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;
44 /** @var array LBFactory information */
46 /** @var string The LoadMonitor subclass name */
47 private $mLoadMonitorClass;
48 /** @var LoadMonitor */
49 private $mLoadMonitor;
51 /** @var bool|DatabaseBase Database connection that caused a problem */
52 private $mErrorConnection;
53 /** @var integer The generic (not query grouped) slave index (of $mServers) */
55 /** @var bool|DBMasterPos False if not set */
57 /** @var bool Whether the generic reader fell back to a lagged slave */
58 private $mLaggedSlaveMode;
59 /** @var string The last DB selection or connection error */
60 private $mLastError = 'Unknown error';
61 /** @var integer Total connections opened */
62 private $connsOpened = 0;
63 /** @var ProcessCacheLRU */
66 /** @var integer Warn when this many connection are held */
67 const CONN_HELD_WARN_THRESHOLD
= 10;
70 * @param array $params Array with keys:
71 * servers Required. Array of server info structures.
72 * loadMonitor Name of a class used to fetch server lag and load.
75 public function __construct( array $params ) {
76 if ( !isset( $params['servers'] ) ) {
77 throw new MWException( __CLASS__
. ': missing servers parameter' );
79 $this->mServers
= $params['servers'];
80 $this->mWaitTimeout
= 10;
82 $this->mReadIndex
= -1;
83 $this->mWriteIndex
= -1;
84 $this->mConns
= array(
86 'foreignUsed' => array(),
87 'foreignFree' => array() );
88 $this->mLoads
= array();
89 $this->mWaitForPos
= false;
90 $this->mLaggedSlaveMode
= false;
91 $this->mErrorConnection
= false;
92 $this->mAllowLagged
= false;
94 if ( isset( $params['loadMonitor'] ) ) {
95 $this->mLoadMonitorClass
= $params['loadMonitor'];
97 $master = reset( $params['servers'] );
98 if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
99 $this->mLoadMonitorClass
= 'LoadMonitorMySQL';
101 $this->mLoadMonitorClass
= 'LoadMonitorNull';
105 foreach ( $params['servers'] as $i => $server ) {
106 $this->mLoads
[$i] = $server['load'];
107 if ( isset( $server['groupLoads'] ) ) {
108 foreach ( $server['groupLoads'] as $group => $ratio ) {
109 if ( !isset( $this->mGroupLoads
[$group] ) ) {
110 $this->mGroupLoads
[$group] = array();
112 $this->mGroupLoads
[$group][$i] = $ratio;
117 $this->mProcCache
= new ProcessCacheLRU( 30 );
121 * Get a LoadMonitor instance
123 * @return LoadMonitor
125 private function getLoadMonitor() {
126 if ( !isset( $this->mLoadMonitor
) ) {
127 $class = $this->mLoadMonitorClass
;
128 $this->mLoadMonitor
= new $class( $this );
131 return $this->mLoadMonitor
;
135 * Get or set arbitrary data used by the parent object, usually an LBFactory
139 public function parentInfo( $x = null ) {
140 return wfSetVar( $this->mParentInfo
, $x );
144 * Given an array of non-normalised probabilities, this function will select
145 * an element and return the appropriate key
147 * @deprecated since 1.21, use ArrayUtils::pickRandom()
149 * @param array $weights
150 * @return bool|int|string
152 public function pickRandom( array $weights ) {
153 return ArrayUtils
::pickRandom( $weights );
157 * @param array $loads
158 * @param bool|string $wiki Wiki to get non-lagged for
159 * @param float $maxLag Restrict the maximum allowed lag to this many seconds
160 * @return bool|int|string
162 private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF
) {
163 $lags = $this->getLagTimes( $wiki );
165 # Unset excessively lagged servers
166 foreach ( $lags as $i => $lag ) {
168 $maxServerLag = $maxLag;
169 if ( isset( $this->mServers
[$i]['max lag'] ) ) {
170 $maxServerLag = min( $maxServerLag, $this->mServers
[$i]['max lag'] );
172 if ( $lag === false ) {
173 wfDebugLog( 'replication', "Server #$i is not replicating" );
175 } elseif ( $lag > $maxServerLag ) {
176 wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
182 # Find out if all the slaves with non-zero load are lagged
184 foreach ( $loads as $load ) {
188 # No appropriate DB servers except maybe the master and some slaves with zero load
189 # Do NOT use the master
190 # Instead, this function will return false, triggering read-only mode,
191 # and a lagged slave will be used instead.
