includes/filerepo/backend/lockmanager/DBLockManager.php

   1 <?php
   2
   3 /**
   4  * Version of LockManager based on using DB table locks.
   5  * This is meant for multi-wiki systems that may share files.
   6  * All locks are blocking, so it might be useful to set a small
   7  * lock-wait timeout via server config to curtail deadlocks.
   8  *
   9  * All lock requests for a resource, identified by a hash string, will map
  10  * to one bucket. Each bucket maps to one or several peer DBs, each on their
  11  * own server, all having the filelocks.sql tables (with row-level locking).
  12  * A majority of peer DBs must agree for a lock to be acquired.
  13  *
  14  * Caching is used to avoid hitting servers that are down.
  15  *
  16  * @ingroup LockManager
  17  * @since 1.19
  18  */
  19 class DBLockManager extends LockManager {
  20         /** @var Array Map of DB names to server config */
  21         protected $dbServers; // (DB name => server config array)
  22         /** @var Array Map of bucket indexes to peer DB lists */
  23         protected $dbsByBucket; // (bucket index => (ldb1, ldb2, ...))
  24         /** @var BagOStuff */
  25         protected $statusCache;
  26
  27         protected $lockExpiry; // integer number of seconds
  28         protected $safeDelay; // integer number of seconds
  29
  30         protected $session = 0; // random integer
  31         /** @var Array Map Database connections (DB name => Database) */
  32         protected $conns = array();
  33
  34         /**
  35          * Construct a new instance from configuration.
  36          *
  37          * $config paramaters include:
  38          *     'dbServers'   : Associative array of DB names to server configuration.
  39          *                     Configuration is an associative array that includes:
  40          *                     'host'        - DB server name
  41          *                     'dbname'      - DB name
  42          *                     'type'        - DB type (mysql,postgres,...)
  43          *                     'user'        - DB user
  44          *                     'password'    - DB user password
  45          *                     'tablePrefix' - DB table prefix
  46          *                     'flags'       - DB flags (see DatabaseBase)
  47          *     'dbsByBucket' : Array of 1-16 consecutive integer keys, starting from 0,
  48          *                     each having an odd-numbered list of DB names (peers) as values.
  49          *                     Any DB named 'localDBMaster' will automatically use the DB master
  50          *                     settings for this wiki (without the need for a dbServers entry).
  51          *     'lockExpiry'  : Lock timeout (seconds) for dropped connections. [optional]
  52          *                     This tells the DB server how long to wait before assuming
  53          *                     connection failure and releasing all the locks for a session.
  54          *
  55          * @param Array $config
  56          */
  57         public function __construct( array $config ) {
  58                 parent::__construct( $config );
  59
  60                 $this->dbServers = isset( $config['dbServers'] )
  61                         ? $config['dbServers']
  62                         : array(); // likely just using 'localDBMaster'
  63                 // Sanitize dbsByBucket config to prevent PHP errors
  64                 $this->dbsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
  65                 $this->dbsByBucket = array_values( $this->dbsByBucket ); // consecutive
  66
  67                 if ( isset( $config['lockExpiry'] ) ) {
  68                         $this->lockExpiry = $config['lockExpiry'];
  69                 } else {
  70                         $met = ini_get( 'max_execution_time' );
  71                         $this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
  72                 }
  73                 $this->safeDelay = ( $this->lockExpiry <= 0 )
  74                         ? 60 // pick a safe-ish number to match DB timeout default
  75                         : $this->lockExpiry; // cover worst case
  76
  77                 foreach ( $this->dbsByBucket as $bucket ) {
  78                         if ( count( $bucket ) > 1 ) {
  79                                 // Tracks peers that couldn't be queried recently to avoid lengthy
  80                                 // connection timeouts. This is useless if each bucket has one peer.
  81                                 $this->statusCache = wfGetMainCache();
  82                                 break;
  83                         }
  84                 }
  85
  86                 $this->session = '';
  87                 for ( $i = 0; $i < 5; $i++ ) {
  88                         $this->session .= mt_rand( 0, 2147483647 );
  89                 }
  90                 $this->session = wfBaseConvert( sha1( $this->session ), 16, 36, 31 );
  91         }
  92
  93         /**
  94          * @see LockManager::doLock()
  95          * @return Status
  96          */
  97         protected function doLock( array $paths, $type ) {
  98                 $status = Status::newGood();
  99
 100                 $pathsToLock = array();
 101                 // Get locks that need to be acquired (buckets => locks)...
