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\IMaintainableDatabase;
  31 use Wikimedia\Rdbms\LoadBalancer;
  32 use Wikimedia\ScopedCallback;
  33 use Wikimedia\WaitConditionLoop;
  34
  35 /**
  36  * Class to store objects in the database
  37  *
  38  * @ingroup Cache
  39  */
  40 class SqlBagOStuff extends MediumSpecificBagOStuff {
  41         /** @var array[] (server index => server config) */
  42         protected $serverInfos;
  43         /** @var string[] (server index => tag/host name) */
  44         protected $serverTags;
  45         /** @var int */
  46         protected $numServerShards;
  47         /** @var int UNIX timestamp */
  48         protected $lastGarbageCollect = 0;
  49         /** @var int */
  50         protected $purgePeriod = 10;
  51         /** @var int */
  52         protected $purgeLimit = 100;
  53         /** @var int */
  54         protected $numTableShards = 1;
  55         /** @var string */
  56         protected $tableName = 'objectcache';
  57         /** @var bool */
  58         protected $replicaOnly = false;
  59
  60         /** @var LoadBalancer|null */
  61         protected $separateMainLB;
  62         /** @var array */
  63         protected $conns;
  64         /** @var array UNIX timestamps */
  65         protected $connFailureTimes = [];
  66         /** @var array Exceptions */
  67         protected $connFailureErrors = [];
  68
  69         /** @var int */
  70         private static $GC_DELAY_SEC = 1;
  71
  72         /** @var string */
  73         private static $OP_SET = 'set';
  74         /** @var string */
  75         private static $OP_ADD = 'add';
  76         /** @var string */
  77         private static $OP_TOUCH = 'touch';
  78         /** @var string */
  79         private static $OP_DELETE = 'delete';
  80
  81         /**
  82          * Constructor. Parameters are:
  83          *   - server:      A server info structure in the format required by each
  84          *                  element in $wgDBServers.
  85          *
  86          *   - servers:     An array of server info structures describing a set of database servers
  87          *                  to distribute keys to. If this is specified, the "server" option will be
  88          *                  ignored. If string keys are used, then they will be used for consistent
  89          *                  hashing *instead* of the host name (from the server config). This is useful
  90          *                  when a cluster is replicated to another site (with different host names)
  91          *                  but each server has a corresponding replica in the other cluster.
  92          *
  93          *   - purgePeriod: The average number of object cache writes in between
  94          *                  garbage collection operations, where expired entries
  95          *                  are removed from the database. Or in other words, the
  96          *                  reciprocal of the probability of purging on any given
  97          *                  write. If this is set to zero, purging will never be done.
  98          *
  99          *   - purgeLimit:  Maximum number of rows to purge at once.
 100          *
 101          *   - tableName:   The table name to use, default is "objectcache".
 102          *
 103          *   - shards:      The number of tables to use for data storage on each server.
 104          *                  If this is more than 1, table names will be formed in the style
 105          *                  objectcacheNNN where NNN is the shard index, between 0 and
 106          *                  shards-1. The number of digits will be the minimum number
 107          *                  required to hold the largest shard index. Data will be
 108          *                  distributed across all tables by key hash. This is for
 109          *                  MySQL bugs 61735 <https://bugs.mysql.com/bug.php?id=61735>
 110          *                  and 61736 <https://bugs.mysql.com/bug.php?id=61736>.
 111          *
 112          *   - replicaOnly: Whether to only use replica DBs and avoid triggering
 113          *                  garbage collection logic of expired items. This only
 114          *                  makes sense if the primary DB is used and only if get()
 115          *                  calls will be used. This is used by ReplicatedBagOStuff.
