includes/filebackend/lockmanager/DBLockManager.php

   1 <?php
   2 /**
   3  * Version of LockManager based on using DB table locks.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup LockManager
  22  */
  23
  24 /**
  25  * Version of LockManager based on using named/row DB locks.
  26  *
  27  * This is meant for multi-wiki systems that may share files.
  28  *
  29  * All lock requests for a resource, identified by a hash string, will map
  30  * to one bucket. Each bucket maps to one or several peer DBs, each on their
  31  * own server, all having the filelocks.sql tables (with row-level locking).
  32  * A majority of peer DBs must agree for a lock to be acquired.
  33  *
  34  * Caching is used to avoid hitting servers that are down.
  35  *
  36  * @ingroup LockManager
  37  * @since 1.19
  38  */
  39 abstract class DBLockManager extends QuorumLockManager {
  40         /** @var Array Map of DB names to server config */
  41         protected $dbServers; // (DB name => server config array)
  42         /** @var BagOStuff */
  43         protected $statusCache;
  44
  45         protected $lockExpiry; // integer number of seconds
  46         protected $safeDelay; // integer number of seconds
  47
  48         protected $session = 0; // random integer
  49         /** @var Array Map Database connections (DB name => Database) */
  50         protected $conns = array();
  51
  52         /**
  53          * Construct a new instance from configuration.
  54          *
  55          * $config paramaters include:
  56          *   - dbServers   : Associative array of DB names to server configuration.
  57          *                   Configuration is an associative array that includes:
  58          *                     - host        : DB server name
  59          *                     - dbname      : DB name
  60          *                     - type        : DB type (mysql,postgres,...)
  61          *                     - user        : DB user
  62          *                     - password    : DB user password
  63          *                     - tablePrefix : DB table prefix
  64          *                     - flags       : DB flags (see DatabaseBase)
  65          *   - dbsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
  66          *                   each having an odd-numbered list of DB names (peers) as values.
  67          *                   Any DB named 'localDBMaster' will automatically use the DB master
  68          *                   settings for this wiki (without the need for a dbServers entry).
  69          *                   Only use 'localDBMaster' if the domain is a valid wiki ID.
  70          *   - lockExpiry  : Lock timeout (seconds) for dropped connections. [optional]
  71          *                   This tells the DB server how long to wait before assuming
  72          *                   connection failure and releasing all the locks for a session.
  73          *
  74          * @param array $config
  75          */
  76         public function __construct( array $config ) {
  77                 parent::__construct( $config );
  78
  79                 $this->dbServers = isset( $config['dbServers'] )
  80                         ? $config['dbServers']
  81                         : array(); // likely just using 'localDBMaster'
  82                 // Sanitize srvsByBucket config to prevent PHP errors
  83                 $this->srvsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
  84                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  85
  86                 if ( isset( $config['lockExpiry'] ) ) {
  87                         $this->lockExpiry = $config['lockExpiry'];
  88                 } else {
  89                         $met = ini_get( 'max_execution_time' );
  90                         $this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
  91                 }
  92                 $this->safeDelay = ( $this->lockExpiry <= 0 )
  93                         ? 60 // pick a safe-ish number to match DB timeout default
  94                         : $this->lockExpiry; // cover worst case
  95
  96                 foreach ( $this->srvsByBucket as $bucket ) {
  97                         if ( count( $bucket ) > 1 ) { // multiple peers
  98                                 // Tracks peers that couldn't be queried recently to avoid lengthy
  99                                 // connection timeouts. This is useless if each bucket has one peer.
 100                                 try {
 101                                         $this->statusCache = ObjectCache::newAccelerator( array() );
 102                                 } catch ( MWException $e ) {
 103                                         trigger_error( __CLASS__ .