195 if ( count( $loads ) == 0 ) {
199 #wfDebugLog( 'connect', var_export( $loads, true ) );
201 # Return a random representative of the remainder
202 return ArrayUtils
::pickRandom( $loads );
206 * Get the index of the reader connection, which may be a slave
207 * This takes into account load ratios and lag times. It should
208 * always return a consistent index during a given invocation
210 * Side effect: opens connections to databases
211 * @param string|bool $group Query group, or false for the generic reader
212 * @param string|bool $wiki Wiki ID, or false for the current wiki
213 * @throws MWException
214 * @return bool|int|string
216 public function getReaderIndex( $group = false, $wiki = false ) {
217 global $wgReadOnly, $wgDBtype;
219 # @todo FIXME: For now, only go through all this for mysql databases
220 if ( $wgDBtype != 'mysql' ) {
221 return $this->getWriterIndex();
224 if ( count( $this->mServers
) == 1 ) {
225 # Skip the load balancing if there's only one server
227 } elseif ( $group === false && $this->mReadIndex
>= 0 ) {
228 # Shortcut if generic reader exists already
229 return $this->mReadIndex
;
232 # Find the relevant load array
233 if ( $group !== false ) {
234 if ( isset( $this->mGroupLoads
[$group] ) ) {
235 $nonErrorLoads = $this->mGroupLoads
[$group];
237 # No loads for this group, return false and the caller can use some other group
238 wfDebug( __METHOD__
. ": no loads for group $group\n" );
243 $nonErrorLoads = $this->mLoads
;
246 if ( !count( $nonErrorLoads ) ) {
247 throw new MWException( "Empty server array given to LoadBalancer" );
250 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
251 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
253 $laggedSlaveMode = false;
255 # No server found yet
257 # First try quickly looking through the available servers for a server that
259 $currentLoads = $nonErrorLoads;
260 while ( count( $currentLoads ) ) {
261 if ( $wgReadOnly ||
$this->mAllowLagged ||
$laggedSlaveMode ) {
262 $i = ArrayUtils
::pickRandom( $currentLoads );
265 if ( $this->mWaitForPos
&& $this->mWaitForPos
->asOfTime() ) {
266 # ChronologyProtecter causes mWaitForPos to be set via sessions.
267 # This triggers doWait() after connect, so it's especially good to
268 # avoid lagged servers so as to avoid just blocking in that method.
269 $ago = microtime( true ) - $this->mWaitForPos
->asOfTime();
270 # Aim for <= 1 second of waiting (being too picky can backfire)
271 $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago +
1 );
273 if ( $i === false ) {
274 # Any server with less lag than it's 'max lag' param is preferable
275 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
277 if ( $i === false && count( $currentLoads ) != 0 ) {
278 # All slaves lagged. Switch to read-only mode
279 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
280 $wgReadOnly = 'The database has been automatically locked ' .
281 'while the slave database servers catch up to the master';
282 $i = ArrayUtils
::pickRandom( $currentLoads );
283 $laggedSlaveMode = true;
287 if ( $i === false ) {
288 # pickRandom() returned false
289 # This is permanent and means the configuration or the load monitor
290 # wants us to return false.
291 wfDebugLog( 'connect', __METHOD__
. ": pickRandom() returned false" );
296 wfDebugLog( 'connect', __METHOD__
.
297 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
299 $conn = $this->openConnection( $i, $wiki );
301 wfDebugLog( 'connect', __METHOD__
. ": Failed connecting to $i/$wiki" );
302 unset( $nonErrorLoads[$i] );
303 unset( $currentLoads[$i] );
308 // Decrement reference counter, we are finished with this connection.
