includes/db/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   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 Database
  22  */
  23
  24 /**
  25  * Database load balancing object
  26  *
  27  * @todo document
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         private $mServers, $mConns, $mLoads, $mGroupLoads;
  32         private $mErrorConnection;
  33         private $mReadIndex, $mAllowLagged;
  34         private $mWaitForPos, $mWaitTimeout;
  35         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  36         private $mParentInfo, $mLagTimes;
  37         private $mLoadMonitorClass, $mLoadMonitor;
  38
  39         /**
  40          * @param array $params with keys:
  41          *    servers           Required. Array of server info structures.
  42          *    masterWaitTimeout Replication lag wait timeout
  43          *    loadMonitor       Name of a class used to fetch server lag and load.
  44          * @throws MWException
  45          */
  46         function __construct( $params ) {
  47                 if ( !isset( $params['servers'] ) ) {
  48                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  49                 }
  50                 $this->mServers = $params['servers'];
  51
  52                 if ( isset( $params['waitTimeout'] ) ) {
  53                         $this->mWaitTimeout = $params['waitTimeout'];
  54                 } else {
  55                         $this->mWaitTimeout = 10;
  56                 }
  57
  58                 $this->mReadIndex = -1;
  59                 $this->mWriteIndex = -1;
  60                 $this->mConns = array(
  61                         'local' => array(),
  62                         'foreignUsed' => array(),
  63                         'foreignFree' => array() );
  64                 $this->mLoads = array();
  65                 $this->mWaitForPos = false;
  66                 $this->mLaggedSlaveMode = false;
  67                 $this->mErrorConnection = false;
  68                 $this->mAllowLagged = false;
  69
  70                 if ( isset( $params['loadMonitor'] ) ) {
  71                         $this->mLoadMonitorClass = $params['loadMonitor'];
  72                 } else {
  73                         $master = reset( $params['servers'] );
  74                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  75                                 $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
  76                         } else {
  77                                 $this->mLoadMonitorClass = 'LoadMonitor_Null';
  78                         }
  79                 }
  80
  81                 foreach ( $params['servers'] as $i => $server ) {
  82                         $this->mLoads[$i] = $server['load'];
  83                         if ( isset( $server['groupLoads'] ) ) {
  84                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  85                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  86                                                 $this->mGroupLoads[$group] = array();
  87                                         }
  88                                         $this->mGroupLoads[$group][$i] = $ratio;
  89                                 }
  90                         }
  91                 }
  92         }
  93
  94         /**
  95          * Get a LoadMonitor instance
  96          *
  97          * @return LoadMonitor
  98          */
  99         function getLoadMonitor() {
 100                 if ( !isset( $this->mLoadMonitor ) ) {
 101                         $class = $this->mLoadMonitorClass;
 102                         $this->mLoadMonitor = new $class( $this );
 103                 }
 104                 return $this->mLoadMonitor;
 105         }
 106
 107         /**
 108          * Get or set arbitrary data used by the parent object, usually an LBFactory
 109          * @param $x
 110          * @return Mixed
 111          */
 112         function parentInfo( $x = null ) {
 113                 return wfSetVar( $this->mParentInfo, $x );
 114         }
 115
 116         /**
 117          * Given an array of non-normalised probabilities, this function will select
 118          * an element and return the appropriate key
 119          *
 120          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 121          *
 122          * @param $weights array
 123          *
 124          * @return bool|int|string
 125          */
 126         function pickRandom( $weights ) {
 127                 return ArrayUtils::pickRandom( $weights );
 128         }
 129
 130         /**
 131          * @param $loads array
 132          * @param $wiki bool
 133          * @return bool|int|string
 134          */
 135         function getRandomNonLagged( $loads, $wiki = false ) {
 136                 # Unset excessively lagged servers
 137                 $lags = $this->getLagTimes( $wiki );
 138                 foreach ( $lags as $i => $lag ) {
 139                         if ( $i != 0 ) {
 140                                 if ( $lag === false ) {
 141                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 142                                         unset( $loads[$i] );
 143                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 144                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 145                                         unset( $loads[$i] );
 146                                 }
 147                         }
 148                 }
 149
 150                 # Find out if all the slaves with non-zero load are lagged
 151                 $sum = 0;
 152                 foreach ( $loads as $load ) {
 153                         $sum += $load;
 154                 }
 155                 if ( $sum == 0 ) {
 156                         # No appropriate DB servers except maybe the master and some slaves with zero load
 157                         # Do NOT use the master
 158                         # Instead, this function will return false, triggering read-only mode,
 159                         # and a lagged slave will be used instead.
