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 LockManager {
  41         /** @var Array Map of DB names to server config */
  42         protected $dbServers; // (DB name => server config array)
  43         /** @var Array Map of bucket indexes to peer DB lists */
  44         protected $dbsByBucket; // (bucket index => (ldb1, ldb2, ...))
  45         /** @var BagOStuff */
  46         protected $statusCache;
  47
  48         protected $lockExpiry; // integer number of seconds
  49         protected $safeDelay; // integer number of seconds
  50
  51         protected $session = 0; // random integer
  52         /** @var Array Map Database connections (DB name => Database) */
  53         protected $conns = array();
  54
  55         /**
  56          * Construct a new instance from configuration.
  57          *
  58          * $config paramaters include:
  59          *     'dbServers'   : Associative array of DB names to server configuration.
  60          *                     Configuration is an associative array that includes:
  61          *                     'host'        - DB server name
  62          *                     'dbname'      - DB name
  63          *                     'type'        - DB type (mysql,postgres,...)
  64          *                     'user'        - DB user
  65          *                     'password'    - DB user password
  66          *                     'tablePrefix' - DB table prefix
  67          *                     'flags'       - DB flags (see DatabaseBase)
  68          *     'dbsByBucket' : Array of 1-16 consecutive integer keys, starting from 0,
  69          *                     each having an odd-numbered list of DB names (peers) as values.
  70          *                     Any DB named 'localDBMaster' will automatically use the DB master
  71          *                     settings for this wiki (without the need for a dbServers entry).
  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 dbsByBucket config to prevent PHP errors
  85                 $this->dbsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
  86                 $this->dbsByBucket = array_values( $this->dbsByBucket ); // 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->dbsByBucket as $bucket ) {
  99                         if ( count( $bucket ) > 1 ) {
 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                                 $this->statusCache = wfGetMainCache();
 103                                 break;
 104                         }
 105                 }
 106
 107                 $this->session = '';
 108                 for ( $i = 0; $i < 5; $i++ ) {
 109                         $this->session .= mt_rand( 0, 2147483647 );
 110                 }
 111                 $this->session = wfBaseConvert( sha1( $this->session ), 16, 36, 31 );
 112         }
 113
 114         /**
 115          * @see LockManager::doLock()
 116          * @return Status
 117          */
 118         protected function doLock( array $paths, $type ) {
 119                 $status = Status::newGood();
 120
 121                 $pathsToLock = array();
 122                 // Get locks that need to be acquired (buckets => locks)...
 123                 foreach ( $paths as $path ) {
 124                         if ( isset( $this->locksHeld[$path][$type] ) ) {
 125                                 ++$this->locksHeld[$path][$type];
 126                         } elseif ( isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
 127                                 $this->locksHeld[$path][$type] = 1;
 128                         } else {
 129                                 $bucket = $this->getBucketFromKey( $path );
 130                                 $pathsToLock[$bucket][] = $path;
 131                         }
 132                 }
 133
 134                 $lockedPaths = array(); // files locked in this attempt
 135                 // Attempt to acquire these locks...
 136                 foreach ( $pathsToLock as $bucket => $paths ) {
 137                         // Try to acquire the locks for this bucket
 138                         $res = $this->doLockingQueryAll( $bucket, $paths, $type );
 139                         if ( $res === 'cantacquire' ) {
 140                                 // Resources already locked by another process.
 141                                 // Abort and unlock everything we just locked.
 142                                 foreach ( $paths as $path ) {
 143                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 144                                 }
 145                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
 146                                 return $status;
 147                         } elseif ( $res !== true ) {
 148                                 // Couldn't contact any DBs for this bucket.
 149                                 // Abort and unlock everything we just locked.