309 // It will be incremented for the caller later.
310 if ( $wiki !== false ) {
311 $this->reuseConnection( $conn );
318 # If all servers were down, quit now
319 if ( !count( $nonErrorLoads ) ) {
320 wfDebugLog( 'connect', "All servers down" );
323 if ( $i !== false ) {
324 # Slave connection successful
325 # Wait for the session master pos for a short time
326 if ( $this->mWaitForPos
&& $i > 0 ) {
327 if ( !$this->doWait( $i ) ) {
328 $this->mServers
[$i]['slave pos'] = $conn->getSlavePos();
331 if ( $this->mReadIndex
<= 0 && $this->mLoads
[$i] > 0 && $group === false ) {
332 $this->mReadIndex
= $i;
334 $serverName = $this->getServerName( $i );
335 wfDebug( __METHOD__
. ": using server $serverName for group '$group'\n" );
342 * Set the master wait position
343 * If a DB_SLAVE connection has been opened already, waits
344 * Otherwise sets a variable telling it to wait if such a connection is opened
345 * @param DBMasterPos $pos
347 public function waitFor( $pos ) {
348 $this->mWaitForPos
= $pos;
349 $i = $this->mReadIndex
;
352 if ( !$this->doWait( $i ) ) {
353 $this->mServers
[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
354 $this->mLaggedSlaveMode
= true;
360 * Set the master wait position and wait for ALL slaves to catch up to it
361 * @param DBMasterPos $pos
362 * @param int $timeout Max seconds to wait; default is mWaitTimeout
363 * @return bool Success (able to connect and no timeouts reached)
365 public function waitForAll( $pos, $timeout = null ) {
366 $this->mWaitForPos
= $pos;
367 $serverCount = count( $this->mServers
);
370 for ( $i = 1; $i < $serverCount; $i++
) {
371 if ( $this->mLoads
[$i] > 0 ) {
372 $ok = $this->doWait( $i, true, $timeout ) && $ok;
380 * Get any open connection to a given server index, local or foreign
381 * Returns false if there is no connection open
384 * @return DatabaseBase|bool False on failure
386 public function getAnyOpenConnection( $i ) {
387 foreach ( $this->mConns
as $conns ) {
388 if ( !empty( $conns[$i] ) ) {
389 return reset( $conns[$i] );
397 * Wait for a given slave to catch up to the master pos stored in $this
398 * @param int $index Server index
399 * @param bool $open Check the server even if a new connection has to be made
400 * @param int $timeout Max seconds to wait; default is mWaitTimeout
403 protected function doWait( $index, $open = false, $timeout = null ) {
404 $close = false; // close the connection afterwards
406 # Find a connection to wait on, creating one if needed and allowed
407 $conn = $this->getAnyOpenConnection( $index );
410 wfDebug( __METHOD__
. ": no connection open\n" );
414 $conn = $this->openConnection( $index, '' );
416 wfDebug( __METHOD__
. ": failed to open connection\n" );
420 // Avoid connection spam in waitForAll() when connections
421 // are made just for the sake of doing this lag check.
426 wfDebug( __METHOD__
. ": Waiting for slave #$index to catch up...\n" );
427 $timeout = $timeout ?
: $this->mWaitTimeout
;
428 $result = $conn->masterPosWait( $this->mWaitForPos
, $timeout );
430 if ( $result == -1 ||
is_null( $result ) ) {
431 # Timed out waiting for slave, use master instead
432 $server = $this->mServers
[$index]['host'];
433 $msg = __METHOD__
. ": Timed out waiting on $server pos {$this->mWaitForPos}";
435 wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
438 wfDebug( __METHOD__
. ": Done\n" );
443 $this->closeConnection( $conn );
450 * Get a connection by index
451 * This is the main entry point for this class.
