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         const GARBAGE_COLLECT_DELAY_SEC = 1;
  72
  73         /**
  74          * Constructor. Parameters are:
  75          *   - server:      A server info structure in the format required by each
  76          *                  element in $wgDBServers.
  77          *
  78          *   - servers:     An array of server info structures describing a set of database servers
  79          *                  to distribute keys to. If this is specified, the "server" option will be
  80          *                  ignored. If string keys are used, then they will be used for consistent
  81          *                  hashing *instead* of the host name (from the server config). This is useful
  82          *                  when a cluster is replicated to another site (with different host names)
  83          *                  but each server has a corresponding replica in the other cluster.
  84          *
  85          *   - purgePeriod: The average number of object cache writes in between
  86          *                  garbage collection operations, where expired entries
  87          *                  are removed from the database. Or in other words, the
  88          *                  reciprocal of the probability of purging on any given
  89          *                  write. If this is set to zero, purging will never be done.
  90          *
  91          *   - purgeLimit:  Maximum number of rows to purge at once.
  92          *
  93          *   - tableName:   The table name to use, default is "objectcache".
  94          *
  95          *   - shards:      The number of tables to use for data storage on each server.
  96          *                  If this is more than 1, table names will be formed in the style
  97          *                  objectcacheNNN where NNN is the shard index, between 0 and
  98          *                  shards-1. The number of digits will be the minimum number
  99          *                  required to hold the largest shard index. Data will be
 100          *                  distributed across all tables by key hash. This is for
 101          *                  MySQL bugs 61735 <https://bugs.mysql.com/bug.php?id=61735>
 102          *                  and 61736 <https://bugs.mysql.com/bug.php?id=61736>.
 103          *
 104          *   - slaveOnly:   Whether to only use replica DBs and avoid triggering
 105          *                  garbage collection logic of expired items. This only
 106          *                  makes sense if the primary DB is used and only if get()
 107          *                  calls will be used. This is used by ReplicatedBagOStuff.
 108          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
 109          *
 110          * @param array $params
 111          */
 112         public function __construct( $params ) {
 113                 parent::__construct( $params );
 114
 115                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 116                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 117
 118                 if ( isset( $params['servers'] ) ) {
 119                         $this->serverInfos = [];
 120                         $this->serverTags = [];
 121                         $this->numServers = count( $params['servers'] );
 122                         $index = 0;
 123                         foreach ( $params['servers'] as $tag => $info ) {
 124                                 $this->serverInfos[$index] = $info;
 125                                 if ( is_string( $tag ) ) {
 126                                         $this->serverTags[$index] = $tag;
 127                                 } else {
 128                                         $this->serverTags[$index] = $info['host'] ?? "#$index";
 129                                 }
 130                                 ++$index;
 131                         }
 132                 } elseif ( isset( $params['server'] ) ) {
 133                         $this->serverInfos = [ $params['server'] ];
 134                         $this->numServers = count( $this->serverInfos );
 135                 } else {
 136                         // Default to using the main wiki's database servers
 137                         $this->serverInfos = false;
 138                         $this->numServers = 1;
 139                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 140                 }
 141                 if ( isset( $params['purgePeriod'] ) ) {
 142                         $this->purgePeriod = intval( $params['purgePeriod'] );
 143                 }
 144                 if ( isset( $params['purgeLimit'] ) ) {
 145                         $this->purgeLimit = intval( $params['purgeLimit'] );
 146                 }
 147                 if ( isset( $params['tableName'] ) ) {
 148                         $this->tableName = $params['tableName'];
 149                 }
 150                 if ( isset( $params['shards'] ) ) {
 151                         $this->shards = intval( $params['shards'] );
 152                 }
 153                 if ( isset( $params['syncTimeout'] ) ) {
 154                         $this->syncTimeout = $params['syncTimeout'];
 155                 }
 156                 $this->replicaOnly = !empty( $params['slaveOnly'] );
 157         }
 158
 159         /**
 160          * Get a connection to the specified database
 161          *
 162          * @param int $serverIndex
 163          * @return Database
 164          * @throws MWException
 165          */
 166         protected function getDB( $serverIndex ) {
 167                 if ( !isset( $this->conns[$serverIndex] ) ) {
 168                         if ( $serverIndex >= $this->numServers ) {
 169                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 170                         }
 171
 172                         # Don't keep timing out trying to connect for each call if the DB is down
 173                         if ( isset( $this->connFailureErrors[$serverIndex] )
