includes/filebackend/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 row locks.
  26  *
  27  * This is meant for multi-wiki systems that may share files.
  28  * All locks are blocking, so it might be useful to set a small
  29  * lock-wait timeout via server config to curtail deadlocks.
  30  *
  31  * All lock requests for a resource, identified by a hash string, will map
  32  * to one bucket. Each bucket maps to one or several peer DBs, each on their
  33  * own server, all having the filelocks.sql tables (with row-level locking).
  34  * A majority of peer DBs must agree for a lock to be acquired.
  35  *
  36  * Caching is used to avoid hitting servers that are down.
  37  *
  38  * @ingroup LockManager
  39  * @since 1.19
  40  */
  41 class DBLockManager extends QuorumLockManager {
  42         /** @var Array Map of DB names to server config */
  43         protected $dbServers; // (DB name => server config array)
  44         /** @var BagOStuff */
  45         protected $statusCache;
  46
  47         protected $lockExpiry; // integer number of seconds
  48         protected $safeDelay; // integer number of seconds
  49
  50         protected $session = 0; // random integer
  51         /** @var Array Map Database connections (DB name => Database) */
  52         protected $conns = array();
  53
  54         /**
  55          * Construct a new instance from configuration.
  56          *
  57          * $config paramaters include:
  58          *   - dbServers   : Associative array of DB names to server configuration.
  59          *                   Configuration is an associative array that includes:
  60          *                     - host        : DB server name
  61          *                     - dbname      : DB name
  62          *                     - type        : DB type (mysql,postgres,...)
  63          *                     - user        : DB user
  64          *                     - password    : DB user password
  65          *                     - tablePrefix : DB table prefix
  66          *                     - flags       : DB flags (see DatabaseBase)
  67          *   - dbsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
  68          *                   each having an odd-numbered list of DB names (peers) as values.
  69          *                   Any DB named 'localDBMaster' will automatically use the DB master
  70          *                   settings for this wiki (without the need for a dbServers entry).
  71          *                   Only use 'localDBMaster' if the domain is a valid wiki ID.
  72          *   - lockExpiry  : Lock timeout (seconds) for dropped connections. [optional]
  73          *                   This tells the DB server how long to wait before assuming
  74          *                   connection failure and releasing all the locks for a session.
  75          *
  76          * @param Array $config
  77          */
  78         public function __construct( array $config ) {
  79                 parent::__construct( $config );
  80
  81                 $this->dbServers = isset( $config['dbServers'] )
  82                         ? $config['dbServers']
  83                         : array(); // likely just using 'localDBMaster'
  84                 // Sanitize srvsByBucket config to prevent PHP errors
  85                 $this->srvsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
  86                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  87
  88                 if ( isset( $config['lockExpiry'] ) ) {
  89                         $this->lockExpiry = $config['lockExpiry'];
  90                 } else {
  91                         $met = ini_get( 'max_execution_time' );
  92                         $this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
  93                 }
  94                 $this->safeDelay = ( $this->lockExpiry <= 0 )
  95                         ? 60 // pick a safe-ish number to match DB timeout default
  96                         : $this->lockExpiry; // cover worst case
  97
  98                 foreach ( $this->srvsByBucket as $bucket ) {
  99                         if ( count( $bucket ) > 1 ) { // multiple peers
 100                                 // Tracks peers that couldn't be queried recently to avoid lengthy
 101                                 // connection timeouts. This is useless if each bucket has one peer.
 102                                 try {
 103                                         $this->statusCache = ObjectCache::newAccelerator( array() );
 104                                 } catch ( MWException $e ) {
 105                                         trigger_error( __CLASS__ .
 106                                                 " using multiple DB peers without apc, xcache, or wincache." );
 107                                 }
 108                                 break;
 109                         }
 110                 }
 111
 112                 $this->session = wfRandomString( 31 );
 113         }
 114
 115         /**
 116          * Get a connection to a lock DB and acquire locks on $paths.
