includes/objectcache/SqlBagOStuff.php

   1 <?php
   2
   3 /**
   4  * Class to store objects in the database
   5  *
   6  * @ingroup Cache
   7  */
   8 class SqlBagOStuff extends BagOStuff {
   9
  10         /**
  11          * @var LoadBalancer
  12          */
  13         var $lb;
  14
  15         /**
  16          * @var DatabaseBase
  17          */
  18         var $db;
  19         var $serverInfo;
  20         var $lastExpireAll = 0;
  21         var $purgePeriod = 100;
  22         var $shards = 1;
  23         var $tableName = 'objectcache';
  24
  25         /**
  26          * Constructor. Parameters are:
  27          *   - server:   A server info structure in the format required by each
  28          *               element in $wgDBServers.
  29          *
  30          *   - purgePeriod: The average number of object cache requests in between
  31          *                  garbage collection operations, where expired entries
  32          *                  are removed from the database. Or in other words, the
  33          *                  reciprocal of the probability of purging on any given
  34          *                  request. If this is set to zero, purging will never be
  35          *                  done.
  36          *
  37          *   - tableName:   The table name to use, default is "objectcache".
  38          *
  39          *   - shards:      The number of tables to use for data storage. If this is
  40          *                  more than 1, table names will be formed in the style
  41          *                  objectcacheNNN where NNN is the shard index, between 0 and
  42          *                  shards-1. The number of digits will be the minimum number
  43          *                  required to hold the largest shard index. Data will be
  44          *                  distributed across all tables by key hash. This is for
  45          *                  MySQL bugs 61735 and 61736.
  46          *
  47          * @param $params array
  48          */
  49         public function __construct( $params ) {
  50                 if ( isset( $params['server'] ) ) {
  51                         $this->serverInfo = $params['server'];
  52                         $this->serverInfo['load'] = 1;
  53                 }
  54                 if ( isset( $params['purgePeriod'] ) ) {
  55                         $this->purgePeriod = intval( $params['purgePeriod'] );
  56                 }
  57                 if ( isset( $params['tableName'] ) ) {
  58                         $this->tableName = $params['tableName'];
  59                 }
  60                 if ( isset( $params['shards'] ) ) {
  61                         $this->shards = intval( $params['shards'] );
  62                 }
  63         }
  64
  65         /**
  66          * @return DatabaseBase
  67          */
  68         protected function getDB() {
  69                 if ( !isset( $this->db ) ) {
  70                         # If server connection info was given, use that
  71                         if ( $this->serverInfo ) {
  72                                 $this->lb = new LoadBalancer( array(
  73                                         'servers' => array( $this->serverInfo ) ) );
  74                                 $this->db = $this->lb->getConnection( DB_MASTER );
  75                                 $this->db->clearFlag( DBO_TRX );
  76                         } else {
  77                                 # We must keep a separate connection to MySQL in order to avoid deadlocks
  78                                 # However, SQLite has an opposite behaviour.
  79                                 # @todo Investigate behaviour for other databases
  80                                 if ( wfGetDB( DB_MASTER )->getType() == 'sqlite' ) {
  81                                         $this->db = wfGetDB( DB_MASTER );
  82                                 } else {
  83                                         $this->lb = wfGetLBFactory()->newMainLB();
  84                                         $this->db = $this->lb->getConnection( DB_MASTER );
  85                                         $this->db->clearFlag( DBO_TRX );
  86                                 }
  87                         }
  88                 }
  89
  90                 return $this->db;
  91         }
  92
  93         /**
  94          * Get the table name for a given key
  95          */
  96         protected function getTableByKey( $key ) {
  97                 if ( $this->shards > 1 ) {
  98                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
  99                         return $this->getTableByShard( $hash % $this->shards );
 100                 } else {
 101                         return $this->tableName;
 102                 }
 103         }
 104
 105         /**
 106          * Get the table name for a given shard index
 107          */
 108         protected function getTableByShard( $index ) {
 109                 if ( $this->shards > 1 ) {
 110                         $decimals = strlen( $this->shards - 1 );
 111                         return $this->tableName .
