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