 104                                                 " using multiple DB peers without apc, xcache, or wincache." );
 105                                 }
 106                                 break;
 107                         }
 108                 }
 109
 110                 $this->session = wfRandomString( 31 );
 111         }
 112
 113         /**
 114          * @see QuorumLockManager::isServerUp()
 115          * @return bool
 116          */
 117         protected function isServerUp( $lockSrv ) {
 118                 if ( !$this->cacheCheckFailures( $lockSrv ) ) {
 119                         return false; // recent failure to connect
 120                 }
 121                 try {
 122                         $this->getConnection( $lockSrv );
 123                 } catch ( DBError $e ) {
 124                         $this->cacheRecordFailure( $lockSrv );
 125                         return false; // failed to connect
 126                 }
 127                 return true;
 128         }
 129
 130         /**
 131          * Get (or reuse) a connection to a lock DB
 132          *
 133          * @param $lockDb string
 134          * @return DatabaseBase
 135          * @throws DBError
 136          */
 137         protected function getConnection( $lockDb ) {
 138                 if ( !isset( $this->conns[$lockDb] ) ) {
 139                         $db = null;
 140                         if ( $lockDb === 'localDBMaster' ) {
 141                                 $lb = wfGetLBFactory()->getMainLB( $this->domain );
 142                                 $db = $lb->getConnection( DB_MASTER, array(), $this->domain );
 143                         } elseif ( isset( $this->dbServers[$lockDb] ) ) {
 144                                 $config = $this->dbServers[$lockDb];
 145                                 $db = DatabaseBase::factory( $config['type'], $config );
 146                         }
 147                         if ( !$db ) {
 148                                 return null; // config error?
 149                         }
 150                         $this->conns[$lockDb] = $db;
 151                         $this->conns[$lockDb]->clearFlag( DBO_TRX );
 152                         # If the connection drops, try to avoid letting the DB rollback
 153                         # and release the locks before the file operations are finished.
 154                         # This won't handle the case of DB server restarts however.
 155                         $options = array();
 156                         if ( $this->lockExpiry > 0 ) {
 157                                 $options['connTimeout'] = $this->lockExpiry;
 158                         }
 159                         $this->conns[$lockDb]->setSessionOptions( $options );
 160                         $this->initConnection( $lockDb, $this->conns[$lockDb] );
 161                 }
 162                 if ( !$this->conns[$lockDb]->trxLevel() ) {
 163                         $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
 164                 }
 165                 return $this->conns[$lockDb];
 166         }
 167
 168         /**
 169          * Do additional initialization for new lock DB connection
 170          *
 171          * @param $lockDb string
 172          * @param $db DatabaseBase
 173          * @return void
 174          * @throws DBError
 175          */
 176         protected function initConnection( $lockDb, DatabaseBase $db ) {}
 177
 178         /**
 179          * Checks if the DB has not recently had connection/query errors.
 180          * This just avoids wasting time on doomed connection attempts.
 181          *
 182          * @param $lockDb string
 183          * @return bool
 184          */
 185         protected function cacheCheckFailures( $lockDb ) {
 186                 return ( $this->statusCache && $this->safeDelay > 0 )
 187                         ? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
 188                         : true;
 189         }
 190
 191         /**
 192          * Log a lock request failure to the cache
 193          *
 194          * @param $lockDb string
 195          * @return bool Success
 196          */
 197         protected function cacheRecordFailure( $lockDb ) {
 198                 return ( $this->statusCache && $this->safeDelay > 0 )
 199                         ? $this->statusCache->set( $this->getMissKey( $lockDb ), 1, $this->safeDelay )
 200                         : true;
 201         }
 202
 203         /**
 204          * Get a cache key for recent query misses for a DB
 205          *
 206          * @param $lockDb string
 207          * @return string
 208          */
 209         protected function getMissKey( $lockDb ) {
 210                 $lockDb = ( $lockDb === 'localDBMaster' ) ? wfWikiID() : $lockDb; // non-relative
 211                 return 'dblockmanager:downservers:' . str_replace( ' ', '_', $lockDb );
 212         }
 213
 214         /**
 215          * Make sure remaining locks get cleared for sanity
 216          */
 217         function __destruct() {
 218                 $this->releaseAllLocks();
 219                 foreach ( $this->conns as $db ) {
 220                         $db->close();
 221                 }
 222         }
 223 }
 224
 225 /**
 226  * MySQL version of DBLockManager that supports shared locks.
