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 $params Array 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          */
  45         function __construct( $params ) {
  46                 if ( !isset( $params['servers'] ) ) {
  47                         throw new MWException( __CLASS__.': missing servers parameter' );
  48                 }
  49                 $this->mServers = $params['servers'];
  50
  51                 if ( isset( $params['waitTimeout'] ) ) {
  52                         $this->mWaitTimeout = $params['waitTimeout'];
  53                 } else {
  54                         $this->mWaitTimeout = 10;
  55                 }
  56
  57                 $this->mReadIndex = -1;
  58                 $this->mWriteIndex = -1;
  59                 $this->mConns = array(
  60                         'local' => array(),
  61                         'foreignUsed' => array(),
  62                         'foreignFree' => array() );
  63                 $this->mLoads = array();
  64                 $this->mWaitForPos = false;
  65                 $this->mLaggedSlaveMode = false;
  66                 $this->mErrorConnection = false;
  67                 $this->mAllowLagged = false;
  68
  69                 if ( isset( $params['loadMonitor'] ) ) {
  70                         $this->mLoadMonitorClass = $params['loadMonitor'];
  71                 } else {
  72                         $master = reset( $params['servers'] );
  73                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  74                                 $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
  75                         } else {
  76                                 $this->mLoadMonitorClass = 'LoadMonitor_Null';
  77                         }
  78                 }
  79
  80                 foreach( $params['servers'] as $i => $server ) {
  81                         $this->mLoads[$i] = $server['load'];
  82                         if ( isset( $server['groupLoads'] ) ) {
  83                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  84                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  85                                                 $this->mGroupLoads[$group] = array();
  86                                         }
  87                                         $this->mGroupLoads[$group][$i] = $ratio;
  88                                 }
  89                         }
  90                 }
  91         }
  92
  93         /**
  94          * Get a LoadMonitor instance
  95          *
  96          * @return LoadMonitor
  97          */
  98         function getLoadMonitor() {
  99                 if ( !isset( $this->mLoadMonitor ) ) {
 100                         $class = $this->mLoadMonitorClass;
 101                         $this->mLoadMonitor = new $class( $this );
 102                 }
 103                 return $this->mLoadMonitor;
 104         }
 105
 106         /**
 107          * Get or set arbitrary data used by the parent object, usually an LBFactory
 108          * @param $x
 109          * @return Mixed
 110          */
 111         function parentInfo( $x = null ) {
 112                 return wfSetVar( $this->mParentInfo, $x );
 113         }
 114
 115         /**
 116          * Given an array of non-normalised probabilities, this function will select
 117          * an element and return the appropriate key
 118          *
 119          * @param $weights array
 120          *
 121          * @return int
 122          */
 123         function pickRandom( $weights ) {
 124                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
 125                         return false;
 126                 }
 127
 128                 $sum = array_sum( $weights );
 129                 if ( $sum == 0 ) {
 130                         # No loads on any of them
 131                         # In previous versions, this triggered an unweighted random selection,
 132                         # but this feature has been removed as of April 2006 to allow for strict
 133                         # separation of query groups.
 134                         return false;
 135                 }
 136                 $max = mt_getrandmax();
 137                 $rand = mt_rand( 0, $max ) / $max * $sum;
 138
 139                 $sum = 0;
 140                 foreach ( $weights as $i => $w ) {
 141                         $sum += $w;
 142                         if ( $sum >= $rand ) {
 143                                 break;
 144                         }
 145                 }
 146                 return $i;
 147         }
 148
 149         /**
 150          * @param $loads array
 151          * @param $wiki bool
 152          * @return bool|int|string
 153          */
 154         function getRandomNonLagged( $loads, $wiki = false ) {
 155                 # Unset excessively lagged servers
 156                 $lags = $this->getLagTimes( $wiki );
 157                 foreach ( $lags as $i => $lag ) {
 158                         if ( $i != 0 ) {
 159                                 if ( $lag === false ) {
 160                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 161                                         unset( $loads[$i] );
 162                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 163                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 164                                         unset( $loads[$i] );
 165                                 }
 166                         }
 167                 }
 168
 169                 # Find out if all the slaves with non-zero load are lagged
 170                 $sum = 0;
 171                 foreach ( $loads as $load ) {
 172                         $sum += $load;
 173                 }
 174                 if ( $sum == 0 ) {
 175                         # No appropriate DB servers except maybe the master and some slaves with zero load
 176                         # Do NOT use the master
 177                         # Instead, this function will return false, triggering read-only mode,
 178                         # and a lagged slave will be used instead.