 116          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
 117          *
 118          * @param array $params
 119          */
 120         public function __construct( $params ) {
 121                 parent::__construct( $params );
 122
 123                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 124                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 125
 126                 if ( isset( $params['servers'] ) ) {
 127                         $this->serverInfos = [];
 128                         $this->serverTags = [];
 129                         $this->numServerShards = count( $params['servers'] );
 130                         $index = 0;
 131                         foreach ( $params['servers'] as $tag => $info ) {
 132                                 $this->serverInfos[$index] = $info;
 133                                 if ( is_string( $tag ) ) {
 134                                         $this->serverTags[$index] = $tag;
 135                                 } else {
 136                                         $this->serverTags[$index] = $info['host'] ?? "#$index";
 137                                 }
 138                                 ++$index;
 139                         }
 140                 } elseif ( isset( $params['server'] ) ) {
 141                         $this->serverInfos = [ $params['server'] ];
 142                         $this->numServerShards = count( $this->serverInfos );
 143                 } else {
 144                         // Default to using the main wiki's database servers
 145                         $this->serverInfos = false;
 146                         $this->numServerShards = 1;
 147                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 148                 }
 149                 if ( isset( $params['purgePeriod'] ) ) {
 150                         $this->purgePeriod = intval( $params['purgePeriod'] );
 151                 }
 152                 if ( isset( $params['purgeLimit'] ) ) {
 153                         $this->purgeLimit = intval( $params['purgeLimit'] );
 154                 }
 155                 if ( isset( $params['tableName'] ) ) {
 156                         $this->tableName = $params['tableName'];
 157                 }
 158                 if ( isset( $params['shards'] ) ) {
 159                         $this->numTableShards = intval( $params['shards'] );
 160                 }
 161                 // Backwards-compatibility for < 1.34
 162                 $this->replicaOnly = $params['replicaOnly'] ?? ( $params['slaveOnly'] ?? false );
 163         }
 164
 165         /**
 166          * Get a connection to the specified database
 167          *
 168          * @param int $shardIndex
 169          * @return IMaintainableDatabase
 170          * @throws MWException
 171          */
 172         private function getDB( $shardIndex ) {
 173                 if ( $shardIndex >= $this->numServerShards ) {
 174                         throw new MWException( __METHOD__ . ": Invalid server index \"$shardIndex\"" );
 175                 }
 176
 177                 # Don't keep timing out trying to connect for each call if the DB is down
 178                 if (
 179                         isset( $this->connFailureErrors[$shardIndex] ) &&
 180                         ( $this->getCurrentTime() - $this->connFailureTimes[$shardIndex] ) < 60
 181                 ) {
 182                         throw $this->connFailureErrors[$shardIndex];
 183                 }
 184
 185                 if ( $this->serverInfos ) {
 186                         if ( !isset( $this->conns[$shardIndex] ) ) {
 187                                 // Use custom database defined by server connection info
 188                                 $info = $this->serverInfos[$shardIndex];
 189                                 $type = $info['type'] ?? 'mysql';
 190                                 $host = $info['host'] ?? '[unknown]';
 191                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 192                                 $db = Database::factory( $type, $info );
 193                                 $db->clearFlag( DBO_TRX ); // auto-commit mode
 194                                 $this->conns[$shardIndex] = $db;
 195                         }
 196                         $db = $this->conns[$shardIndex];
 197                 } else {
 198                         // Use the main LB database
 199                         $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 200                         $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 201                         if ( $lb->getServerType( $lb->getWriterIndex() ) !== 'sqlite' ) {
 202                                 // Keep a separate connection to avoid contention and deadlocks
 203                                 $db = $lb->getConnectionRef( $index, [], false, $lb::CONN_TRX_AUTOCOMMIT );
 204                         } else {
 205                                 // However, SQLite has the opposite behavior due to DB-level locking.
 206                                 // Stock sqlite MediaWiki installs use a separate sqlite cache DB instead.
 207                                 $db = $lb->getConnectionRef( $index );
 208                         }
 209                 }
 210
 211                 $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 212
 213                 return $db;
 214         }
 215
 216         /**
 217          * Get the server index and table name for a given key
 218          * @param string $key
 219          * @return array Server index and table name
 220          */
 221         private function getTableByKey( $key ) {
 222                 if ( $this->numTableShards > 1 ) {
 223                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 224                         $tableIndex = $hash % $this->numTableShards;
 225                 } else {
 226                         $tableIndex = 0;
 227                 }
 228                 if ( $this->numServerShards > 1 ) {
 229                         $sortedServers = $this->serverTags;
 230                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 231                         reset( $sortedServers );
 232                         $shardIndex = key( $sortedServers );
 233                 } else {
 234                         $shardIndex = 0;
 235                 }
 236                 return [ $shardIndex, $this->getTableNameByShard( $tableIndex ) ];
 237         }
 238
 239         /**
 240          * Get the table name for a given shard index
 241          * @param int $index
 242          * @return string
 243          */
 244         private function getTableNameByShard( $index ) {
 245                 if ( $this->numTableShards > 1 ) {
 246                         $decimals = strlen( $this->numTableShards - 1 );
 247                         return $this->tableName .