 227  * All locks are non-blocking, which avoids deadlocks.
 228  *
 229  * @ingroup LockManager
 230  */
 231 class MySqlLockManager extends DBLockManager {
 232         /** @var Array Mapping of lock types to the type actually used */
 233         protected $lockTypeMap = array(
 234                 self::LOCK_SH => self::LOCK_SH,
 235                 self::LOCK_UW => self::LOCK_SH,
 236                 self::LOCK_EX => self::LOCK_EX
 237         );
 238
 239         /**
 240          * @param $lockDb string
 241          * @param $db DatabaseBase
 242          */
 243         protected function initConnection( $lockDb, DatabaseBase $db ) {
 244                 # Let this transaction see lock rows from other transactions
 245                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
 246         }
 247
 248         /**
 249          * Get a connection to a lock DB and acquire locks on $paths.
 250          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 251          *
 252          * @see DBLockManager::getLocksOnServer()
 253          * @return Status
 254          */
 255         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 256                 $status = Status::newGood();
 257
 258                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 259
 260                 $keys = array(); // list of hash keys for the paths
 261                 $data = array(); // list of rows to insert
 262                 $checkEXKeys = array(); // list of hash keys that this has no EX lock on
 263                 # Build up values for INSERT clause
 264                 foreach ( $paths as $path ) {
 265                         $key = $this->sha1Base36Absolute( $path );
 266                         $keys[] = $key;
 267                         $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
 268                         if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
 269                                 $checkEXKeys[] = $key;
 270                         }
 271                 }
 272
 273                 # Block new writers (both EX and SH locks leave entries here)...
 274                 $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
 275                 # Actually do the locking queries...
 276                 if ( $type == self::LOCK_SH ) { // reader locks
 277                         $blocked = false;
 278                         # Bail if there are any existing writers...
 279                         if ( count( $checkEXKeys ) ) {
 280                                 $blocked = $db->selectField( 'filelocks_exclusive', '1',
 281                                         array( 'fle_key' => $checkEXKeys ),
 282                                         __METHOD__
 283                                 );
 284                         }
 285                         # Other prospective writers that haven't yet updated filelocks_exclusive
 286                         # will recheck filelocks_shared after doing so and bail due to this entry.
 287                 } else { // writer locks
 288                         $encSession = $db->addQuotes( $this->session );
 289                         # Bail if there are any existing writers...
 290                         # This may detect readers, but the safe check for them is below.
 291                         # Note: if two writers come at the same time, both bail :)
 292                         $blocked = $db->selectField( 'filelocks_shared', '1',
 293                                 array( 'fls_key' => $keys, "fls_session != $encSession" ),
 294                                 __METHOD__
 295                         );
 296                         if ( !$blocked ) {
 297                                 # Build up values for INSERT clause
 298                                 $data = array();
 299                                 foreach ( $keys as $key ) {
 300                                         $data[] = array( 'fle_key' => $key );
 301                                 }
 302                                 # Block new readers/writers...
 303                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 304                                 # Bail if there are any existing readers...
