current wiki
683 * @return DatabaseBase|bool Returns false on errors
685 public function openConnection( $i, $wiki = false ) {
686 if ( $wiki !== false ) {
687 $conn = $this->openForeignConnection( $i, $wiki );
688 } elseif ( isset( $this->mConns
['local'][$i][0] ) ) {
689 $conn = $this->mConns
['local'][$i][0];
691 $server = $this->mServers
[$i];
692 $server['serverIndex'] = $i;
693 $conn = $this->reallyOpenConnection( $server, false );
694 $serverName = $this->getServerName( $i );
695 if ( $conn->isOpen() ) {
696 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
697 $this->mConns
['local'][$i][0] = $conn;
699 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
700 $this->mErrorConnection
= $conn;
705 if ( $conn && !$conn->isOpen() ) {
706 // Connection was made but later unrecoverably lost for some reason.
707 // Do not return a handle that will just throw exceptions on use,
708 // but let the calling code (e.g. getReaderIndex) try another server.
709 // See DatabaseMyslBase::ping() for how this can happen.
710 $this->mErrorConnection
= $conn;
718 * Open a connection to a foreign DB, or return one if it is already open.
720 * Increments a reference count on the returned connection which locks the
721 * connection to the requested wiki. This reference count can be
722 * decremented by calling reuseConnection().
724 * If a connection is open to the appropriate server already, but with the wrong
725 * database, it will be switched to the right database and returned, as long as
726 * it has been freed first with reuseConnection().
728 * On error, returns false, and the connection which caused the
729 * error will be available via $this->mErrorConnection.
731 * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
733 * @param int $i Server index
734 * @param string $wiki Wiki ID to open
735 * @return DatabaseBase
737 private function openForeignConnection( $i, $wiki ) {
738 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
739 if ( isset( $this->mConns
['foreignUsed'][$i][$wiki] ) ) {
740 // Reuse an already-used connection
741 $conn = $this->mConns
['foreignUsed'][$i][$wiki];
742 wfDebug( __METHOD__
. ": reusing connection $i/$wiki\n" );
743 } elseif ( isset( $this->mConns
['foreignFree'][$i][$wiki] ) ) {
744 // Reuse a free connection for the same wiki
745 $conn = $this->mConns
['foreignFree'][$i][$wiki];
746 unset( $this->mConns
['foreignFree'][$i][$wiki] );
747 $this->mConns
['foreignUsed'][$i][$wiki] = $conn;
748 wfDebug( __METHOD__
. ": reusing free connection $i/$wiki\n" );
749 } elseif ( !empty( $this->mConns
['foreignFree'][$i] ) ) {
750 // Reuse a connection from another wiki
751 $conn = reset( $this->mConns
['foreignFree'][$i] );
752 $oldWiki = key( $this->mConns
['foreignFree'][$i] );
754 // The empty string as a DB name means "don't care".
755 // DatabaseMysqlBase::open() already handle this on connection.
756 if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
757 $this->mLastError
= "Error selecting database $dbName on server " .
758 $conn->getServer() . " from client host " . wfHostname() . "\n";
759 $this->mErrorConnection
= $conn;
762 $conn->tablePrefix( $prefix );
763 unset( $this->mConns
['foreignFree'][$i][$oldWiki] );
764 $this->mConns
['foreignUsed'][$i][$wiki] = $conn;
765 wfDebug( __METHOD__
. ": reusing free connection from $oldWiki for $wiki\n" );
768 // Open a new connection
769 $server = $this->mServers
[$i];
770 $server['serverIndex'] = $i;
771 $server['foreignPoolRefCount'] = 0;
772 $server['foreign'] = true;
773 $conn = $this->reallyOpenConnection( $server, $dbName );
774 if ( !$conn->isOpen() ) {
775 wfDebug( __METHOD__
. ": error opening connection for $i/$wiki\n" );
776 $this->mErrorConnection
= $conn;
779 $conn->tablePrefix( $prefix );
780 $this->mConns
['foreignUsed'][$i][$wiki] = $conn;
781 wfDebug( __METHOD__
. ": opened new connection for $i/$wiki\n" );
785 // Increment reference count
787 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
788 $conn->setLBInfo( 'foreignPoolRefCount', $refCount +
1 );
795 * Test if the specified index represents an open connection
797 * @param int $index Server index
801 private function isOpen( $index ) {
802 if ( !is_integer( $index ) ) {
806 return (bool)$this->getAnyOpenConnection( $index );
810 * Really opens a connection. Uncached.