 248                                 sprintf( "%0{$decimals}d", $index );
 249                 } else {
 250                         return $this->tableName;
 251                 }
 252         }
 253
 254         protected function doGet( $key, $flags = 0, &$casToken = null ) {
 255                 $casToken = null;
 256
 257                 $blobs = $this->fetchBlobMulti( [ $key ] );
 258                 if ( array_key_exists( $key, $blobs ) ) {
 259                         $blob = $blobs[$key];
 260                         $value = $this->unserialize( $blob );
 261
 262                         $casToken = ( $value !== false ) ? $blob : null;
 263
 264                         return $value;
 265                 }
 266
 267                 return false;
 268         }
 269
 270         protected function doGetMulti( array $keys, $flags = 0 ) {
 271                 $values = [];
 272
 273                 $blobs = $this->fetchBlobMulti( $keys );
 274                 foreach ( $blobs as $key => $blob ) {
 275                         $values[$key] = $this->unserialize( $blob );
 276                 }
 277
 278                 return $values;
 279         }
 280
 281         private function fetchBlobMulti( array $keys, $flags = 0 ) {
 282                 $values = []; // array of (key => value)
 283
 284                 $keysByTable = [];
 285                 foreach ( $keys as $key ) {
 286                         list( $shardIndex, $tableName ) = $this->getTableByKey( $key );
 287                         $keysByTable[$shardIndex][$tableName][] = $key;
 288                 }
 289
 290                 $dataRows = [];
 291                 foreach ( $keysByTable as $shardIndex => $serverKeys ) {
 292                         try {
 293                                 $db = $this->getDB( $shardIndex );
 294                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 295                                         $res = $db->select( $tableName,
 296                                                 [ 'keyname', 'value', 'exptime' ],
 297                                                 [ 'keyname' => $tableKeys ],
 298                                                 __METHOD__,
 299                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 300                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 301                                                 // We do not want to flush the TRX as that can break callers.
 302                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 303                                         );
 304                                         if ( $res === false ) {
 305                                                 continue;
 306                                         }
 307                                         foreach ( $res as $row ) {
 308                                                 $row->shardIndex = $shardIndex;
 309                                                 $row->tableName = $tableName;
 310                                                 $dataRows[$row->keyname] = $row;
 311                                         }
 312                                 }
 313                         } catch ( DBError $e ) {
 314                                 $this->handleReadError( $e, $shardIndex );
 315                         }
 316                 }
 317
 318                 foreach ( $keys as $key ) {
 319                         if ( isset( $dataRows[$key] ) ) { // HIT?
 320                                 $row = $dataRows[$key];
 321                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 322                                 $db = null; // in case of connection failure
 323                                 try {
 324                                         $db = $this->getDB( $row->shardIndex );
 325                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 326                                                 $this->debug( "get: key has expired" );
 327                                         } else { // HIT
 328                                                 $values[$key] = $db->decodeBlob( $row->value );
 329                                         }
 330                                 } catch ( DBQueryError $e ) {
 331                                         $this->handleWriteError( $e, $db, $row->shardIndex );
 332                                 }
 333                         } else { // MISS
 334                                 $this->debug( 'get: no matching rows' );
 335                         }
 336                 }
 337
 338                 return $values;
 339         }
 340
 341         protected function doSetMulti( array $data, $exptime = 0, $flags = 0 ) {
 342                 return $this->modifyMulti( $data, $exptime, $flags, self::$OP_SET );
 343         }
 344
 345         /**
 346          * @param mixed[]|null[] $data Map of (key => new value or null)
 347          * @param int $exptime UNIX timestamp, TTL in seconds, or 0 (no expiration)
 348          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 349          * @param string $op Cache operation
 350          * @return bool
 351          */
 352         private function modifyMulti( array $data, $exptime, $flags, $op ) {
 353                 $keysByTable = [];
 354                 foreach ( $data as $key => $value ) {
 355                         list( $shardIndex, $tableName ) = $this->getTableByKey( $key );
 356                         $keysByTable[$shardIndex][$tableName][] = $key;
 357                 }
 358
 359                 $exptime = $this->getExpirationAsTimestamp( $exptime );
 360
 361                 $result = true;
 362                 /** @noinspection PhpUnusedLocalVariableInspection */
 363                 $silenceScope = $this->silenceTransactionProfiler();
 364                 foreach ( $keysByTable as $shardIndex => $serverKeys ) {
 365                         $db = null; // in case of connection failure
 366                         try {
 367                                 $db = $this->getDB( $shardIndex );
 368                                 $this->occasionallyGarbageCollect( $db ); // expire old entries if any
 369                                 $dbExpiry = $exptime ? $db->timestamp( $exptime ) : $this->getMaxDateTime( $db );
