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