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