includes/objectcache/SqlBagOStuff.php

   1 <?php
   2 /**
   3  * Object caching using a SQL database.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Cache
  22  */
  23
  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;
  33
  34 /**
  35  * Class to store objects in the database
  36  *
  37  * @ingroup Cache
  38  */
  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;
  44         /** @var int */
  45         protected $numServers;
  46         /** @var int UNIX timestamp */
  47         protected $lastGarbageCollect = 0;
  48         /** @var int */
  49         protected $purgePeriod = 10;
  50         /** @var int */
  51         protected $purgeLimit = 100;
  52         /** @var int */
  53         protected $shards = 1;
  54         /** @var string */
  55         protected $tableName = 'objectcache';
  56         /** @var bool */
  57         protected $replicaOnly = false;
  58         /** @var int */
  59         protected $syncTimeout = 3;
  60
  61         /** @var LoadBalancer|null */
  62         protected $separateMainLB;
  63         /** @var array */
  64         protected $conns;
  65         /** @var array UNIX timestamps */
  66         protected $connFailureTimes = [];
  67         /** @var array Exceptions */
  68         protected $connFailureErrors = [];
  69
  70         /** @var int */
  71         private static $GARBAGE_COLLECT_DELAY_SEC = 1;
  72
  73         /** @var string */
  74         private static $OP_SET = 'set';
  75         /** @var string */
  76         private static $OP_ADD = 'add';
  77         /** @var string */
  78         private static $OP_TOUCH = 'touch';
  79         /** @var string */
  80         private static $OP_DELETE = 'delete';
  81
  82         /**
  83          * Constructor. Parameters are:
  84          *   - server:      A server info structure in the format required by each
  85          *                  element in $wgDBServers.
  86          *
  87          *   - servers:     An array of server info structures describing a set of database servers
  88          *                  to distribute keys to. If this is specified, the "server" option will be
  89          *                  ignored. If string keys are used, then they will be used for consistent
  90          *                  hashing *instead* of the host name (from the server config). This is useful
  91          *                  when a cluster is replicated to another site (with different host names)
  92          *                  but each server has a corresponding replica in the other cluster.
  93          *
  94          *   - purgePeriod: The average number of object cache writes in between
  95          *                  garbage collection operations, where expired entries
  96          *                  are removed from the database. Or in other words, the
  97          *                  reciprocal of the probability of purging on any given
  98          *                  write. If this is set to zero, purging will never be done.
  99          *
 100          *   - purgeLimit:  Maximum number of rows to purge at once.
 101          *
 102          *   - tableName:   The table name to use, default is "objectcache".
 103          *
 104          *   - shards:      The number of tables to use for data storage on each server.
 105          *                  If this is more than 1, table names will be formed in the style
 106          *                  objectcacheNNN where NNN is the shard index, between 0 and
 107          *                  shards-1. The number of digits will be the minimum number
 108          *                  required to hold the largest shard index. Data will be
 109          *                  distributed across all tables by key hash. This is for
 110          *                  MySQL bugs 61735 <https://bugs.mysql.com/bug.php?id=61735>
 111          *                  and 61736 <https://bugs.mysql.com/bug.php?id=61736>.
 112          *
 113          *   - replicaOnly: Whether to only use replica DBs and avoid triggering
 114          *                  garbage collection logic of expired items. This only
 115          *                  makes sense if the primary DB is used and only if get()
 116          *                  calls will be used. This is used by ReplicatedBagOStuff.