 174                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 175                         ) {
 176                                 throw $this->connFailureErrors[$serverIndex];
 177                         }
 178
 179                         if ( $this->serverInfos ) {
 180                                 // Use custom database defined by server connection info
 181                                 $info = $this->serverInfos[$serverIndex];
 182                                 $type = $info['type'] ?? 'mysql';
 183                                 $host = $info['host'] ?? '[unknown]';
 184                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 185                                 $db = Database::factory( $type, $info );
 186                                 $db->clearFlag( DBO_TRX ); // auto-commit mode
 187                         } else {
 188                                 // Use the main LB database
 189                                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 190                                 $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 191                                 if ( $lb->getServerType( $lb->getWriterIndex() ) !== 'sqlite' ) {
 192                                         // Keep a separate connection to avoid contention and deadlocks
 193                                         $db = $lb->getConnection( $index, [], false, $lb::CONN_TRX_AUTOCOMMIT );
 194                                 } else {
 195                                         // However, SQLite has the opposite behavior due to DB-level locking.
 196                                         // Stock sqlite MediaWiki installs use a separate sqlite cache DB instead.
 197                                         $db = $lb->getConnection( $index );
 198                                 }
 199                         }
 200
 201                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 202                         $this->conns[$serverIndex] = $db;
 203                 }
 204
 205                 return $this->conns[$serverIndex];
 206         }
 207
 208         /**
 209          * Get the server index and table name for a given key
 210          * @param string $key
 211          * @return array Server index and table name
 212          */
 213         protected function getTableByKey( $key ) {
 214                 if ( $this->shards > 1 ) {
 215                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 216                         $tableIndex = $hash % $this->shards;
 217                 } else {
 218                         $tableIndex = 0;
 219                 }
 220                 if ( $this->numServers > 1 ) {
 221                         $sortedServers = $this->serverTags;
 222                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 223                         reset( $sortedServers );
 224                         $serverIndex = key( $sortedServers );
 225                 } else {
 226                         $serverIndex = 0;
 227                 }
 228                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 229         }
 230
 231         /**
 232          * Get the table name for a given shard index
 233          * @param int $index
 234          * @return string
 235          */
 236         protected function getTableNameByShard( $index ) {
 237                 if ( $this->shards > 1 ) {
 238                         $decimals = strlen( $this->shards - 1 );
 239                         return $this->tableName .
 240                                 sprintf( "%0{$decimals}d", $index );
 241                 } else {
 242                         return $this->tableName;
 243                 }
 244         }
 245
 246         protected function doGet( $key, $flags = 0, &$casToken = null ) {
 247                 $casToken = null;
 248
 249                 $blobs = $this->fetchBlobMulti( [ $key ] );
 250                 if ( array_key_exists( $key, $blobs ) ) {
 251                         $blob = $blobs[$key];
 252                         $value = $this->unserialize( $blob );
 253
 254                         $casToken = ( $value !== false ) ? $blob : null;
 255
 256                         return $value;
 257                 }
 258
 259                 return false;
 260         }
 261
 262         protected function doGetMulti( array $keys, $flags = 0 ) {
 263                 $values = [];
 264
 265                 $blobs = $this->fetchBlobMulti( $keys );
 266                 foreach ( $blobs as $key => $blob ) {
 267                         $values[$key] = $this->unserialize( $blob );
 268                 }
 269
 270                 return $values;
 271         }
 272
 273         protected function fetchBlobMulti( array $keys, $flags = 0 ) {
 274                 $values = []; // array of (key => value)
 275
 276                 $keysByTable = [];
 277                 foreach ( $keys as $key ) {
 278                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 279                         $keysByTable[$serverIndex][$tableName][] = $key;
 280                 }
 281
 282                 $dataRows = [];
 283                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 284                         try {
 285                                 $db = $this->getDB( $serverIndex );
 286                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 287                                         $res = $db->select( $tableName,
 288                                                 [ 'keyname', 'value', 'exptime' ],
 289                                                 [ 'keyname' => $tableKeys ],
 290                                                 __METHOD__,
 291                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 292                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 293                                                 // We do not want to flush the TRX as that can break callers.
