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          * @param array $config Parameters 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         public function __construct( array $config ) {
  75                 parent::__construct( $config );
  76
  77                 $this->dbServers = isset( $config['dbServers'] )
  78                         ? $config['dbServers']
  79                         : array(); // likely just using 'localDBMaster'
  80                 // Sanitize srvsByBucket config to prevent PHP errors
  81                 $this->srvsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
  82                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  83
  84                 if ( isset( $config['lockExpiry'] ) ) {
  85                         $this->lockExpiry = $config['lockExpiry'];
  86                 } else {
  87                         $met = ini_get( 'max_execution_time' );
  88                         $this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
  89                 }
  90                 $this->safeDelay = ( $this->lockExpiry <= 0 )
  91                         ? 60 // pick a safe-ish number to match DB timeout default
  92                         : $this->lockExpiry; // cover worst case
  93
  94                 foreach ( $this->srvsByBucket as $bucket ) {
  95                         if ( count( $bucket ) > 1 ) { // multiple peers
  96                                 // Tracks peers that couldn't be queried recently to avoid lengthy
  97                                 // connection timeouts. This is useless if each bucket has one peer.
  98                                 try {
  99                                         $this->statusCache = ObjectCache::newAccelerator( array() );
 100                                 } catch ( Exception $e ) {
 101                                         trigger_error( __CLASS__ .
 102                                                 " using multiple DB peers without apc, xcache, or wincache." );
 103                                 }
 104                                 break;
 105                         }
 106                 }
 107
 108                 $this->session = wfRandomString( 31 );
 109         }
 110
 111         // @todo change this code to work in one batch
 112         protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
 113                 $status = Status::newGood();
 114                 foreach ( $pathsByType as $type => $paths ) {
 115                         $status->merge( $this->doGetLocksOnServer( $lockSrv, $paths, $type ) );
 116                 }
 117
 118                 return $status;
 119         }
 120
 121         protected function freeLocksOnServer( $lockSrv, array $pathsByType ) {
 122                 return Status::newGood();
 123         }
 124
 125         /**
 126          * @see QuorumLockManager::isServerUp()
 127          * @param string $lockSrv
 128          * @return bool
 129          */
 130         protected function isServerUp( $lockSrv ) {
 131                 if ( !$this->cacheCheckFailures( $lockSrv ) ) {
 132                         return false; // recent failure to connect
 133                 }
 134                 try {
 135                         $this->getConnection( $lockSrv );
 136                 } catch ( DBError $e ) {
 137                         $this->cacheRecordFailure( $lockSrv );
 138
 139                         return false; // failed to connect
 140                 }
 141
 142                 return true;
 143         }
 144
 145         /**
 146          * Get (or reuse) a connection to a lock DB
 147          *
 148          * @param string $lockDb
 149          * @return DatabaseBase
 150          * @throws DBError
 151          */
 152         protected function getConnection( $lockDb ) {
 153                 if ( !isset( $this->conns[$lockDb] ) ) {
 154                         $db = null;
 155                         if ( $lockDb === 'localDBMaster' ) {
 156                                 $lb = wfGetLBFactory()->getMainLB( $this->domain );
 157                                 $db = $lb->getConnection( DB_MASTER, array(), $this->domain );
 158                         } elseif ( isset( $this->dbServers[$lockDb] ) ) {
 159                                 $config = $this->dbServers[$lockDb];
 160                                 $db = DatabaseBase::factory( $config['type'], $config );
 161                         }
 162                         if ( !$db ) {
 163                                 return null; // config error?
 164                         }
 165                         $this->conns[$lockDb] = $db;
 166                         $this->conns[$lockDb]->clearFlag( DBO_TRX );
 167                         # If the connection drops, try to avoid letting the DB rollback
 168                         # and release the locks before the file operations are finished.
 169                         # This won't handle the case of DB server restarts however.
 170                         $options = array();
 171                         if ( $this->lockExpiry > 0 ) {
 172                                 $options['connTimeout'] = $this->lockExpiry;
 173                         }
 174                         $this->conns[$lockDb]->setSessionOptions( $options );
 175                         $this->initConnection( $lockDb, $this->conns[$lockDb] );
 176                 }
 177                 if ( !$this->conns[$lockDb]->trxLevel() ) {
 178                         $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
 179                 }
 180
 181                 return $this->conns[$lockDb];
 182         }
 183
 184         /**
 185          * Do additional initialization for new lock DB connection
 186          *
 187          * @param string $lockDb
 188          * @param DatabaseBase $db
 189          * @throws DBError
 190          */
 191         protected function initConnection( $lockDb, DatabaseBase $db ) {
 192         }
 193
 194         /**
 195          * Checks if the DB has not recently had connection/query errors.
