3 * Object caching using a SQL database.
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
24 use MediaWiki\MediaWikiServices
;
25 use Wikimedia\Rdbms\Database
;
26 use Wikimedia\Rdbms\IDatabase
;
27 use Wikimedia\Rdbms\DBError
;
28 use Wikimedia\Rdbms\DBQueryError
;
29 use Wikimedia\Rdbms\DBConnectionError
;
30 use Wikimedia\Rdbms\LoadBalancer
;
31 use Wikimedia\ScopedCallback
;
32 use Wikimedia\WaitConditionLoop
;
35 * Class to store objects in the database
39 class SqlBagOStuff
extends BagOStuff
{
40 /** @var array[] (server index => server config) */
41 protected $serverInfos;
42 /** @var string[] (server index => tag/host name) */
43 protected $serverTags;
45 protected $numServers;
47 protected $lastExpireAll = 0;
49 protected $purgePeriod = 100;
51 protected $shards = 1;
53 protected $tableName = 'objectcache';
55 protected $replicaOnly = false;
57 protected $syncTimeout = 3;
59 /** @var LoadBalancer|null */
60 protected $separateMainLB;
63 /** @var array UNIX timestamps */
64 protected $connFailureTimes = [];
65 /** @var array Exceptions */
66 protected $connFailureErrors = [];
69 * Constructor. Parameters are:
70 * - server: A server info structure in the format required by each
71 * element in $wgDBServers.
73 * - servers: An array of server info structures describing a set of database servers
74 * to distribute keys to. If this is specified, the "server" option will be
75 * ignored. If string keys are used, then they will be used for consistent
76 * hashing *instead* of the host name (from the server config). This is useful
77 * when a cluster is replicated to another site (with different host names)
78 * but each server has a corresponding replica in the other cluster.
80 * - purgePeriod: The average number of object cache requests in between
81 * garbage collection operations, where expired entries
82 * are removed from the database. Or in other words, the
83 * reciprocal of the probability of purging on any given
84 * request. If this is set to zero, purging will never be
87 * - tableName: The table name to use, default is "objectcache".
89 * - shards: The number of tables to use for data storage on each server.
90 * If this is more than 1, table names will be formed in the style
91 * objectcacheNNN where NNN is the shard index, between 0 and
92 * shards-1. The number of digits will be the minimum number
93 * required to hold the largest shard index. Data will be
94 * distributed across all tables by key hash. This is for
95 * MySQL bugs 61735 and 61736.
96 * - slaveOnly: Whether to only use replica DBs and avoid triggering
97 * garbage collection logic of expired items. This only
98 * makes sense if the primary DB is used and only if get()
99 * calls will be used. This is used by ReplicatedBagOStuff.
100 * - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
102 * @param array $params
104 public function __construct( $params ) {
105 parent
::__construct( $params );
107 $this->attrMap
[self
::ATTR_EMULATION
] = self
::QOS_EMULATION_SQL
;
108 $this->attrMap
[self
::ATTR_SYNCWRITES
] = self
::QOS_SYNCWRITES_NONE
;
110 if ( isset( $params['servers'] ) ) {
111 $this->serverInfos
= [];
112 $this->serverTags
= [];
113 $this->numServers
= count( $params['servers'] );
115 foreach ( $params['servers'] as $tag => $info ) {
116 $this->serverInfos
[$index] = $info;
117 if ( is_string( $tag ) ) {
118 $this->serverTags
[$index] = $tag;
120 $this->serverTags
[$index] = $info['host'] ??
"#$index";
124 } elseif ( isset( $params['server'] ) ) {
125 $this->serverInfos
= [ $params['server'] ];
126 $this->numServers
= count( $this->serverInfos
);
128 // Default to using the main wiki's database servers
129 $this->serverInfos
= false;
130 $this->numServers
= 1;
131 $this->attrMap
[self
::ATTR_SYNCWRITES
] = self
::QOS_SYNCWRITES_BE
;
133 if ( isset( $params['purgePeriod'] ) ) {
134 $this->purgePeriod
= intval( $params['purgePeriod'] );
136 if ( isset( $params['tableName'] ) ) {
137 $this->tableName
= $params['tableName'];
139 if ( isset( $params['shards'] ) ) {
140 $this->shards
= intval( $params['shards'] );
142 if ( isset( $params['syncTimeout'] ) ) {
143 $this->syncTimeout
= $params['syncTimeout'];
145 $this->replicaOnly
= !empty( $params['slaveOnly'] );
149 * Get a connection to the specified database
151 * @param int $serverIndex
153 * @throws MWException
155 protected function getDB( $serverIndex ) {
156 if ( !isset( $this->conns
[$serverIndex] ) ) {
157 if ( $serverIndex >= $this->numServers
) {
158 throw new MWException( __METHOD__
. ": Invalid server index \"$serverIndex\"" );
161 # Don't keep timing out trying to connect for each call if the DB is down
162 if ( isset( $this->connFailureErrors
[$serverIndex] )
163 && ( time() - $this->connFailureTimes
[$serverIndex] ) < 60
165 throw $this->connFailureErrors
[$serverIndex];
168 if ( $this->serverInfos
) {
169 // Use custom database defined by server connection info
170 $info = $this->serverInfos
[$serverIndex];
171 $type = $info['type'] ??