 117          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
 118          *
 119          * @param array $params
 120          */
 121         public function __construct( $params ) {
 122                 parent::__construct( $params );
 123
 124                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 125                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 126
 127                 if ( isset( $params['servers'] ) ) {
 128                         $this->serverInfos = [];
 129                         $this->serverTags = [];
 130                         $this->numServers = count( $params['servers'] );
 131                         $index = 0;
 132                         foreach ( $params['servers'] as $tag => $info ) {
 133                                 $this->serverInfos[$index] = $info;
 134                                 if ( is_string( $tag ) ) {
 135                                         $this->serverTags[$index] = $tag;
 136                                 } else {
 137                                         $this->serverTags[$index] = $info['host'] ?? "#$index";
 138                                 }
 139                                 ++$index;
 140                         }
 141                 } elseif ( isset( $params['server'] ) ) {
 142                         $this->serverInfos = [ $params['server'] ];
 143                         $this->numServers = count( $this->serverInfos );
 144                 } else {
 145                         // Default to using the main wiki's database servers
 146                         $this->serverInfos = false;
 147                         $this->numServers = 1;
 148                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 149                 }
 150                 if ( isset( $params['purgePeriod'] ) ) {
 151                         $this->purgePeriod = intval( $params['purgePeriod'] );
 152                 }
 153                 if ( isset( $params['purgeLimit'] ) ) {
 154                         $this->purgeLimit = intval( $params['purgeLimit'] );
 155                 }
 156                 if ( isset( $params['tableName'] ) ) {
 157                         $this->tableName = $params['tableName'];
 158                 }
 159                 if ( isset( $params['shards'] ) ) {
 160                         $this->shards = intval( $params['shards'] );
 161                 }
 162                 if ( isset( $params['syncTimeout'] ) ) {
 163                         $this->syncTimeout = $params['syncTimeout'];
 164                 }
 165                 // Backwards-compatibility for < 1.34
 166                 $this->replicaOnly = $params['replicaOnly'] ?? ( $params['slaveOnly'] ?? false );
 167         }
 168
 169         /**
 170          * Get a connection to the specified database
 171          *
 172          * @param int $serverIndex
 173          * @return Database
 174          * @throws MWException
 175          */
 176         protected function getDB( $serverIndex ) {
 177                 if ( $serverIndex >= $this->numServers ) {
 178                         throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 179                 }
 180
 181                 # Don't keep timing out trying to connect for each call if the DB is down
 182                 if (
 183                         isset( $this->connFailureErrors[$serverIndex] ) &&
 184                         ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 185                 ) {
 186                         throw $this->connFailureErrors[$serverIndex];
 187                 }
 188
 189                 if ( $this->serverInfos ) {
 190                         if ( !isset( $this->conns[$serverIndex] ) ) {
 191                                 // Use custom database defined by server connection info
 192                                 $info = $this->serverInfos[$serverIndex];
 193                                 $type = $info['type'] ?? 'mysql';
 194                                 $host = $info['host'] ?? '[unknown]';
 195                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 196                                 $db = Database::factory( $type, $info );
 197                                 $db->clearFlag( DBO_TRX ); // auto-commit mode
 198                                 $this->conns[$serverIndex] = $db;
 199                         }
 200                         $db = $this->conns[$serverIndex];
 201                 } else {
 202                         // Use the main LB database
 203                         $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 204                         $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 205                         if ( $lb->getServerType( $lb->getWriterIndex() ) !== 'sqlite' ) {
 206                                 // Keep a separate connection to avoid contention and deadlocks
 207                                 $db = $lb->getConnection( $index, [], false, $lb::CONN_TRX_AUTOCOMMIT );
 208                         } else {
 209                                 // However, SQLite has the opposite behavior due to DB-level locking.
 210                                 // Stock sqlite MediaWiki installs use a separate sqlite cache DB instead.
 211                                 $db = $lb->getConnection( $index );
 212                         }
 213                 }
 214
 215                 $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 216
 217                 return $db;
 218         }
 219
 220         /**
 221          * Get the server index and table name for a given key
 222          * @param string $key
 223          * @return array Server index and table name
 224          */
 225         protected function getTableByKey( $key ) {
 226                 if ( $this->shards > 1 ) {
 227                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 228                         $tableIndex = $hash % $this->shards;
 229                 } else {
 230                         $tableIndex = 0;
 231                 }
 232                 if ( $this->numServers > 1 ) {
 233                         $sortedServers = $this->serverTags;
 234                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 235                         reset( $sortedServers );
 236                         $serverIndex = key( $sortedServers );
 237                 } else {
 238                         $serverIndex = 0;
 239                 }
 240                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 241         }
 242
 243         /**
 244          * Get the table name for a given shard index
 245          * @param int $index
 246          * @return string
 247          */
 248         protected function getTableNameByShard( $index ) {
 249                 if ( $this->shards > 1 ) {
 250                         $decimals = strlen( $this->shards - 1 );
 251                         return $this->tableName .