 150                                 $status->fatal( 'lockmanager-fail-db-bucket', $bucket );
 151                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
 152                                 return $status;
 153                         }
 154                         // Record these locks as active
 155                         foreach ( $paths as $path ) {
 156                                 $this->locksHeld[$path][$type] = 1; // locked
 157                         }
 158                         // Keep track of what locks were made in this attempt
 159                         $lockedPaths = array_merge( $lockedPaths, $paths );
 160                 }
 161
 162                 return $status;
 163         }
 164
 165         /**
 166          * @see LockManager::doUnlock()
 167          * @return Status
 168          */
 169         protected function doUnlock( array $paths, $type ) {
 170                 $status = Status::newGood();
 171
 172                 foreach ( $paths as $path ) {
 173                         if ( !isset( $this->locksHeld[$path] ) ) {
 174                                 $status->warning( 'lockmanager-notlocked', $path );
 175                         } elseif ( !isset( $this->locksHeld[$path][$type] ) ) {
 176                                 $status->warning( 'lockmanager-notlocked', $path );
 177                         } else {
 178                                 --$this->locksHeld[$path][$type];
 179                                 if ( $this->locksHeld[$path][$type] <= 0 ) {
 180                                         unset( $this->locksHeld[$path][$type] );
 181                                 }
 182                                 if ( !count( $this->locksHeld[$path] ) ) {
 183                                         unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
 184                                 }
 185                         }
 186                 }
 187
 188                 // Reference count the locks held and COMMIT when zero
 189                 if ( !count( $this->locksHeld ) ) {
 190                         $status->merge( $this->finishLockTransactions() );
 191                 }
 192
 193                 return $status;
 194         }
 195
 196         /**
 197          * Get a connection to a lock DB and acquire locks on $paths.
 198          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 199          *
 200          * @param $lockDb string
 201          * @param $paths Array
 202          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 203          * @return bool Resources able to be locked
 204          * @throws DBError
 205          */
 206         protected function doLockingQuery( $lockDb, array $paths, $type ) {
 207                 if ( $type == self::LOCK_EX ) { // writer locks
 208                         $db = $this->getConnection( $lockDb );
 209                         if ( !$db ) {
 210                                 return false; // bad config
 211                         }
 212                         $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 213                         # Build up values for INSERT clause
 214                         $data = array();
 215                         foreach ( $keys as $key ) {
 216                                 $data[] = array( 'fle_key' => $key );
 217                         }
 218                         # Wait on any existing writers and block new ones if we get in
 219                         $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 220                 }
 221                 return true;
 222         }
 223
 224         /**
 225          * Attempt to acquire locks with the peers for a bucket.
 226          * This should avoid throwing any exceptions.
 227          *
 228          * @param $bucket integer
 229          * @param $paths Array List of resource keys to lock
 230          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 231          * @return bool|string One of (true, 'cantacquire', 'dberrors')
 232          */
 233         protected function doLockingQueryAll( $bucket, array $paths, $type ) {
 234                 $yesVotes = 0; // locks made on trustable DBs
 235                 $votesLeft = count( $this->dbsByBucket[$bucket] ); // remaining DBs
 236                 $quorum = floor( $votesLeft/2 + 1 ); // simple majority
 237                 // Get votes for each DB, in order, until we have enough...
 238                 foreach ( $this->dbsByBucket[$bucket] as $lockDb ) {
 239                         // Check that DB is not *known* to be down
 240                         if ( $this->cacheCheckFailures( $lockDb ) ) {
 241                                 try {
 242                                         // Attempt to acquire the lock on this DB
 243                                         if ( !$this->doLockingQuery( $lockDb, $paths, $type ) ) {
 244                                                 return 'cantacquire'; // vetoed; resource locked
 245                                         }
 246                                         ++$yesVotes; // success for this peer
 247                                         if ( $yesVotes >= $quorum ) {
 248                                                 return true; // lock obtained
 249                                         }
 250                                 } catch ( DBConnectionError $e ) {
 251                                         $this->cacheRecordFailure( $lockDb );
 252                                 } catch ( DBError $e ) {
 253                                         if ( $this->lastErrorIndicatesLocked( $lockDb ) ) {
 254                                                 return 'cantacquire'; // vetoed; resource locked
 255                                         }
 256                                 }
 257                         }
 258                         --$votesLeft;
 259                         $votesNeeded = $quorum - $yesVotes;
 260                         if ( $votesNeeded > $votesLeft ) {
 261                                 // In "trust cache" mode we don't have to meet the quorum
 262                                 break; // short-circuit
 263                         }
 264                 }
 265                 // At this point, we must not have meet the quorum
 266                 return 'dberrors'; // not enough votes to ensure correctness
 267         }
 268
 269         /**
 270          * Get (or reuse) a connection to a lock DB
 271          *
 272          * @param $lockDb string
 273          * @return DatabaseBase
 274          * @throws DBError
 275          */
 276         protected function getConnection( $lockDb ) {
 277                 if ( !isset( $this->conns[$lockDb] ) ) {
 278                         $db = null;
 279                         if ( $lockDb === 'localDBMaster' ) {
 280                                 $lb = wfGetLBFactory()->newMainLB();
 281                                 $db = $lb->getConnection( DB_MASTER );
 282                         } elseif ( isset( $this->dbServers[$lockDb] ) ) {
 283                                 $config = $this->dbServers[$lockDb];
 284                                 $db = DatabaseBase::factory( $config['type'], $config );
 285                         }
 286                         if ( !$db ) {
 287                                 return null; // config error?