'mysql';
172 $host = $info['host'] ??
'[unknown]';
173 $this->logger
->debug( __CLASS__
. ": connecting to $host" );
174 $db = Database
::factory( $type, $info );
175 $db->clearFlag( DBO_TRX
); // auto-commit mode
177 // Use the main LB database
178 $lb = MediaWikiServices
::getInstance()->getDBLoadBalancer();
179 $index = $this->replicaOnly ? DB_REPLICA
: DB_MASTER
;
180 if ( $lb->getServerType( $lb->getWriterIndex() ) !== 'sqlite' ) {
181 // Keep a separate connection to avoid contention and deadlocks
182 $db = $lb->getConnection( $index, [], false, $lb::CONN_TRX_AUTOCOMMIT
);
184 // However, SQLite has the opposite behavior due to DB-level locking.
185 // Stock sqlite MediaWiki installs use a separate sqlite cache DB instead.
186 $db = $lb->getConnection( $index );
190 $this->logger
->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
191 $this->conns
[$serverIndex] = $db;
194 return $this->conns
[$serverIndex];
198 * Get the server index and table name for a given key
200 * @return array Server index and table name
202 protected function getTableByKey( $key ) {
203 if ( $this->shards
> 1 ) {
204 $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
205 $tableIndex = $hash %
$this->shards
;
209 if ( $this->numServers
> 1 ) {
210 $sortedServers = $this->serverTags
;
211 ArrayUtils
::consistentHashSort( $sortedServers, $key );
212 reset( $sortedServers );
213 $serverIndex = key( $sortedServers );
217 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
221 * Get the table name for a given shard index
225 protected function getTableNameByShard( $index ) {
226 if ( $this->shards
> 1 ) {
227 $decimals = strlen( $this->shards
- 1 );
228 return $this->tableName
.
229 sprintf( "%0{$decimals}d", $index );
231 return $this->tableName
;
235 protected function doGet( $key, $flags = 0 ) {
238 return $this->getWithToken( $key, $casToken, $flags );
241 protected function getWithToken( $key, &$casToken, $flags = 0 ) {
242 $values = $this->getMulti( [ $key ] );
243 if ( array_key_exists( $key, $values ) ) {
244 $casToken = $values[$key];
245 return $values[$key];
250 public function getMulti( array $keys, $flags = 0 ) {
251 $values = []; // array of (key => value)
254 foreach ( $keys as $key ) {
255 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
256 $keysByTable[$serverIndex][$tableName][] = $key;
259 $this->garbageCollect(); // expire old entries if any
262 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
264 $db = $this->getDB( $serverIndex );
265 foreach ( $serverKeys as $tableName => $tableKeys ) {
266 $res = $db->select( $tableName,
267 [ 'keyname', 'value', 'exptime' ],
268 [ 'keyname' => $tableKeys ],
270 // Approximate write-on-the-fly BagOStuff API via blocking.
271 // This approximation fails if a ROLLBACK happens (which is rare).
272 // We do not want to flush the TRX as that can break callers.
273 $db->trxLevel() ?
[ 'LOCK IN SHARE MODE' ] : []
275 if ( $res === false ) {
278 foreach ( $res as $row ) {
279 $row->serverIndex
= $serverIndex;
280 $row->tableName
= $tableName;
281 $dataRows[$row->keyname
] = $row;
284 } catch ( DBError
$e ) {
285 $this->handleReadError( $e, $serverIndex );
289 foreach ( $keys as $key ) {
290 if ( isset( $dataRows[$key] ) ) { // HIT?