811 * Returns a Database object whether or not the connection was successful.
814 * @param array $server
815 * @param bool $dbNameOverride
816 * @throws MWException
817 * @return DatabaseBase
819 protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
820 if ( $this->disabled
) {
821 throw new DBAccessError();
824 if ( !is_array( $server ) ) {
825 throw new MWException( 'You must update your load-balancing configuration. ' .
826 'See DefaultSettings.php entry for $wgDBservers.' );
829 if ( $dbNameOverride !== false ) {
830 $server['dbname'] = $dbNameOverride;
833 // Let the handle know what the cluster master is (e.g. "db1052")
834 $masterName = $this->getServerName( 0 );
835 $server['clusterMasterHost'] = $masterName;
837 // Log when many connection are made on requests
838 if ( ++
$this->connsOpened
>= self
::CONN_HELD_WARN_THRESHOLD
) {
839 wfDebugLog( 'DBPerformance', __METHOD__
. ": " .
840 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
841 wfBacktrace( true ) );
846 $db = DatabaseBase
::factory( $server['type'], $server );
847 } catch ( DBConnectionError
$e ) {
848 // FIXME: This is probably the ugliest thing I have ever done to
849 // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
853 $db->setLBInfo( $server );
854 $db->setLazyMasterHandle(
855 $this->getLazyConnectionRef( DB_MASTER
, [], $db->getWikiID() )
857 $db->setTransactionProfiler( $this->trxProfiler
);
863 * @throws DBConnectionError
866 private function reportConnectionError() {
867 $conn = $this->mErrorConnection
; // The connection which caused the error
869 'method' => __METHOD__
,
870 'last_error' => $this->mLastError
,
873 if ( !is_object( $conn ) ) {
874 // No last connection, probably due to all servers being too busy
876 "LB failure with no last connection. Connection error: {last_error}",
880 // If all servers were busy, mLastError will contain something sensible
881 throw new DBConnectionError( null, $this->mLastError
);
883 $context['db_server'] = $conn->getProperty( 'mServer' );
885 "Connection error: {last_error} ({db_server})",
889 // throws DBConnectionError
890 $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
893 return false; /* not reached */
900 public function getWriterIndex() {
905 * Returns true if the specified index is a valid server index
910 public function haveIndex( $i ) {
911 return array_key_exists( $i, $this->mServers
);
915 * Returns true if the specified index is valid and has non-zero load
920 public function isNonZeroLoad( $i ) {
921 return array_key_exists( $i, $this->mServers
) && $this->mLoads
[$i] != 0;
925 * Get the number of defined servers (not the number of open connections)
929 public function getServerCount() {
930 return count( $this->mServers
);
934 * Get the host name or IP address of the server with the specified index
935 * Prefer a readable name if available.
939 public function getServerName( $i ) {
940 if ( isset( $this->mServers
[$i]['hostName'] ) ) {
941 $name = $this->mServers
[$i]['hostName'];
942 } elseif ( isset( $this->mServers
[$i]['host'] ) ) {
943 $name = $this->mServers
[$i]['host'];
948 return ( $name != '' ) ?
$name : 'localhost';
952 * Return the server info structure for a given index, or false if the index is invalid.
956 public function getServerInfo( $i ) {
957 if ( isset( $this->mServers
[$i] ) ) {
958 return $this->mServers
[$i];
965 * Sets the server info structure for the given index. Entry at index $i
966 * is created if it doesn't exist
968 * @param array $serverInfo
970 public function setServerInfo( $i, array $serverInfo ) {
971 $this->mServers
[$i] = $serverInfo;
975 * Get the current master position for chronology control purposes
978 public function getMasterPos() {
979 # If this entire request was served from a slave without opening a connection to the
980 # master (however unlikely that may be), then we can fetch the position from the slave.
981 $masterConn = $this->getAnyOpenConnection( 0 );
982 if ( !$masterConn ) {
983 $serverCount = count( $this->mServers
);
984 for ( $i = 1; $i < $serverCount; $i++
) {
985 $conn = $this->getAnyOpenConnection( $i );
987 return $conn->getSlavePos();
991 return $masterConn->getMasterPos();
998 * Disable this load balancer. All connections are closed, and any attempt to
999 * open a new connection will result in a DBAccessError.
1003 public function disable() {
1005 $this->disabled
= true;
1009 * Close all open connections
1011 public function closeAll() {
1012 $this->forEachOpenConnection( function ( DatabaseBase
$conn ) {
1018 'foreignFree' => [],
1019 'foreignUsed' => [],
1021 $this->connsOpened
= 0;
1025 * Close a connection
1026 * Using this function makes sure the LoadBalancer knows the connection is closed.