 288                         }
 289                         $this->conns[$lockDb] = $db;
 290                         $this->conns[$lockDb]->clearFlag( DBO_TRX );
 291                         # If the connection drops, try to avoid letting the DB rollback
 292                         # and release the locks before the file operations are finished.
 293                         # This won't handle the case of DB server restarts however.
 294                         $options = array();
 295                         if ( $this->lockExpiry > 0 ) {
 296                                 $options['connTimeout'] = $this->lockExpiry;
 297                         }
 298                         $this->conns[$lockDb]->setSessionOptions( $options );
 299                         $this->initConnection( $lockDb, $this->conns[$lockDb] );
 300                 }
 301                 if ( !$this->conns[$lockDb]->trxLevel() ) {
 302                         $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
 303                 }
 304                 return $this->conns[$lockDb];
 305         }
 306
 307         /**
 308          * Do additional initialization for new lock DB connection
 309          *
 310          * @param $lockDb string
 311          * @param $db DatabaseBase
 312          * @return void
 313          * @throws DBError
 314          */
 315         protected function initConnection( $lockDb, DatabaseBase $db ) {}
 316
 317         /**
 318          * Commit all changes to lock-active databases.
 319          * This should avoid throwing any exceptions.
 320          *
 321          * @return Status
 322          */
 323         protected function finishLockTransactions() {
 324                 $status = Status::newGood();
 325                 foreach ( $this->conns as $lockDb => $db ) {
 326                         if ( $db->trxLevel() ) { // in transaction
 327                                 try {
 328                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 329                                 } catch ( DBError $e ) {
 330                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 331                                 }
 332                         }
 333                 }
 334                 return $status;
 335         }
 336
 337         /**
 338          * Check if the last DB error for $lockDb indicates
 339          * that a requested resource was locked by another process.
 340          * This should avoid throwing any exceptions.
 341          *
 342          * @param $lockDb string
 343          * @return bool
 344          */
 345         protected function lastErrorIndicatesLocked( $lockDb ) {
 346                 if ( isset( $this->conns[$lockDb] ) ) { // sanity
 347                         $db = $this->conns[$lockDb];
 348                         return ( $db->wasDeadlock() || $db->wasLockTimeout() );
 349                 }
 350                 return false;
 351         }
 352
 353         /**
 354          * Checks if the DB has not recently had connection/query errors.
 355          * This just avoids wasting time on doomed connection attempts.
 356          *
 357          * @param $lockDb string
 358          * @return bool
 359          */
 360         protected function cacheCheckFailures( $lockDb ) {
 361                 if ( $this->statusCache && $this->safeDelay > 0 ) {
 362                         $path = $this->getMissKey( $lockDb );
 363                         $misses = $this->statusCache->get( $path );
 364                         return !$misses;
 365                 }
 366                 return true;
 367         }
 368
 369         /**
 370          * Log a lock request failure to the cache
 371          *
 372          * @param $lockDb string
 373          * @return bool Success
 374          */
 375         protected function cacheRecordFailure( $lockDb ) {
 376                 if ( $this->statusCache && $this->safeDelay > 0 ) {
 377                         $path = $this->getMissKey( $lockDb );
 378                         $misses = $this->statusCache->get( $path );
 379                         if ( $misses ) {
 380                                 return $this->statusCache->incr( $path );
 381                         } else {
 382                                 return $this->statusCache->add( $path, 1, $this->safeDelay );
 383                         }
 384                 }
 385                 return true;
 386         }
 387
 388         /**
 389          * Get a cache key for recent query misses for a DB
 390          *
 391          * @param $lockDb string
 392          * @return string
 393          */
 394         protected function getMissKey( $lockDb ) {
 395                 return 'lockmanager:querymisses:' . str_replace( ' ', '_', $lockDb );
 396         }
 397
 398         /**
 399          * Get the bucket for resource path.