 112                                 sprintf( "%0{$decimals}d", $index );
 113                 } else {
 114                         return $this->tableName;
 115                 }
 116         }
 117
 118         public function get( $key ) {
 119                 # expire old entries if any
 120                 $this->garbageCollect();
 121                 $db = $this->getDB();
 122                 $tableName = $this->getTableByKey( $key );
 123                 $row = $db->selectRow( $tableName, array( 'value', 'exptime' ),
 124                         array( 'keyname' => $key ), __METHOD__ );
 125
 126                 if ( !$row ) {
 127                         $this->debug( 'get: no matching rows' );
 128                         return false;
 129                 }
 130
 131                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 132
 133                 if ( $this->isExpired( $row->exptime ) ) {
 134                         $this->debug( "get: key has expired, deleting" );
 135                         try {
 136                                 $db->begin();
 137                                 # Put the expiry time in the WHERE condition to avoid deleting a
 138                                 # newly-inserted value
 139                                 $db->delete( $tableName,
 140                                         array(
 141                                                 'keyname' => $key,
 142                                                 'exptime' => $row->exptime
 143                                         ), __METHOD__ );
 144                                 $db->commit();
 145                         } catch ( DBQueryError $e ) {
 146                                 $this->handleWriteError( $e );
 147                         }
 148
 149                         return false;
 150                 }
 151
 152                 return $this->unserialize( $db->decodeBlob( $row->value ) );
 153         }
 154
 155         public function set( $key, $value, $exptime = 0 ) {
 156                 $db = $this->getDB();
 157                 $exptime = intval( $exptime );
 158
 159                 if ( $exptime < 0 ) {
 160                         $exptime = 0;
 161                 }
 162
 163                 if ( $exptime == 0 ) {
 164                         $encExpiry = $this->getMaxDateTime();
 165                 } else {
 166                         if ( $exptime < 3.16e8 ) { # ~10 years
 167                                 $exptime += time();
 168                         }
 169
 170                         $encExpiry = $db->timestamp( $exptime );
 171                 }
 172                 try {
 173                         $db->begin();
 174                         // (bug 24425) use a replace if the db supports it instead of
 175                         // delete/insert to avoid clashes with conflicting keynames
 176                         $db->replace(
 177                                 $this->getTableByKey( $key ),
 178                                 array( 'keyname' ),
 179                                 array(
 180                                         'keyname' => $key,
 181                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 182                                         'exptime' => $encExpiry
 183                                 ), __METHOD__ );
 184                         $db->commit();
 185                 } catch ( DBQueryError $e ) {
 186                         $this->handleWriteError( $e );
 187
 188                         return false;
 189                 }
 190
 191                 return true;
 192         }
 193
 194         public function delete( $key, $time = 0 ) {
 195                 $db = $this->getDB();
 196
 197                 try {
 198                         $db->begin();
 199                         $db->delete(
 200                                 $this->getTableByKey( $key ),
 201                                 array( 'keyname' => $key ),
 202                                 __METHOD__ );
 203                         $db->commit();
 204                 } catch ( DBQueryError $e ) {
 205                         $this->handleWriteError( $e );
 206
 207                         return false;
 208                 }
 209
 210                 return true;
 211         }
 212
 213         public function incr( $key, $step = 1 ) {
 214                 $db = $this->getDB();
 215                 $tableName = $this->getTableByKey( $key );
 216                 $step = intval( $step );
 217
 218                 try {
 219                         $db->begin();
 220                         $row = $db->selectRow(
 221                                 $tableName,
 222                                 array( 'value', 'exptime' ),
 223                                 array( 'keyname' => $key ),
 224                                 __METHOD__,
 225                                 array( 'FOR UPDATE' ) );
 226                         if ( $row === false ) {
 227                                 // Missing
 228                                 $db->commit();
 229
 230                                 return null;
 231                         }
 232                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 233                         if ( $this->isExpired( $row->exptime ) ) {
 234                                 // Expired, do not reinsert
 235                                 $db->commit();
 236
 237                                 return null;
 238                         }
 239
 240                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 241                         $newValue = $oldValue + $step;
 242                         $db->insert( $tableName,
 243                                 array(
 244                                         'keyname' => $key,
 245                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 246                                         'exptime' => $row->exptime
 247                                 ), __METHOD__, 'IGNORE' );
 248
 249                         if ( $db->affectedRows() == 0 ) {
 250                                 // Race condition. See bug 28611
 251                                 $newValue = null;
 252                         }
 253                         $db->commit();
 254                 } catch ( DBQueryError $e ) {
 255                         $this->handleWriteError( $e );
 256
 257                         return null;
 258                 }
 259
 260                 return $newValue;
 261         }
 262
 263         public function keys() {
 264                 $db = $this->getDB();
 265                 $result = array();
 266
 267                 for ( $i = 0; $i < $this->shards; $i++ ) {
 268                         $res = $db->select( $this->getTableByShard( $i ),
 269                                 array( 'keyname' ), false, __METHOD__ );
 270                         foreach ( $res as $row ) {
 271                                 $result[] = $row->keyname;
 272                         }
 273                 }
 274
 275                 return $result;
 276         }
 277
 278         protected function isExpired( $exptime ) {
 279                 return $exptime != $this->getMaxDateTime() && wfTimestamp( TS_UNIX, $exptime ) < time();
 280         }
 281
 282         protected function getMaxDateTime() {
 283                 if ( time() > 0x7fffffff ) {
 284                         return $this->getDB()->timestamp( 1 << 62 );
 285                 } else {
 286                         return $this->getDB()->timestamp( 0x7fffffff );
 287                 }
 288         }
 289
 290         protected function garbageCollect() {
 291                 if ( !$this->purgePeriod ) {
 292                         // Disabled
 293                         return;
 294                 }
 295                 // Only purge on one in every $this->purgePeriod requests.