 160                         return false;
 161                 }
 162
 163                 if ( count( $loads ) == 0 ) {
 164                         return false;
 165                 }
 166
 167                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 168
 169                 # Return a random representative of the remainder
 170                 return ArrayUtils::pickRandom( $loads );
 171         }
 172
 173         /**
 174          * Get the index of the reader connection, which may be a slave
 175          * This takes into account load ratios and lag times. It should
 176          * always return a consistent index during a given invocation
 177          *
 178          * Side effect: opens connections to databases
 179          * @param $group bool
 180          * @param $wiki bool
 181          * @throws MWException
 182          * @return bool|int|string
 183          */
 184         function getReaderIndex( $group = false, $wiki = false ) {
 185                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 186
 187                 # @todo FIXME: For now, only go through all this for mysql databases
 188                 if ( $wgDBtype != 'mysql' ) {
 189                         return $this->getWriterIndex();
 190                 }
 191
 192                 if ( count( $this->mServers ) == 1 ) {
 193                         # Skip the load balancing if there's only one server
 194                         return 0;
 195                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 196                         # Shortcut if generic reader exists already
 197                         return $this->mReadIndex;
 198                 }
 199
 200                 wfProfileIn( __METHOD__ );
 201
 202                 $totalElapsed = 0;
 203
 204                 # convert from seconds to microseconds
 205                 $timeout = $wgDBClusterTimeout * 1e6;
 206
 207                 # Find the relevant load array
 208                 if ( $group !== false ) {
 209                         if ( isset( $this->mGroupLoads[$group] ) ) {
 210                                 $nonErrorLoads = $this->mGroupLoads[$group];
 211                         } else {
 212                                 # No loads for this group, return false and the caller can use some other group
 213                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 214                                 wfProfileOut( __METHOD__ );
 215                                 return false;
 216                         }
 217                 } else {
 218                         $nonErrorLoads = $this->mLoads;
 219                 }
 220
 221                 if ( !$nonErrorLoads ) {
 222                         wfProfileOut( __METHOD__ );
 223                         throw new MWException( "Empty server array given to LoadBalancer" );
 224                 }
 225
 226                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 227                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 228
 229                 $laggedSlaveMode = false;
 230
 231                 # First try quickly looking through the available servers for a server that
 232                 # meets our criteria
 233                 do {
 234                         $totalThreadsConnected = 0;
 235                         $overloadedServers = 0;
 236                         $currentLoads = $nonErrorLoads;
 237                         while ( count( $currentLoads ) ) {
 238                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 239                                         $i = ArrayUtils::pickRandom( $currentLoads );
 240                                 } else {
 241                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 242                                         if ( $i === false && count( $currentLoads ) != 0 ) {
 243                                                 # All slaves lagged. Switch to read-only mode
 244                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 245                                                 $wgReadOnly = 'The database has been automatically locked ' .
 246                                                         'while the slave database servers catch up to the master';
 247                                                 $i = ArrayUtils::pickRandom( $currentLoads );
 248                                                 $laggedSlaveMode = true;
 249                                         }
 250                                 }
 251
 252                                 if ( $i === false ) {
 253                                         # pickRandom() returned false
 254                                         # This is permanent and means the configuration or the load monitor
 255                                         # wants us to return false.
 256                                         wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 257                                         wfProfileOut( __METHOD__ );
 258                                         return false;
 259                                 }
 260
 261                                 wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 262                                 $conn = $this->openConnection( $i, $wiki );
 263
 264                                 if ( !$conn ) {
 265                                         wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 266                                         unset( $nonErrorLoads[$i] );
 267                                         unset( $currentLoads[$i] );
 268                                         continue;
 269                                 }
 270
 271                                 // Perform post-connection backoff
 272                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 273                                         ? $this->mServers[$i]['max threads'] : false;
 274                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 275
 276                                 // Decrement reference counter, we are finished with this connection.
 277                                 // It will be incremented for the caller later.