 370                         } catch ( DBError $e ) {
 371                                 $this->handleWriteError( $e, $db, $shardIndex );
 372                                 $result = false;
 373                                 continue;
 374                         }
 375
 376                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 377                                 try {
 378                                         $result = $this->updateTableKeys(
 379                                                 $op,
 380                                                 $db,
 381                                                 $tableName,
 382                                                 $tableKeys,
 383                                                 $data,
 384                                                 $dbExpiry
 385                                         ) && $result;
 386                                 } catch ( DBError $e ) {
 387                                         $this->handleWriteError( $e, $db, $shardIndex );
 388                                         $result = false;
 389                                 }
 390
 391                         }
 392                 }
 393
 394                 if ( $this->fieldHasFlags( $flags, self::WRITE_SYNC ) ) {
 395                         $result = $this->waitForReplication() && $result;
 396                 }
 397
 398                 return $result;
 399         }
 400
 401         /**
 402          * @param string $op
 403          * @param IDatabase $db
 404          * @param string $table
 405          * @param string[] $tableKeys Keys in $data to update
 406          * @param mixed[]|null[] $data Map of (key => new value or null)
 407          * @param string $dbExpiry DB-encoded expiry
 408          * @return bool
 409          * @throws DBError
 410          * @throws InvalidArgumentException
 411          */
 412         private function updateTableKeys( $op, $db, $table, $tableKeys, $data, $dbExpiry ) {
 413                 $success = true;
 414
 415                 if ( $op === self::$OP_ADD ) {
 416                         $rows = [];
 417                         foreach ( $tableKeys as $key ) {
 418                                 $rows[] = [
 419                                         'keyname' => $key,
 420                                         'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 421                                         'exptime' => $dbExpiry
 422                                 ];
 423                         }
 424                         $db->delete(
 425                                 $table,
 426                                 [
 427                                         'keyname' => $tableKeys,
 428                                         'exptime <= ' . $db->addQuotes( $db->timestamp() )
 429                                 ],
 430                                 __METHOD__
 431                         );
 432                         $db->insert( $table, $rows, __METHOD__, [ 'IGNORE' ] );
 433
 434                         $success = ( $db->affectedRows() == count( $rows ) );
 435                 } elseif ( $op === self::$OP_SET ) {
 436                         $rows = [];
 437                         foreach ( $tableKeys as $key ) {
 438                                 $rows[] = [
 439                                         'keyname' => $key,
 440                                         'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 441                                         'exptime' => $dbExpiry
 442                                 ];
 443                         }
 444                         $db->replace( $table, [ 'keyname' ], $rows, __METHOD__ );
 445                 } elseif ( $op === self::$OP_DELETE ) {
 446                         $db->delete( $table, [ 'keyname' => $tableKeys ], __METHOD__ );
 447                 } elseif ( $op === self::$OP_TOUCH ) {
 448                         $db->update(
 449                                 $table,
 450                                 [ 'exptime' => $dbExpiry ],
 451                                 [
 452                                         'keyname' => $tableKeys,
 453                                         'exptime > ' . $db->addQuotes( $db->timestamp() )
 454                                 ],
 455                                 __METHOD__
 456                         );
 457
 458                         $success = ( $db->affectedRows() == count( $tableKeys ) );
 459                 } else {
 460                         throw new InvalidArgumentException( "Invalid operation '$op'" );
 461                 }
 462
 463                 return $success;
 464         }
 465
 466         protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 467                 return $this->modifyMulti( [ $key => $value ], $exptime, $flags, self::$OP_SET );
 468         }
 469
 470         protected function doAdd( $key, $value, $exptime = 0, $flags = 0 ) {
 471                 return $this->modifyMulti( [ $key => $value ], $exptime, $flags, self::$OP_ADD );
 472         }
 473
 474         protected function doCas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 475                 list( $shardIndex, $tableName ) = $this->getTableByKey( $key );
 476                 $exptime = $this->getExpirationAsTimestamp( $exptime );
 477
 478                 /** @noinspection PhpUnusedLocalVariableInspection */
 479                 $silenceScope = $this->silenceTransactionProfiler();
 480                 $db = null; // in case of connection failure
 481                 try {
 482                         $db = $this->getDB( $shardIndex );
 483                         // (T26425) use a replace if the db supports it instead of
 484                         // delete/insert to avoid clashes with conflicting keynames
 485                         $db->update(
 486                                 $tableName,
 487                                 [
 488                                         'keyname' => $key,
 489                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 490                                         'exptime' => $exptime