 196          * This just avoids wasting time on doomed connection attempts.
 197          *
 198          * @param string $lockDb
 199          * @return bool
 200          */
 201         protected function cacheCheckFailures( $lockDb ) {
 202                 return ( $this->statusCache && $this->safeDelay > 0 )
 203                         ? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
 204                         : true;
 205         }
 206
 207         /**
 208          * Log a lock request failure to the cache
 209          *
 210          * @param string $lockDb
 211          * @return bool Success
 212          */
 213         protected function cacheRecordFailure( $lockDb ) {
 214                 return ( $this->statusCache && $this->safeDelay > 0 )
 215                         ? $this->statusCache->set( $this->getMissKey( $lockDb ), 1, $this->safeDelay )
 216                         : true;
 217         }
 218
 219         /**
 220          * Get a cache key for recent query misses for a DB
 221          *
 222          * @param string $lockDb
 223          * @return string
 224          */
 225         protected function getMissKey( $lockDb ) {
 226                 $lockDb = ( $lockDb === 'localDBMaster' ) ? wfWikiID() : $lockDb; // non-relative
 227                 return 'dblockmanager:downservers:' . str_replace( ' ', '_', $lockDb );
 228         }
 229
 230         /**
 231          * Make sure remaining locks get cleared for sanity
 232          */
 233         function __destruct() {
 234                 $this->releaseAllLocks();
 235                 foreach ( $this->conns as $db ) {
 236                         $db->close();
 237                 }
 238         }
 239 }
 240
 241 /**
 242  * MySQL version of DBLockManager that supports shared locks.
 243  * All locks are non-blocking, which avoids deadlocks.
 244  *
 245  * @ingroup LockManager
 246  */
 247 class MySqlLockManager extends DBLockManager {
 248         /** @var array Mapping of lock types to the type actually used */
 249         protected $lockTypeMap = array(
 250                 self::LOCK_SH => self::LOCK_SH,
 251                 self::LOCK_UW => self::LOCK_SH,
 252                 self::LOCK_EX => self::LOCK_EX
 253         );
 254
 255         /**
 256          * @param string $lockDb
 257          * @param DatabaseBase $db
 258          */
 259         protected function initConnection( $lockDb, DatabaseBase $db ) {
 260                 # Let this transaction see lock rows from other transactions
 261                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
 262         }
 263
 264         /**
 265          * Get a connection to a lock DB and acquire locks on $paths.
 266          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
 267          *
 268          * @see DBLockManager::getLocksOnServer()
 269          * @param string $lockSrv
 270          * @param array $paths
 271          * @param string $type
 272          * @return Status
 273          */
 274         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
 275                 $status = Status::newGood();
 276
 277                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 278
 279                 $keys = array(); // list of hash keys for the paths
 280                 $data = array(); // list of rows to insert
 281                 $checkEXKeys = array(); // list of hash keys that this has no EX lock on
 282                 # Build up values for INSERT clause
 283                 foreach ( $paths as $path ) {
 284                         $key = $this->sha1Base36Absolute( $path );
 285                         $keys[] = $key;
 286                         $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
 287                         if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
 288                                 $checkEXKeys[] = $key;
 289                         }
 290                 }
 291
 292                 # Block new writers (both EX and SH locks leave entries here)...
 293                 $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
 294                 # Actually do the locking queries...
 295                 if ( $type == self::LOCK_SH ) { // reader locks
 296                         $blocked = false;
 297                         # Bail if there are any existing writers...
 298                         if ( count( $checkEXKeys ) ) {
 299                                 $blocked = $db->selectField( 'filelocks_exclusive', '1',
 300                                         array( 'fle_key' => $checkEXKeys ),
 301                                         __METHOD__
 302                                 );
 303                         }
 304                         # Other prospective writers that haven't yet updated filelocks_exclusive
 305                         # will recheck filelocks_shared after doing so and bail due to this entry.
 306                 } else { // writer locks
 307                         $encSession = $db->addQuotes( $this->session );
 308                         # Bail if there are any existing writers...
 309                         # This may detect readers, but the safe check for them is below.