1027 * If you use $conn->close() directly, the load balancer won't update its state.
1028 * @param DatabaseBase $conn
1030 public function closeConnection( $conn ) {
1032 foreach ( $this->mConns
as $i1 => $conns2 ) {
1033 foreach ( $conns2 as $i2 => $conns3 ) {
1034 foreach ( $conns3 as $i3 => $candidateConn ) {
1035 if ( $conn === $candidateConn ) {
1037 unset( $this->mConns
[$i1][$i2][$i3] );
1038 --$this->connsOpened
;
1051 * Commit transactions on all open connections
1052 * @param string $fname Caller name
1054 public function commitAll( $fname = __METHOD__
) {
1055 $this->forEachOpenConnection( function ( DatabaseBase
$conn ) use ( $fname ) {
1056 $conn->commit( $fname, 'flush' );
1061 * Perform all pre-commit callbacks that remain part of the atomic transactions
1062 * and disable any post-commit callbacks until runMasterPostCommitCallbacks()
1065 public function runMasterPreCommitCallbacks() {
1066 $this->forEachOpenMasterConnection( function ( DatabaseBase
$conn ) {
1067 // Any error will cause all DB transactions to be rolled back together.
1068 $conn->runOnTransactionPreCommitCallbacks();
1069 // Defer post-commit callbacks until COMMIT finishes for all DBs.
1070 $conn->setPostCommitCallbackSupression( true );
1075 * Perform all pre-commit checks for things like replication safety
1076 * @param array $options Includes:
1077 * - maxWriteDuration : max write query duration time in seconds
1078 * @throws DBTransactionError
1081 public function approveMasterChanges( array $options ) {
1082 $limit = isset( $options['maxWriteDuration'] ) ?
$options['maxWriteDuration'] : 0;
1083 $this->forEachOpenMasterConnection( function ( DatabaseBase
$conn ) use ( $limit ) {
1084 // Assert that the time to replicate the transaction will be sane.
1085 // If this fails, then all DB transactions will be rollback back together.
1086 $time = $conn->pendingWriteQueryDuration();
1087 if ( $limit > 0 && $time > $limit ) {
1088 throw new DBTransactionError(
1090 wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1097 * Issue COMMIT on all master connections where writes where done
1098 * @param string $fname Caller name
1100 public function commitMasterChanges( $fname = __METHOD__
) {
1101 $this->forEachOpenMasterConnection( function ( DatabaseBase
$conn ) use ( $fname ) {
1102 if ( $conn->writesOrCallbacksPending() ) {
1103 $conn->commit( $fname, 'flush' );
1109 * Issue all pending post-commit callbacks
1112 public function runMasterPostCommitCallbacks() {
1113 $this->forEachOpenMasterConnection( function ( DatabaseBase
$db ) {
1114 $db->setPostCommitCallbackSupression( false );
1115 $db->runOnTransactionIdleCallbacks( IDatabase
::TRIGGER_COMMIT
);
1120 * Issue ROLLBACK only on master, only if queries were done on connection
1121 * @param string $fname Caller name
1122 * @throws DBExpectedError
1125 public function rollbackMasterChanges( $fname = __METHOD__
) {
1126 $failedServers = [];
1128 $masterIndex = $this->getWriterIndex();
1129 foreach ( $this->mConns
as $conns2 ) {
1130 if ( empty( $conns2[$masterIndex] ) ) {
1133 /** @var DatabaseBase $conn */
1134 foreach ( $conns2[$masterIndex] as $conn ) {
1135 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1137 $conn->rollback( $fname, 'flush' );
1138 } catch ( DBError
$e ) {
1139 MWExceptionHandler
::logException( $e );
1140 $failedServers[] = $conn->getServer();
1146 if ( $failedServers ) {
1147 throw new DBExpectedError( null, "Rollback failed on server(s) " .