 491                                                 ? $db->timestamp( $exptime )
 492                                                 : $this->getMaxDateTime( $db )
 493                                 ],
 494                                 [
 495                                         'keyname' => $key,
 496                                         'value' => $db->encodeBlob( $casToken ),
 497                                         'exptime > ' . $db->addQuotes( $db->timestamp() )
 498                                 ],
 499                                 __METHOD__
 500                         );
 501                 } catch ( DBQueryError $e ) {
 502                         $this->handleWriteError( $e, $db, $shardIndex );
 503
 504                         return false;
 505                 }
 506
 507                 $success = (bool)$db->affectedRows();
 508                 if ( $this->fieldHasFlags( $flags, self::WRITE_SYNC ) ) {
 509                         $success = $this->waitForReplication() && $success;
 510                 }
 511
 512                 return $success;
 513         }
 514
 515         protected function doDeleteMulti( array $keys, $flags = 0 ) {
 516                 return $this->modifyMulti(
 517                         array_fill_keys( $keys, null ),
 518                         0,
 519                         $flags,
 520                         self::$OP_DELETE
 521                 );
 522         }
 523
 524         protected function doDelete( $key, $flags = 0 ) {
 525                 return $this->modifyMulti( [ $key => null ], 0, $flags, self::$OP_DELETE );
 526         }
 527
 528         public function incr( $key, $step = 1 ) {
 529                 list( $shardIndex, $tableName ) = $this->getTableByKey( $key );
 530
 531                 $newCount = false;
 532                 /** @noinspection PhpUnusedLocalVariableInspection */
 533                 $silenceScope = $this->silenceTransactionProfiler();
 534                 $db = null; // in case of connection failure
 535                 try {
 536                         $db = $this->getDB( $shardIndex );
 537                         $encTimestamp = $db->addQuotes( $db->timestamp() );
 538                         $db->update(
 539                                 $tableName,
 540                                 [ 'value = value + ' . (int)$step ],
 541                                 [ 'keyname' => $key, "exptime > $encTimestamp" ],
 542                                 __METHOD__
 543                         );
 544                         if ( $db->affectedRows() > 0 ) {
 545                                 $newValue = $db->selectField(
 546                                         $tableName,
 547                                         'value',
 548                                         [ 'keyname' => $key, "exptime > $encTimestamp" ],
 549                                         __METHOD__
 550                                 );
 551                                 if ( $this->isInteger( $newValue ) ) {
 552                                         $newCount = (int)$newValue;
 553                                 }
 554                         }
 555                 } catch ( DBError $e ) {
 556                         $this->handleWriteError( $e, $db, $shardIndex );
 557                 }
 558
 559                 return $newCount;
 560         }
 561
 562         public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
 563                 return $this->modifyMulti(
 564                         array_fill_keys( $keys, null ),
 565                         $exptime,
 566                         $flags,
 567                         self::$OP_TOUCH
 568                 );
 569         }
 570
 571         protected function doChangeTTL( $key, $exptime, $flags ) {
 572                 return $this->modifyMulti( [ $key => null ], $exptime, $flags, self::$OP_TOUCH );
 573         }
 574
 575         /**
 576          * @param IDatabase $db
 577          * @param string $exptime
 578          * @return bool
 579          */
 580         private function isExpired( $db, $exptime ) {
 581                 return (
 582                         $exptime != $this->getMaxDateTime( $db ) &&
 583                         wfTimestamp( TS_UNIX, $exptime ) < $this->getCurrentTime()
 584                 );
 585         }
 586
 587         /**
 588          * @param IDatabase $db
 589          * @return string
 590          */
 591         private function getMaxDateTime( $db ) {
 592                 if ( (int)$this->getCurrentTime() > 0x7fffffff ) {
 593                         return $db->timestamp( 1 << 62 );
 594                 } else {
 595                         return $db->timestamp( 0x7fffffff );
 596                 }
 597         }
 598
 599         /**
 600          * @param IDatabase $db
 601          * @throws DBError
 602          */
 603         private function occasionallyGarbageCollect( IDatabase $db ) {
 604                 if (
 605                         // Random purging is enabled
 606                         $this->purgePeriod &&
 607                         // Only purge on one in every $this->purgePeriod writes
 608                         mt_rand( 0, $this->purgePeriod - 1 ) == 0 &&
 609                         // Avoid repeating the delete within a few seconds
 610                         ( $this->getCurrentTime() - $this->lastGarbageCollect ) > self::$GC_DELAY_SEC
 611                 ) {
 612                         $garbageCollector = function () use ( $db ) {
 613                                 $this->deleteServerObjectsExpiringBefore(
 614                                         $db, $this->getCurrentTime(),
 615                                         null,
 616                                         $this->purgeLimit
 617                                 );
 618                                 $this->lastGarbageCollect = time();
 619                         };
 620                         if ( $this->asyncHandler ) {
 621                                 $this->lastGarbageCollect = $this->getCurrentTime(); // avoid duplicate enqueues
 622                                 ( $this->asyncHandler )( $garbageCollector );
 623                         } else {
 624                                 $garbageCollector();