 294                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 295                                         );
 296                                         if ( $res === false ) {
 297                                                 continue;
 298                                         }
 299                                         foreach ( $res as $row ) {
 300                                                 $row->serverIndex = $serverIndex;
 301                                                 $row->tableName = $tableName;
 302                                                 $dataRows[$row->keyname] = $row;
 303                                         }
 304                                 }
 305                         } catch ( DBError $e ) {
 306                                 $this->handleReadError( $e, $serverIndex );
 307                         }
 308                 }
 309
 310                 foreach ( $keys as $key ) {
 311                         if ( isset( $dataRows[$key] ) ) { // HIT?
 312                                 $row = $dataRows[$key];
 313                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 314                                 $db = null;
 315                                 try {
 316                                         $db = $this->getDB( $row->serverIndex );
 317                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 318                                                 $this->debug( "get: key has expired" );
 319                                         } else { // HIT
 320                                                 $values[$key] = $db->decodeBlob( $row->value );
 321                                         }
 322                                 } catch ( DBQueryError $e ) {
 323                                         $this->handleWriteError( $e, $db, $row->serverIndex );
 324                                 }
 325                         } else { // MISS
 326                                 $this->debug( 'get: no matching rows' );
 327                         }
 328                 }
 329
 330                 return $values;
 331         }
 332
 333         public function setMulti( array $data, $expiry = 0, $flags = 0 ) {
 334                 return $this->insertMulti( $data, $expiry, $flags, true );
 335         }
 336
 337         private function insertMulti( array $data, $expiry, $flags, $replace ) {
 338                 $keysByTable = [];
 339                 foreach ( $data as $key => $value ) {
 340                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 341                         $keysByTable[$serverIndex][$tableName][] = $key;
 342                 }
 343
 344                 $result = true;
 345                 $exptime = (int)$expiry;
 346                 /** @noinspection PhpUnusedLocalVariableInspection */
 347                 $silenceScope = $this->silenceTransactionProfiler();
 348                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 349                         $db = null;
 350                         try {
 351                                 $db = $this->getDB( $serverIndex );
 352                                 $this->occasionallyGarbageCollect( $db );
 353                         } catch ( DBError $e ) {
 354                                 $this->handleWriteError( $e, $db, $serverIndex );
 355                                 $result = false;
 356                                 continue;
 357                         }
 358
 359                         if ( $exptime < 0 ) {
 360                                 $exptime = 0;
 361                         }
 362
 363                         if ( $exptime == 0 ) {
 364                                 $encExpiry = $this->getMaxDateTime( $db );
 365                         } else {
 366                                 $exptime = $this->convertToExpiry( $exptime );
 367                                 $encExpiry = $db->timestamp( $exptime );
 368                         }
 369                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 370                                 $rows = [];
 371                                 foreach ( $tableKeys as $key ) {
 372                                         $rows[] = [
 373                                                 'keyname' => $key,
 374                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 375                                                 'exptime' => $encExpiry,
 376                                         ];
 377                                 }
 378
 379                                 try {
 380                                         if ( $replace ) {
 381                                                 $db->replace( $tableName, [ 'keyname' ], $rows, __METHOD__ );
 382                                         } else {
 383                                                 $db->insert( $tableName, $rows, __METHOD__, [ 'IGNORE' ] );
 384                                                 $result = ( $db->affectedRows() > 0 && $result );
 385                                         }
 386                                 } catch ( DBError $e ) {
 387                                         $this->handleWriteError( $e, $db, $serverIndex );
 388                                         $result = false;
 389                                 }
 390
 391                         }
 392                 }
 393
 394                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 395                         $result = $this->waitForReplication() && $result;
 396                 }
 397
 398                 return $result;
 399         }
 400
 401         protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 402                 $ok = $this->insertMulti( [ $key => $value ], $exptime, $flags, true );
 403
 404                 return $ok;
 405         }
