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 /**
  25  * Class to store objects in the database
  26  *
  27  * @ingroup Cache
  28  */
  29 class SqlBagOStuff extends BagOStuff {
  30
  31         /**
  32          * @var LoadBalancer
  33          */
  34         var $lb;
  35
  36         /**
  37          * @var DatabaseBase
  38          */
  39         var $db;
  40         var $serverInfo;
  41         var $lastExpireAll = 0;
  42         var $purgePeriod = 100;
  43         var $shards = 1;
  44         var $tableName = 'objectcache';
  45
  46         /**
  47          * Constructor. Parameters are:
  48          *   - server:   A server info structure in the format required by each
  49          *               element in $wgDBServers.
  50          *
  51          *   - purgePeriod: The average number of object cache requests in between
  52          *                  garbage collection operations, where expired entries
  53          *                  are removed from the database. Or in other words, the
  54          *                  reciprocal of the probability of purging on any given
  55          *                  request. If this is set to zero, purging will never be
  56          *                  done.
  57          *
  58          *   - tableName:   The table name to use, default is "objectcache".
  59          *
  60          *   - shards:      The number of tables to use for data storage. If this is
  61          *                  more than 1, table names will be formed in the style
  62          *                  objectcacheNNN where NNN is the shard index, between 0 and
  63          *                  shards-1. The number of digits will be the minimum number
  64          *                  required to hold the largest shard index. Data will be
  65          *                  distributed across all tables by key hash. This is for
  66          *                  MySQL bugs 61735 and 61736.
  67          *
  68          * @param $params array
  69          */
  70         public function __construct( $params ) {
  71                 if ( isset( $params['server'] ) ) {
  72                         $this->serverInfo = $params['server'];
  73                         $this->serverInfo['load'] = 1;
  74                 }
  75                 if ( isset( $params['purgePeriod'] ) ) {
  76                         $this->purgePeriod = intval( $params['purgePeriod'] );
  77                 }
  78                 if ( isset( $params['tableName'] ) ) {
  79                         $this->tableName = $params['tableName'];
  80                 }
  81                 if ( isset( $params['shards'] ) ) {
  82                         $this->shards = intval( $params['shards'] );
  83                 }
  84         }
  85
  86         /**
  87          * @return DatabaseBase
  88          */
  89         protected function getDB() {
  90                 if ( !isset( $this->db ) ) {
  91                         # If server connection info was given, use that
  92                         if ( $this->serverInfo ) {
  93                                 $this->lb = new LoadBalancer( array(
  94                                         'servers' => array( $this->serverInfo ) ) );
  95                                 $this->db = $this->lb->getConnection( DB_MASTER );
  96                                 $this->db->clearFlag( DBO_TRX );
  97                         } else {
  98                                 # We must keep a separate connection to MySQL in order to avoid deadlocks
  99                                 # However, SQLite has an opposite behaviour.
 100                                 # @todo Investigate behaviour for other databases
 101                                 if ( wfGetDB( DB_MASTER )->getType() == 'sqlite' ) {
 102                                         $this->db = wfGetDB( DB_MASTER );
 103                                 } else {
 104                                         $this->lb = wfGetLBFactory()->newMainLB();
 105                                         $this->db = $this->lb->getConnection( DB_MASTER );
 106                                         $this->db->clearFlag( DBO_TRX );
 107                                 }
 108                         }
 109                 }
 110
 111                 return $this->db;
 112         }
 113
 114         /**
 115          * Get the table name for a given key
 116          * @return string
 117          */
 118         protected function getTableByKey( $key ) {
 119                 if ( $this->shards > 1 ) {
 120                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 121                         return $this->getTableByShard( $hash % $this->shards );
 122                 } else {
 123                         return $this->tableName;
 124                 }
 125         }
 126
 127         /**
 128          * Get the table name for a given shard index
 129          * @return string
 130          */
 131         protected function getTableByShard( $index ) {
 132                 if ( $this->shards > 1 ) {
 133                         $decimals = strlen( $this->shards - 1 );
 134                         return $this->tableName .
