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