 406
 407         public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 408                 $added = $this->insertMulti( [ $key => $value ], $exptime, $flags, false );
 409
 410                 return $added;
 411         }
 412
 413         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 414                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 415                 $db = null;
 416                 /** @noinspection PhpUnusedLocalVariableInspection */
 417                 $silenceScope = $this->silenceTransactionProfiler();
 418                 try {
 419                         $db = $this->getDB( $serverIndex );
 420                         $exptime = intval( $exptime );
 421
 422                         if ( $exptime < 0 ) {
 423                                 $exptime = 0;
 424                         }
 425
 426                         if ( $exptime == 0 ) {
 427                                 $encExpiry = $this->getMaxDateTime( $db );
 428                         } else {
 429                                 $exptime = $this->convertToExpiry( $exptime );
 430                                 $encExpiry = $db->timestamp( $exptime );
 431                         }
 432                         // (T26425) use a replace if the db supports it instead of
 433                         // delete/insert to avoid clashes with conflicting keynames
 434                         $db->update(
 435                                 $tableName,
 436                                 [
 437                                         'keyname' => $key,
 438                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 439                                         'exptime' => $encExpiry
 440                                 ],
 441                                 [
 442                                         'keyname' => $key,
 443                                         'value' => $db->encodeBlob( $casToken )
 444                                 ],
 445                                 __METHOD__
 446                         );
 447                 } catch ( DBQueryError $e ) {
 448                         $this->handleWriteError( $e, $db, $serverIndex );
 449
 450                         return false;
 451                 }
 452
 453                 return (bool)$db->affectedRows();
 454         }
 455
 456         public function deleteMulti( array $keys, $flags = 0 ) {
 457                 return $this->purgeMulti( $keys, $flags );
 458         }
 459
 460         public function purgeMulti( array $keys, $flags = 0 ) {
 461                 $keysByTable = [];
 462                 foreach ( $keys as $key ) {
 463                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 464                         $keysByTable[$serverIndex][$tableName][] = $key;
 465                 }
 466
 467                 $result = true;
 468                 /** @noinspection PhpUnusedLocalVariableInspection */
 469                 $silenceScope = $this->silenceTransactionProfiler();
 470                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 471                         $db = null;
 472                         try {
 473                                 $db = $this->getDB( $serverIndex );
 474                         } catch ( DBError $e ) {
 475                                 $this->handleWriteError( $e, $db, $serverIndex );
 476                                 $result = false;
 477                                 continue;
 478                         }
 479
 480                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 481                                 try {
 482                                         $db->delete( $tableName, [ 'keyname' => $tableKeys ], __METHOD__ );
 483                                 } catch ( DBError $e ) {
 484                                         $this->handleWriteError( $e, $db, $serverIndex );
 485                                         $result = false;
 486                                 }
 487
 488                         }
 489                 }
 490
 491                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 492                         $result = $this->waitForReplication() && $result;
 493                 }
 494
 495                 return $result;
 496         }
 497
 498         protected function doDelete( $key, $flags = 0 ) {
 499                 $ok = $this->purgeMulti( [ $key ], $flags );
 500
 501                 return $ok;
 502         }
 503
 504         public function incr( $key, $step = 1 ) {
 505                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 506                 $db = null;
 507                 /** @noinspection PhpUnusedLocalVariableInspection */
 508                 $silenceScope = $this->silenceTransactionProfiler();
 509                 try {
 510                         $db = $this->getDB( $serverIndex );
 511                         $step = intval( $step );
 512                         $row = $db->selectRow(
 513                                 $tableName,
 514                                 [ 'value', 'exptime' ],
 515                                 [ 'keyname' => $key ],
 516                                 __METHOD__,
 517                                 [ 'FOR UPDATE' ]
 518                         );
 519                         if ( $row === false ) {
 520                                 // Missing
 521                                 return false;
 522                         }
 523                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 524                         if ( $this->isExpired( $db, $row->exptime ) ) {
 525                                 // Expired, do not reinsert
 526                                 return false;
 527                         }
 528
 529                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 530                         $newValue = $oldValue + $step;
