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