453 * @param int $i Server index
454 * @param array|string|bool $groups Query group(s), or false for the generic reader
455 * @param string|bool $wiki Wiki ID, or false for the current wiki
457 * @throws MWException
458 * @return DatabaseBase
460 public function getConnection( $i, $groups = array(), $wiki = false ) {
461 if ( $i === null ||
$i === false ) {
462 throw new MWException( 'Attempt to call ' . __METHOD__
.
463 ' with invalid server index' );
466 if ( $wiki === wfWikiID() ) {
470 $groups = ( $groups === false ||
$groups === array() )
471 ?
array( false ) // check one "group": the generic pool
474 $masterOnly = ( $i == DB_MASTER ||
$i == $this->getWriterIndex() );
475 $oldConnsOpened = $this->connsOpened
; // connections open now
477 if ( $i == DB_MASTER
) {
478 $i = $this->getWriterIndex();
480 # Try to find an available server in any the query groups (in order)
481 foreach ( $groups as $group ) {
482 $groupIndex = $this->getReaderIndex( $group, $wiki );
483 if ( $groupIndex !== false ) {
490 # Operation-based index
491 if ( $i == DB_SLAVE
) {
492 $this->mLastError
= 'Unknown error'; // reset error string
493 # Try the general server pool if $groups are unavailable.
494 $i = in_array( false, $groups, true )
495 ?
false // don't bother with this if that is what was tried above
496 : $this->getReaderIndex( false, $wiki );
497 # Couldn't find a working server in getReaderIndex()?
498 if ( $i === false ) {
499 $this->mLastError
= 'No working slave server: ' . $this->mLastError
;
501 return $this->reportConnectionError();
505 # Now we have an explicit index into the servers array
506 $conn = $this->openConnection( $i, $wiki );
509 return $this->reportConnectionError();
512 # Profile any new connections that happen
513 if ( $this->connsOpened
> $oldConnsOpened ) {
514 $host = $conn->getServer();
515 $dbname = $conn->getDBname();
516 $trxProf = Profiler
::instance()->getTransactionProfiler();
517 $trxProf->recordConnection( $host, $dbname, $masterOnly );
524 * Mark a foreign connection as being available for reuse under a different
525 * DB name or prefix. This mechanism is reference-counted, and must be called
526 * the same number of times as getConnection() to work.
528 * @param DatabaseBase $conn
529 * @throws MWException
531 public function reuseConnection( $conn ) {
532 $serverIndex = $conn->getLBInfo( 'serverIndex' );
533 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
534 if ( $serverIndex === null ||
$refCount === null ) {
535 wfDebug( __METHOD__
. ": this connection was not opened as a foreign connection\n" );
538 * This can happen in code like:
539 * foreach ( $dbs as $db ) {
540 * $conn = $lb->getConnection( DB_SLAVE, array(), $db );
542 * $lb->reuseConnection( $conn );
544 * When a connection to the local DB is opened in this way, reuseConnection()
551 $dbName = $conn->getDBname();
552 $prefix = $conn->tablePrefix();
553 if ( strval( $prefix ) !== '' ) {
554 $wiki = "$dbName-$prefix";
558 if ( $this->mConns
['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
559 throw new MWException( __METHOD__
. ": connection not found, has " .
560 "the connection been freed already?" );
562 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
563 if ( $refCount <= 0 ) {
564 $this->mConns
['foreignFree'][$serverIndex][$wiki] = $conn;
565 unset( $this->mConns
['foreignUsed'][$serverIndex][$wiki] );
566 wfDebug( __METHOD__
. ": freed connection $serverIndex/$wiki\n" );
568 wfDebug( __METHOD__
. ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
573 * Get a database connection handle reference
575 * The handle's methods wrap simply wrap those of a DatabaseBase handle
577 * @see LoadBalancer::getConnection() for parameter information
580 * @param array|string|bool $groups Query group(s), or false for the generic reader
581 * @param string|bool $wiki Wiki ID, or false for the current wiki
584 public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
585 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
589 * Get a database connection handle reference without connecting yet
591 * The handle's methods wrap simply wrap those of a DatabaseBase handle
593 * @see LoadBalancer::getConnection() for parameter information
596 * @param array|string|bool $groups Query group(s), or false for the generic reader
597 * @param string|bool $wiki Wiki ID, or false for the current wiki
600 public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
601 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
605 * Open a connection to the server given by the specified index
606 * Index must be an actual index into the array.
