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