 305                                 $blocked = $db->selectField( 'filelocks_shared', '1',
 306                                         array( 'fls_key' => $keys, "fls_session != $encSession" ),
 307                                         __METHOD__
 308                                 );
 309                         }
 310                 }
 311
 312                 if ( $blocked ) {
 313                         foreach ( $paths as $path ) {
 314                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 315                         }
 316                 }
 317
 318                 return $status;
 319         }
 320
 321         /**
 322          * @see QuorumLockManager::freeLocksOnServer()
 323          * @return Status
 324          */
 325         protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
 326                 return Status::newGood(); // not supported
 327         }
 328
 329         /**
 330          * @see QuorumLockManager::releaseAllLocks()
 331          * @return Status
 332          */
 333         protected function releaseAllLocks() {
 334                 $status = Status::newGood();
 335
 336                 foreach ( $this->conns as $lockDb => $db ) {
 337                         if ( $db->trxLevel() ) { // in transaction
 338                                 try {
 339                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 340                                 } catch ( DBError $e ) {
 341                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 342                                 }
 343                         }
 344                 }
 345
 346                 return $status;
 347         }
 348 }
 349
 350 /**
 351  * PostgreSQL version of DBLockManager that supports shared locks.
 352  * All locks are non-blocking, which avoids deadlocks.
 353  *
 354  * @ingroup LockManager
 355  */
 356 class PostgreSqlLockManager extends DBLockManager {
 357         /** @var Array Mapping of lock types to the type actually used */
 358         protected $lockTypeMap = array(
 359                 self::LOCK_SH => self::LOCK_SH,
 360                 self::LOCK_UW => self::LOCK_SH,
 361                 self::LOCK_EX => self::LOCK_EX
 362         );
 363
 364         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 365                 $status = Status::newGood();
 366                 if ( !count( $paths ) ) {
 367                         return $status; // nothing to lock
 368                 }
 369
 370                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 371                 $bigints = array_unique( array_map(
 372                         function( $key ) {
 373                                 return wfBaseConvert( substr( $key, 0, 15 ), 16, 10 );
 374                         },
 375                         array_map( array( $this, 'sha1Base16Absolute' ), $paths )
 376                 ) );
 377
 378                 // Try to acquire all the locks...
 379                 $fields = array();
 380                 foreach ( $bigints as $bigint ) {
 381                         $fields[] = ( $type == self::LOCK_SH )
 382                                 ? "pg_try_advisory_lock_shared({$db->addQuotes( $bigint )}) AS K$bigint"
 383                                 : "pg_try_advisory_lock({$db->addQuotes( $bigint )}) AS K$bigint";
 384                 }
 385                 $res = $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
 386                 $row = (array)$res->fetchObject();
 387
 388                 if ( in_array( 'f', $row ) ) {
 389                         // Release any acquired locks if some could not be acquired...
 390                         $fields = array();
 391                         foreach ( $row as $kbigint => $ok ) {
 392                                 if ( $ok === 't' ) { // locked
 393                                         $bigint = substr( $kbigint, 1 ); // strip off the "K"
 394                                         $fields[] = ( $type == self::LOCK_SH )
 395                                                 ? "pg_advisory_unlock_shared({$db->addQuotes( $bigint )})"
 396                                                 : "pg_advisory_unlock({$db->addQuotes( $bigint )})";
 397                                 }
 398                         }
 399                         if ( count( $fields ) ) {
 400                                 $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
 401                         }
 402                         foreach ( $paths as $path ) {
 403                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 404                         }
 405                 }
 406
 407                 return $status;
 408         }
 409
 410         /**
 411          * @see QuorumLockManager::freeLocksOnServer()
 412          * @return Status
 413          */
 414         protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
 415                 return Status::newGood(); // not supported
 416         }
 417
 418         /**
 419          * @see QuorumLockManager::releaseAllLocks()
 420          * @return Status
 421          */
 422         protected function releaseAllLocks() {
 423                 $status = Status::newGood();
 424
 425                 foreach ( $this->conns as $lockDb => $db ) {
 426                         try {
 427                                 $db->query( "SELECT pg_advisory_unlock_all()", __METHOD__ );
 428                         } catch ( DBError $e ) {
 429                                 $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 430                         }
 431                 }
 432
 433                 return $status;
 434         }
 435 }