 625                         }
 626                 }
 627         }
 628
 629         public function expireAll() {
 630                 $this->deleteObjectsExpiringBefore( $this->getCurrentTime() );
 631         }
 632
 633         public function deleteObjectsExpiringBefore(
 634                 $timestamp,
 635                 callable $progress = null,
 636                 $limit = INF
 637         ) {
 638                 /** @noinspection PhpUnusedLocalVariableInspection */
 639                 $silenceScope = $this->silenceTransactionProfiler();
 640
 641                 $shardIndexes = range( 0, $this->numServerShards - 1 );
 642                 shuffle( $shardIndexes );
 643
 644                 $ok = true;
 645
 646                 $keysDeletedCount = 0;
 647                 foreach ( $shardIndexes as $numServersDone => $shardIndex ) {
 648                         $db = null; // in case of connection failure
 649                         try {
 650                                 $db = $this->getDB( $shardIndex );
 651                                 $this->deleteServerObjectsExpiringBefore(
 652                                         $db,
 653                                         $timestamp,
 654                                         $progress,
 655                                         $limit,
 656                                         $numServersDone,
 657                                         $keysDeletedCount
 658                                 );
 659                         } catch ( DBError $e ) {
 660                                 $this->handleWriteError( $e, $db, $shardIndex );
 661                                 $ok = false;
 662                         }
 663                 }
 664
 665                 return $ok;
 666         }
 667
 668         /**
 669          * @param IDatabase $db
 670          * @param string|int $timestamp
 671          * @param callable|null $progressCallback
 672          * @param int $limit
 673          * @param int $serversDoneCount
 674          * @param int &$keysDeletedCount
 675          * @throws DBError
 676          */
 677         private function deleteServerObjectsExpiringBefore(
 678                 IDatabase $db,
 679                 $timestamp,
 680                 $progressCallback,
 681                 $limit,
 682                 $serversDoneCount = 0,
 683                 &$keysDeletedCount = 0
 684         ) {
 685                 $cutoffUnix = wfTimestamp( TS_UNIX, $timestamp );
 686                 $shardIndexes = range( 0, $this->numTableShards - 1 );
 687                 shuffle( $shardIndexes );
 688
 689                 foreach ( $shardIndexes as $numShardsDone => $shardIndex ) {
 690                         $continue = null; // last exptime
 691                         $lag = null; // purge lag
 692                         do {
 693                                 $res = $db->select(
 694                                         $this->getTableNameByShard( $shardIndex ),
 695                                         [ 'keyname', 'exptime' ],
 696                                         array_merge(
 697                                                 [ 'exptime < ' . $db->addQuotes( $db->timestamp( $cutoffUnix ) ) ],
 698                                                 $continue ? [ 'exptime >= ' . $db->addQuotes( $continue ) ] : []
 699                                         ),
 700                                         __METHOD__,
 701                                         [ 'LIMIT' => min( $limit, 100 ), 'ORDER BY' => 'exptime' ]
 702                                 );
 703
 704                                 if ( $res->numRows() ) {
 705                                         $row = $res->current();
 706                                         if ( $lag === null ) {
 707                                                 $lag = max( $cutoffUnix - wfTimestamp( TS_UNIX, $row->exptime ), 1 );
 708                                         }
 709
 710                                         $keys = [];
 711                                         foreach ( $res as $row ) {
 712                                                 $keys[] = $row->keyname;
 713                                                 $continue = $row->exptime;
 714                                         }
 715
 716                                         $db->delete(
 717                                                 $this->getTableNameByShard( $shardIndex ),
 718                                                 [
 719                                                         'exptime < ' . $db->addQuotes( $db->timestamp( $cutoffUnix ) ),
 720                                                         'keyname' => $keys
 721                                                 ],
 722                                                 __METHOD__
 723                                         );
 724                                         $keysDeletedCount += $db->affectedRows();
 725                                 }
 726
 727                                 if ( is_callable( $progressCallback ) ) {
 728                                         if ( $lag ) {
 729                                                 $remainingLag = $cutoffUnix - wfTimestamp( TS_UNIX, $continue );
 730                                                 $processedLag = max( $lag - $remainingLag, 0 );
 731                                                 $doneRatio = ( $numShardsDone + $processedLag / $lag ) / $this->numTableShards;
 732                                         } else {
 733                                                 $doneRatio = 1;
 734                                         }
 735
 736                                         $overallRatio = ( $doneRatio / $this->numServerShards )
 737                                                 + ( $serversDoneCount / $this->numServerShards );
 738                                         call_user_func( $progressCallback, $overallRatio * 100 );
 739                                 }
 740                         } while ( $res->numRows() && $keysDeletedCount < $limit );
 741                 }
 742         }
 743
 744         /**
 745          * Delete content of shard tables in every server.
