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          * @param $paths array
 117          * @param $type int
 118          * @return Status
 119          */
 120         protected function doLock( array $paths, $type ) {
 121                 $status = Status::newGood();
 122
 123                 $pathsToLock = array();
 124                 // Get locks that need to be acquired (buckets => locks)...
 125                 foreach ( $paths as $path ) {
 126                         if ( isset( $this->locksHeld[$path][$type] ) ) {
 127                                 ++$this->locksHeld[$path][$type];
 128                         } elseif ( isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
 129                                 $this->locksHeld[$path][$type] = 1;
 130                         } else {
 131                                 $bucket = $this->getBucketFromKey( $path );
 132                                 $pathsToLock[$bucket][] = $path;
 133                         }
 134                 }
 135
 136                 $lockedPaths = array(); // files locked in this attempt
 137                 // Attempt to acquire these locks...
 138                 foreach ( $pathsToLock as $bucket => $paths ) {
 139                         // Try to acquire the locks for this bucket
 140                         $res = $this->doLockingQueryAll( $bucket, $paths, $type );
 141                         if ( $res === 'cantacquire' ) {
 142                                 // Resources already locked by another process.
 143                                 // Abort and unlock everything we just locked.
 144                                 foreach ( $paths as $path ) {
 145                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 146                                 }
 147                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
 148                                 return $status;
 149                         } elseif ( $res !== true ) {
 150                                 // Couldn't contact any DBs for this bucket.
 151                                 // Abort and unlock everything we just locked.
 152                                 $status->fatal( 'lockmanager-fail-db-bucket', $bucket );
 153                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
 154                                 return $status;
 155                         }
 156                         // Record these locks as active
 157                         foreach ( $paths as $path ) {
 158                                 $this->locksHeld[$path][$type] = 1; // locked
 159                         }
 160                         // Keep track of what locks were made in this attempt
 161                         $lockedPaths = array_merge( $lockedPaths, $paths );
 162                 }
 163
 164                 return $status;
 165         }
 166
 167         /**
 168          * @see LockManager::doUnlock()
 169          * @param $paths array
 170          * @param $type int
 171          * @return Status
 172          */
 173         protected function doUnlock( array $paths, $type ) {
 174                 $status = Status::newGood();
 175
 176                 foreach ( $paths as $path ) {
 177                         if ( !isset( $this->locksHeld[$path] ) ) {
 178                                 $status->warning( 'lockmanager-notlocked', $path );
 179                         } elseif ( !isset( $this->locksHeld[$path][$type] ) ) {
 180                                 $status->warning( 'lockmanager-notlocked', $path );
 181                         } else {
 182                                 --$this->locksHeld[$path][$type];
 183                                 if ( $this->locksHeld[$path][$type] <= 0 ) {
 184                                         unset( $this->locksHeld[$path][$type] );
 185                                 }
 186                                 if ( !count( $this->locksHeld[$path] ) ) {
 187                                         unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
 188                                 }
 189                         }
 190                 }
 191
 192                 // Reference count the locks held and COMMIT when zero
 193                 if ( !count( $this->locksHeld ) ) {
 194                         $status->merge( $this->finishLockTransactions() );
 195                 }
 196
 197                 return $status;
 198         }
 199
 200         /**
 201          * Get a connection to a lock DB and acquire locks on $paths.
 202          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 203          *
 204          * @param $lockDb string
 205          * @param $paths Array
 206          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 207          * @return bool Resources able to be locked
 208          * @throws DBError
 209          */
 210         protected function doLockingQuery( $lockDb, array $paths, $type ) {
 211                 if ( $type == self::LOCK_EX ) { // writer locks
 212                         $db = $this->getConnection( $lockDb );
 213                         if ( !$db ) {
 214                                 return false; // bad config
 215                         }
 216                         $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 217                         # Build up values for INSERT clause
 218                         $data = array();
 219                         foreach ( $keys as $key ) {
 220                                 $data[] = array( 'fle_key' => $key );
 221                         }
 222                         # Wait on any existing writers and block new ones if we get in
 223                         $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 224                 }
 225                 return true;
 226         }
 227
 228         /**
 229          * Attempt to acquire locks with the peers for a bucket.
 230          * This should avoid throwing any exceptions.
 231          *
 232          * @param $bucket integer
 233          * @param $paths Array List of resource keys to lock
 234          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 235          * @return bool|string One of (true, 'cantacquire', 'dberrors')
 236          */
 237         protected function doLockingQueryAll( $bucket, array $paths, $type ) {
 238                 $yesVotes = 0; // locks made on trustable DBs
 239                 $votesLeft = count( $this->dbsByBucket[$bucket] ); // remaining DBs
 240                 $quorum = floor( $votesLeft/2 + 1 ); // simple majority
 241                 // Get votes for each DB, in order, until we have enough...