 102                 foreach ( $paths as $path ) {
 103                         if ( isset( $this->locksHeld[$path][$type] ) ) {
 104                                 ++$this->locksHeld[$path][$type];
 105                         } elseif ( isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
 106                                 $this->locksHeld[$path][$type] = 1;
 107                         } else {
 108                                 $bucket = $this->getBucketFromKey( $path );
 109                                 $pathsToLock[$bucket][] = $path;
 110                         }
 111                 }
 112
 113                 $lockedPaths = array(); // files locked in this attempt
 114                 // Attempt to acquire these locks...
 115                 foreach ( $pathsToLock as $bucket => $paths ) {
 116                         // Try to acquire the locks for this bucket
 117                         $res = $this->doLockingQueryAll( $bucket, $paths, $type );
 118                         if ( $res === 'cantacquire' ) {
 119                                 // Resources already locked by another process.
 120                                 // Abort and unlock everything we just locked.
 121                                 foreach ( $paths as $path ) {
 122                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 123                                 }
 124                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
 125                                 return $status;
 126                         } elseif ( $res !== true ) {
 127                                 // Couldn't contact any DBs for this bucket.
 128                                 // Abort and unlock everything we just locked.
 129                                 $status->fatal( 'lockmanager-fail-db-bucket', $bucket );
 130                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
 131                                 return $status;
 132                         }
 133                         // Record these locks as active
 134                         foreach ( $paths as $path ) {
 135                                 $this->locksHeld[$path][$type] = 1; // locked
 136                         }
 137                         // Keep track of what locks were made in this attempt
 138                         $lockedPaths = array_merge( $lockedPaths, $paths );
 139                 }
 140
 141                 return $status;
 142         }
 143
 144         /**
 145          * @see LockManager::doUnlock()
 146          * @return Status
 147          */
 148         protected function doUnlock( array $paths, $type ) {
 149                 $status = Status::newGood();
 150
 151                 foreach ( $paths as $path ) {
 152                         if ( !isset( $this->locksHeld[$path] ) ) {
 153                                 $status->warning( 'lockmanager-notlocked', $path );
 154                         } elseif ( !isset( $this->locksHeld[$path][$type] ) ) {
 155                                 $status->warning( 'lockmanager-notlocked', $path );
 156                         } else {
 157                                 --$this->locksHeld[$path][$type];
 158                                 if ( $this->locksHeld[$path][$type] <= 0 ) {
 159                                         unset( $this->locksHeld[$path][$type] );
 160                                 }
 161                                 if ( !count( $this->locksHeld[$path] ) ) {
 162                                         unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
 163                                 }
 164                         }
 165                 }
 166
 167                 // Reference count the locks held and COMMIT when zero
 168                 if ( !count( $this->locksHeld ) ) {
 169                         $status->merge( $this->finishLockTransactions() );
 170                 }
 171
 172                 return $status;
 173         }
 174
 175         /**
 176          * Get a connection to a lock DB and acquire locks on $paths.
 177          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 178          *
 179          * @param $lockDb string
 180          * @param $paths Array
 181          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 182          * @return bool Resources able to be locked
 183          * @throws DBError
 184          */
 185         protected function doLockingQuery( $lockDb, array $paths, $type ) {
 186                 if ( $type == self::LOCK_EX ) { // writer locks
 187                         $db = $this->getConnection( $lockDb );
 188                         if ( !$db ) {
 189                                 return false; // bad config
 190                         }
 191                         $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 192                         # Build up values for INSERT clause
 193                         $data = array();
 194                         foreach ( $keys as $key ) {
 195                                 $data[] = array( 'fle_key' => $key );
 196                         }
 197                         # Wait on any existing writers and block new ones if we get in
 198                         $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 199                 }
 200                 return true;
 201         }
 202
 203         /**
 204          * Attempt to acquire locks with the peers for a bucket.
 205          * This should avoid throwing any exceptions.
 206          *
 207          * @param $bucket integer
 208          * @param $paths Array List of resource keys to lock
 209          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 210          * @return bool|string One of (true, 'cantacquire', 'dberrors')
 211          */
 212         protected function doLockingQueryAll( $bucket, array $paths, $type ) {
 213                 $yesVotes = 0; // locks made on trustable DBs
 214                 $votesLeft = count( $this->dbsByBucket[$bucket] ); // remaining DBs
 215                 $quorum = floor( $votesLeft/2 + 1 ); // simple majority
 216                 // Get votes for each DB, in order, until we have enough...