 252                                 sprintf( "%0{$decimals}d", $index );
 253                 } else {
 254                         return $this->tableName;
 255                 }
 256         }
 257
 258         protected function doGet( $key, $flags = 0, &$casToken = null ) {
 259                 $casToken = null;
 260
 261                 $blobs = $this->fetchBlobMulti( [ $key ] );
 262                 if ( array_key_exists( $key, $blobs ) ) {
 263                         $blob = $blobs[$key];
 264                         $value = $this->unserialize( $blob );
 265
 266                         $casToken = ( $value !== false ) ? $blob : null;
 267
 268                         return $value;
 269                 }
 270
 271                 return false;
 272         }
 273
 274         protected function doGetMulti( array $keys, $flags = 0 ) {
 275                 $values = [];
 276
 277                 $blobs = $this->fetchBlobMulti( $keys );
 278                 foreach ( $blobs as $key => $blob ) {
 279                         $values[$key] = $this->unserialize( $blob );
 280                 }
 281
 282                 return $values;
 283         }
 284
 285         protected function fetchBlobMulti( array $keys, $flags = 0 ) {
 286                 $values = []; // array of (key => value)
 287
 288                 $keysByTable = [];
 289                 foreach ( $keys as $key ) {
 290                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 291                         $keysByTable[$serverIndex][$tableName][] = $key;
 292                 }
 293
 294                 $dataRows = [];
 295                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 296                         try {
 297                                 $db = $this->getDB( $serverIndex );
 298                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 299                                         $res = $db->select( $tableName,
 300                                                 [ 'keyname', 'value', 'exptime' ],
 301                                                 [ 'keyname' => $tableKeys ],
 302                                                 __METHOD__,
 303                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 304                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 305                                                 // We do not want to flush the TRX as that can break callers.
 306                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 307                                         );
 308                                         if ( $res === false ) {
 309                                                 continue;
 310                                         }
 311                                         foreach ( $res as $row ) {
 312                                                 $row->serverIndex = $serverIndex;
 313                                                 $row->tableName = $tableName;
 314                                                 $dataRows[$row->keyname] = $row;
 315                                         }
 316                                 }
 317                         } catch ( DBError $e ) {
 318                                 $this->handleReadError( $e, $serverIndex );
 319                         }
 320                 }
 321
 322                 foreach ( $keys as $key ) {
 323                         if ( isset( $dataRows[$key] ) ) { // HIT?
 324                                 $row = $dataRows[$key];
 325                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 326                                 $db = null; // in case of connection failure
 327                                 try {
 328                                         $db = $this->getDB( $row->serverIndex );
 329                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 330                                                 $this->debug( "get: key has expired" );
 331                                         } else { // HIT
 332                                                 $values[$key] = $db->decodeBlob( $row->value );
 333                                         }
 334                                 } catch ( DBQueryError $e ) {
 335                                         $this->handleWriteError( $e, $db, $row->serverIndex );
 336                                 }
 337                         } else { // MISS
 338                                 $this->debug( 'get: no matching rows' );
 339                         }
 340                 }
 341
 342                 return $values;
 343         }
 344
 345         protected function doSetMulti( array $data, $exptime = 0, $flags = 0 ) {
 346                 return $this->modifyMulti( $data, $exptime, $flags, self::$OP_SET );
 347         }
 348
 349         /**
 350          * @param mixed[]|null[] $data Map of (key => new value or null)
 351          * @param int $exptime UNIX timestamp, TTL in seconds, or 0 (no expiration)
 352          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 353          * @param string $op Cache operation
 354          * @return bool
 355          */
 356         private function modifyMulti( array $data, $exptime, $flags, $op ) {
 357                 $keysByTable = [];
 358                 foreach ( $data as $key => $value ) {
 359                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 360                         $keysByTable[$serverIndex][$tableName][] = $key;
 361                 }
 362
 363                 $exptime = $this->convertToExpiry( $exptime );
 364
 365                 $result = true;
 366                 /** @noinspection PhpUnusedLocalVariableInspection */
 367                 $silenceScope = $this->silenceTransactionProfiler();
 368                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 369                         $db = null; // in case of connection failure
 370                         try {
 371                                 $db = $this->getDB( $serverIndex );
 372                                 $this->occasionallyGarbageCollect( $db ); // expire old entries if any
 373                                 $dbExpiry = $exptime ? $db->timestamp( $exptime ) : $this->getMaxDateTime( $db );