 278                                 if ( $wiki !== false ) {
 279                                         $this->reuseConnection( $conn );
 280                                 }
 281
 282                                 if ( $backoff ) {
 283                                         # Post-connection overload, don't use this server for now
 284                                         $totalThreadsConnected += $backoff;
 285                                         $overloadedServers++;
 286                                         unset( $currentLoads[$i] );
 287                                 } else {
 288                                         # Return this server
 289                                         break 2;
 290                                 }
 291                         }
 292
 293                         # No server found yet
 294                         $i = false;
 295
 296                         # If all servers were down, quit now
 297                         if ( !count( $nonErrorLoads ) ) {
 298                                 wfDebugLog( 'connect', "All servers down\n" );
 299                                 break;
 300                         }
 301
 302                         # Some servers must have been overloaded
 303                         if ( $overloadedServers == 0 ) {
 304                                 throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
 305                         }
 306                         # Back off for a while
 307                         # Scale the sleep time by the number of connected threads, to produce a
 308                         # roughly constant global poll rate
 309                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 310                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 311                 } while ( $totalElapsed < $timeout );
 312
 313                 if ( $totalElapsed >= $timeout ) {
 314                         wfDebugLog( 'connect', "All servers busy\n" );
 315                         $this->mErrorConnection = false;
 316                         $this->mLastError = 'All servers busy';
 317                 }
 318
 319                 if ( $i !== false ) {
 320                         # Slave connection successful
 321                         # Wait for the session master pos for a short time
 322                         if ( $this->mWaitForPos && $i > 0 ) {
 323                                 if ( !$this->doWait( $i ) ) {
 324                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 325                                 }
 326                         }
 327                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 328                                 $this->mReadIndex = $i;
 329                         }
 330                 }
 331                 wfProfileOut( __METHOD__ );
 332                 return $i;
 333         }
 334
 335         /**
 336          * Wait for a specified number of microseconds, and return the period waited
 337          * @param $t int
 338          * @return int
 339          */
 340         function sleep( $t ) {
 341                 wfProfileIn( __METHOD__ );
 342                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 343                 usleep( $t );
 344                 wfProfileOut( __METHOD__ );
 345                 return $t;
 346         }
 347
 348         /**
 349          * Set the master wait position
 350          * If a DB_SLAVE connection has been opened already, waits
 351          * Otherwise sets a variable telling it to wait if such a connection is opened
 352          * @param $pos DBMasterPos
 353          */
 354         public function waitFor( $pos ) {
 355                 wfProfileIn( __METHOD__ );
 356                 $this->mWaitForPos = $pos;
 357                 $i = $this->mReadIndex;
 358
 359                 if ( $i > 0 ) {
 360                         if ( !$this->doWait( $i ) ) {
 361                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 362                                 $this->mLaggedSlaveMode = true;
 363                         }
 364                 }
 365                 wfProfileOut( __METHOD__ );
 366         }
 367
 368         /**
 369          * Set the master wait position and wait for ALL slaves to catch up to it
 370          * @param $pos DBMasterPos
 371          */
 372         public function waitForAll( $pos ) {
 373                 wfProfileIn( __METHOD__ );
 374                 $this->mWaitForPos = $pos;
 375                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 376                         if ( $this->mLoads[$i] > 0 ) {
 377                                 $this->doWait( $i, true );
 378                         }
 379                 }
 380                 wfProfileOut( __METHOD__ );
 381         }
 382
 383         /**
 384          * Get any open connection to a given server index, local or foreign
 385          * Returns false if there is no connection open
 386          *
 387          * @param $i int
 388          * @return DatabaseBase|bool False on failure
 389          */
 390         function getAnyOpenConnection( $i ) {
 391                 foreach ( $this->mConns as $conns ) {
 392                         if ( !empty( $conns[$i] ) ) {
 393                                 return reset( $conns[$i] );
 394                         }
 395                 }
 396                 return false;
 397         }
 398
 399         /**
 400          * Wait for a given slave to catch up to the master pos stored in $this
 401          * @param $index
 402          * @param $open bool
 403          * @return bool
 404          */
 405         protected function doWait( $index, $open = false ) {
 406                 # Find a connection to wait on
 407                 $conn = $this->getAnyOpenConnection( $index );
 408                 if ( !$conn ) {
 409                         if ( !$open ) {
 410                                 wfDebug( __METHOD__ . ": no connection open\n" );
 411                                 return false;
 412                         } else {
 413                                 $conn = $this->openConnection( $index, '' );
 414                                 if ( !$conn ) {
 415                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 416                                         return false;
 417                                 }
 418                         }
 419                 }
 420
 421                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 422                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 423
 424                 if ( $result == -1 || is_null( $result ) ) {
 425                         # Timed out waiting for slave, use master instead
 426                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 427                         return false;
 428                 } else {
 429                         wfDebug( __METHOD__ . ": Done\n" );
 430                         return true;
 431                 }
 432         }
 433
 434         /**
 435          * Get a connection by index
 436          * This is the main entry point for this class.