 746          * Return true if the operation is successful, false otherwise.
 747          * @return bool
 748          */
 749         public function deleteAll() {
 750                 /** @noinspection PhpUnusedLocalVariableInspection */
 751                 $silenceScope = $this->silenceTransactionProfiler();
 752                 for ( $shardIndex = 0; $shardIndex < $this->numServerShards; $shardIndex++ ) {
 753                         $db = null; // in case of connection failure
 754                         try {
 755                                 $db = $this->getDB( $shardIndex );
 756                                 for ( $i = 0; $i < $this->numTableShards; $i++ ) {
 757                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 758                                 }
 759                         } catch ( DBError $e ) {
 760                                 $this->handleWriteError( $e, $db, $shardIndex );
 761                                 return false;
 762                         }
 763                 }
 764                 return true;
 765         }
 766
 767         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 768                 // Avoid deadlocks and allow lock reentry if specified
 769                 if ( isset( $this->locks[$key] ) ) {
 770                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 771                                 ++$this->locks[$key]['depth'];
 772                                 return true;
 773                         } else {
 774                                 return false;
 775                         }
 776                 }
 777
 778                 list( $shardIndex ) = $this->getTableByKey( $key );
 779
 780                 $db = null; // in case of connection failure
 781                 try {
 782                         $db = $this->getDB( $shardIndex );
 783                         $ok = $db->lock( $key, __METHOD__, $timeout );
 784                         if ( $ok ) {
 785                                 $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 786                         }
 787
 788                         $this->logger->warning(
 789                                 __METHOD__ . " failed due to timeout for {key}.",
 790                                 [ 'key' => $key, 'timeout' => $timeout ]
 791                         );
 792
 793                         return $ok;
 794                 } catch ( DBError $e ) {
 795                         $this->handleWriteError( $e, $db, $shardIndex );
 796                         $ok = false;
 797                 }
 798
 799                 return $ok;
 800         }
 801
 802         public function unlock( $key ) {
 803                 if ( !isset( $this->locks[$key] ) ) {
 804                         return false;
 805                 }
 806
 807                 if ( --$this->locks[$key]['depth'] <= 0 ) {
 808                         unset( $this->locks[$key] );
 809
 810                         list( $shardIndex ) = $this->getTableByKey( $key );
 811
 812                         $db = null; // in case of connection failure
 813                         try {
 814                                 $db = $this->getDB( $shardIndex );
 815                                 $ok = $db->unlock( $key, __METHOD__ );
 816                                 if ( !$ok ) {
 817                                         $this->logger->warning(
 818                                                 __METHOD__ . ' failed to release lock for {key}.',
 819                                                 [ 'key' => $key ]
 820                                         );
 821                                 }
 822                         } catch ( DBError $e ) {
 823                                 $this->handleWriteError( $e, $db, $shardIndex );
 824                                 $ok = false;
 825                         }
 826
 827                         return $ok;
 828                 }
 829
 830                 return true;
 831         }
 832
 833         /**
 834          * Serialize an object and, if possible, compress the representation.
 835          * On typical message and page data, this can provide a 3X decrease
 836          * in storage requirements.
 837          *
 838          * @param mixed $data
 839          * @return string|int
 840          */
 841         protected function serialize( $data ) {
 842                 if ( is_int( $data ) ) {
 843                         return $data;
 844                 }
 845
 846                 $serial = serialize( $data );
 847                 if ( function_exists( 'gzdeflate' ) ) {
 848                         $serial = gzdeflate( $serial );
 849                 }
 850
 851                 return $serial;
 852         }
 853
 854         /**
 855          * Unserialize and, if necessary, decompress an object.
 856          * @param string $serial
 857          * @return mixed
 858          */
 859         protected function unserialize( $serial ) {
 860                 if ( $this->isInteger( $serial ) ) {
 861                         return (int)$serial;
 862                 }
 863
 864                 if ( function_exists( 'gzinflate' ) ) {
 865                         Wikimedia\suppressWarnings();
 866                         $decomp = gzinflate( $serial );
 867                         Wikimedia\restoreWarnings();
 868
 869                         if ( $decomp !== false ) {
 870                                 $serial = $decomp;
 871                         }
 872                 }
 873
 874                 return unserialize( $serial );
 875         }
 876
 877         /**
 878          * Handle a DBError which occurred during a read operation.
 879          *
 880          * @param DBError $exception
 881          * @param int $shardIndex
 882          */
 883         private function handleReadError( DBError $exception, $shardIndex ) {
 884                 if ( $exception instanceof DBConnectionError ) {
 885                         $this->markServerDown( $exception, $shardIndex );
 886                 }
 887
 888                 $this->setAndLogDBError( $exception );
 889         }
 890
 891         /**
 892          * Handle a DBQueryError which occurred during a write operation.