 135                                 sprintf( "%0{$decimals}d", $index );
 136                 } else {
 137                         return $this->tableName;
 138                 }
 139         }
 140
 141         public function get( $key ) {
 142                 $values = $this->getMulti( array( $key ) );
 143                 return $values[$key];
 144         }
 145
 146         public function getMulti( array $keys ) {
 147                 $values = array(); // array of (key => value)
 148
 149                 $keysByTableName = array();
 150                 foreach ( $keys as $key ) {
 151                         $tableName = $this->getTableByKey( $key );
 152                         if ( !isset( $keysByTableName[$tableName] ) ) {
 153                                 $keysByTableName[$tableName] = array();
 154                         }
 155                         $keysByTableName[$tableName][] = $key;
 156                 }
 157
 158                 $db = $this->getDB();
 159                 $this->garbageCollect(); // expire old entries if any
 160
 161                 $dataRows = array();
 162                 foreach ( $keysByTableName as $tableName => $tableKeys ) {
 163                         $res = $db->select( $tableName,
 164                                 array( 'keyname', 'value', 'exptime' ),
 165                                 array( 'keyname' => $tableKeys ),
 166                                 __METHOD__ );
 167                         foreach ( $res as $row ) {
 168                                 $dataRows[$row->keyname] = $row;
 169                         }
 170                 }
 171
 172                 foreach ( $keys as $key ) {
 173                         if ( isset( $dataRows[$key] ) ) { // HIT?
 174                                 $row = $dataRows[$key];
 175                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 176                                 if ( $this->isExpired( $row->exptime ) ) { // MISS
 177                                         $this->debug( "get: key has expired, deleting" );
 178                                         try {
 179                                                 $db->begin( __METHOD__ );
 180                                                 # Put the expiry time in the WHERE condition to avoid deleting a
 181                                                 # newly-inserted value
 182                                                 $db->delete( $this->getTableByKey( $key ),
 183                                                         array( 'keyname' => $key, 'exptime' => $row->exptime ),
 184                                                         __METHOD__ );
 185                                                 $db->commit( __METHOD__ );
 186                                         } catch ( DBQueryError $e ) {
 187                                                 $this->handleWriteError( $e );
 188                                         }
 189                                         $values[$key] = false;
 190                                 } else { // HIT
 191                                         $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 192                                 }
 193                         } else { // MISS
 194                                 $values[$key] = false;
 195                                 $this->debug( 'get: no matching rows' );
 196                         }
 197                 }
 198
 199                 return $values;
 200         }
 201
 202         public function set( $key, $value, $exptime = 0 ) {
 203                 $db = $this->getDB();
 204                 $exptime = intval( $exptime );
 205
 206                 if ( $exptime < 0 ) {
 207                         $exptime = 0;
 208                 }
 209
 210                 if ( $exptime == 0 ) {
 211                         $encExpiry = $this->getMaxDateTime();
 212                 } else {
 213                         if ( $exptime < 3.16e8 ) { # ~10 years
 214                                 $exptime += time();
 215                         }
 216
 217                         $encExpiry = $db->timestamp( $exptime );
 218                 }
 219                 try {
 220                         $db->begin( __METHOD__ );
 221                         // (bug 24425) use a replace if the db supports it instead of
 222                         // delete/insert to avoid clashes with conflicting keynames
 223                         $db->replace(
 224                                 $this->getTableByKey( $key ),
 225                                 array( 'keyname' ),
 226                                 array(
 227                                         'keyname' => $key,
 228                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 229                                         'exptime' => $encExpiry
 230                                 ), __METHOD__ );
 231                         $db->commit( __METHOD__ );
 232                 } catch ( DBQueryError $e ) {
 233                         $this->handleWriteError( $e );
 234
 235                         return false;
 236                 }
 237
 238                 return true;
 239         }
 240
 241         public function delete( $key, $time = 0 ) {
 242                 $db = $this->getDB();
 243
 244                 try {
 245                         $db->begin( __METHOD__ );
 246                         $db->delete(
 247                                 $this->getTableByKey( $key ),
 248                                 array( 'keyname' => $key ),
 249                                 __METHOD__ );
 250                         $db->commit( __METHOD__ );
 251                 } catch ( DBQueryError $e ) {
 252                         $this->handleWriteError( $e );
 253
 254                         return false;
 255                 }
 256
 257                 return true;
 258         }
 259
 260         public function incr( $key, $step = 1 ) {
 261                 $db = $this->getDB();
 262                 $tableName = $this->getTableByKey( $key );
 263                 $step = intval( $step );
 264
 265                 try {
 266                         $db->begin( __METHOD__ );