 437          *
 438          * @param $i Integer: server index
 439          * @param array $groups query groups
 440          * @param bool|string $wiki Wiki ID
 441          *
 442          * @throws MWException
 443          * @return DatabaseBase
 444          */
 445         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 446                 wfProfileIn( __METHOD__ );
 447
 448                 if ( $i == DB_LAST ) {
 449                         wfProfileOut( __METHOD__ );
 450                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 451                 } elseif ( $i === null || $i === false ) {
 452                         wfProfileOut( __METHOD__ );
 453                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 454                 }
 455
 456                 if ( $wiki === wfWikiID() ) {
 457                         $wiki = false;
 458                 }
 459
 460                 # Query groups
 461                 if ( $i == DB_MASTER ) {
 462                         $i = $this->getWriterIndex();
 463                 } elseif ( !is_array( $groups ) ) {
 464                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 465                         if ( $groupIndex !== false ) {
 466                                 $serverName = $this->getServerName( $groupIndex );
 467                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 468                                 $i = $groupIndex;
 469                         }
 470                 } else {
 471                         foreach ( $groups as $group ) {
 472                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 473                                 if ( $groupIndex !== false ) {
 474                                         $serverName = $this->getServerName( $groupIndex );
 475                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 476                                         $i = $groupIndex;
 477                                         break;
 478                                 }
 479                         }
 480                 }
 481
 482                 # Operation-based index
 483                 if ( $i == DB_SLAVE ) {
 484                         $this->mLastError = 'Unknown error'; // reset error string
 485                         $i = $this->getReaderIndex( false, $wiki );
 486                         # Couldn't find a working server in getReaderIndex()?
 487                         if ( $i === false ) {
 488                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 489                                 wfProfileOut( __METHOD__ );
 490                                 return $this->reportConnectionError();
 491                         }
 492                 }
 493
 494                 # Now we have an explicit index into the servers array
 495                 $conn = $this->openConnection( $i, $wiki );
 496                 if ( !$conn ) {
 497                         wfProfileOut( __METHOD__ );
 498                         return $this->reportConnectionError();
 499                 }
 500
 501                 wfProfileOut( __METHOD__ );
 502                 return $conn;
 503         }
 504
 505         /**
 506          * Mark a foreign connection as being available for reuse under a different
 507          * DB name or prefix. This mechanism is reference-counted, and must be called
 508          * the same number of times as getConnection() to work.
 509          *
 510          * @param DatabaseBase $conn
 511          * @throws MWException
 512          */
 513         public function reuseConnection( $conn ) {
 514                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 515                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 516                 $dbName = $conn->getDBname();
 517                 $prefix = $conn->tablePrefix();
 518                 if ( strval( $prefix ) !== '' ) {
 519                         $wiki = "$dbName-$prefix";
 520                 } else {
 521                         $wiki = $dbName;
 522                 }
 523                 if ( $serverIndex === null || $refCount === null ) {
 524                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 525                         /**
 526                          * This can happen in code like:
 527                          *   foreach ( $dbs as $db ) {
 528                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 529                          *     ...
 530                          *     $lb->reuseConnection( $conn );
 531                          *   }
 532                          * When a connection to the local DB is opened in this way, reuseConnection()
 533                          * should be ignored
 534                          */
 535                         return;
 536                 }
 537                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 538                         throw new MWException( __METHOD__ . ": connection not found, has the connection been freed already?" );
 539                 }
 540                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 541                 if ( $refCount <= 0 ) {
 542                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 543                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 544                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 545                 } else {
 546                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 547                 }
 548         }
 549
 550         /**
 551          * Get a database connection handle reference
 552          *
 553          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 554          *
 555          * @see LoadBalancer::getConnection() for parameter information
 556          *
 557          * @param integer $db
 558          * @param mixed $groups
 559          * @param string $wiki
 560          * @return DBConnRef
 561          */
 562         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 563                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 564         }
 565
 566         /**
 567          * Get a database connection handle reference without connecting yet
 568          *
 569          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 570          *
 571          * @see LoadBalancer::getConnection() for parameter information
 572          *
 573          * @param integer $db
 574          * @param mixed $groups
 575          * @param string $wiki
 576          * @return DBConnRef
 577          */
 578         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 579                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 580         }
 581
 582         /**
 583          * Open a connection to the server given by the specified index
 584          * Index must be an actual index into the array.