 310                         # Note: if two writers come at the same time, both bail :)
 311                         $blocked = $db->selectField( 'filelocks_shared', '1',
 312                                 array( 'fls_key' => $keys, "fls_session != $encSession" ),
 313                                 __METHOD__
 314                         );
 315                         if ( !$blocked ) {
 316                                 # Build up values for INSERT clause
 317                                 $data = array();
 318                                 foreach ( $keys as $key ) {
 319                                         $data[] = array( 'fle_key' => $key );
 320                                 }
 321                                 # Block new readers/writers...
 322                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 323                                 # Bail if there are any existing readers...
 324                                 $blocked = $db->selectField( 'filelocks_shared', '1',
 325                                         array( 'fls_key' => $keys, "fls_session != $encSession" ),
 326                                         __METHOD__
 327                                 );
 328                         }
 329                 }
 330
 331                 if ( $blocked ) {
 332                         foreach ( $paths as $path ) {
 333                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 334                         }
 335                 }
 336
 337                 return $status;
 338         }
 339
 340         /**
 341          * @see QuorumLockManager::releaseAllLocks()
 342          * @return Status
 343          */
 344         protected function releaseAllLocks() {
 345                 $status = Status::newGood();
 346
 347                 foreach ( $this->conns as $lockDb => $db ) {
 348                         if ( $db->trxLevel() ) { // in transaction
 349                                 try {
 350                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 351                                 } catch ( DBError $e ) {
 352                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 353                                 }
 354                         }
 355                 }
 356
 357                 return $status;
 358         }
 359 }
 360
 361 /**
 362  * PostgreSQL version of DBLockManager that supports shared locks.
 363  * All locks are non-blocking, which avoids deadlocks.
 364  *
 365  * @ingroup LockManager
 366  */
 367 class PostgreSqlLockManager extends DBLockManager {
 368         /** @var array Mapping of lock types to the type actually used */
 369         protected $lockTypeMap = array(
 370                 self::LOCK_SH => self::LOCK_SH,
 371                 self::LOCK_UW => self::LOCK_SH,
 372                 self::LOCK_EX => self::LOCK_EX
 373         );
 374
 375         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
 376                 $status = Status::newGood();
 377                 if ( !count( $paths ) ) {
 378                         return $status; // nothing to lock
 379                 }
 380
 381                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 382                 $bigints = array_unique( array_map(
 383                         function ( $key ) {
 384                                 return wfBaseConvert( substr( $key, 0, 15 ), 16, 10 );
 385                         },
 386                         array_map( array( $this, 'sha1Base16Absolute' ), $paths )
 387                 ) );
 388
 389                 // Try to acquire all the locks...
 390                 $fields = array();
 391                 foreach ( $bigints as $bigint ) {
 392                         $fields[] = ( $type == self::LOCK_SH )
 393                                 ? "pg_try_advisory_lock_shared({$db->addQuotes( $bigint )}) AS K$bigint"
 394                                 : "pg_try_advisory_lock({$db->addQuotes( $bigint )}) AS K$bigint";
 395                 }
 396                 $res = $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
 397                 $row = (array)$res->fetchObject();
 398
 399                 if ( in_array( 'f', $row ) ) {
 400                         // Release any acquired locks if some could not be acquired...
 401                         $fields = array();
 402                         foreach ( $row as $kbigint => $ok ) {
 403                                 if ( $ok === 't' ) { // locked
 404                                         $bigint = substr( $kbigint, 1 ); // strip off the "K"
 405                                         $fields[] = ( $type == self::LOCK_SH )
 406                                                 ? "pg_advisory_unlock_shared({$db->addQuotes( $bigint )})"
 407                                                 : "pg_advisory_unlock({$db->addQuotes( $bigint )})";
 408                                 }
 409                         }
 410                         if ( count( $fields ) ) {
 411                                 $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
 412                         }
 413                         foreach ( $paths as $path ) {
 414                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 415                         }
 416                 }
 417
 418                 return $status;
 419         }
 420
 421         /**
 422          * @see QuorumLockManager::releaseAllLocks()
 423          * @return Status
 424          */
 425         protected function releaseAllLocks() {
 426                 $status = Status::newGood();
 427
 428                 foreach ( $this->conns as $lockDb => $db ) {
 429                         try {
 430                                 $db->query( "SELECT pg_advisory_unlock_all()", __METHOD__ );
 431                         } catch ( DBError $e ) {
 432                                 $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 433                         }
 434                 }
 435
 436                 return $status;
 437         }
 438 }