 374                         } catch ( DBError $e ) {
 375                                 $this->handleWriteError( $e, $db, $serverIndex );
 376                                 $result = false;
 377                                 continue;
 378                         }
 379
 380                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 381                                 try {
 382                                         $result = $this->updateTableKeys(
 383                                                 $op,
 384                                                 $db,
 385                                                 $tableName,
 386                                                 $tableKeys,
 387                                                 $data,
 388                                                 $dbExpiry
 389                                         ) && $result;
 390                                 } catch ( DBError $e ) {
 391                                         $this->handleWriteError( $e, $db, $serverIndex );
 392                                         $result = false;
 393                                 }
 394
 395                         }
 396                 }
 397
 398                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 399                         $result = $this->waitForReplication() && $result;
 400                 }
 401
 402                 return $result;
 403         }
 404
 405         /**
 406          * @param string $op
 407          * @param IDatabase $db
 408          * @param string $table
 409          * @param string[] $tableKeys Keys in $data to update
 410          * @param mixed[]|null[] $data Map of (key => new value or null)
 411          * @param string $dbExpiry DB-encoded expiry
 412          * @return bool
 413          * @throws DBError
 414          * @throws InvalidArgumentException
 415          */
 416         private function updateTableKeys( $op, $db, $table, $tableKeys, $data, $dbExpiry ) {
 417                 $success = true;
 418
 419                 if ( $op === self::$OP_ADD ) {
 420                         $rows = [];
 421                         foreach ( $tableKeys as $key ) {
 422                                 $rows[] = [
 423                                         'keyname' => $key,
 424                                         'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 425                                         'exptime' => $dbExpiry
 426                                 ];
 427                         }
 428                         $db->delete(
 429                                 $table,
 430                                 [
 431                                         'keyname' => $tableKeys,
 432                                         'exptime <= ' . $db->addQuotes( $db->timestamp() )
 433                                 ],
 434                                 __METHOD__
 435                         );
 436                         $db->insert( $table, $rows, __METHOD__, [ 'IGNORE' ] );
 437
 438                         $success = ( $db->affectedRows() == count( $rows ) );
 439                 } elseif ( $op === self::$OP_SET ) {
 440                         $rows = [];
 441                         foreach ( $tableKeys as $key ) {
 442                                 $rows[] = [
 443                                         'keyname' => $key,
 444                                         'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 445                                         'exptime' => $dbExpiry
 446                                 ];
 447                         }
 448                         $db->replace( $table, [ 'keyname' ], $rows, __METHOD__ );
 449                 } elseif ( $op === self::$OP_DELETE ) {
 450                         $db->delete( $table, [ 'keyname' => $tableKeys ], __METHOD__ );
 451                 } elseif ( $op === self::$OP_TOUCH ) {
 452                         $db->update(
 453                                 $table,
 454                                 [ 'exptime' => $dbExpiry ],
 455                                 [
 456                                         'keyname' => $tableKeys,
 457                                         'exptime > ' . $db->addQuotes( $db->timestamp() )
 458                                 ],
 459                                 __METHOD__
 460                         );
 461
 462                         $success = ( $db->affectedRows() == count( $tableKeys ) );
 463                 } else {
 464                         throw new InvalidArgumentException( "Invalid operation '$op'" );
 465                 }
 466
 467                 return $success;
 468         }
 469
 470         protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 471                 return $this->modifyMulti( [ $key => $value ], $exptime, $flags, self::$OP_SET );
 472         }
 473
 474         public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 475                 return $this->modifyMulti( [ $key => $value ], $exptime, $flags, self::$OP_ADD );
 476         }
 477
 478         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 479                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 480                 $exptime = $this->convertToExpiry( $exptime );
 481
 482                 /** @noinspection PhpUnusedLocalVariableInspection */
 483                 $silenceScope = $this->silenceTransactionProfiler();
 484                 $db = null; // in case of connection failure
 485                 try {
 486                         $db = $this->getDB( $serverIndex );
 487                         // (T26425) use a replace if the db supports it instead of
 488                         // delete/insert to avoid clashes with conflicting keynames
 489                         $db->update(
 490                                 $tableName,
 491                                 [
 492                                         'keyname' => $key,
 493                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 494                                         'exptime' => $exptime
