includes/filerepo/backend/lockmanager/DBLockManager.php

   1 <?php
   2 /**
   3  * Version of LockManager based on using DB table locks.
   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 LockManager
  22  */
  23
  24 /**
  25  * Version of LockManager based on using DB table locks.
  26  * This is meant for multi-wiki systems that may share files.
  27  * All locks are blocking, so it might be useful to set a small
  28  * lock-wait timeout via server config to curtail deadlocks.
  29  *
  30  * All lock requests for a resource, identified by a hash string, will map
  31  * to one bucket. Each bucket maps to one or several peer DBs, each on their
  32  * own server, all having the filelocks.sql tables (with row-level locking).
  33  * A majority of peer DBs must agree for a lock to be acquired.
  34  *
  35  * Caching is used to avoid hitting servers that are down.
  36  *
  37  * @ingroup LockManager
  38  * @since 1.19
  39  */
  40 class DBLockManager extends QuorumLockManager {
  41         /** @var Array Map of DB names to server config */
  42         protected $dbServers; // (DB name => server config array)
  43         /** @var BagOStuff */
  44         protected $statusCache;
  45
  46         protected $lockExpiry; // integer number of seconds
  47         protected $safeDelay; // integer number of seconds
  48
  49         protected $session = 0; // random integer
  50         /** @var Array Map Database connections (DB name => Database) */
  51         protected $conns = array();
  52
  53         /**
  54          * Construct a new instance from configuration.
  55          *
  56          * $config paramaters include:
  57          *     'dbServers'   : Associative array of DB names to server configuration.
  58          *                     Configuration is an associative array that includes:
  59          *                     'host'        - DB server name
  60          *                     'dbname'      - DB name
  61          *                     'type'        - DB type (mysql,postgres,...)
  62          *                     'user'        - DB user
  63          *                     'password'    - DB user password
  64          *                     'tablePrefix' - DB table prefix
  65          *                     'flags'       - DB flags (see DatabaseBase)
  66          *     'dbsByBucket' : Array of 1-16 consecutive integer keys, starting from 0,
  67          *                     each having an odd-numbered list of DB names (peers) as values.
  68          *                     Any DB named 'localDBMaster' will automatically use the DB master
  69          *                     settings for this wiki (without the need for a dbServers entry).
  70          *     'lockExpiry'  : Lock timeout (seconds) for dropped connections. [optional]
  71          *                     This tells the DB server how long to wait before assuming
  72          *                     connection failure and releasing all the locks for a session.
  73          *
  74          * @param Array $config
  75          */
  76         public function __construct( array $config ) {
  77                 parent::__construct( $config );
  78
  79                 $this->dbServers = isset( $config['dbServers'] )
  80                         ? $config['dbServers']
  81                         : array(); // likely just using 'localDBMaster'
  82                 // Sanitize srvsByBucket config to prevent PHP errors
  83                 $this->srvsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
  84                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  85
  86                 if ( isset( $config['lockExpiry'] ) ) {
  87                         $this->lockExpiry = $config['lockExpiry'];
  88                 } else {
  89                         $met = ini_get( 'max_execution_time' );
  90                         $this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
  91                 }
  92                 $this->safeDelay = ( $this->lockExpiry <= 0 )
  93                         ? 60 // pick a safe-ish number to match DB timeout default
  94                         : $this->lockExpiry; // cover worst case
  95
  96                 foreach ( $this->srvsByBucket as $bucket ) {
  97                         if ( count( $bucket ) > 1 ) { // multiple peers
  98                                 // Tracks peers that couldn't be queried recently to avoid lengthy
  99                                 // connection timeouts. This is useless if each bucket has one peer.
 100                                 try {
 101                                         $this->statusCache = ObjectCache::newAccelerator( array() );
 102                                 } catch ( MWException $e ) {
 103                                         trigger_error( __CLASS__ .
 104                                                 " using multiple DB peers without apc, xcache, or wincache." );
 105                                 }
 106                                 break;
 107                         }
 108                 }
 109
 110                 $this->session = wfRandomString( 31 );
 111         }
 112
 113         /**
 114          * Get a connection to a lock DB and acquire locks on $paths.