 242                 foreach ( $this->dbsByBucket[$bucket] as $lockDb ) {
 243                         // Check that DB is not *known* to be down
 244                         if ( $this->cacheCheckFailures( $lockDb ) ) {
 245                                 try {
 246                                         // Attempt to acquire the lock on this DB
 247                                         if ( !$this->doLockingQuery( $lockDb, $paths, $type ) ) {
 248                                                 return 'cantacquire'; // vetoed; resource locked
 249                                         }
 250                                         ++$yesVotes; // success for this peer
 251                                         if ( $yesVotes >= $quorum ) {
 252                                                 return true; // lock obtained
 253                                         }
 254                                 } catch ( DBConnectionError $e ) {
 255                                         $this->cacheRecordFailure( $lockDb );
 256                                 } catch ( DBError $e ) {
 257                                         if ( $this->lastErrorIndicatesLocked( $lockDb ) ) {
 258                                                 return 'cantacquire'; // vetoed; resource locked
 259                                         }
 260                                 }
 261                         }
 262                         --$votesLeft;
 263                         $votesNeeded = $quorum - $yesVotes;
 264                         if ( $votesNeeded > $votesLeft ) {
 265                                 // In "trust cache" mode we don't have to meet the quorum
 266                                 break; // short-circuit
 267                         }
 268                 }
 269                 // At this point, we must not have meet the quorum
 270                 return 'dberrors'; // not enough votes to ensure correctness
 271         }
 272
 273         /**
 274          * Get (or reuse) a connection to a lock DB
 275          *
 276          * @param $lockDb string
 277          * @return DatabaseBase
 278          * @throws DBError
 279          */
 280         protected function getConnection( $lockDb ) {
 281                 if ( !isset( $this->conns[$lockDb] ) ) {
 282                         $db = null;
 283                         if ( $lockDb === 'localDBMaster' ) {
 284                                 $lb = wfGetLBFactory()->newMainLB();
 285                                 $db = $lb->getConnection( DB_MASTER );
 286                         } elseif ( isset( $this->dbServers[$lockDb] ) ) {
 287                                 $config = $this->dbServers[$lockDb];
 288                                 $db = DatabaseBase::factory( $config['type'], $config );
 289                         }
 290                         if ( !$db ) {
 291                                 return null; // config error?
 292                         }
 293                         $this->conns[$lockDb] = $db;
 294                         $this->conns[$lockDb]->clearFlag( DBO_TRX );
 295                         # If the connection drops, try to avoid letting the DB rollback
 296                         # and release the locks before the file operations are finished.
 297                         # This won't handle the case of DB server restarts however.
 298                         $options = array();
 299                         if ( $this->lockExpiry > 0 ) {
 300                                 $options['connTimeout'] = $this->lockExpiry;
 301                         }
 302                         $this->conns[$lockDb]->setSessionOptions( $options );
 303                         $this->initConnection( $lockDb, $this->conns[$lockDb] );
 304                 }
 305                 if ( !$this->conns[$lockDb]->trxLevel() ) {
 306                         $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
 307                 }
 308                 return $this->conns[$lockDb];
 309         }
 310
 311         /**
 312          * Do additional initialization for new lock DB connection
 313          *
 314          * @param $lockDb string
 315          * @param $db DatabaseBase
 316          * @return void
 317          * @throws DBError
 318          */
 319         protected function initConnection( $lockDb, DatabaseBase $db ) {}
 320
 321         /**
 322          * Commit all changes to lock-active databases.
 323          * This should avoid throwing any exceptions.
 324          *
 325          * @return Status
 326          */
 327         protected function finishLockTransactions() {
 328                 $status = Status::newGood();
 329                 foreach ( $this->conns as $lockDb => $db ) {
 330                         if ( $db->trxLevel() ) { // in transaction
 331                                 try {
 332                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 333                                 } catch ( DBError $e ) {
 334                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 335                                 }
 336                         }
 337                 }
 338                 return $status;
 339         }
 340
 341         /**
 342          * Check if the last DB error for $lockDb indicates
 343          * that a requested resource was locked by another process.
 344          * This should avoid throwing any exceptions.
 345          *
 346          * @param $lockDb string
 347          * @return bool
 348          */
 349         protected function lastErrorIndicatesLocked( $lockDb ) {
 350                 if ( isset( $this->conns[$lockDb] ) ) { // sanity
 351                         $db = $this->conns[$lockDb];
 352                         return ( $db->wasDeadlock() || $db->wasLockTimeout() );
 353                 }
 354                 return false;
 355         }
 356
 357         /**
 358          * Checks if the DB has not recently had connection/query errors.
 359          * This just avoids wasting time on doomed connection attempts.