 495                                                 ? $db->timestamp( $exptime )
 496                                                 : $this->getMaxDateTime( $db )
 497                                 ],
 498                                 [
 499                                         'keyname' => $key,
 500                                         'value' => $db->encodeBlob( $casToken ),
 501                                         'exptime > ' . $db->addQuotes( $db->timestamp() )
 502                                 ],
 503                                 __METHOD__
 504                         );
 505                 } catch ( DBQueryError $e ) {
 506                         $this->handleWriteError( $e, $db, $serverIndex );
 507
 508                         return false;
 509                 }
 510
 511                 return (bool)$db->affectedRows();
 512         }
 513
 514         protected function doDeleteMulti( array $keys, $flags = 0 ) {
 515                 return $this->modifyMulti(
 516                         array_fill_keys( $keys, null ),
 517                         0,
 518                         $flags,
 519                         self::$OP_DELETE
 520                 );
 521         }
 522
 523         protected function doDelete( $key, $flags = 0 ) {
 524                 return $this->modifyMulti( [ $key => null ], 0, $flags, self::$OP_DELETE );
 525         }
 526
 527         public function incr( $key, $step = 1 ) {
 528                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 529
 530                 $newCount = false;
 531                 /** @noinspection PhpUnusedLocalVariableInspection */
 532                 $silenceScope = $this->silenceTransactionProfiler();
 533                 $db = null; // in case of connection failure
 534                 try {
 535                         $db = $this->getDB( $serverIndex );
 536                         $encTimestamp = $db->addQuotes( $db->timestamp() );
 537                         $db->update(
 538                                 $tableName,
 539                                 [ 'value = value + ' . (int)$step ],
 540                                 [ 'keyname' => $key, "exptime > $encTimestamp" ],
 541                                 __METHOD__
 542                         );
 543                         if ( $db->affectedRows() > 0 ) {
 544                                 $newValue = $db->selectField(
 545                                         $tableName,
 546                                         'value',
 547                                         [ 'keyname' => $key, "exptime > $encTimestamp" ],
 548                                         __METHOD__
 549                                 );
 550                                 if ( $this->isInteger( $newValue ) ) {
 551                                         $newCount = (int)$newValue;
 552                                 }
 553                         }
 554                 } catch ( DBError $e ) {
 555                         $this->handleWriteError( $e, $db, $serverIndex );
 556                 }
 557
 558                 return $newCount;
 559         }
 560
 561         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 562                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
 563                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 564                         $ok = $this->waitForReplication() && $ok;
 565                 }
 566
 567                 return $ok;
 568         }
 569
 570         protected function doChangeTTLMulti( array $keys, $exptime, $flags = 0 ) {
 571                 return $this->modifyMulti(
 572                         array_fill_keys( $keys, null ),
 573                         $exptime,
 574                         $flags,
 575                         self::$OP_TOUCH
 576                 );
 577         }
 578
 579         protected function doChangeTTL( $key, $exptime, $flags ) {
 580                 return $this->modifyMulti( [ $key => null ], $exptime, $flags, self::$OP_TOUCH );
 581         }
 582
 583         /**
 584          * @param IDatabase $db
 585          * @param string $exptime
 586          * @return bool
 587          */
 588         protected function isExpired( $db, $exptime ) {
 589                 return (
 590                         $exptime != $this->getMaxDateTime( $db ) &&
 591                         wfTimestamp( TS_UNIX, $exptime ) < time()
 592                 );
 593         }
 594
 595         /**
 596          * @param IDatabase $db
 597          * @return string
 598          */
 599         protected function getMaxDateTime( $db ) {
 600                 if ( time() > 0x7fffffff ) {
 601                         return $db->timestamp( 1 << 62 );
 602                 } else {
 603                         return $db->timestamp( 0x7fffffff );
 604                 }
 605         }
 606
 607         /**
 608          * @param IDatabase $db
 609          * @throws DBError
 610          */
 611         protected function occasionallyGarbageCollect( IDatabase $db ) {
 612                 if (
 613                         // Random purging is enabled
 614                         $this->purgePeriod &&
 615                         // Only purge on one in every $this->purgePeriod writes
 616                         mt_rand( 0, $this->purgePeriod - 1 ) == 0 &&
 617                         // Avoid repeating the delete within a few seconds
 618                         ( time() - $this->lastGarbageCollect ) > self::$GARBAGE_COLLECT_DELAY_SEC
 619                 ) {
 620                         $garbageCollector = function () use ( $db ) {
 621                                 $this->deleteServerObjectsExpiringBefore( $db, time(), null, $this->purgeLimit );
 622                                 $this->lastGarbageCollect = time();
 623                         };
 624                         if ( $this->asyncHandler ) {
 625                                 $this->lastGarbageCollect = time(); // avoid duplicate enqueues
 626                                 ( $this->asyncHandler )( $garbageCollector );
 627                         } else {
 628                                 $garbageCollector();