 117          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 118          *
 119          * @see QuorumLockManager::getLocksOnServer()
 120          * @return Status
 121          */
 122         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 123                 $status = Status::newGood();
 124
 125                 if ( $type == self::LOCK_EX ) { // writer locks
 126                         try {
 127                                 $keys = array_unique( array_map( array( $this, 'sha1Base36Absolute' ), $paths ) );
 128                                 # Build up values for INSERT clause
 129                                 $data = array();
 130                                 foreach ( $keys as $key ) {
 131                                         $data[] = array( 'fle_key' => $key );
 132                                 }
 133                                 # Wait on any existing writers and block new ones if we get in
 134                                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 135                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 136                         } catch ( DBError $e ) {
 137                                 foreach ( $paths as $path ) {
 138                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 139                                 }
 140                         }
 141                 }
 142
 143                 return $status;
 144         }
 145
 146         /**
 147          * @see QuorumLockManager::freeLocksOnServer()
 148          * @return Status
 149          */
 150         protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
 151                 return Status::newGood(); // not supported
 152         }
 153
 154         /**
 155          * @see QuorumLockManager::releaseAllLocks()
 156          * @return Status
 157          */
 158         protected function releaseAllLocks() {
 159                 $status = Status::newGood();
 160
 161                 foreach ( $this->conns as $lockDb => $db ) {
 162                         if ( $db->trxLevel() ) { // in transaction
 163                                 try {
 164                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 165                                 } catch ( DBError $e ) {
 166                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 167                                 }
 168                         }
 169                 }
 170
 171                 return $status;
 172         }
 173
 174         /**
 175          * @see QuorumLockManager::isServerUp()
 176          * @return bool
 177          */
 178         protected function isServerUp( $lockSrv ) {
 179                 if ( !$this->cacheCheckFailures( $lockSrv ) ) {
 180                         return false; // recent failure to connect
 181                 }
 182                 try {
 183                         $this->getConnection( $lockSrv );
 184                 } catch ( DBError $e ) {
 185                         $this->cacheRecordFailure( $lockSrv );
 186                         return false; // failed to connect
 187                 }
 188                 return true;
 189         }
 190
 191         /**
 192          * Get (or reuse) a connection to a lock DB
 193          *
 194          * @param $lockDb string
 195          * @return DatabaseBase
 196          * @throws DBError
 197          */
 198         protected function getConnection( $lockDb ) {
 199                 if ( !isset( $this->conns[$lockDb] ) ) {
 200                         $db = null;
 201                         if ( $lockDb === 'localDBMaster' ) {
 202                                 $lb = wfGetLBFactory()->getMainLB( $this->domain );
 203                                 $db = $lb->getConnection( DB_MASTER, array(), $this->domain );
 204                         } elseif ( isset( $this->dbServers[$lockDb] ) ) {
 205                                 $config = $this->dbServers[$lockDb];
 206                                 $db = DatabaseBase::factory( $config['type'], $config );
 207                         }
 208                         if ( !$db ) {
 209                                 return null; // config error?
 210                         }
 211                         $this->conns[$lockDb] = $db;
 212                         $this->conns[$lockDb]->clearFlag( DBO_TRX );
 213                         # If the connection drops, try to avoid letting the DB rollback
 214                         # and release the locks before the file operations are finished.
 215                         # This won't handle the case of DB server restarts however.
 216                         $options = array();
 217                         if ( $this->lockExpiry > 0 ) {
 218                                 $options['connTimeout'] = $this->lockExpiry;
 219                         }
 220                         $this->conns[$lockDb]->setSessionOptions( $options );
 221                         $this->initConnection( $lockDb, $this->conns[$lockDb] );
 222                 }
 223                 if ( !$this->conns[$lockDb]->trxLevel() ) {
 224                         $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
 225                 }
 226                 return $this->conns[$lockDb];
 227         }
 228
 229         /**
 230          * Do additional initialization for new lock DB connection
 231          *
 232          * @param $lockDb string
 233          * @param $db DatabaseBase
 234          * @return void
 235          * @throws DBError
 236          */
 237         protected function initConnection( $lockDb, DatabaseBase $db ) {}
 238
 239         /**
 240          * Checks if the DB has not recently had connection/query errors.
 241          * This just avoids wasting time on doomed connection attempts.