 360          *
 361          * @param $lockDb string
 362          * @return bool
 363          */
 364         protected function cacheCheckFailures( $lockDb ) {
 365                 if ( $this->statusCache && $this->safeDelay > 0 ) {
 366                         $path = $this->getMissKey( $lockDb );
 367                         $misses = $this->statusCache->get( $path );
 368                         return !$misses;
 369                 }
 370                 return true;
 371         }
 372
 373         /**
 374          * Log a lock request failure to the cache
 375          *
 376          * @param $lockDb string
 377          * @return bool Success
 378          */
 379         protected function cacheRecordFailure( $lockDb ) {
 380                 if ( $this->statusCache && $this->safeDelay > 0 ) {
 381                         $path = $this->getMissKey( $lockDb );
 382                         $misses = $this->statusCache->get( $path );
 383                         if ( $misses ) {
 384                                 return $this->statusCache->incr( $path );
 385                         } else {
 386                                 return $this->statusCache->add( $path, 1, $this->safeDelay );
 387                         }
 388                 }
 389                 return true;
 390         }
 391
 392         /**
 393          * Get a cache key for recent query misses for a DB
 394          *
 395          * @param $lockDb string
 396          * @return string
 397          */
 398         protected function getMissKey( $lockDb ) {
 399                 return 'lockmanager:querymisses:' . str_replace( ' ', '_', $lockDb );
 400         }
 401
 402         /**
 403          * Get the bucket for resource path.
 404          * This should avoid throwing any exceptions.
 405          *
 406          * @param $path string
 407          * @return integer
 408          */
 409         protected function getBucketFromKey( $path ) {
 410                 $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
 411                 return intval( base_convert( $prefix, 16, 10 ) ) % count( $this->dbsByBucket );
 412         }
 413
 414         /**
 415          * Make sure remaining locks get cleared for sanity
 416          */
 417         function __destruct() {
 418                 foreach ( $this->conns as $lockDb => $db ) {
 419                         if ( $db->trxLevel() ) { // in transaction
 420                                 try {
 421                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 422                                 } catch ( DBError $e ) {
 423                                         // oh well
 424                                 }
 425                         }
 426                         $db->close();
 427                 }
 428         }
 429 }
 430
 431 /**
 432  * MySQL version of DBLockManager that supports shared locks.
 433  * All locks are non-blocking, which avoids deadlocks.
 434  *
 435  * @ingroup LockManager
 436  */
 437 class MySqlLockManager extends DBLockManager {
 438         /** @var Array Mapping of lock types to the type actually used */
 439         protected $lockTypeMap = array(
 440                 self::LOCK_SH => self::LOCK_SH,
 441                 self::LOCK_UW => self::LOCK_SH,
 442                 self::LOCK_EX => self::LOCK_EX
 443         );
 444
 445         /**
 446          * @param $lockDb string
 447          * @param $db DatabaseBase
 448          */
 449         protected function initConnection( $lockDb, DatabaseBase $db ) {
 450                 # Let this transaction see lock rows from other transactions
 451                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
 452         }
 453
 454         /**
 455          * @param $lockDb string
 456          * @param $paths array
 457          * @param $type int
 458          * @return bool
 459          */
 460         protected function doLockingQuery( $lockDb, array $paths, $type ) {
 461                 $db = $this->getConnection( $lockDb );
 462                 if ( !$db ) {
 463                         return false;
 464                 }
 465                 $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 466                 # Build up values for INSERT clause
 467                 $data = array();
 468                 foreach ( $keys as $key ) {
 469                         $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
 470                 }
 471                 # Block new writers...
 472                 $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
 473                 # Actually do the locking queries...
 474                 if ( $type == self::LOCK_SH ) { // reader locks
 475                         # Bail if there are any existing writers...
 476                         $blocked = $db->selectField( 'filelocks_exclusive', '1',
 477                                 array( 'fle_key' => $keys ),
 478                                 __METHOD__
 479                         );
 480                         # Prospective writers that haven't yet updated filelocks_exclusive
 481                         # will recheck filelocks_shared after doing so and bail due to our entry.
 482                 } else { // writer locks
 483                         $encSession = $db->addQuotes( $this->session );
 484                         # Bail if there are any existing writers...
 485                         # The may detect readers, but the safe check for them is below.
 486                         # Note: if two writers come at the same time, both bail :)
 487                         $blocked = $db->selectField( 'filelocks_shared', '1',
 488                                 array( 'fls_key' => $keys, "fls_session != $encSession" ),
 489                                 __METHOD__
 490                         );
 491                         if ( !$blocked ) {
 492                                 # Build up values for INSERT clause
 493                                 $data = array();
 494                                 foreach ( $keys as $key ) {
 495                                         $data[] = array( 'fle_key' => $key );
 496                                 }
 497                                 # Block new readers/writers...
 498                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 499                                 # Bail if there are any existing readers...
 500                                 $blocked = $db->selectField( 'filelocks_shared', '1',
 501                                         array( 'fls_key' => $keys, "fls_session != $encSession" ),
 502                                         __METHOD__
 503                                 );
 504                         }
 505                 }
 506                 return !$blocked;
 507         }
 508 }