 115          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 116          *
 117          * @see QuorumLockManager::getLocksOnServer()
 118          * @return Status
 119          */
 120         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 121                 $status = Status::newGood();
 122
 123                 if ( $type == self::LOCK_EX ) { // writer locks
 124                         try {
 125                                 $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 126                                 # Build up values for INSERT clause
 127                                 $data = array();
 128                                 foreach ( $keys as $key ) {
 129                                         $data[] = array( 'fle_key' => $key );
 130                                 }
 131                                 # Wait on any existing writers and block new ones if we get in
 132                                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 133                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 134                         } catch ( DBError $e ) {
 135                                 foreach ( $paths as $path ) {
 136                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 137                                 }
 138                         }
 139                 }
 140
 141                 return $status;
 142         }
 143
 144         /**
 145          * @see QuorumLockManager::freeLocksOnServer()
 146          * @return Status
 147          */
 148         protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
 149                 return Status::newGood(); // not supported
 150         }
 151
 152         /**
 153          * @see QuorumLockManager::releaseAllLocks()
 154          * @return Status
 155          */
 156         protected function releaseAllLocks() {
 157                 $status = Status::newGood();
 158
 159                 foreach ( $this->conns as $lockDb => $db ) {
 160                         if ( $db->trxLevel() ) { // in transaction
 161                                 try {
 162                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 163                                 } catch ( DBError $e ) {
 164                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 165                                 }
 166                         }
 167                 }
 168
 169                 return $status;
 170         }
 171
 172         /**
 173          * @see QuorumLockManager::isServerUp()
 174          * @return bool
 175          */
 176         protected function isServerUp( $lockSrv ) {
 177                 if ( !$this->cacheCheckFailures( $lockSrv ) ) {
 178                         return false; // recent failure to connect
 179                 }
 180                 try {
 181                         $this->getConnection( $lockSrv );
 182                 } catch ( DBError $e ) {
 183                         $this->cacheRecordFailure( $lockSrv );
 184                         return false; // failed to connect
 185                 }
 186                 return true;
 187         }
 188
 189         /**
 190          * Get (or reuse) a connection to a lock DB
 191          *
 192          * @param $lockDb string
 193          * @return DatabaseBase
 194          * @throws DBError
 195          */
 196         protected function getConnection( $lockDb ) {
 197                 if ( !isset( $this->conns[$lockDb] ) ) {
 198                         $db = null;
 199                         if ( $lockDb === 'localDBMaster' ) {
 200                                 $lb = wfGetLBFactory()->newMainLB();
 201                                 $db = $lb->getConnection( DB_MASTER );
 202                         } elseif ( isset( $this->dbServers[$lockDb] ) ) {
 203                                 $config = $this->dbServers[$lockDb];
 204                                 $db = DatabaseBase::factory( $config['type'], $config );
 205                         }
 206                         if ( !$db ) {
 207                                 return null; // config error?
 208                         }
 209                         $this->conns[$lockDb] = $db;
 210                         $this->conns[$lockDb]->clearFlag( DBO_TRX );
 211                         # If the connection drops, try to avoid letting the DB rollback
 212                         # and release the locks before the file operations are finished.
 213                         # This won't handle the case of DB server restarts however.
 214                         $options = array();
 215                         if ( $this->lockExpiry > 0 ) {
 216                                 $options['connTimeout'] = $this->lockExpiry;
 217                         }
 218                         $this->conns[$lockDb]->setSessionOptions( $options );
 219                         $this->initConnection( $lockDb, $this->conns[$lockDb] );
 220                 }
 221                 if ( !$this->conns[$lockDb]->trxLevel() ) {
 222                         $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
 223                 }
 224                 return $this->conns[$lockDb];
 225         }
 226
 227         /**
 228          * Do additional initialization for new lock DB connection
 229          *
 230          * @param $lockDb string
 231          * @param $db DatabaseBase
 232          * @return void
 233          * @throws DBError
 234          */
 235         protected function initConnection( $lockDb, DatabaseBase $db ) {}
 236
 237         /**
 238          * Checks if the DB has not recently had connection/query errors.
 239          * This just avoids wasting time on doomed connection attempts.