 893          *
 894          * @param DBError $exception
 895          * @param IDatabase|null $db DB handle or null if connection failed
 896          * @param int $shardIndex
 897          * @throws Exception
 898          */
 899         private function handleWriteError( DBError $exception, $db, $shardIndex ) {
 900                 if ( !( $db instanceof IDatabase ) ) {
 901                         $this->markServerDown( $exception, $shardIndex );
 902                 }
 903
 904                 $this->setAndLogDBError( $exception );
 905         }
 906
 907         /**
 908          * @param DBError $exception
 909          */
 910         private function setAndLogDBError( DBError $exception ) {
 911                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 912                 if ( $exception instanceof DBConnectionError ) {
 913                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 914                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 915                 } else {
 916                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 917                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 918                 }
 919         }
 920
 921         /**
 922          * Mark a server down due to a DBConnectionError exception
 923          *
 924          * @param DBError $exception
 925          * @param int $shardIndex
 926          */
 927         private function markServerDown( DBError $exception, $shardIndex ) {
 928                 unset( $this->conns[$shardIndex] ); // bug T103435
 929
 930                 $now = $this->getCurrentTime();
 931                 if ( isset( $this->connFailureTimes[$shardIndex] ) ) {
 932                         if ( $now - $this->connFailureTimes[$shardIndex] >= 60 ) {
 933                                 unset( $this->connFailureTimes[$shardIndex] );
 934                                 unset( $this->connFailureErrors[$shardIndex] );
 935                         } else {
 936                                 $this->logger->debug( __METHOD__ . ": Server #$shardIndex already down" );
 937                                 return;
 938                         }
 939                 }
 940                 $this->logger->info( __METHOD__ . ": Server #$shardIndex down until " . ( $now + 60 ) );
 941                 $this->connFailureTimes[$shardIndex] = $now;
 942                 $this->connFailureErrors[$shardIndex] = $exception;
 943         }
 944
 945         /**
 946          * Create shard tables. For use from eval.php.
 947          */
 948         public function createTables() {
 949                 for ( $shardIndex = 0; $shardIndex < $this->numServerShards; $shardIndex++ ) {
 950                         $db = $this->getDB( $shardIndex );
 951                         if ( $db->getType() !== 'mysql' ) {
 952                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 953                         }
 954
 955                         for ( $i = 0; $i < $this->numTableShards; $i++ ) {
 956                                 $db->query(
 957                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 958                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 959                                         __METHOD__ );
 960                         }
 961                 }
 962         }
 963
 964         /**
 965          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 966          */
 967         private function usesMainDB() {
 968                 return !$this->serverInfos;
 969         }
 970
 971         private function waitForReplication() {
 972                 if ( !$this->usesMainDB() ) {
 973                         // Custom DB server list; probably doesn't use replication
 974                         return true;
 975                 }
 976
 977                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 978                 if ( $lb->getServerCount() <= 1 ) {
 979                         return true; // no replica DBs
 980                 }
 981
 982                 // Main LB is used; wait for any replica DBs to catch up
 983                 try {
 984                         $masterPos = $lb->getMasterPos();
 985                         if ( !$masterPos ) {
 986                                 return true; // not applicable
 987                         }
 988
 989                         $loop = new WaitConditionLoop(
 990                                 function () use ( $lb, $masterPos ) {
 991                                         return $lb->waitForAll( $masterPos, 1 );
 992                                 },
 993                                 $this->syncTimeout,
 994                                 $this->busyCallbacks
 995                         );
 996
 997                         return ( $loop->invoke() === $loop::CONDITION_REACHED );
 998                 } catch ( DBError $e ) {
 999                         $this->setAndLogDBError( $e );
1000
1001                         return false;
1002                 }
1003         }
1004
1005         /**
1006          * Silence the transaction profiler until the return value falls out of scope
1007          *
1008          * @return ScopedCallback|null
1009          */
1010         private function silenceTransactionProfiler() {
1011                 if ( !$this->usesMainDB() ) {
1012                         // Custom DB is configured which either has no TransactionProfiler injected,
1013                         // or has one specific for cache use, which we shouldn't silence
1014                         return null;
1015                 }
1016
1017                 $trxProfiler = Profiler::instance()->getTransactionProfiler();
1018                 $oldSilenced = $trxProfiler->setSilenced( true );
1019                 return new ScopedCallback( function () use ( $trxProfiler, $oldSilenced ) {
1020                         $trxProfiler->setSilenced( $oldSilenced );
1021                 } );
1022         }
1023 }