 585          * If the server is already open, returns it.
 586          *
 587          * On error, returns false, and the connection which caused the
 588          * error will be available via $this->mErrorConnection.
 589          *
 590          * @param $i Integer server index
 591          * @param string $wiki wiki ID to open
 592          * @return DatabaseBase
 593          *
 594          * @access private
 595          */
 596         function openConnection( $i, $wiki = false ) {
 597                 wfProfileIn( __METHOD__ );
 598                 if ( $wiki !== false ) {
 599                         $conn = $this->openForeignConnection( $i, $wiki );
 600                         wfProfileOut( __METHOD__ );
 601                         return $conn;
 602                 }
 603                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 604                         $conn = $this->mConns['local'][$i][0];
 605                 } else {
 606                         $server = $this->mServers[$i];
 607                         $server['serverIndex'] = $i;
 608                         $conn = $this->reallyOpenConnection( $server, false );
 609                         if ( $conn->isOpen() ) {
 610                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 611                                 $this->mConns['local'][$i][0] = $conn;
 612                         } else {
 613                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 614                                 $this->mErrorConnection = $conn;
 615                                 $conn = false;
 616                         }
 617                 }
 618                 wfProfileOut( __METHOD__ );
 619                 return $conn;
 620         }
 621
 622         /**
 623          * Open a connection to a foreign DB, or return one if it is already open.
 624          *
 625          * Increments a reference count on the returned connection which locks the
 626          * connection to the requested wiki. This reference count can be
 627          * decremented by calling reuseConnection().
 628          *
 629          * If a connection is open to the appropriate server already, but with the wrong
 630          * database, it will be switched to the right database and returned, as long as
 631          * it has been freed first with reuseConnection().
 632          *
 633          * On error, returns false, and the connection which caused the
 634          * error will be available via $this->mErrorConnection.
 635          *
 636          * @param $i Integer: server index
 637          * @param string $wiki wiki ID to open
 638          * @return DatabaseBase
 639          */
 640         function openForeignConnection( $i, $wiki ) {
 641                 wfProfileIn( __METHOD__ );
 642                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 643                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 644                         // Reuse an already-used connection
 645                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 646                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 647                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 648                         // Reuse a free connection for the same wiki
 649                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 650                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 651                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 652                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 653                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 654                         // Reuse a connection from another wiki
 655                         $conn = reset( $this->mConns['foreignFree'][$i] );
 656                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 657
 658                         if ( !$conn->selectDB( $dbName ) ) {
 659                                 $this->mLastError = "Error selecting database $dbName on server " .
 660                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 661                                 $this->mErrorConnection = $conn;
 662                                 $conn = false;
 663                         } else {
 664                                 $conn->tablePrefix( $prefix );
 665                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 666                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 667                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 668                         }
 669                 } else {
 670                         // Open a new connection
 671                         $server = $this->mServers[$i];
 672                         $server['serverIndex'] = $i;
 673                         $server['foreignPoolRefCount'] = 0;
 674                         $server['foreign'] = true;
 675                         $conn = $this->reallyOpenConnection( $server, $dbName );
 676                         if ( !$conn->isOpen() ) {
 677                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 678                                 $this->mErrorConnection = $conn;
 679                                 $conn = false;
 680                         } else {
 681                                 $conn->tablePrefix( $prefix );
 682                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 683                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 684                         }
 685                 }
 686
 687                 // Increment reference count
 688                 if ( $conn ) {
 689                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 690                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 691                 }
 692                 wfProfileOut( __METHOD__ );
 693                 return $conn;
 694         }
 695
 696         /**
 697          * Test if the specified index represents an open connection
 698          *
 699          * @param $index Integer: server index
 700          * @access private
 701          * @return bool
 702          */
 703         function isOpen( $index ) {
 704                 if ( !is_integer( $index ) ) {
 705                         return false;
 706                 }
 707                 return (bool)$this->getAnyOpenConnection( $index );
 708         }
 709
 710         /**
 711          * Really opens a connection. Uncached.
 712          * Returns a Database object whether or not the connection was successful.