 296                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 297                         return;
 298                 }
 299                 $now = time();
 300                 // Avoid repeating the delete within a few seconds
 301                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 302                         $this->lastExpireAll = $now;
 303                         $this->expireAll();
 304                 }
 305         }
 306
 307         public function expireAll() {
 308                 $db = $this->getDB();
 309                 $now = $db->timestamp();
 310
 311                 try {
 312                         for ( $i = 0; $i < $this->shards; $i++ ) {
 313                                 $db->begin();
 314                                 $db->delete(
 315                                         $this->getTableByShard( $i ),
 316                                         array( 'exptime < ' . $db->addQuotes( $now ) ),
 317                                         __METHOD__ );
 318                                 $db->commit();
 319                         }
 320                 } catch ( DBQueryError $e ) {
 321                         $this->handleWriteError( $e );
 322                 }
 323         }
 324
 325         public function deleteAll() {
 326                 $db = $this->getDB();
 327
 328                 try {
 329                         for ( $i = 0; $i < $this->shards; $i++ ) {
 330                                 $db->begin();
 331                                 $db->delete( $this->getTableByShard( $i ), '*', __METHOD__ );
 332                                 $db->commit();
 333                         }
 334                 } catch ( DBQueryError $e ) {
 335                         $this->handleWriteError( $e );
 336                 }
 337         }
 338
 339         /**
 340          * Serialize an object and, if possible, compress the representation.
 341          * On typical message and page data, this can provide a 3X decrease
 342          * in storage requirements.
 343          *
 344          * @param $data mixed
 345          * @return string
 346          */
 347         protected function serialize( &$data ) {
 348                 $serial = serialize( $data );
 349
 350                 if ( function_exists( 'gzdeflate' ) ) {
 351                         return gzdeflate( $serial );
 352                 } else {
 353                         return $serial;
 354                 }
 355         }
 356
 357         /**
 358          * Unserialize and, if necessary, decompress an object.
 359          * @param $serial string
 360          * @return mixed
 361          */
 362         protected function unserialize( $serial ) {
 363                 if ( function_exists( 'gzinflate' ) ) {
 364                         wfSuppressWarnings();
 365                         $decomp = gzinflate( $serial );
 366                         wfRestoreWarnings();
 367
 368                         if ( false !== $decomp ) {
 369                                 $serial = $decomp;
 370                         }
 371                 }
 372
 373                 $ret = unserialize( $serial );
 374
 375                 return $ret;
 376         }
 377
 378         /**
 379          * Handle a DBQueryError which occurred during a write operation.
 380          * Ignore errors which are due to a read-only database, rethrow others.
 381          */
 382         protected function handleWriteError( $exception ) {
 383                 $db = $this->getDB();
 384
 385                 if ( !$db->wasReadOnlyError() ) {
 386                         throw $exception;
 387                 }
 388
 389                 try {
 390                         $db->rollback();
 391                 } catch ( DBQueryError $e ) {
 392                 }
 393
 394                 wfDebug( __METHOD__ . ": ignoring query error\n" );
 395                 $db->ignoreErrors( false );
 396         }
 397
 398         /**
 399          * Create shard tables. For use from eval.php.
 400          */
 401         public function createTables() {
 402                 $db = $this->getDB();
 403                 if ( $db->getType() !== 'mysql'
 404                         || version_compare( $db->getServerVersion(), '4.1.0', '<' ) )
 405                 {
 406                         throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 407                 }
 408
 409                 for ( $i = 0; $i < $this->shards; $i++ ) {
 410                         $db->begin();
 411                         $db->query(
 412                                 'CREATE TABLE ' . $db->tableName( $this->getTableByShard( $i ) ) .
 413                                 ' LIKE ' . $db->tableName( 'objectcache' ),
 414                                 __METHOD__ );
 415                         $db->commit();
 416                 }
 417         }
 418 }
 419
 420 /**
 421  * Backwards compatibility alias
 422  */
 423 class MediaWikiBagOStuff extends SqlBagOStuff { }
 424