 267                         $row = $db->selectRow(
 268                                 $tableName,
 269                                 array( 'value', 'exptime' ),
 270                                 array( 'keyname' => $key ),
 271                                 __METHOD__,
 272                                 array( 'FOR UPDATE' ) );
 273                         if ( $row === false ) {
 274                                 // Missing
 275                                 $db->commit( __METHOD__ );
 276
 277                                 return null;
 278                         }
 279                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 280                         if ( $this->isExpired( $row->exptime ) ) {
 281                                 // Expired, do not reinsert
 282                                 $db->commit( __METHOD__ );
 283
 284                                 return null;
 285                         }
 286
 287                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 288                         $newValue = $oldValue + $step;
 289                         $db->insert( $tableName,
 290                                 array(
 291                                         'keyname' => $key,
 292                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 293                                         'exptime' => $row->exptime
 294                                 ), __METHOD__, 'IGNORE' );
 295
 296                         if ( $db->affectedRows() == 0 ) {
 297                                 // Race condition. See bug 28611
 298                                 $newValue = null;
 299                         }
 300                         $db->commit( __METHOD__ );
 301                 } catch ( DBQueryError $e ) {
 302                         $this->handleWriteError( $e );
 303
 304                         return null;
 305                 }
 306
 307                 return $newValue;
 308         }
 309
 310         public function keys() {
 311                 $db = $this->getDB();
 312                 $result = array();
 313
 314                 for ( $i = 0; $i < $this->shards; $i++ ) {
 315                         $res = $db->select( $this->getTableByShard( $i ),
 316                                 array( 'keyname' ), false, __METHOD__ );
 317                         foreach ( $res as $row ) {
 318                                 $result[] = $row->keyname;
 319                         }
 320                 }
 321
 322                 return $result;
 323         }
 324
 325         protected function isExpired( $exptime ) {
 326                 return $exptime != $this->getMaxDateTime() && wfTimestamp( TS_UNIX, $exptime ) < time();
 327         }
 328
 329         protected function getMaxDateTime() {
 330                 if ( time() > 0x7fffffff ) {
 331                         return $this->getDB()->timestamp( 1 << 62 );
 332                 } else {
 333                         return $this->getDB()->timestamp( 0x7fffffff );
 334                 }
 335         }
 336
 337         protected function garbageCollect() {
 338                 if ( !$this->purgePeriod ) {
 339                         // Disabled
 340                         return;
 341                 }
 342                 // Only purge on one in every $this->purgePeriod requests.
 343                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 344                         return;
 345                 }
 346                 $now = time();
 347                 // Avoid repeating the delete within a few seconds
 348                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 349                         $this->lastExpireAll = $now;
 350                         $this->expireAll();
 351                 }
 352         }
 353
 354         public function expireAll() {
 355                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 356         }
 357
 358         /**
 359          * Delete objects from the database which expire before a certain date.
 360          * @return bool
 361          */
 362         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 363                 $db = $this->getDB();
 364                 $dbTimestamp = $db->timestamp( $timestamp );
 365                 $totalSeconds = false;
 366                 $baseConds = array( 'exptime < ' . $db->addQuotes( $dbTimestamp ) );
 367
 368                 try {
 369                         for ( $i = 0; $i < $this->shards; $i++ ) {
 370                                 $maxExpTime = false;
 371                                 while ( true ) {
 372                                         $conds = $baseConds;
 373                                         if ( $maxExpTime !== false ) {
 374                                                 $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 375                                         }
 376                                         $rows = $db->select(
 377                                                 $this->getTableByShard( $i ),
 378                                                 array( 'keyname', 'exptime' ),
 379                                                 $conds,
 380                                                 __METHOD__,
 381                                                 array( 'LIMIT' => 100, 'ORDER BY' => 'exptime' ) );
 382                                         if ( !$rows->numRows() ) {
 383                                                 break;
 384                                         }
 385                                         $keys = array();
 386                                         $row = $rows->current();
 387                                         $minExpTime = $row->exptime;
 388                                         if ( $totalSeconds === false ) {
 389                                                 $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 390                                                         - wfTimestamp( TS_UNIX, $minExpTime );
 391                                         }
 392                                         foreach ( $rows as $row ) {
 393                                                 $keys[] = $row->keyname;