 400          * This should avoid throwing any exceptions.
 401          *
 402          * @param $path string
 403          * @return integer
 404          */
 405         protected function getBucketFromKey( $path ) {
 406                 $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
 407                 return intval( base_convert( $prefix, 16, 10 ) ) % count( $this->dbsByBucket );
 408         }
 409
 410         /**
 411          * Make sure remaining locks get cleared for sanity
 412          */
 413         function __destruct() {
 414                 foreach ( $this->conns as $lockDb => $db ) {
 415                         if ( $db->trxLevel() ) { // in transaction
 416                                 try {
 417                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 418                                 } catch ( DBError $e ) {
 419                                         // oh well
 420                                 }
 421                         }
 422                         $db->close();
 423                 }
 424         }
 425 }
 426
 427 /**
 428  * MySQL version of DBLockManager that supports shared locks.
 429  * All locks are non-blocking, which avoids deadlocks.
 430  *
 431  * @ingroup LockManager
 432  */
 433 class MySqlLockManager extends DBLockManager {
 434         /** @var Array Mapping of lock types to the type actually used */
 435         protected $lockTypeMap = array(
 436                 self::LOCK_SH => self::LOCK_SH,
 437                 self::LOCK_UW => self::LOCK_SH,
 438                 self::LOCK_EX => self::LOCK_EX
 439         );
 440
 441         protected function initConnection( $lockDb, DatabaseBase $db ) {
 442                 # Let this transaction see lock rows from other transactions
 443                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
 444         }
 445
 446         protected function doLockingQuery( $lockDb, array $paths, $type ) {
 447                 $db = $this->getConnection( $lockDb );
 448                 if ( !$db ) {
 449                         return false;
 450                 }
 451                 $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 452                 # Build up values for INSERT clause
 453                 $data = array();
 454                 foreach ( $keys as $key ) {
 455                         $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
 456                 }
 457                 # Block new writers...
 458                 $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
 459                 # Actually do the locking queries...
 460                 if ( $type == self::LOCK_SH ) { // reader locks
 461                         # Bail if there are any existing writers...
 462                         $blocked = $db->selectField( 'filelocks_exclusive', '1',
 463                                 array( 'fle_key' => $keys ),
 464                                 __METHOD__
 465                         );
 466                         # Prospective writers that haven't yet updated filelocks_exclusive
 467                         # will recheck filelocks_shared after doing so and bail due to our entry.
 468                 } else { // writer locks
 469                         $encSession = $db->addQuotes( $this->session );
 470                         # Bail if there are any existing writers...
 471                         # The may detect readers, but the safe check for them is below.
 472                         # Note: if two writers come at the same time, both bail :)
 473                         $blocked = $db->selectField( 'filelocks_shared', '1',
 474                                 array( 'fls_key' => $keys, "fls_session != $encSession" ),
 475                                 __METHOD__
 476                         );
 477                         if ( !$blocked ) {
 478                                 # Build up values for INSERT clause
 479                                 $data = array();
 480                                 foreach ( $keys as $key ) {
 481                                         $data[] = array( 'fle_key' => $key );
 482                                 }
 483                                 # Block new readers/writers...
 484                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 485                                 # Bail if there are any existing readers...
 486                                 $blocked = $db->selectField( 'filelocks_shared', '1',
 487                                         array( 'fls_key' => $keys, "fls_session != $encSession" ),
 488                                         __METHOD__
 489                                 );
 490                         }
 491                 }
 492                 return !$blocked;
 493         }
 494 }