 531                         $db->insert(
 532                                 $tableName,
 533                                 [
 534                                         'keyname' => $key,
 535                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 536                                         'exptime' => $row->exptime
 537                                 ],
 538                                 __METHOD__,
 539                                 [ 'IGNORE' ]
 540                         );
 541
 542                         if ( $db->affectedRows() == 0 ) {
 543                                 // Race condition. See T30611
 544                                 $newValue = false;
 545                         }
 546                 } catch ( DBError $e ) {
 547                         $this->handleWriteError( $e, $db, $serverIndex );
 548                         return false;
 549                 }
 550
 551                 return $newValue;
 552         }
 553
 554         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 555                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
 556                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 557                         $ok = $this->waitForReplication() && $ok;
 558                 }
 559
 560                 return $ok;
 561         }
 562
 563         public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 564                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 565                 $db = null;
 566                 /** @noinspection PhpUnusedLocalVariableInspection */
 567                 $silenceScope = $this->silenceTransactionProfiler();
 568                 try {
 569                         $db = $this->getDB( $serverIndex );
 570                         if ( $exptime == 0 ) {
 571                                 $timestamp = $this->getMaxDateTime( $db );
 572                         } else {
 573                                 $timestamp = $db->timestamp( $this->convertToExpiry( $exptime ) );
 574                         }
 575                         $db->update(
 576                                 $tableName,
 577                                 [ 'exptime' => $timestamp ],
 578                                 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
 579                                 __METHOD__
 580                         );
 581                         if ( $db->affectedRows() == 0 ) {
 582                                 $exists = (bool)$db->selectField(
 583                                         $tableName,
 584                                         1,
 585                                         [ 'keyname' => $key, 'exptime' => $timestamp ],
 586                                         __METHOD__,
 587                                         [ 'FOR UPDATE' ]
 588                                 );
 589
 590                                 return $exists;
 591                         }
 592                 } catch ( DBError $e ) {
 593                         $this->handleWriteError( $e, $db, $serverIndex );
 594                         return false;
 595                 }
 596
 597                 return true;
 598         }
 599
 600         /**
 601          * @param IDatabase $db
 602          * @param string $exptime
 603          * @return bool
 604          */
 605         protected function isExpired( $db, $exptime ) {
 606                 return (
 607                         $exptime != $this->getMaxDateTime( $db ) &&
 608                         wfTimestamp( TS_UNIX, $exptime ) < time()
 609                 );
 610         }
 611
 612         /**
 613          * @param IDatabase $db
 614          * @return string
 615          */
 616         protected function getMaxDateTime( $db ) {
 617                 if ( time() > 0x7fffffff ) {
 618                         return $db->timestamp( 1 << 62 );
 619                 } else {
 620                         return $db->timestamp( 0x7fffffff );
 621                 }
 622         }
 623
 624         /**
 625          * @param IDatabase $db
 626          * @throws DBError
 627          */
 628         protected function occasionallyGarbageCollect( IDatabase $db ) {
 629                 if (
 630                         // Random purging is enabled
 631                         $this->purgePeriod &&
 632                         // This is not using a replica DB
 633                         !$this->replicaOnly &&
 634                         // Only purge on one in every $this->purgePeriod writes
 635                         mt_rand( 0, $this->purgePeriod - 1 ) == 0 &&
 636                         // Avoid repeating the delete within a few seconds
 637                         ( time() - $this->lastGarbageCollect ) > self::GARBAGE_COLLECT_DELAY_SEC
 638                 ) {
 639                         $garbageCollector = function () use ( $db ) {
 640                                 $this->deleteServerObjectsExpiringBefore( $db, time(), null, $this->purgeLimit );
 641                                 $this->lastGarbageCollect = time();
 642                         };
 643                         if ( $this->asyncHandler ) {
 644                                 $this->lastGarbageCollect = time(); // avoid duplicate enqueues
 645                                 ( $this->asyncHandler )( $garbageCollector );
 646                         } else {
 647                                 $garbageCollector();
 648                         }
 649                 }
 650         }
 651
 652         public function expireAll() {
 653                 $this->deleteObjectsExpiringBefore( time() );
 654         }
 655
 656         public function deleteObjectsExpiringBefore(
 657                 $timestamp,
 658                 callable $progressCallback = null,