 713          * @access private
 714          *
 715          * @param $server
 716          * @param $dbNameOverride bool
 717          * @throws MWException
 718          * @return DatabaseBase
 719          */
 720         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 721                 if ( !is_array( $server ) ) {
 722                         throw new MWException( 'You must update your load-balancing configuration. ' .
 723                                 'See DefaultSettings.php entry for $wgDBservers.' );
 724                 }
 725
 726                 if ( $dbNameOverride !== false ) {
 727                         $server['dbname'] = $dbNameOverride;
 728                 }
 729
 730                 # Create object
 731                 try {
 732                         $db = DatabaseBase::factory( $server['type'], $server );
 733                 } catch ( DBConnectionError $e ) {
 734                         // FIXME: This is probably the ugliest thing I have ever done to
 735                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 736                         $db = $e->db;
 737                 }
 738
 739                 $db->setLBInfo( $server );
 740                 if ( isset( $server['fakeSlaveLag'] ) ) {
 741                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 742                 }
 743                 if ( isset( $server['fakeMaster'] ) ) {
 744                         $db->setFakeMaster( true );
 745                 }
 746                 return $db;
 747         }
 748
 749         /**
 750          * @throws DBConnectionError
 751          * @return bool
 752          */
 753         private function reportConnectionError() {
 754                 $conn = $this->mErrorConnection; // The connection which caused the error
 755
 756                 if ( !is_object( $conn ) ) {
 757                         // No last connection, probably due to all servers being too busy
 758                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 759
 760                         // If all servers were busy, mLastError will contain something sensible
 761                         throw new DBConnectionError( null, $this->mLastError );
 762                 } else {
 763                         $server = $conn->getProperty( 'mServer' );
 764                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 765                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 766                 }
 767                 return false; /* not reached */
 768         }
 769
 770         /**
 771          * @return int
 772          */
 773         function getWriterIndex() {
 774                 return 0;
 775         }
 776
 777         /**
 778          * Returns true if the specified index is a valid server index
 779          *
 780          * @param $i
 781          * @return bool
 782          */
 783         function haveIndex( $i ) {
 784                 return array_key_exists( $i, $this->mServers );
 785         }
 786
 787         /**
 788          * Returns true if the specified index is valid and has non-zero load
 789          *
 790          * @param $i
 791          * @return bool
 792          */
 793         function isNonZeroLoad( $i ) {
 794                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 795         }
 796
 797         /**
 798          * Get the number of defined servers (not the number of open connections)
 799          *
 800          * @return int
 801          */
 802         function getServerCount() {
 803                 return count( $this->mServers );
 804         }
 805
 806         /**
 807          * Get the host name or IP address of the server with the specified index
 808          * Prefer a readable name if available.
 809          * @param $i
 810          * @return string
 811          */
 812         function getServerName( $i ) {
 813                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 814                         return $this->mServers[$i]['hostName'];
 815                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 816                         return $this->mServers[$i]['host'];
 817                 } else {
 818                         return '';
 819                 }
 820         }
 821
 822         /**
 823          * Return the server info structure for a given index, or false if the index is invalid.
 824          * @param $i
 825          * @return bool
 826          */
 827         function getServerInfo( $i ) {
 828                 if ( isset( $this->mServers[$i] ) ) {
 829                         return $this->mServers[$i];
 830                 } else {
 831                         return false;
 832                 }
 833         }
 834
 835         /**
 836          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 837          * @param $i
 838          * @param $serverInfo
 839          */
 840         function setServerInfo( $i, $serverInfo ) {
 841                 $this->mServers[$i] = $serverInfo;
 842         }
 843
 844         /**
 845          * Get the current master position for chronology control purposes
 846          * @return mixed
 847          */
 848         function getMasterPos() {
 849                 # If this entire request was served from a slave without opening a connection to the
 850                 # master (however unlikely that may be), then we can fetch the position from the slave.