 179                         return false;
 180                 }
 181
 182                 if ( count( $loads ) == 0 ) {
 183                         return false;
 184                 }
 185
 186                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 187
 188                 # Return a random representative of the remainder
 189                 return $this->pickRandom( $loads );
 190         }
 191
 192         /**
 193          * Get the index of the reader connection, which may be a slave
 194          * This takes into account load ratios and lag times. It should
 195          * always return a consistent index during a given invocation
 196          *
 197          * Side effect: opens connections to databases
 198          * @param $group bool
 199          * @param $wiki bool
 200          * @return bool|int|string
 201          */
 202         function getReaderIndex( $group = false, $wiki = false ) {
 203                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 204
 205                 # @todo FIXME: For now, only go through all this for mysql databases
 206                 if ($wgDBtype != 'mysql') {
 207                         return $this->getWriterIndex();
 208                 }
 209
 210                 if ( count( $this->mServers ) == 1 )  {
 211                         # Skip the load balancing if there's only one server
 212                         return 0;
 213                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 214                         # Shortcut if generic reader exists already
 215                         return $this->mReadIndex;
 216                 }
 217
 218                 wfProfileIn( __METHOD__ );
 219
 220                 $totalElapsed = 0;
 221
 222                 # convert from seconds to microseconds
 223                 $timeout = $wgDBClusterTimeout * 1e6;
 224
 225                 # Find the relevant load array
 226                 if ( $group !== false ) {
 227                         if ( isset( $this->mGroupLoads[$group] ) ) {
 228                                 $nonErrorLoads = $this->mGroupLoads[$group];
 229                         } else {
 230                                 # No loads for this group, return false and the caller can use some other group
 231                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 232                                 wfProfileOut( __METHOD__ );
 233                                 return false;
 234                         }
 235                 } else {
 236                         $nonErrorLoads = $this->mLoads;
 237                 }
 238
 239                 if ( !$nonErrorLoads ) {
 240                         throw new MWException( "Empty server array given to LoadBalancer" );
 241                 }
 242
 243                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 244                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 245
 246                 $laggedSlaveMode = false;
 247
 248                 # First try quickly looking through the available servers for a server that
 249                 # meets our criteria
 250                 do {
 251                         $totalThreadsConnected = 0;
 252                         $overloadedServers = 0;
 253                         $currentLoads = $nonErrorLoads;
 254                         while ( count( $currentLoads ) ) {
 255                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 256                                         $i = $this->pickRandom( $currentLoads );
 257                                 } else {
 258                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 259                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 260                                                 # All slaves lagged. Switch to read-only mode
 261                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 262                                                 $wgReadOnly = 'The database has been automatically locked ' .
 263                                                         'while the slave database servers catch up to the master';
 264                                                 $i = $this->pickRandom( $currentLoads );
 265                                                 $laggedSlaveMode = true;
 266                                         }
 267                                 }
 268
 269                                 if ( $i === false ) {
 270                                         # pickRandom() returned false
 271                                         # This is permanent and means the configuration or the load monitor
 272                                         # wants us to return false.
 273                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 274                                         wfProfileOut( __METHOD__ );
 275                                         return false;
 276                                 }
 277
 278                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 279                                 $conn = $this->openConnection( $i, $wiki );
 280
 281                                 if ( !$conn ) {
 282                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 283                                         unset( $nonErrorLoads[$i] );
 284                                         unset( $currentLoads[$i] );
 285                                         continue;
 286                                 }
 287
 288                                 // Perform post-connection backoff
 289                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 290                                         ? $this->mServers[$i]['max threads'] : false;
 291                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 292
 293                                 // Decrement reference counter, we are finished with this connection.
 294                                 // It will be incremented for the caller later.