607 * If the server is already open, returns it.
609 * On error, returns false, and the connection which caused the
610 * error will be available via $this->mErrorConnection.
612 * @param int $i Server index
613 * @param string|bool $wiki Wiki ID, or false for the current wiki
614 * @return DatabaseBase
618 public function openConnection( $i, $wiki = false ) {
619 if ( $wiki !== false ) {
620 $conn = $this->openForeignConnection( $i, $wiki );
624 if ( isset( $this->mConns
['local'][$i][0] ) ) {
625 $conn = $this->mConns
['local'][$i][0];
627 $server = $this->mServers
[$i];
628 $server['serverIndex'] = $i;
629 $conn = $this->reallyOpenConnection( $server, false );
630 if ( $conn->isOpen() ) {
631 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
632 $this->mConns
['local'][$i][0] = $conn;
634 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
635 $this->mErrorConnection
= $conn;
644 * Open a connection to a foreign DB, or return one if it is already open.
646 * Increments a reference count on the returned connection which locks the
647 * connection to the requested wiki. This reference count can be
648 * decremented by calling reuseConnection().
650 * If a connection is open to the appropriate server already, but with the wrong
651 * database, it will be switched to the right database and returned, as long as
652 * it has been freed first with reuseConnection().
654 * On error, returns false, and the connection which caused the
655 * error will be available via $this->mErrorConnection.
657 * @param int $i Server index
658 * @param string $wiki Wiki ID to open
659 * @return DatabaseBase
661 private function openForeignConnection( $i, $wiki ) {
662 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
663 if ( isset( $this->mConns
['foreignUsed'][$i][$wiki] ) ) {
664 // Reuse an already-used connection
665 $conn = $this->mConns
['foreignUsed'][$i][$wiki];
666 wfDebug( __METHOD__
. ": reusing connection $i/$wiki\n" );
667 } elseif ( isset( $this->mConns
['foreignFree'][$i][$wiki] ) ) {
668 // Reuse a free connection for the same wiki
669 $conn = $this->mConns
['foreignFree'][$i][$wiki];
670 unset( $this->mConns
['foreignFree'][$i][$wiki] );
671 $this->mConns
['foreignUsed'][$i][$wiki] = $conn;
672 wfDebug( __METHOD__
. ": reusing free connection $i/$wiki\n" );
673 } elseif ( !empty( $this->mConns
['foreignFree'][$i] ) ) {
674 // Reuse a connection from another wiki
675 $conn = reset( $this->mConns
['foreignFree'][$i] );
676 $oldWiki = key( $this->mConns
['foreignFree'][$i] );
678 // The empty string as a DB name means "don't care".
679 // DatabaseMysqlBase::open() already handle this on connection.
680 if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
681 $this->mLastError
= "Error selecting database $dbName on server " .
682 $conn->getServer() . " from client host " . wfHostname() . "\n";
683 $this->mErrorConnection
= $conn;
686 $conn->tablePrefix( $prefix );
687 unset( $this->mConns
['foreignFree'][$i][$oldWiki] );
688 $this->mConns
['foreignUsed'][$i][$wiki] = $conn;
689 wfDebug( __METHOD__
. ": reusing free connection from $oldWiki for $wiki\n" );
692 // Open a new connection
693 $server = $this->mServers
[$i];
694 $server['serverIndex'] = $i;
695 $server['foreignPoolRefCount'] = 0;
696 $server['foreign'] = true;
697 $conn = $this->reallyOpenConnection( $server, $dbName );
698 if ( !$conn->isOpen() ) {
699 wfDebug( __METHOD__
. ": error opening connection for $i/$wiki\n" );
700 $this->mErrorConnection
= $conn;
703 $conn->tablePrefix( $prefix );
704 $this->mConns
['foreignUsed'][$i][$wiki] = $conn;
705 wfDebug( __METHOD__
. ": opened new connection for $i/$wiki\n" );
709 // Increment reference count
711 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
712 $conn->setLBInfo( 'foreignPoolRefCount', $refCount +
1 );
719 * Test if the specified index represents an open connection
721 * @param int $index Server index
725 private function isOpen( $index ) {
726 if ( !is_integer( $index ) ) {
730 return (bool)$this->getAnyOpenConnection( $index );
734 * Really opens a connection. Uncached.