 659                 $limit = INF
 660         ) {
 661                 /** @noinspection PhpUnusedLocalVariableInspection */
 662                 $silenceScope = $this->silenceTransactionProfiler();
 663
 664                 $serverIndexes = range( 0, $this->numServers - 1 );
 665                 shuffle( $serverIndexes );
 666
 667                 $ok = true;
 668
 669                 $keysDeletedCount = 0;
 670                 foreach ( $serverIndexes as $numServersDone => $serverIndex ) {
 671                         $db = null;
 672                         try {
 673                                 $db = $this->getDB( $serverIndex );
 674                                 $this->deleteServerObjectsExpiringBefore(
 675                                         $db,
 676                                         $timestamp,
 677                                         $progressCallback,
 678                                         $limit,
 679                                         $numServersDone,
 680                                         $keysDeletedCount
 681                                 );
 682                         } catch ( DBError $e ) {
 683                                 $this->handleWriteError( $e, $db, $serverIndex );
 684                                 $ok = false;
 685                         }
 686                 }
 687
 688                 return $ok;
 689         }
 690
 691         /**
 692          * @param IDatabase $db
 693          * @param string|int $timestamp
 694          * @param callable|null $progressCallback
 695          * @param int $limit
 696          * @param int $serversDoneCount
 697          * @param int &$keysDeletedCount
 698          * @throws DBError
 699          */
 700         private function deleteServerObjectsExpiringBefore(
 701                 IDatabase $db,
 702                 $timestamp,
 703                 $progressCallback,
 704                 $limit,
 705                 $serversDoneCount = 0,
 706                 &$keysDeletedCount = 0
 707         ) {
 708                 $cutoffUnix = wfTimestamp( TS_UNIX, $timestamp );
 709                 $shardIndexes = range( 0, $this->shards - 1 );
 710                 shuffle( $shardIndexes );
 711
 712                 foreach ( $shardIndexes as $numShardsDone => $shardIndex ) {
 713                         $continue = null; // last exptime
 714                         $lag = null; // purge lag
 715                         do {
 716                                 $res = $db->select(
 717                                         $this->getTableNameByShard( $shardIndex ),
 718                                         [ 'keyname', 'exptime' ],
 719                                         array_merge(
 720                                                 [ 'exptime < ' . $db->addQuotes( $db->timestamp( $cutoffUnix ) ) ],
 721                                                 $continue ? [ 'exptime >= ' . $db->addQuotes( $continue ) ] : []
 722                                         ),
 723                                         __METHOD__,
 724                                         [ 'LIMIT' => min( $limit, 100 ), 'ORDER BY' => 'exptime' ]
 725                                 );
 726
 727                                 if ( $res->numRows() ) {
 728                                         $row = $res->current();
 729                                         if ( $lag === null ) {
 730                                                 $lag = max( $cutoffUnix - wfTimestamp( TS_UNIX, $row->exptime ), 1 );
 731                                         }
 732
 733                                         $keys = [];
 734                                         foreach ( $res as $row ) {
 735                                                 $keys[] = $row->keyname;
 736                                                 $continue = $row->exptime;
 737                                         }
 738
 739                                         $db->delete(
 740                                                 $this->getTableNameByShard( $shardIndex ),
 741                                                 [
 742                                                         'exptime < ' . $db->addQuotes( $db->timestamp( $cutoffUnix ) ),
 743                                                         'keyname' => $keys
 744                                                 ],
 745                                                 __METHOD__
 746                                         );
 747                                         $keysDeletedCount += $db->affectedRows();
 748                                 }
 749
 750                                 if ( is_callable( $progressCallback ) ) {
 751                                         if ( $lag ) {
 752                                                 $remainingLag = $cutoffUnix - wfTimestamp( TS_UNIX, $continue );
 753                                                 $processedLag = max( $lag - $remainingLag, 0 );
 754                                                 $doneRatio = ( $numShardsDone + $processedLag / $lag ) / $this->shards;
 755                                         } else {
 756                                                 $doneRatio = 1;
 757                                         }
 758
 759                                         $overallRatio = ( $doneRatio / $this->numServers )
 760                                                 + ( $serversDoneCount / $this->numServers );
 761                                         call_user_func( $progressCallback, $overallRatio * 100 );
 762                                 }
 763                         } while ( $res->numRows() && $keysDeletedCount < $limit );
 764                 }
 765         }
 766
 767         /**
 768          * Delete content of shard tables in every server.