1148 implode( ', ', array_unique( $failedServers ) ) );
1153 * @return bool Whether a master connection is already open
1156 public function hasMasterConnection() {
1157 return $this->isOpen( $this->getWriterIndex() );
1161 * Determine if there are pending changes in a transaction by this thread
1165 public function hasMasterChanges() {
1166 $masterIndex = $this->getWriterIndex();
1167 foreach ( $this->mConns
as $conns2 ) {
1168 if ( empty( $conns2[$masterIndex] ) ) {
1171 /** @var DatabaseBase $conn */
1172 foreach ( $conns2[$masterIndex] as $conn ) {
1173 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1182 * Get the timestamp of the latest write query done by this thread
1184 * @return float|bool UNIX timestamp or false
1186 public function lastMasterChangeTimestamp() {
1188 $masterIndex = $this->getWriterIndex();
1189 foreach ( $this->mConns
as $conns2 ) {
1190 if ( empty( $conns2[$masterIndex] ) ) {
1193 /** @var DatabaseBase $conn */
1194 foreach ( $conns2[$masterIndex] as $conn ) {
1195 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1202 * Check if this load balancer object had any recent or still
1203 * pending writes issued against it by this PHP thread
1205 * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1209 public function hasOrMadeRecentMasterChanges( $age = null ) {
1210 $age = ( $age === null ) ?
$this->mWaitTimeout
: $age;
1212 return ( $this->hasMasterChanges()
1213 ||
$this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1217 * Get the list of callers that have pending master changes
1222 public function pendingMasterChangeCallers() {
1225 $masterIndex = $this->getWriterIndex();
1226 foreach ( $this->mConns
as $conns2 ) {
1227 if ( empty( $conns2[$masterIndex] ) ) {
1230 /** @var DatabaseBase $conn */
1231 foreach ( $conns2[$masterIndex] as $conn ) {
1232 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1240 * @param mixed $value
1243 public function waitTimeout( $value = null ) {
1244 return wfSetVar( $this->mWaitTimeout
, $value );
1248 * @note This method will trigger a DB connection if not yet done
1250 * @param string|bool $wiki Wiki ID, or false for the current wiki
1251 * @return bool Whether the generic connection for reads is highly "lagged"
1253 public function getLaggedSlaveMode( $wiki = false ) {
1254 // No-op if there is only one DB (also avoids recursion)
1255 if ( !$this->laggedSlaveMode
&& $this->getServerCount() > 1 ) {
1257 // See if laggedSlaveMode gets set
1258 $conn = $this->getConnection( DB_SLAVE
, false, $wiki );
1259 $this->reuseConnection( $conn );
1260 } catch ( DBConnectionError
$e ) {
1261 // Avoid expensive re-connect attempts and failures
1262 $this->slavesDownMode
= true;
1263 $this->laggedSlaveMode
= true;
1267 return $this->laggedSlaveMode
;
1271 * @note This method will never cause a new DB connection
1272 * @return bool Whether any generic connection used for reads was highly "lagged"
1275 public function laggedSlaveUsed() {
1276 return $this->laggedSlaveMode
;
1280 * @note This method may trigger a DB connection if not yet done
1281 * @param string|bool $wiki Wiki ID, or false for the current wiki
1282 * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1283 * @return string|bool Reason the master is read-only or false if it is not
1286 public function getReadOnlyReason( $wiki = false, DatabaseBase
$conn = null ) {
1287 if ( $this->readOnlyReason
!== false ) {
1288 return $this->readOnlyReason
;
1289 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1290 if ( $this->slavesDownMode
) {
1291 return 'The database has been automatically locked ' .
1292 'until the slave database servers become available';
1294 return 'The database has been automatically locked ' .
1295 'while the slave database servers catch up to the master.';
1297 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1298 return 'The database master is running in read-only mode.';
1305 * @param string $wiki Wiki ID, or false for the current wiki
1306 * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1309 private function masterRunningReadOnly( $wiki, DatabaseBase
$conn = null ) {
1310 $cache = $this->wanCache
;
1311 $masterServer = $this->getServerName( $this->getWriterIndex() );
1313 return (bool)$cache->getWithSetCallback(
1314 $cache->makeGlobalKey( __CLASS__
, 'server-read-only', $masterServer ),
1315 self
::TTL_CACHE_READONLY
,
1316 function () use ( $wiki, $conn ) {
1317 $this->trxProfiler
->setSilenced( true );
1319 $dbw = $conn ?