 242          *
 243          * @param $lockDb string
 244          * @return bool
 245          */
 246         protected function cacheCheckFailures( $lockDb ) {
 247                 return ( $this->statusCache && $this->safeDelay > 0 )
 248                         ? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
 249                         : true;
 250         }
 251
 252         /**
 253          * Log a lock request failure to the cache
 254          *
 255          * @param $lockDb string
 256          * @return bool Success
 257          */
 258         protected function cacheRecordFailure( $lockDb ) {
 259                 return ( $this->statusCache && $this->safeDelay > 0 )
 260                         ? $this->statusCache->set( $this->getMissKey( $lockDb ), 1, $this->safeDelay )
 261                         : true;
 262         }
 263
 264         /**
 265          * Get a cache key for recent query misses for a DB
 266          *
 267          * @param $lockDb string
 268          * @return string
 269          */
 270         protected function getMissKey( $lockDb ) {
 271                 $lockDb = ( $lockDb === 'localDBMaster' ) ? wfWikiID() : $lockDb; // non-relative
 272                 return 'dblockmanager:downservers:' . str_replace( ' ', '_', $lockDb );
 273         }
 274
 275         /**
 276          * Make sure remaining locks get cleared for sanity
 277          */
 278         function __destruct() {
 279                 foreach ( $this->conns as $db ) {
 280                         if ( $db->trxLevel() ) { // in transaction
 281                                 try {
 282                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 283                                 } catch ( DBError $e ) {
 284                                         // oh well
 285                                 }
 286                         }
 287                         $db->close();
 288                 }
 289         }
 290 }
 291
 292 /**
 293  * MySQL version of DBLockManager that supports shared locks.
 294  * All locks are non-blocking, which avoids deadlocks.
 295  *
 296  * @ingroup LockManager
 297  */
 298 class MySqlLockManager extends DBLockManager {
 299         /** @var Array Mapping of lock types to the type actually used */
 300         protected $lockTypeMap = array(
 301                 self::LOCK_SH => self::LOCK_SH,
 302                 self::LOCK_UW => self::LOCK_SH,
 303                 self::LOCK_EX => self::LOCK_EX
 304         );
 305
 306         /**
 307          * @param $lockDb string
 308          * @param $db DatabaseBase
 309          */
 310         protected function initConnection( $lockDb, DatabaseBase $db ) {
 311                 # Let this transaction see lock rows from other transactions
 312                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
 313         }
 314
 315         /**
 316          * Get a connection to a lock DB and acquire locks on $paths.
 317          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 318          *
 319          * @see DBLockManager::getLocksOnServer()
 320          * @return Status
 321          */
 322         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 323                 $status = Status::newGood();
 324
 325                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 326                 $keys = array_unique( array_map( array( $this, 'sha1Base36Absolute' ), $paths ) );
 327                 # Build up values for INSERT clause
 328                 $data = array();
 329                 foreach ( $keys as $key ) {
 330                         $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
 331                 }
 332                 # Block new writers...
 333                 $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
 334                 # Actually do the locking queries...
 335                 if ( $type == self::LOCK_SH ) { // reader locks
 336                         # Bail if there are any existing writers...
 337                         $blocked = $db->selectField( 'filelocks_exclusive', '1',
 338                                 array( 'fle_key' => $keys ),
 339                                 __METHOD__
 340                         );
 341                         # Prospective writers that haven't yet updated filelocks_exclusive
 342                         # will recheck filelocks_shared after doing so and bail due to our entry.
 343                 } else { // writer locks
 344                         $encSession = $db->addQuotes( $this->session );
 345                         # Bail if there are any existing writers...
 346                         # The may detect readers, but the safe check for them is below.
 347                         # Note: if two writers come at the same time, both bail :)
 348                         $blocked = $db->selectField( 'filelocks_shared', '1',
 349                                 array( 'fls_key' => $keys, "fls_session != $encSession" ),
 350                                 __METHOD__
 351                         );
 352                         if ( !$blocked ) {
 353                                 # Build up values for INSERT clause
 354                                 $data = array();
 355                                 foreach ( $keys as $key ) {
 356                                         $data[] = array( 'fle_key' => $key );
 357                                 }
 358                                 # Block new readers/writers...
 359                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 360                                 # Bail if there are any existing readers...
 361                                 $blocked = $db->selectField( 'filelocks_shared', '1',
 362                                         array( 'fls_key' => $keys, "fls_session != $encSession" ),
 363                                         __METHOD__
 364                                 );
 365                         }
 366                 }
 367
 368                 if ( $blocked ) {
 369                         foreach ( $paths as $path ) {
 370                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 371                         }
 372                 }
 373
 374                 return $status;
 375         }
 376 }