 851                 $masterConn = $this->getAnyOpenConnection( 0 );
 852                 if ( !$masterConn ) {
 853                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 854                                 $conn = $this->getAnyOpenConnection( $i );
 855                                 if ( $conn ) {
 856                                         wfDebug( "Master pos fetched from slave\n" );
 857                                         return $conn->getSlavePos();
 858                                 }
 859                         }
 860                 } else {
 861                         wfDebug( "Master pos fetched from master\n" );
 862                         return $masterConn->getMasterPos();
 863                 }
 864                 return false;
 865         }
 866
 867         /**
 868          * Close all open connections
 869          */
 870         function closeAll() {
 871                 foreach ( $this->mConns as $conns2 ) {
 872                         foreach ( $conns2 as $conns3 ) {
 873                                 foreach ( $conns3 as $conn ) {
 874                                         $conn->close();
 875                                 }
 876                         }
 877                 }
 878                 $this->mConns = array(
 879                         'local' => array(),
 880                         'foreignFree' => array(),
 881                         'foreignUsed' => array(),
 882                 );
 883         }
 884
 885         /**
 886          * Deprecated function, typo in function name
 887          *
 888          * @deprecated in 1.18
 889          * @param $conn
 890          */
 891         function closeConnecton( $conn ) {
 892                 wfDeprecated( __METHOD__, '1.18' );
 893                 $this->closeConnection( $conn );
 894         }
 895
 896         /**
 897          * Close a connection
 898          * Using this function makes sure the LoadBalancer knows the connection is closed.
 899          * If you use $conn->close() directly, the load balancer won't update its state.
 900          * @param $conn DatabaseBase
 901          */
 902         function closeConnection( $conn ) {
 903                 $done = false;
 904                 foreach ( $this->mConns as $i1 => $conns2 ) {
 905                         foreach ( $conns2 as $i2 => $conns3 ) {
 906                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 907                                         if ( $conn === $candidateConn ) {
 908                                                 $conn->close();
 909                                                 unset( $this->mConns[$i1][$i2][$i3] );
 910                                                 $done = true;
 911                                                 break;
 912                                         }
 913                                 }
 914                         }
 915                 }
 916                 if ( !$done ) {
 917                         $conn->close();
 918                 }
 919         }
 920
 921         /**
 922          * Commit transactions on all open connections
 923          */
 924         function commitAll() {
 925                 foreach ( $this->mConns as $conns2 ) {
 926                         foreach ( $conns2 as $conns3 ) {
 927                                 foreach ( $conns3 as $conn ) {
 928                                         if ( $conn->trxLevel() ) {
 929                                                 $conn->commit( __METHOD__, 'flush' );
 930                                         }
 931                                 }
 932                         }
 933                 }
 934         }
 935
 936         /**
 937          *  Issue COMMIT only on master, only if queries were done on connection
 938          */
 939         function commitMasterChanges() {
 940                 // Always 0, but who knows.. :)
 941                 $masterIndex = $this->getWriterIndex();
 942                 foreach ( $this->mConns as $conns2 ) {
 943                         if ( empty( $conns2[$masterIndex] ) ) {
 944                                 continue;
 945                         }
 946                         foreach ( $conns2[$masterIndex] as $conn ) {
 947                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 948                                         $conn->commit( __METHOD__, 'flush' );
 949                                 }
 950                         }
 951                 }
 952         }
 953
 954         /**
 955          * @param $value null
 956          * @return Mixed
 957          */
 958         function waitTimeout( $value = null ) {
 959                 return wfSetVar( $this->mWaitTimeout, $value );
 960         }
 961
 962         /**
 963          * @return bool
 964          */
 965         function getLaggedSlaveMode() {
 966                 return $this->mLaggedSlaveMode;
 967         }
 968
 969         /**
 970          * Disables/enables lag checks
 971          * @param $mode null
 972          * @return bool
 973          */
 974         function allowLagged( $mode = null ) {
 975                 if ( $mode === null ) {
 976                         return $this->mAllowLagged;
 977                 }
 978                 $this->mAllowLagged = $mode;
 979                 return $this->mAllowLagged;
 980         }
 981
 982         /**
 983          * @return bool
 984          */
 985         function pingAll() {
 986                 $success = true;
 987                 foreach ( $this->mConns as $conns2 ) {
 988                         foreach ( $conns2 as $conns3 ) {
 989                                 foreach ( $conns3 as $conn ) {
 990                                         if ( !$conn->ping() ) {
 991                                                 $success = false;
 992                                         }
 993                                 }
 994                         }
 995                 }
 996                 return $success;
 997         }
 998
 999         /**
1000          * Call a function with each open connection object
1001          * @param $callback
1002          * @param array $params
1003          */
1004         function forEachOpenConnection( $callback, $params = array() ) {
1005                 foreach ( $this->mConns as $conns2 ) {
1006                         foreach ( $conns2 as $conns3 ) {
1007                                 foreach ( $conns3 as $conn ) {
1008                                         $mergedParams = array_merge( array( $conn ), $params );
1009                                         call_user_func_array( $callback, $mergedParams );
1010                                 }
1011                         }
1012                 }
1013         }
1014
1015         /**
1016          * Get the hostname and lag time of the most-lagged slave.