 394                                                 $maxExpTime = $row->exptime;
 395                                         }
 396
 397                                         $db->begin( __METHOD__ );
 398                                         $db->delete(
 399                                                 $this->getTableByShard( $i ),
 400                                                 array(
 401                                                         'exptime >= ' . $db->addQuotes( $minExpTime ),
 402                                                         'exptime < ' . $db->addQuotes( $dbTimestamp ),
 403                                                         'keyname' => $keys
 404                                                 ),
 405                                                 __METHOD__ );
 406                                         $db->commit( __METHOD__ );
 407
 408                                         if ( $progressCallback ) {
 409                                                 if ( intval( $totalSeconds ) === 0 ) {
 410                                                         $percent = 0;
 411                                                 } else {
 412                                                         $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 413                                                                 - wfTimestamp( TS_UNIX, $maxExpTime );
 414                                                         if ( $remainingSeconds > $totalSeconds ) {
 415                                                                 $totalSeconds = $remainingSeconds;
 416                                                         }
 417                                                         $percent = ( $i + $remainingSeconds / $totalSeconds )
 418                                                                 / $this->shards * 100;
 419                                                 }
 420                                                 call_user_func( $progressCallback, $percent );
 421                                         }
 422                                 }
 423                         }
 424                 } catch ( DBQueryError $e ) {
 425                         $this->handleWriteError( $e );
 426                 }
 427                 return true;
 428         }
 429
 430         public function deleteAll() {
 431                 $db = $this->getDB();
 432
 433                 try {
 434                         for ( $i = 0; $i < $this->shards; $i++ ) {
 435                                 $db->begin( __METHOD__ );
 436                                 $db->delete( $this->getTableByShard( $i ), '*', __METHOD__ );
 437                                 $db->commit( __METHOD__ );
 438                         }
 439                 } catch ( DBQueryError $e ) {
 440                         $this->handleWriteError( $e );
 441                 }
 442         }
 443
 444         /**
 445          * Serialize an object and, if possible, compress the representation.
 446          * On typical message and page data, this can provide a 3X decrease
 447          * in storage requirements.
 448          *
 449          * @param $data mixed
 450          * @return string
 451          */
 452         protected function serialize( &$data ) {
 453                 $serial = serialize( $data );
 454
 455                 if ( function_exists( 'gzdeflate' ) ) {
 456                         return gzdeflate( $serial );
 457                 } else {
 458                         return $serial;
 459                 }
 460         }
 461
 462         /**
 463          * Unserialize and, if necessary, decompress an object.
 464          * @param $serial string
 465          * @return mixed
 466          */
 467         protected function unserialize( $serial ) {
 468                 if ( function_exists( 'gzinflate' ) ) {
 469                         wfSuppressWarnings();
 470                         $decomp = gzinflate( $serial );
 471                         wfRestoreWarnings();
 472
 473                         if ( false !== $decomp ) {
 474                                 $serial = $decomp;
 475                         }
 476                 }
 477
 478                 $ret = unserialize( $serial );
 479
 480                 return $ret;
 481         }
 482
 483         /**
 484          * Handle a DBQueryError which occurred during a write operation.
 485          * Ignore errors which are due to a read-only database, rethrow others.
 486          */
 487         protected function handleWriteError( $exception ) {
 488                 $db = $this->getDB();
 489
 490                 if ( !$db->wasReadOnlyError() ) {
 491                         throw $exception;
 492                 }
 493
 494                 try {
 495                         $db->rollback( __METHOD__ );
 496                 } catch ( DBQueryError $e ) {
 497                 }
 498
 499                 wfDebug( __METHOD__ . ": ignoring query error\n" );
 500                 $db->ignoreErrors( false );
 501         }
 502
 503         /**
 504          * Create shard tables. For use from eval.php.
 505          */
 506         public function createTables() {
 507                 $db = $this->getDB();
 508                 if ( $db->getType() !== 'mysql'
 509                         || version_compare( $db->getServerVersion(), '4.1.0', '<' ) )
 510                 {
 511                         throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 512                 }
 513
 514                 for ( $i = 0; $i < $this->shards; $i++ ) {
 515                         $db->begin( __METHOD__ );
 516                         $db->query(
 517                                 'CREATE TABLE ' . $db->tableName( $this->getTableByShard( $i ) ) .
 518                                 ' LIKE ' . $db->tableName( 'objectcache' ),
 519                                 __METHOD__ );
 520                         $db->commit( __METHOD__ );
 521                 }
 522         }
 523 }
 524
 525 /**
 526  * Backwards compatibility alias
 527  */
 528 class MediaWikiBagOStuff extends SqlBagOStuff { }
 529