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