735 * Returns a Database object whether or not the connection was successful.
738 * @param array $server
739 * @param bool $dbNameOverride
740 * @throws MWException
741 * @return DatabaseBase
743 protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
744 if ( !is_array( $server ) ) {
745 throw new MWException( 'You must update your load-balancing configuration. ' .
746 'See DefaultSettings.php entry for $wgDBservers.' );
749 if ( $dbNameOverride !== false ) {
750 $server['dbname'] = $dbNameOverride;
753 // Log when many connection are made on requests
754 if ( ++
$this->connsOpened
>= self
::CONN_HELD_WARN_THRESHOLD
) {
755 $masterAddr = $this->getServerName( 0 );
756 wfDebugLog( 'DBPerformance', __METHOD__
. ": " .
757 "{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
758 wfBacktrace( true ) );
763 $db = DatabaseBase
::factory( $server['type'], $server );
764 } catch ( DBConnectionError
$e ) {
765 // FIXME: This is probably the ugliest thing I have ever done to
766 // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
770 $db->setLBInfo( $server );
771 if ( isset( $server['fakeSlaveLag'] ) ) {
772 $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
774 if ( isset( $server['fakeMaster'] ) ) {
775 $db->setFakeMaster( true );
782 * @throws DBConnectionError
785 private function reportConnectionError() {
786 $conn = $this->mErrorConnection
; // The connection which caused the error
788 'method' => __METHOD__
,
789 'last_error' => $this->mLastError
,
792 if ( !is_object( $conn ) ) {
793 // No last connection, probably due to all servers being too busy
795 "LB failure with no last connection. Connection error: {last_error}",
799 // If all servers were busy, mLastError will contain something sensible
800 throw new DBConnectionError( null, $this->mLastError
);
802 $context['db_server'] = $conn->getProperty( 'mServer' );
804 "Connection error: {last_error} ({db_server})",
807 $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
810 return false; /* not reached */
816 private function getWriterIndex() {
821 * Returns true if the specified index is a valid server index
826 public function haveIndex( $i ) {
827 return array_key_exists( $i, $this->mServers
);
831 * Returns true if the specified index is valid and has non-zero load
836 public function isNonZeroLoad( $i ) {
837 return array_key_exists( $i, $this->mServers
) && $this->mLoads
[$i] != 0;
841 * Get the number of defined servers (not the number of open connections)
845 public function getServerCount() {
846 return count( $this->mServers
);
850 * Get the host name or IP address of the server with the specified index
851 * Prefer a readable name if available.
855 public function getServerName( $i ) {
856 if ( isset( $this->mServers
[$i]['hostName'] ) ) {
857 return $this->mServers
[$i]['hostName'];
858 } elseif ( isset( $this->mServers
[$i]['host'] ) ) {
859 return $this->mServers
[$i]['host'];
866 * Return the server info structure for a given index, or false if the index is invalid.
870 public function getServerInfo( $i ) {
871 if ( isset( $this->mServers
[$i] ) ) {
872 return $this->mServers
[$i];
879 * Sets the server info structure for the given index. Entry at index $i
880 * is created if it doesn't exist
882 * @param array $serverInfo
884 public function setServerInfo( $i, array $serverInfo ) {
885 $this->mServers
[$i] = $serverInfo;
889 * Get the current master position for chronology control purposes
892 public function getMasterPos() {
893 # If this entire request was served from a slave without opening a connection to the
894 # master (however unlikely that may be), then we can fetch the position from the slave.