: $this->getConnection( DB_MASTER
, [], $wiki );
1320 $readOnly = (int)$dbw->serverIsReadOnly();
1321 } catch ( DBError
$e ) {
1324 $this->trxProfiler
->setSilenced( false );
1327 [ 'pcTTL' => $cache::TTL_PROC_LONG
, 'busyValue' => 0 ]
1332 * Disables/enables lag checks
1333 * @param null|bool $mode
1336 public function allowLagged( $mode = null ) {
1337 if ( $mode === null ) {
1338 return $this->mAllowLagged
;
1340 $this->mAllowLagged
= $mode;
1342 return $this->mAllowLagged
;
1348 public function pingAll() {
1350 $this->forEachOpenConnection( function ( DatabaseBase
$conn ) use ( &$success ) {
1351 if ( !$conn->ping() ) {
1360 * Call a function with each open connection object
1361 * @param callable $callback
1362 * @param array $params
1364 public function forEachOpenConnection( $callback, array $params = [] ) {
1365 foreach ( $this->mConns
as $connsByServer ) {
1366 foreach ( $connsByServer as $serverConns ) {
1367 foreach ( $serverConns as $conn ) {
1368 $mergedParams = array_merge( [ $conn ], $params );
1369 call_user_func_array( $callback, $mergedParams );
1376 * Call a function with each open connection object to a master
1377 * @param callable $callback
1378 * @param array $params
1381 public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1382 $masterIndex = $this->getWriterIndex();
1383 foreach ( $this->mConns
as $connsByServer ) {
1384 if ( isset( $connsByServer[$masterIndex] ) ) {
1385 /** @var DatabaseBase $conn */
1386 foreach ( $connsByServer[$masterIndex] as $conn ) {
1387 $mergedParams = array_merge( [ $conn ], $params );
1388 call_user_func_array( $callback, $mergedParams );
1395 * Get the hostname and lag time of the most-lagged slave
1397 * This is useful for maintenance scripts that need to throttle their updates.
1398 * May attempt to open connections to slaves on the default DB. If there is
1399 * no lag, the maximum lag will be reported as -1.
1401 * @param bool|string $wiki Wiki ID, or false for the default database
1402 * @return array ( host, max lag, index of max lagged host )
1404 public function getMaxLag( $wiki = false ) {
1409 if ( $this->getServerCount() <= 1 ) {
1410 return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1413 $lagTimes = $this->getLagTimes( $wiki );
1414 foreach ( $lagTimes as $i => $lag ) {
1415 if ( $this->mLoads
[$i] > 0 && $lag > $maxLag ) {
1417 $host = $this->mServers
[$i]['host'];
1422 return [ $host, $maxLag, $maxIndex ];
1426 * Get an estimate of replication lag (in seconds) for each server
1428 * Results are cached for a short time in memcached/process cache
1430 * Values may be "false" if replication is too broken to estimate
1432 * @param string|bool $wiki
1433 * @return int[] Map of (server index => float|int|bool)
1435 public function getLagTimes( $wiki = false ) {
1436 if ( $this->getServerCount() <= 1 ) {
1437 return [ 0 => 0 ]; // no replication = no lag
1440 # Send the request to the load monitor
1441 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers
), $wiki );
1445 * Get the lag in seconds for a given connection, or zero if this load
1446 * balancer does not have replication enabled.
1448 * This should be used in preference to Database::getLag() in cases where
1449 * replication may not be in use, since there is no way to determine if
1450 * replication is in use at the connection level without running
1451 * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1452 * function instead of Database::getLag() avoids a fatal error in this
1453 * case on many installations.
1455 * @param IDatabase $conn
1456 * @return int|bool Returns false on error
1458 public function safeGetLag( IDatabase
$conn ) {
1459 if ( $this->getServerCount() == 1 ) {
1462 return $conn->getLag();
1467 * Wait for a slave DB to reach a specified master position
1469 * This will connect to the master to get an accurate position if $pos is not given
1471 * @param IDatabase $conn Slave DB
1472 * @param DBMasterPos|bool $pos Master position; default: current position
1473 * @param integer $timeout Timeout in seconds
1474 * @return bool Success
1477 public function safeWaitForMasterPos( IDatabase
$conn, $pos = false, $timeout = 10 ) {
1478 if ( $this->getServerCount() == 1 ||
!$conn->getLBInfo( 'slave' ) ) {
1479 return true; // server is not a slave DB
1482 $pos = $pos ?
: $this->getConnection( DB_MASTER
)->getMasterPos();
1483 if ( !( $pos instanceof DBMasterPos
) ) {
1484 return false; // something is misconfigured
1487 $result = $conn->masterPosWait( $pos, $timeout );
1488 if ( $result == -1 ||
is_null( $result ) ) {
1489 $msg = __METHOD__
. ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1490 wfDebugLog( 'replication', "$msg\n" );
1491 wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1494 wfDebugLog( 'replication', __METHOD__
. ": Done\n" );
1502 * Clear the cache for slag lag delay times
1504 * This is only used for testing
1506 public function clearLagTimeCache() {
1507 $this->getLoadMonitor()->clearCaches();