291 $row = $dataRows[$key];
292 $this->debug( "get: retrieved data; expiry time is " . $row->exptime
);
295 $db = $this->getDB( $row->serverIndex
);
296 if ( $this->isExpired( $db, $row->exptime
) ) { // MISS
297 $this->debug( "get: key has expired" );
299 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value
) );
301 } catch ( DBQueryError
$e ) {
302 $this->handleWriteError( $e, $db, $row->serverIndex
);
305 $this->debug( 'get: no matching rows' );
312 public function setMulti( array $data, $expiry = 0 ) {
314 foreach ( $data as $key => $value ) {
315 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
316 $keysByTable[$serverIndex][$tableName][] = $key;
319 $this->garbageCollect(); // expire old entries if any
322 $exptime = (int)$expiry;
323 $silenceScope = $this->silenceTransactionProfiler();
324 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
327 $db = $this->getDB( $serverIndex );
328 } catch ( DBError
$e ) {
329 $this->handleWriteError( $e, $db, $serverIndex );
334 if ( $exptime < 0 ) {
338 if ( $exptime == 0 ) {
339 $encExpiry = $this->getMaxDateTime( $db );
341 $exptime = $this->convertExpiry( $exptime );
342 $encExpiry = $db->timestamp( $exptime );
344 foreach ( $serverKeys as $tableName => $tableKeys ) {
346 foreach ( $tableKeys as $key ) {
349 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
350 'exptime' => $encExpiry,
361 } catch ( DBError
$e ) {
362 $this->handleWriteError( $e, $db, $serverIndex );
373 public function set( $key, $value, $exptime = 0, $flags = 0 ) {
374 $ok = $this->setMulti( [ $key => $value ], $exptime );
375 if ( ( $flags & self
::WRITE_SYNC
) == self
::WRITE_SYNC
) {
376 $ok = $this->waitForReplication() && $ok;
382 protected function cas( $casToken, $key, $value, $exptime = 0 ) {
383 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
385 $silenceScope = $this->silenceTransactionProfiler();
387 $db = $this->getDB( $serverIndex );
388 $exptime = intval( $exptime );
390 if ( $exptime < 0 ) {
394 if ( $exptime == 0 ) {
395 $encExpiry = $this->getMaxDateTime( $db );
397 $exptime = $this->convertExpiry( $exptime );
398 $encExpiry = $db->timestamp( $exptime );
400 // (T26425) use a replace if the db supports it instead of
401 // delete/insert to avoid clashes with conflicting keynames
406 'value' => $db->encodeBlob( $this->serialize( $value ) ),
407 'exptime' => $encExpiry
411 'value' => $db->encodeBlob( $this->serialize( $casToken ) )
415 } catch ( DBQueryError
$e ) {
416 $this->handleWriteError( $e, $db, $serverIndex );
421 return (bool)$db->affectedRows();
424 public function delete( $key ) {
425 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
427 $silenceScope = $this->silenceTransactionProfiler();
429 $db = $this->getDB( $serverIndex );
432 [ 'keyname' => $key ],
434 } catch ( DBError
$e ) {
435 $this->handleWriteError( $e, $db, $serverIndex );
442 public function incr( $key, $step = 1 ) {
443 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
445 $silenceScope = $this->silenceTransactionProfiler();
447 $db = $this->getDB( $serverIndex );
448 $step = intval( $step );
449 $row = $db->selectRow(
451 [ 'value', 'exptime' ],
452 [ 'keyname' => $key ],
455 if ( $row === false ) {
460 $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__
);
461 if ( $this->isExpired( $db, $row->exptime
) ) {
462 // Expired, do not reinsert
467 $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value
) ) );
468 $newValue = $oldValue +
$step;
469 $db->insert( $tableName,
472 'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
473 'exptime' => $row->exptime
474 ], __METHOD__
, 'IGNORE' );
476 if ( $db->affectedRows() == 0 ) {
477 // Race condition. See T30611
480 } catch ( DBError
$e ) {
481 $this->handleWriteError( $e, $db, $serverIndex );
488 public function merge( $key, callable
$callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
489 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
490 if ( ( $flags & self
::WRITE_SYNC
) == self
::WRITE_SYNC
) {
491 $ok = $this->waitForReplication() && $ok;
497 public function changeTTL( $key, $expiry = 0 ) {
498 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
500 $silenceScope = $this->silenceTransactionProfiler();
502 $db = $this->getDB( $serverIndex );
505 [ 'exptime' => $db->timestamp( $this->convertExpiry( $expiry ) ) ],
506 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
509 if ( $db->affectedRows() == 0 ) {
512 } catch ( DBError
$e ) {
513 $this->handleWriteError( $e, $db, $serverIndex );
521 * @param IDatabase $db
522 * @param string $exptime
525 protected function isExpired( $db, $exptime ) {
526 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX
, $exptime ) < time();
530 * @param IDatabase $db
533 protected function getMaxDateTime( $db ) {
534 if ( time() > 0x7fffffff ) {
535 return $db->timestamp( 1 << 62 );
537 return $db->timestamp( 0x7fffffff );
541 protected function garbageCollect() {
542 if ( !$this->purgePeriod ||
$this->replicaOnly
) {
546 // Only purge on one in every $this->purgePeriod requests.