895 $masterConn = $this->getAnyOpenConnection( 0 );
896 if ( !$masterConn ) {
897 $serverCount = count( $this->mServers
);
898 for ( $i = 1; $i < $serverCount; $i++
) {
899 $conn = $this->getAnyOpenConnection( $i );
901 wfDebug( "Master pos fetched from slave\n" );
903 return $conn->getSlavePos();
907 wfDebug( "Master pos fetched from master\n" );
909 return $masterConn->getMasterPos();
916 * Close all open connections
918 public function closeAll() {
919 foreach ( $this->mConns
as $conns2 ) {
920 foreach ( $conns2 as $conns3 ) {
921 /** @var DatabaseBase $conn */
922 foreach ( $conns3 as $conn ) {
927 $this->mConns
= array(
929 'foreignFree' => array(),
930 'foreignUsed' => array(),
932 $this->connsOpened
= 0;
937 * Using this function makes sure the LoadBalancer knows the connection is closed.
938 * If you use $conn->close() directly, the load balancer won't update its state.
939 * @param DatabaseBase $conn
941 public function closeConnection( $conn ) {
943 foreach ( $this->mConns
as $i1 => $conns2 ) {
944 foreach ( $conns2 as $i2 => $conns3 ) {
945 foreach ( $conns3 as $i3 => $candidateConn ) {
946 if ( $conn === $candidateConn ) {
948 unset( $this->mConns
[$i1][$i2][$i3] );
949 --$this->connsOpened
;
962 * Commit transactions on all open connections
964 public function commitAll() {
965 foreach ( $this->mConns
as $conns2 ) {
966 foreach ( $conns2 as $conns3 ) {
967 /** @var DatabaseBase[] $conns3 */
968 foreach ( $conns3 as $conn ) {
969 if ( $conn->trxLevel() ) {
970 $conn->commit( __METHOD__
, 'flush' );
978 * Issue COMMIT only on master, only if queries were done on connection
980 public function commitMasterChanges() {
981 // Always 0, but who knows.. :)
982 $masterIndex = $this->getWriterIndex();
983 foreach ( $this->mConns
as $conns2 ) {
984 if ( empty( $conns2[$masterIndex] ) ) {
987 /** @var DatabaseBase $conn */
988 foreach ( $conns2[$masterIndex] as $conn ) {
989 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
990 $conn->commit( __METHOD__
, 'flush' );
997 * Issue ROLLBACK only on master, only if queries were done on connection
1000 public function rollbackMasterChanges() {
1001 // Always 0, but who knows.. :)
1002 $masterIndex = $this->getWriterIndex();
1003 foreach ( $this->mConns
as $conns2 ) {
1004 if ( empty( $conns2[$masterIndex] ) ) {
1007 /** @var DatabaseBase $conn */
1008 foreach ( $conns2[$masterIndex] as $conn ) {
1009 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1010 $conn->rollback( __METHOD__
, 'flush' );
1017 * @return bool Whether a master connection is already open
1020 public function hasMasterConnection() {
1021 return $this->isOpen( $this->getWriterIndex() );
1025 * Determine if there are any pending changes that need to be rolled back
1030 public function hasMasterChanges() {
1031 // Always 0, but who knows.. :)
1032 $masterIndex = $this->getWriterIndex();
1033 foreach ( $this->mConns
as $conns2 ) {
1034 if ( empty( $conns2[$masterIndex] ) ) {
1037 /** @var DatabaseBase $conn */
1038 foreach ( $conns2[$masterIndex] as $conn ) {
1039 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1048 * @param mixed $value
1051 public function waitTimeout( $value = null ) {
1052 return wfSetVar( $this->mWaitTimeout
, $value );
1058 public function getLaggedSlaveMode() {
1059 return $this->mLaggedSlaveMode
;
1063 * Disables/enables lag checks
1064 * @param null|bool $mode
1067 public function allowLagged( $mode = null ) {
1068 if ( $mode === null ) {
1069 return $this->mAllowLagged
;
1071 $this->mAllowLagged
= $mode;
1073 return $this->mAllowLagged
;
1079 public function pingAll() {
1081 foreach ( $this->mConns
as $conns2 ) {
1082 foreach ( $conns2 as $conns3 ) {
1083 /** @var DatabaseBase[] $conns3 */
1084 foreach ( $conns3 as $conn ) {
1085 if ( !$conn->ping() ) {
1096 * Call a function with each open connection object
1097 * @param callable $callback
1098 * @param array $params
1100 public function forEachOpenConnection( $callback, array $params = array() ) {
1101 foreach ( $this->mConns
as $conns2 ) {
1102 foreach ( $conns2 as $conns3 ) {
1103 foreach ( $conns3 as $conn ) {
1104 $mergedParams = array_merge( array( $conn ), $params );
1105 call_user_func_array( $callback, $mergedParams );
1112 * Get the hostname and lag time of the most-lagged slave
1114 * This is useful for maintenance scripts that need to throttle their updates.
