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