547 if ( $this->purgePeriod
!== 1 && mt_rand( 0, $this->purgePeriod
- 1 ) ) {
551 // Avoid repeating the delete within a few seconds
552 if ( $now > ( $this->lastExpireAll +
1 ) ) {
553 $this->lastExpireAll
= $now;
558 public function expireAll() {
559 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
563 * Delete objects from the database which expire before a certain date.
564 * @param string $timestamp
565 * @param bool|callable $progressCallback
568 public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
569 $silenceScope = $this->silenceTransactionProfiler();
570 for ( $serverIndex = 0; $serverIndex < $this->numServers
; $serverIndex++
) {
573 $db = $this->getDB( $serverIndex );
574 $dbTimestamp = $db->timestamp( $timestamp );
575 $totalSeconds = false;
576 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
577 for ( $i = 0; $i < $this->shards
; $i++
) {
581 if ( $maxExpTime !== false ) {
582 $conds[] = 'exptime >= ' . $db->addQuotes( $maxExpTime );
585 $this->getTableNameByShard( $i ),
586 [ 'keyname', 'exptime' ],
589 [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
590 if ( $rows === false ||
!$rows->numRows() ) {
594 $row = $rows->current();
595 $minExpTime = $row->exptime
;
596 if ( $totalSeconds === false ) {
597 $totalSeconds = wfTimestamp( TS_UNIX
, $timestamp )
598 - wfTimestamp( TS_UNIX
, $minExpTime );
600 foreach ( $rows as $row ) {
601 $keys[] = $row->keyname
;
602 $maxExpTime = $row->exptime
;
606 $this->getTableNameByShard( $i ),
608 'exptime >= ' . $db->addQuotes( $minExpTime ),
609 'exptime < ' . $db->addQuotes( $dbTimestamp ),
614 if ( $progressCallback ) {
615 if ( intval( $totalSeconds ) === 0 ) {
618 $remainingSeconds = wfTimestamp( TS_UNIX
, $timestamp )
619 - wfTimestamp( TS_UNIX
, $maxExpTime );
620 if ( $remainingSeconds > $totalSeconds ) {
621 $totalSeconds = $remainingSeconds;
623 $processedSeconds = $totalSeconds - $remainingSeconds;
624 $percent = ( $i +
$processedSeconds / $totalSeconds )
625 / $this->shards
* 100;
627 $percent = ( $percent / $this->numServers
)
628 +
( $serverIndex / $this->numServers
* 100 );
629 call_user_func( $progressCallback, $percent );
633 } catch ( DBError
$e ) {
634 $this->handleWriteError( $e, $db, $serverIndex );
642 * Delete content of shard tables in every server.
643 * Return true if the operation is successful, false otherwise.
646 public function deleteAll() {
647 $silenceScope = $this->silenceTransactionProfiler();
648 for ( $serverIndex = 0; $serverIndex < $this->numServers
; $serverIndex++
) {
651 $db = $this->getDB( $serverIndex );
652 for ( $i = 0; $i < $this->shards
; $i++
) {
653 $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__
);
655 } catch ( DBError
$e ) {
656 $this->handleWriteError( $e, $db, $serverIndex );
664 * Serialize an object and, if possible, compress the representation.
665 * On typical message and page data, this can provide a 3X decrease
666 * in storage requirements.
668 * @param mixed &$data
671 protected function serialize( &$data ) {
672 $serial = serialize( $data );
674 if ( function_exists( 'gzdeflate' ) ) {
675 return gzdeflate( $serial );
682 * Unserialize and, if necessary, decompress an object.
683 * @param string $serial
686 protected function unserialize( $serial ) {
687 if ( function_exists( 'gzinflate' ) ) {
688 Wikimedia\
suppressWarnings();
689 $decomp = gzinflate( $serial );
690 Wikimedia\restoreWarnings
();
692 if ( false !== $decomp ) {
697 $ret = unserialize( $serial );
703 * Handle a DBError which occurred during a read operation.