1115 * May attempt to open connections to slaves on the default DB. If there is
1116 * no lag, the maximum lag will be reported as -1.
1118 * @param bool|string $wiki Wiki ID, or false for the default database
1119 * @return array ( host, max lag, index of max lagged host )
1121 public function getMaxLag( $wiki = false ) {
1126 if ( $this->getServerCount() <= 1 ) {
1127 return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1130 $lagTimes = $this->getLagTimes( $wiki );
1131 foreach ( $lagTimes as $i => $lag ) {
1132 if ( $lag > $maxLag ) {
1134 $host = $this->mServers
[$i]['host'];
1139 return array( $host, $maxLag, $maxIndex );
1143 * Get lag time for each server
1145 * Results are cached for a short time in memcached/process cache
1147 * @param string|bool $wiki
1148 * @return int[] Map of (server index => seconds)
1150 public function getLagTimes( $wiki = false ) {
1151 if ( $this->getServerCount() <= 1 ) {
1152 return array( 0 => 0 ); // no replication = no lag
1155 if ( $this->mProcCache
->has( 'slave_lag', 'times', 1 ) ) {
1156 return $this->mProcCache
->get( 'slave_lag', 'times' );
1159 # Send the request to the load monitor
1160 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers
), $wiki );
1162 $this->mProcCache
->set( 'slave_lag', 'times', $times );
1168 * Get the lag in seconds for a given connection, or zero if this load
1169 * balancer does not have replication enabled.
1171 * This should be used in preference to Database::getLag() in cases where
1172 * replication may not be in use, since there is no way to determine if
1173 * replication is in use at the connection level without running
1174 * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1175 * function instead of Database::getLag() avoids a fatal error in this
1176 * case on many installations.
1178 * @param DatabaseBase $conn
1181 public function safeGetLag( $conn ) {
1182 if ( $this->getServerCount() == 1 ) {
1185 return $conn->getLag();
1190 * Clear the cache for slag lag delay times
1192 public function clearLagTimeCache() {
1193 $this->mProcCache
->clear( 'slave_lag' );
1198 * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1199 * as well handling deferring the actual network connection until the handle is used
1204 class DBConnRef
implements IDatabase
{
1205 /** @var LoadBalancer */
1208 /** @var DatabaseBase|null */
1211 /** @var array|null */
1215 * @param LoadBalancer $lb
1216 * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1218 public function __construct( LoadBalancer
$lb, $conn ) {
1220 if ( $conn instanceof DatabaseBase
) {
1221 $this->conn
= $conn;
1223 $this->params
= $conn;
1227 public function __call( $name, $arguments ) {
1228 if ( $this->conn
=== null ) {
1229 list( $db, $groups, $wiki ) = $this->params
;
1230 $this->conn
= $this->lb
->getConnection( $db, $groups, $wiki );
1233 return call_user_func_array( array( $this->conn
, $name ), $arguments );
1236 public function __destruct() {
1237 if ( $this->conn
!== null ) {
1238 $this->lb
->reuseConnection( $this->conn
);