 629                         }
 630                 }
 631         }
 632
 633         public function expireAll() {
 634                 $this->deleteObjectsExpiringBefore( time() );
 635         }
 636
 637         public function deleteObjectsExpiringBefore(
 638                 $timestamp,
 639                 callable $progress = null,
 640                 $limit = INF
 641         ) {
 642                 /** @noinspection PhpUnusedLocalVariableInspection */
 643                 $silenceScope = $this->silenceTransactionProfiler();
 644
 645                 $serverIndexes = range( 0, $this->numServers - 1 );
 646                 shuffle( $serverIndexes );
 647
 648                 $ok = true;
 649
 650                 $keysDeletedCount = 0;
 651                 foreach ( $serverIndexes as $numServersDone => $serverIndex ) {
 652                         $db = null; // in case of connection failure
 653                         try {
 654                                 $db = $this->getDB( $serverIndex );
 655                                 $this->deleteServerObjectsExpiringBefore(
 656                                         $db,
 657                                         $timestamp,
 658                                         $progress,
 659                                         $limit,
 660                                         $numServersDone,
 661                                         $keysDeletedCount
 662                                 );
 663                         } catch ( DBError $e ) {
 664                                 $this->handleWriteError( $e, $db, $serverIndex );
 665                                 $ok = false;
 666                         }
 667                 }
 668
 669                 return $ok;
 670         }
 671
 672         /**
 673          * @param IDatabase $db
 674          * @param string|int $timestamp
 675          * @param callable|null $progressCallback
 676          * @param int $limit
 677          * @param int $serversDoneCount
 678          * @param int &$keysDeletedCount
 679          * @throws DBError
 680          */
 681         private function deleteServerObjectsExpiringBefore(
 682                 IDatabase $db,
 683                 $timestamp,
 684                 $progressCallback,
 685                 $limit,
 686                 $serversDoneCount = 0,
 687                 &$keysDeletedCount = 0
 688         ) {
 689                 $cutoffUnix = wfTimestamp( TS_UNIX, $timestamp );
 690                 $shardIndexes = range( 0, $this->shards - 1 );
 691                 shuffle( $shardIndexes );
 692
 693                 foreach ( $shardIndexes as $numShardsDone => $shardIndex ) {
 694                         $continue = null; // last exptime
 695                         $lag = null; // purge lag
 696                         do {
 697                                 $res = $db->select(
 698                                         $this->getTableNameByShard( $shardIndex ),
 699                                         [ 'keyname', 'exptime' ],
 700                                         array_merge(
 701                                                 [ 'exptime < ' . $db->addQuotes( $db->timestamp( $cutoffUnix ) ) ],
 702                                                 $continue ? [ 'exptime >= ' . $db->addQuotes( $continue ) ] : []
 703                                         ),
 704                                         __METHOD__,
 705                                         [ 'LIMIT' => min( $limit, 100 ), 'ORDER BY' => 'exptime' ]
 706                                 );
 707
 708                                 if ( $res->numRows() ) {
 709                                         $row = $res->current();
 710                                         if ( $lag === null ) {
 711                                                 $lag = max( $cutoffUnix - wfTimestamp( TS_UNIX, $row->exptime ), 1 );
 712                                         }
 713
 714                                         $keys = [];
 715                                         foreach ( $res as $row ) {
 716                                                 $keys[] = $row->keyname;
 717                                                 $continue = $row->exptime;
 718                                         }
 719
 720                                         $db->delete(
 721                                                 $this->getTableNameByShard( $shardIndex ),
 722                                                 [
 723                                                         'exptime < ' . $db->addQuotes( $db->timestamp( $cutoffUnix ) ),
 724                                                         'keyname' => $keys
 725                                                 ],
 726                                                 __METHOD__
 727                                         );
 728                                         $keysDeletedCount += $db->affectedRows();
 729                                 }
 730
 731                                 if ( is_callable( $progressCallback ) ) {
 732                                         if ( $lag ) {
 733                                                 $remainingLag = $cutoffUnix - wfTimestamp( TS_UNIX, $continue );
 734                                                 $processedLag = max( $lag - $remainingLag, 0 );
 735                                                 $doneRatio = ( $numShardsDone + $processedLag / $lag ) / $this->shards;
 736                                         } else {
 737                                                 $doneRatio = 1;
 738                                         }
 739
 740                                         $overallRatio = ( $doneRatio / $this->numServers )
 741                                                 + ( $serversDoneCount / $this->numServers );
 742                                         call_user_func( $progressCallback, $overallRatio * 100 );
 743                                 }
 744                         } while ( $res->numRows() && $keysDeletedCount < $limit );
 745                 }
 746         }
 747
 748         /**
 749          * Delete content of shard tables in every server.