1017          * This is useful for maintenance scripts that need to throttle their updates.
1018          * May attempt to open connections to slaves on the default DB. If there is
1019          * no lag, the maximum lag will be reported as -1.
1020          *
1021          * @param string $wiki Wiki ID, or false for the default database
1022          *
1023          * @return array ( host, max lag, index of max lagged host )
1024          */
1025         function getMaxLag( $wiki = false ) {
1026                 $maxLag = -1;
1027                 $host = '';
1028                 $maxIndex = 0;
1029                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1030                         foreach ( $this->mServers as $i => $conn ) {
1031                                 $conn = false;
1032                                 if ( $wiki === false ) {
1033                                         $conn = $this->getAnyOpenConnection( $i );
1034                                 }
1035                                 if ( !$conn ) {
1036                                         $conn = $this->openConnection( $i, $wiki );
1037                                 }
1038                                 if ( !$conn ) {
1039                                         continue;
1040                                 }
1041                                 $lag = $conn->getLag();
1042                                 if ( $lag > $maxLag ) {
1043                                         $maxLag = $lag;
1044                                         $host = $this->mServers[$i]['host'];
1045                                         $maxIndex = $i;
1046                                 }
1047                         }
1048                 }
1049                 return array( $host, $maxLag, $maxIndex );
1050         }
1051
1052         /**
1053          * Get lag time for each server
1054          * Results are cached for a short time in memcached, and indefinitely in the process cache
1055          *
1056          * @param $wiki
1057          *
1058          * @return array
1059          */
1060         function getLagTimes( $wiki = false ) {
1061                 # Try process cache
1062                 if ( isset( $this->mLagTimes ) ) {
1063                         return $this->mLagTimes;
1064                 }
1065                 if ( $this->getServerCount() == 1 ) {
1066                         # No replication
1067                         $this->mLagTimes = array( 0 => 0 );
1068                 } else {
1069                         # Send the request to the load monitor
1070                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1071                                 array_keys( $this->mServers ), $wiki );
1072                 }
1073                 return $this->mLagTimes;
1074         }
1075
1076         /**
1077          * Get the lag in seconds for a given connection, or zero if this load
1078          * balancer does not have replication enabled.
1079          *
1080          * This should be used in preference to Database::getLag() in cases where
1081          * replication may not be in use, since there is no way to determine if
1082          * replication is in use at the connection level without running
1083          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1084          * function instead of Database::getLag() avoids a fatal error in this
1085          * case on many installations.
1086          *
1087          * @param $conn DatabaseBase
1088          *
1089          * @return int
1090          */
1091         function safeGetLag( $conn ) {
1092                 if ( $this->getServerCount() == 1 ) {
1093                         return 0;
1094                 } else {
1095                         return $conn->getLag();
1096                 }
1097         }
1098
1099         /**
1100          * Clear the cache for getLagTimes
1101          */
1102         function clearLagTimeCache() {
1103                 $this->mLagTimes = null;
1104         }
1105 }
1106
1107 /**
1108  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1109  * as well handling deferring the actual network connection until the handle is used
1110  *
1111  * @ingroup Database
1112  * @since 1.22
1113  */
1114 class DBConnRef implements IDatabase {
1115         /** @var LoadBalancer */
1116         protected $lb;
1117         /** @var DatabaseBase|null */
1118         protected $conn;
1119         /** @var Array|null */
1120         protected $params;
1121
1122         /**
1123          * @param $lb LoadBalancer
1124          * @param $conn DatabaseBase|array Connection or (server index, group, wiki ID) array
1125          */
1126         public function __construct( LoadBalancer $lb, $conn ) {
1127                 $this->lb = $lb;
1128                 if ( $conn instanceof DatabaseBase ) {
1129                         $this->conn = $conn;
1130                 } else {
1131                         $this->params = $conn;
1132                 }
1133         }
1134
1135         public function __call( $name, $arguments ) {
1136                 if ( $this->conn === null ) {
1137                         list( $db, $groups, $wiki ) = $this->params;
1138                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1139                 }
1140                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1141         }
1142
1143         function __destruct() {
1144                 if ( $this->conn !== null ) {
1145                         $this->lb->reuseConnection( $this->conn );
1146                 }
1147         }
1148 }