705 * @param DBError $exception
706 * @param int $serverIndex
708 protected function handleReadError( DBError
$exception, $serverIndex ) {
709 if ( $exception instanceof DBConnectionError
) {
710 $this->markServerDown( $exception, $serverIndex );
712 $this->logger
->error( "DBError: {$exception->getMessage()}" );
713 if ( $exception instanceof DBConnectionError
) {
714 $this->setLastError( BagOStuff
::ERR_UNREACHABLE
);
715 $this->logger
->debug( __METHOD__
. ": ignoring connection error" );
717 $this->setLastError( BagOStuff
::ERR_UNEXPECTED
);
718 $this->logger
->debug( __METHOD__
. ": ignoring query error" );
723 * Handle a DBQueryError which occurred during a write operation.
725 * @param DBError $exception
726 * @param IDatabase|null $db DB handle or null if connection failed
727 * @param int $serverIndex
730 protected function handleWriteError( DBError
$exception, IDatabase
$db = null, $serverIndex ) {
732 $this->markServerDown( $exception, $serverIndex );
733 } elseif ( $db->wasReadOnlyError() ) {
734 if ( $db->trxLevel() && $this->usesMainDB() ) {
735 // Errors like deadlocks and connection drops already cause rollback.
736 // For consistency, we have no choice but to throw an error and trigger
737 // complete rollback if the main DB is also being used as the cache DB.
742 $this->logger
->error( "DBError: {$exception->getMessage()}" );
743 if ( $exception instanceof DBConnectionError
) {
744 $this->setLastError( BagOStuff
::ERR_UNREACHABLE
);
745 $this->logger
->debug( __METHOD__
. ": ignoring connection error" );
747 $this->setLastError( BagOStuff
::ERR_UNEXPECTED
);
748 $this->logger
->debug( __METHOD__
. ": ignoring query error" );
753 * Mark a server down due to a DBConnectionError exception
755 * @param DBError $exception
756 * @param int $serverIndex
758 protected function markServerDown( DBError
$exception, $serverIndex ) {
759 unset( $this->conns
[$serverIndex] ); // bug T103435
761 if ( isset( $this->connFailureTimes
[$serverIndex] ) ) {
762 if ( time() - $this->connFailureTimes
[$serverIndex] >= 60 ) {
763 unset( $this->connFailureTimes
[$serverIndex] );
764 unset( $this->connFailureErrors
[$serverIndex] );
766 $this->logger
->debug( __METHOD__
. ": Server #$serverIndex already down" );
771 $this->logger
->info( __METHOD__
. ": Server #$serverIndex down until " . ( $now +
60 ) );
772 $this->connFailureTimes
[$serverIndex] = $now;
773 $this->connFailureErrors
[$serverIndex] = $exception;
777 * Create shard tables. For use from eval.php.
779 public function createTables() {
780 for ( $serverIndex = 0; $serverIndex < $this->numServers
; $serverIndex++
) {
781 $db = $this->getDB( $serverIndex );
782 if ( $db->getType() !== 'mysql' ) {
783 throw new MWException( __METHOD__
. ' is not supported on this DB server' );
786 for ( $i = 0; $i < $this->shards
; $i++
) {
788 'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
789 ' LIKE ' . $db->tableName( 'objectcache' ),
796 * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
798 protected function usesMainDB() {
799 return !$this->serverInfos
;
802 protected function waitForReplication() {
803 if ( !$this->usesMainDB() ) {
804 // Custom DB server list; probably doesn't use replication
808 $lb = MediaWikiServices
::getInstance()->getDBLoadBalancer();
809 if ( $lb->getServerCount() <= 1 ) {
810 return true; // no replica DBs
813 // Main LB is used; wait for any replica DBs to catch up
814 $masterPos = $lb->getMasterPos();
816 return true; // not applicable
819 $loop = new WaitConditionLoop(
820 function () use ( $lb, $masterPos ) {
821 return $lb->waitForAll( $masterPos, 1 );
827 return ( $loop->invoke() === $loop::CONDITION_REACHED
);
831 * Returns a ScopedCallback which resets the silence flag in the transaction profiler when it is
832 * destroyed on the end of a scope, for example on return or throw
833 * @return ScopedCallback
836 protected function silenceTransactionProfiler() {
837 $trxProfiler = Profiler
::instance()->getTransactionProfiler();
838 $oldSilenced = $trxProfiler->setSilenced( true );
839 return new ScopedCallback( function () use ( $trxProfiler, $oldSilenced ) {
840 $trxProfiler->setSilenced( $oldSilenced );