 217                 foreach ( $this->dbsByBucket[$bucket] as $lockDb ) {
 218                         // Check that DB is not *known* to be down
 219                         if ( $this->cacheCheckFailures( $lockDb ) ) {
 220                                 try {
 221                                         // Attempt to acquire the lock on this DB
 222                                         if ( !$this->doLockingQuery( $lockDb, $paths, $type ) ) {
 223                                                 return 'cantacquire'; // vetoed; resource locked
 224                                         }
 225                                         ++$yesVotes; // success for this peer
 226                                         if ( $yesVotes >= $quorum ) {
 227                                                 return true; // lock obtained
 228                                         }
 229                                 } catch ( DBConnectionError $e ) {
 230                                         $this->cacheRecordFailure( $lockDb );
 231                                 } catch ( DBError $e ) {
 232                                         if ( $this->lastErrorIndicatesLocked( $lockDb ) ) {
 233                                                 return 'cantacquire'; // vetoed; resource locked
 234                                         }
 235                                 }
 236                         }
 237                         --$votesLeft;
 238                         $votesNeeded = $quorum - $yesVotes;
 239                         if ( $votesNeeded > $votesLeft ) {
 240                                 // In "trust cache" mode we don't have to meet the quorum
 241                                 break; // short-circuit
 242                         }
 243                 }
 244                 // At this point, we must not have meet the quorum
 245                 return 'dberrors'; // not enough votes to ensure correctness
 246         }
 247
 248         /**
 249          * Get (or reuse) a connection to a lock DB
 250          *
 251          * @param $lockDb string
 252          * @return DatabaseBase
 253          * @throws DBError
 254          */
 255         protected function getConnection( $lockDb ) {
 256                 if ( !isset( $this->conns[$lockDb] ) ) {
 257                         $db = null;
 258                         if ( $lockDb === 'localDBMaster' ) {
 259                                 $lb = wfGetLBFactory()->newMainLB();
 260                                 $db = $lb->getConnection( DB_MASTER );
 261                         } elseif ( isset( $this->dbServers[$lockDb] ) ) {
 262                                 $config = $this->dbServers[$lockDb];
 263                                 $db = DatabaseBase::factory( $config['type'], $config );
 264                         }
 265                         if ( !$db ) {
 266                                 return null; // config error?
 267                         }
 268                         $this->conns[$lockDb] = $db;
 269                         $this->conns[$lockDb]->clearFlag( DBO_TRX );
 270                         # If the connection drops, try to avoid letting the DB rollback
 271                         # and release the locks before the file operations are finished.
 272                         # This won't handle the case of DB server restarts however.
 273                         $options = array();
 274                         if ( $this->lockExpiry > 0 ) {
 275                                 $options['connTimeout'] = $this->lockExpiry;
 276                         }
 277                         $this->conns[$lockDb]->setSessionOptions( $options );
 278                         $this->initConnection( $lockDb, $this->conns[$lockDb] );
 279                 }
 280                 if ( !$this->conns[$lockDb]->trxLevel() ) {
 281                         $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
 282                 }
 283                 return $this->conns[$lockDb];
 284         }
 285
 286         /**
 287          * Do additional initialization for new lock DB connection
 288          *
 289          * @param $lockDb string
 290          * @param $db DatabaseBase
 291          * @return void
 292          * @throws DBError
 293          */
 294         protected function initConnection( $lockDb, DatabaseBase $db ) {}
 295
 296         /**
 297          * Commit all changes to lock-active databases.
 298          * This should avoid throwing any exceptions.
 299          *
 300          * @return Status
 301          */
 302         protected function finishLockTransactions() {
 303                 $status = Status::newGood();
 304                 foreach ( $this->conns as $lockDb => $db ) {
 305                         if ( $db->trxLevel() ) { // in transaction
 306                                 try {
 307                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 308                                 } catch ( DBError $e ) {
 309                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 310                                 }
 311                         }
 312                 }
 313                 return $status;
 314         }
 315
 316         /**
 317          * Check if the last DB error for $lockDb indicates
 318          * that a requested resource was locked by another process.
 319          * This should avoid throwing any exceptions.
 320          *
 321          * @param $lockDb string
 322          * @return bool
 323          */
 324         protected function lastErrorIndicatesLocked( $lockDb ) {
 325                 if ( isset( $this->conns[$lockDb] ) ) { // sanity
 326                         $db = $this->conns[$lockDb];
 327                         return ( $db->wasDeadlock() || $db->wasLockTimeout() );
 328                 }
 329                 return false;
 330         }
 331
 332         /**
 333          * Checks if the DB has not recently had connection/query errors.
 334          * This just avoids wasting time on doomed connection attempts.