 240          *
 241          * @param $lockDb string
 242          * @return bool
 243          */
 244         protected function cacheCheckFailures( $lockDb ) {
 245                 return ( $this->statusCache && $this->safeDelay > 0 )
 246                         ? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
 247                         : true;
 248         }
 249
 250         /**
 251          * Log a lock request failure to the cache
 252          *
 253          * @param $lockDb string
 254          * @return bool Success
 255          */
 256         protected function cacheRecordFailure( $lockDb ) {
 257                 return ( $this->statusCache && $this->safeDelay > 0 )
 258                         ? $this->statusCache->set( $this->getMissKey( $lockDb ), 1, $this->safeDelay )
 259                         : true;
 260         }
 261
 262         /**
 263          * Get a cache key for recent query misses for a DB
 264          *
 265          * @param $lockDb string
 266          * @return string
 267          */
 268         protected function getMissKey( $lockDb ) {
 269                 $lockDb = ( $lockDb === 'localDBMaster' ) ? wfWikiID() : $lockDb; // non-relative
 270                 return 'dblockmanager:downservers:' . str_replace( ' ', '_', $lockDb );
 271         }
 272
 273         /**
 274          * Make sure remaining locks get cleared for sanity
 275          */
 276         function __destruct() {
 277                 foreach ( $this->conns as $db ) {
 278                         if ( $db->trxLevel() ) { // in transaction
 279                                 try {
 280                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 281                                 } catch ( DBError $e ) {
 282                                         // oh well
 283                                 }
 284                         }
 285                         $db->close();
 286                 }
 287         }
 288 }
 289
 290 /**
 291  * MySQL version of DBLockManager that supports shared locks.
 292  * All locks are non-blocking, which avoids deadlocks.
 293  *
 294  * @ingroup LockManager
 295  */
 296 class MySqlLockManager extends DBLockManager {
 297         /** @var Array Mapping of lock types to the type actually used */
 298         protected $lockTypeMap = array(
 299                 self::LOCK_SH => self::LOCK_SH,
 300                 self::LOCK_UW => self::LOCK_SH,
 301                 self::LOCK_EX => self::LOCK_EX
 302         );
 303
 304         /**
 305          * @param $lockDb string
 306          * @param $db DatabaseBase
 307          */
 308         protected function initConnection( $lockDb, DatabaseBase $db ) {
 309                 # Let this transaction see lock rows from other transactions
 310                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
 311         }
 312
 313         /**
 314          * Get a connection to a lock DB and acquire locks on $paths.
 315          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 316          *
 317          * @see DBLockManager::getLocksOnServer()
 318          * @return Status
 319          */
 320         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 321                 $status = Status::newGood();
 322
 323                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 324                 $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 325                 # Build up values for INSERT clause
 326                 $data = array();
 327                 foreach ( $keys as $key ) {
 328                         $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
 329                 }
 330                 # Block new writers...
 331                 $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
 332                 # Actually do the locking queries...
 333                 if ( $type == self::LOCK_SH ) { // reader locks
 334                         # Bail if there are any existing writers...
 335                         $blocked = $db->selectField( 'filelocks_exclusive', '1',
 336                                 array( 'fle_key' => $keys ),
 337                                 __METHOD__
 338                         );
 339                         # Prospective writers that haven't yet updated filelocks_exclusive
 340                         # will recheck filelocks_shared after doing so and bail due to our entry.
 341                 } else { // writer locks
 342                         $encSession = $db->addQuotes( $this->session );
 343                         # Bail if there are any existing writers...
 344                         # The may detect readers, but the safe check for them is below.
 345                         # Note: if two writers come at the same time, both bail :)
 346                         $blocked = $db->selectField( 'filelocks_shared', '1',
 347                                 array( 'fls_key' => $keys, "fls_session != $encSession" ),
 348                                 __METHOD__
 349                         );
 350                         if ( !$blocked ) {
 351                                 # Build up values for INSERT clause
 352                                 $data = array();
 353                                 foreach ( $keys as $key ) {
 354                                         $data[] = array( 'fle_key' => $key );
 355                                 }
 356                                 # Block new readers/writers...
 357                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 358                                 # Bail if there are any existing readers...
 359                                 $blocked = $db->selectField( 'filelocks_shared', '1',
 360                                         array( 'fls_key' => $keys, "fls_session != $encSession" ),
 361                                         __METHOD__
 362                                 );
 363                         }
 364                 }
 365
 366                 if ( $blocked ) {
 367                         foreach ( $paths as $path ) {
 368                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 369                         }
 370                 }
 371
 372                 return $status;
 373         }
 374 }