 769          * Return true if the operation is successful, false otherwise.
 770          * @return bool
 771          */
 772         public function deleteAll() {
 773                 /** @noinspection PhpUnusedLocalVariableInspection */
 774                 $silenceScope = $this->silenceTransactionProfiler();
 775                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 776                         $db = null;
 777                         try {
 778                                 $db = $this->getDB( $serverIndex );
 779                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 780                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 781                                 }
 782                         } catch ( DBError $e ) {
 783                                 $this->handleWriteError( $e, $db, $serverIndex );
 784                                 return false;
 785                         }
 786                 }
 787                 return true;
 788         }
 789
 790         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 791                 // Avoid deadlocks and allow lock reentry if specified
 792                 if ( isset( $this->locks[$key] ) ) {
 793                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 794                                 ++$this->locks[$key]['depth'];
 795                                 return true;
 796                         } else {
 797                                 return false;
 798                         }
 799                 }
 800
 801                 list( $serverIndex ) = $this->getTableByKey( $key );
 802
 803                 $db = null;
 804                 try {
 805                         $db = $this->getDB( $serverIndex );
 806                         $ok = $db->lock( $key, __METHOD__, $timeout );
 807                         if ( $ok ) {
 808                                 $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 809                         }
 810
 811                         $this->logger->warning(
 812                                 __METHOD__ . " failed due to timeout for {key}.",
 813                                 [ 'key' => $key, 'timeout' => $timeout ]
 814                         );
 815
 816                         return $ok;
 817                 } catch ( DBError $e ) {
 818                         $this->handleWriteError( $e, $db, $serverIndex );
 819                         $ok = false;
 820                 }
 821
 822                 return $ok;
 823         }
 824
 825         public function unlock( $key ) {
 826                 if ( !isset( $this->locks[$key] ) ) {
 827                         return false;
 828                 }
 829
 830                 if ( --$this->locks[$key]['depth'] <= 0 ) {
 831                         unset( $this->locks[$key] );
 832
 833                         list( $serverIndex ) = $this->getTableByKey( $key );
 834
 835                         $db = null;
 836                         try {
 837                                 $db = $this->getDB( $serverIndex );
 838                                 $ok = $db->unlock( $key, __METHOD__ );
 839                                 if ( !$ok ) {
 840                                         $this->logger->warning(
 841                                                 __METHOD__ . ' failed to release lock for {key}.',
 842                                                 [ 'key' => $key ]
 843                                         );
 844                                 }
 845                         } catch ( DBError $e ) {
 846                                 $this->handleWriteError( $e, $db, $serverIndex );
 847                                 $ok = false;
 848                         }
 849                 } else {
 850                         $ok = false;
 851                 }
 852
 853                 return $ok;
 854         }
 855
 856         /**
 857          * Serialize an object and, if possible, compress the representation.
 858          * On typical message and page data, this can provide a 3X decrease
 859          * in storage requirements.
 860          *
 861          * @param mixed $data
 862          * @return string
 863          */
 864         protected function serialize( $data ) {
 865                 $serial = serialize( $data );
 866
 867                 if ( function_exists( 'gzdeflate' ) ) {
 868                         return gzdeflate( $serial );
 869                 } else {
 870                         return $serial;
 871                 }
 872         }
 873
 874         /**
 875          * Unserialize and, if necessary, decompress an object.
 876          * @param string $serial
 877          * @return mixed
 878          */
 879         protected function unserialize( $serial ) {
 880                 if ( function_exists( 'gzinflate' ) ) {
 881                         Wikimedia\suppressWarnings();
 882                         $decomp = gzinflate( $serial );
 883                         Wikimedia\restoreWarnings();
 884
 885                         if ( $decomp !== false ) {
 886                                 $serial = $decomp;
 887                         }
 888                 }
 889
 890                 $ret = unserialize( $serial );
 891
 892                 return $ret;
 893         }
 894
 895         /**
 896          * Handle a DBError which occurred during a read operation.