 750          * Return true if the operation is successful, false otherwise.
 751          * @return bool
 752          */
 753         public function deleteAll() {
 754                 /** @noinspection PhpUnusedLocalVariableInspection */
 755                 $silenceScope = $this->silenceTransactionProfiler();
 756                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 757                         $db = null; // in case of connection failure
 758                         try {
 759                                 $db = $this->getDB( $serverIndex );
 760                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 761                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 762                                 }
 763                         } catch ( DBError $e ) {
 764                                 $this->handleWriteError( $e, $db, $serverIndex );
 765                                 return false;
 766                         }
 767                 }
 768                 return true;
 769         }
 770
 771         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 772                 // Avoid deadlocks and allow lock reentry if specified
 773                 if ( isset( $this->locks[$key] ) ) {
 774                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 775                                 ++$this->locks[$key]['depth'];
 776                                 return true;
 777                         } else {
 778                                 return false;
 779                         }
 780                 }
 781
 782                 list( $serverIndex ) = $this->getTableByKey( $key );
 783
 784                 $db = null; // in case of connection failure
 785                 try {
 786                         $db = $this->getDB( $serverIndex );
 787                         $ok = $db->lock( $key, __METHOD__, $timeout );
 788                         if ( $ok ) {
 789                                 $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 790                         }
 791
 792                         $this->logger->warning(
 793                                 __METHOD__ . " failed due to timeout for {key}.",
 794                                 [ 'key' => $key, 'timeout' => $timeout ]
 795                         );
 796
 797                         return $ok;
 798                 } catch ( DBError $e ) {
 799                         $this->handleWriteError( $e, $db, $serverIndex );
 800                         $ok = false;
 801                 }
 802
 803                 return $ok;
 804         }
 805
 806         public function unlock( $key ) {
 807                 if ( !isset( $this->locks[$key] ) ) {
 808                         return false;
 809                 }
 810
 811                 if ( --$this->locks[$key]['depth'] <= 0 ) {
 812                         unset( $this->locks[$key] );
 813
 814                         list( $serverIndex ) = $this->getTableByKey( $key );
 815
 816                         $db = null; // in case of connection failure
 817                         try {
 818                                 $db = $this->getDB( $serverIndex );
 819                                 $ok = $db->unlock( $key, __METHOD__ );
 820                                 if ( !$ok ) {
 821                                         $this->logger->warning(
 822                                                 __METHOD__ . ' failed to release lock for {key}.',
 823                                                 [ 'key' => $key ]
 824                                         );
 825                                 }
 826                         } catch ( DBError $e ) {
 827                                 $this->handleWriteError( $e, $db, $serverIndex );
 828                                 $ok = false;
 829                         }
 830
 831                         return $ok;
 832                 }
 833
 834                 return true;
 835         }
 836
 837         /**
 838          * Serialize an object and, if possible, compress the representation.
 839          * On typical message and page data, this can provide a 3X decrease
 840          * in storage requirements.
 841          *
 842          * @param mixed $data
 843          * @return string|int
 844          */
 845         protected function serialize( $data ) {
 846                 if ( is_int( $data ) ) {
 847                         return $data;
 848                 }
 849
 850                 $serial = serialize( $data );
 851                 if ( function_exists( 'gzdeflate' ) ) {
 852                         $serial = gzdeflate( $serial );
 853                 }
 854
 855                 return $serial;
 856         }
 857
 858         /**
 859          * Unserialize and, if necessary, decompress an object.
 860          * @param string $serial
 861          * @return mixed
 862          */
 863         protected function unserialize( $serial ) {
 864                 if ( $this->isInteger( $serial ) ) {
 865                         return (int)$serial;
 866                 }
 867
 868                 if ( function_exists( 'gzinflate' ) ) {
 869                         Wikimedia\suppressWarnings();
 870                         $decomp = gzinflate( $serial );
 871                         Wikimedia\restoreWarnings();
 872
 873                         if ( $decomp !== false ) {
 874                                 $serial = $decomp;
 875                         }
 876                 }
 877
 878                 return unserialize( $serial );
 879         }
 880
 881         /**
 882          * Handle a DBError which occurred during a read operation.