 335          *
 336          * @param $lockDb string
 337          * @return bool
 338          */
 339         protected function cacheCheckFailures( $lockDb ) {
 340                 if ( $this->statusCache && $this->safeDelay > 0 ) {
 341                         $path = $this->getMissKey( $lockDb );
 342                         $misses = $this->statusCache->get( $path );
 343                         return !$misses;
 344                 }
 345                 return true;
 346         }
 347
 348         /**
 349          * Log a lock request failure to the cache
 350          *
 351          * @param $lockDb string
 352          * @return bool Success
 353          */
 354         protected function cacheRecordFailure( $lockDb ) {
 355                 if ( $this->statusCache && $this->safeDelay > 0 ) {
 356                         $path = $this->getMissKey( $lockDb );
 357                         $misses = $this->statusCache->get( $path );
 358                         if ( $misses ) {
 359                                 return $this->statusCache->incr( $path );
 360                         } else {
 361                                 return $this->statusCache->add( $path, 1, $this->safeDelay );
 362                         }
 363                 }
 364                 return true;
 365         }
 366
 367         /**
 368          * Get a cache key for recent query misses for a DB
 369          *
 370          * @param $lockDb string
 371          * @return string
 372          */
 373         protected function getMissKey( $lockDb ) {
 374                 return 'lockmanager:querymisses:' . str_replace( ' ', '_', $lockDb );
 375         }
 376
 377         /**
 378          * Get the bucket for resource path.
 379          * This should avoid throwing any exceptions.
 380          *
 381          * @param $path string
 382          * @return integer
 383          */
 384         protected function getBucketFromKey( $path ) {
 385                 $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
 386                 return intval( base_convert( $prefix, 16, 10 ) ) % count( $this->dbsByBucket );
 387         }
 388
 389         /**
 390          * Make sure remaining locks get cleared for sanity
 391          */
 392         function __destruct() {
 393                 foreach ( $this->conns as $lockDb => $db ) {
 394                         if ( $db->trxLevel() ) { // in transaction
 395                                 try {
 396                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 397                                 } catch ( DBError $e ) {
 398                                         // oh well
 399                                 }
 400                         }
 401                         $db->close();
 402                 }
 403         }
 404 }
 405
 406 /**
 407  * MySQL version of DBLockManager that supports shared locks.
 408  * All locks are non-blocking, which avoids deadlocks.
 409  *
 410  * @ingroup LockManager
 411  */
 412 class MySqlLockManager extends DBLockManager {
 413         /** @var Array Mapping of lock types to the type actually used */
 414         protected $lockTypeMap = array(
 415                 self::LOCK_SH => self::LOCK_SH,
 416                 self::LOCK_UW => self::LOCK_SH,
 417                 self::LOCK_EX => self::LOCK_EX
 418         );
 419
 420         protected function initConnection( $lockDb, DatabaseBase $db ) {
 421                 # Let this transaction see lock rows from other transactions
 422                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
 423         }
 424
 425         protected function doLockingQuery( $lockDb, array $paths, $type ) {
 426                 $db = $this->getConnection( $lockDb );
 427                 if ( !$db ) {
 428                         return false;
 429                 }
 430                 $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 431                 # Build up values for INSERT clause
 432                 $data = array();
 433                 foreach ( $keys as $key ) {
 434                         $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
 435                 }
 436                 # Block new writers...
 437                 $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
 438                 # Actually do the locking queries...
 439                 if ( $type == self::LOCK_SH ) { // reader locks
 440                         # Bail if there are any existing writers...
 441                         $blocked = $db->selectField( 'filelocks_exclusive', '1',
 442                                 array( 'fle_key' => $keys ),
 443                                 __METHOD__
 444                         );
 445                         # Prospective writers that haven't yet updated filelocks_exclusive
 446                         # will recheck filelocks_shared after doing so and bail due to our entry.
 447                 } else { // writer locks
 448                         $encSession = $db->addQuotes( $this->session );
 449                         # Bail if there are any existing writers...
 450                         # The may detect readers, but the safe check for them is below.
 451                         # Note: if two writers come at the same time, both bail :)
 452                         $blocked = $db->selectField( 'filelocks_shared', '1',
 453                                 array( 'fls_key' => $keys, "fls_session != $encSession" ),
 454                                 __METHOD__
 455                         );
 456                         if ( !$blocked ) {
 457                                 # Build up values for INSERT clause
 458                                 $data = array();
 459                                 foreach ( $keys as $key ) {
 460                                         $data[] = array( 'fle_key' => $key );
 461                                 }
 462                                 # Block new readers/writers...
 463                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 464                                 # Bail if there are any existing readers...
 465                                 $blocked = $db->selectField( 'filelocks_shared', '1',
 466                                         array( 'fls_key' => $keys, "fls_session != $encSession" ),
 467                                         __METHOD__
 468                                 );
 469                         }
 470                 }
 471                 return !$blocked;
 472         }
 473 }