 897          *
 898          * @param DBError $exception
 899          * @param int $serverIndex
 900          */
 901         protected function handleReadError( DBError $exception, $serverIndex ) {
 902                 if ( $exception instanceof DBConnectionError ) {
 903                         $this->markServerDown( $exception, $serverIndex );
 904                 }
 905
 906                 $this->setAndLogDBError( $exception );
 907         }
 908
 909         /**
 910          * Handle a DBQueryError which occurred during a write operation.
 911          *
 912          * @param DBError $exception
 913          * @param IDatabase|null $db DB handle or null if connection failed
 914          * @param int $serverIndex
 915          * @throws Exception
 916          */
 917         protected function handleWriteError( DBError $exception, $db, $serverIndex ) {
 918                 if ( !( $db instanceof IDatabase ) ) {
 919                         $this->markServerDown( $exception, $serverIndex );
 920                 }
 921
 922                 $this->setAndLogDBError( $exception );
 923         }
 924
 925         /**
 926          * @param DBError $exception
 927          */
 928         private function setAndLogDBError( DBError $exception ) {
 929                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 930                 if ( $exception instanceof DBConnectionError ) {
 931                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 932                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 933                 } else {
 934                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 935                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 936                 }
 937         }
 938
 939         /**
 940          * Mark a server down due to a DBConnectionError exception
 941          *
 942          * @param DBError $exception
 943          * @param int $serverIndex
 944          */
 945         protected function markServerDown( DBError $exception, $serverIndex ) {
 946                 unset( $this->conns[$serverIndex] ); // bug T103435
 947
 948                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 949                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 950                                 unset( $this->connFailureTimes[$serverIndex] );
 951                                 unset( $this->connFailureErrors[$serverIndex] );
 952                         } else {
 953                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 954                                 return;
 955                         }
 956                 }
 957                 $now = time();
 958                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 959                 $this->connFailureTimes[$serverIndex] = $now;
 960                 $this->connFailureErrors[$serverIndex] = $exception;
 961         }
 962
 963         /**
 964          * Create shard tables. For use from eval.php.
 965          */
 966         public function createTables() {
 967                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 968                         $db = $this->getDB( $serverIndex );
 969                         if ( $db->getType() !== 'mysql' ) {
 970                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 971                         }
 972
 973                         for ( $i = 0; $i < $this->shards; $i++ ) {
 974                                 $db->query(
 975                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 976                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 977                                         __METHOD__ );
 978                         }
 979                 }
 980         }
 981
 982         /**
 983          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 984          */
 985         protected function usesMainDB() {
 986                 return !$this->serverInfos;
 987         }
 988
 989         protected function waitForReplication() {
 990                 if ( !$this->usesMainDB() ) {
 991                         // Custom DB server list; probably doesn't use replication
 992                         return true;
 993                 }
 994
 995                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 996                 if ( $lb->getServerCount() <= 1 ) {
 997                         return true; // no replica DBs
 998                 }
 999
1000                 // Main LB is used; wait for any replica DBs to catch up
1001                 try {
1002                         $masterPos = $lb->getMasterPos();
1003                         if ( !$masterPos ) {
1004                                 return true; // not applicable
1005                         }
1006
1007                         $loop = new WaitConditionLoop(
1008                                 function () use ( $lb, $masterPos ) {
1009                                         return $lb->waitForAll( $masterPos, 1 );
1010                                 },
1011                                 $this->syncTimeout,
1012                                 $this->busyCallbacks
1013                         );
1014
1015                         return ( $loop->invoke() === $loop::CONDITION_REACHED );
1016                 } catch ( DBError $e ) {
1017                         $this->setAndLogDBError( $e );
1018
1019                         return false;
1020                 }
1021         }
1022
1023         /**
1024          * Returns a ScopedCallback which resets the silence flag in the transaction profiler when it is
1025          * destroyed on the end of a scope, for example on return or throw
1026          * @return ScopedCallback
1027          * @since 1.32
1028          */
1029         protected function silenceTransactionProfiler() {
1030                 $trxProfiler = Profiler::instance()->getTransactionProfiler();
1031                 $oldSilenced = $trxProfiler->setSilenced( true );
1032                 return new ScopedCallback( function () use ( $trxProfiler, $oldSilenced ) {
1033                         $trxProfiler->setSilenced( $oldSilenced );
1034                 } );
1035         }
1036 }