 883          *
 884          * @param DBError $exception
 885          * @param int $serverIndex
 886          */
 887         protected function handleReadError( DBError $exception, $serverIndex ) {
 888                 if ( $exception instanceof DBConnectionError ) {
 889                         $this->markServerDown( $exception, $serverIndex );
 890                 }
 891
 892                 $this->setAndLogDBError( $exception );
 893         }
 894
 895         /**
 896          * Handle a DBQueryError which occurred during a write operation.
 897          *
 898          * @param DBError $exception
 899          * @param IDatabase|null $db DB handle or null if connection failed
 900          * @param int $serverIndex
 901          * @throws Exception
 902          */
 903         protected function handleWriteError( DBError $exception, $db, $serverIndex ) {
 904                 if ( !( $db instanceof IDatabase ) ) {
 905                         $this->markServerDown( $exception, $serverIndex );
 906                 }
 907
 908                 $this->setAndLogDBError( $exception );
 909         }
 910
 911         /**
 912          * @param DBError $exception
 913          */
 914         private function setAndLogDBError( DBError $exception ) {
 915                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 916                 if ( $exception instanceof DBConnectionError ) {
 917                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 918                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 919                 } else {
 920                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 921                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 922                 }
 923         }
 924
 925         /**
 926          * Mark a server down due to a DBConnectionError exception
 927          *
 928          * @param DBError $exception
 929          * @param int $serverIndex
 930          */
 931         protected function markServerDown( DBError $exception, $serverIndex ) {
 932                 unset( $this->conns[$serverIndex] ); // bug T103435
 933
 934                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 935                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 936                                 unset( $this->connFailureTimes[$serverIndex] );
 937                                 unset( $this->connFailureErrors[$serverIndex] );
 938                         } else {
 939                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 940                                 return;
 941                         }
 942                 }
 943                 $now = time();
 944                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 945                 $this->connFailureTimes[$serverIndex] = $now;
 946                 $this->connFailureErrors[$serverIndex] = $exception;
 947         }
 948
 949         /**
 950          * Create shard tables. For use from eval.php.
 951          */
 952         public function createTables() {
 953                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 954                         $db = $this->getDB( $serverIndex );
 955                         if ( $db->getType() !== 'mysql' ) {
 956                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 957                         }
 958
 959                         for ( $i = 0; $i < $this->shards; $i++ ) {
 960                                 $db->query(
 961                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 962                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 963                                         __METHOD__ );
 964                         }
 965                 }
 966         }
 967
 968         /**
 969          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 970          */
 971         protected function usesMainDB() {
 972                 return !$this->serverInfos;
 973         }
 974
 975         protected function waitForReplication() {
 976                 if ( !$this->usesMainDB() ) {
 977                         // Custom DB server list; probably doesn't use replication
 978                         return true;
 979                 }
 980
 981                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 982                 if ( $lb->getServerCount() <= 1 ) {
 983                         return true; // no replica DBs
 984                 }
 985
 986                 // Main LB is used; wait for any replica DBs to catch up
 987                 try {
 988                         $masterPos = $lb->getMasterPos();
 989                         if ( !$masterPos ) {
 990                                 return true; // not applicable
 991                         }
 992
 993                         $loop = new WaitConditionLoop(
 994                                 function () use ( $lb, $masterPos ) {
 995                                         return $lb->waitForAll( $masterPos, 1 );
 996                                 },
 997                                 $this->syncTimeout,
 998                                 $this->busyCallbacks
 999                         );
1000
1001                         return ( $loop->invoke() === $loop::CONDITION_REACHED );
1002                 } catch ( DBError $e ) {
1003                         $this->setAndLogDBError( $e );
1004
1005                         return false;
1006                 }
1007         }
1008
1009         /**
1010          * Returns a ScopedCallback which resets the silence flag in the transaction profiler when it is
1011          * destroyed on the end of a scope, for example on return or throw
1012          * @return ScopedCallback
1013          * @since 1.32
1014          */
1015         protected function silenceTransactionProfiler() {
1016                 $trxProfiler = Profiler::instance()->getTransactionProfiler();
1017                 $oldSilenced = $trxProfiler->setSilenced( true );
1018                 return new ScopedCallback( function () use ( $trxProfiler, $oldSilenced ) {
1019                         $trxProfiler->setSilenced( $oldSilenced );
1020                 } );
1021         }
1022 }