 295                                 if ( $wiki !== false ) {
 296                                         $this->reuseConnection( $conn );
 297                                 }
 298
 299                                 if ( $backoff ) {
 300                                         # Post-connection overload, don't use this server for now
 301                                         $totalThreadsConnected += $backoff;
 302                                         $overloadedServers++;
 303                                         unset( $currentLoads[$i] );
 304                                 } else {
 305                                         # Return this server
 306                                         break 2;
 307                                 }
 308                         }
 309
 310                         # No server found yet
 311                         $i = false;
 312
 313                         # If all servers were down, quit now
 314                         if ( !count( $nonErrorLoads ) ) {
 315                                 wfDebugLog( 'connect', "All servers down\n" );
 316                                 break;
 317                         }
 318
 319                         # Some servers must have been overloaded
 320                         if ( $overloadedServers == 0 ) {
 321                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 322                         }
 323                         # Back off for a while
 324                         # Scale the sleep time by the number of connected threads, to produce a
 325                         # roughly constant global poll rate
 326                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 327                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 328                 } while ( $totalElapsed < $timeout );
 329
 330                 if ( $totalElapsed >= $timeout ) {
 331                         wfDebugLog( 'connect', "All servers busy\n" );
 332                         $this->mErrorConnection = false;
 333                         $this->mLastError = 'All servers busy';
 334                 }
 335
 336                 if ( $i !== false ) {
 337                         # Slave connection successful
 338                         # Wait for the session master pos for a short time
 339                         if ( $this->mWaitForPos && $i > 0 ) {
 340                                 if ( !$this->doWait( $i ) ) {
 341                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 342                                 }
 343                         }
 344                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 345                                 $this->mReadIndex = $i;
 346                         }
 347                 }
 348                 wfProfileOut( __METHOD__ );
 349                 return $i;
 350         }
 351
 352         /**
 353          * Wait for a specified number of microseconds, and return the period waited
 354          * @param $t int
 355          * @return int
 356          */
 357         function sleep( $t ) {
 358                 wfProfileIn( __METHOD__ );
 359                 wfDebug( __METHOD__.": waiting $t us\n" );
 360                 usleep( $t );
 361                 wfProfileOut( __METHOD__ );
 362                 return $t;
 363         }
 364
 365         /**
 366          * Set the master wait position
 367          * If a DB_SLAVE connection has been opened already, waits
 368          * Otherwise sets a variable telling it to wait if such a connection is opened
 369          * @param $pos int
 370          */
 371         public function waitFor( $pos ) {
 372                 wfProfileIn( __METHOD__ );
 373                 $this->mWaitForPos = $pos;
 374                 $i = $this->mReadIndex;
 375
 376                 if ( $i > 0 ) {
 377                         if ( !$this->doWait( $i ) ) {
 378                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 379                                 $this->mLaggedSlaveMode = true;
 380                         }
 381                 }
 382                 wfProfileOut( __METHOD__ );
 383         }
 384
 385         /**
 386          * Set the master wait position and wait for ALL slaves to catch up to it
 387          * @param $pos int
 388          */
 389         public function waitForAll( $pos ) {
 390                 wfProfileIn( __METHOD__ );
 391                 $this->mWaitForPos = $pos;
 392                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 393                         $this->doWait( $i , true );
 394                 }
 395                 wfProfileOut( __METHOD__ );
 396         }
 397
 398         /**
 399          * Get any open connection to a given server index, local or foreign
 400          * Returns false if there is no connection open
 401          *
 402          * @param $i int
 403          * @return DatabaseBase|bool False on failure
 404          */
 405         function getAnyOpenConnection( $i ) {
 406                 foreach ( $this->mConns as $conns ) {
 407                         if ( !empty( $conns[$i] ) ) {
 408                                 return reset( $conns[$i] );
 409                         }
 410                 }
 411                 return false;
 412         }
 413
 414         /**
 415          * Wait for a given slave to catch up to the master pos stored in $this
 416          * @param $index
 417          * @param $open bool
 418          * @return bool
 419          */
 420         function doWait( $index, $open = false ) {
 421                 # Find a connection to wait on
 422                 $conn = $this->getAnyOpenConnection( $index );
 423                 if ( !$conn ) {
 424                         if ( !$open ) {
 425                                 wfDebug( __METHOD__ . ": no connection open\n" );
 426                                 return false;
 427                         } else {
 428                                 $conn = $this->openConnection( $index );
 429                                 if ( !$conn ) {
 430                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 431                                         return false;
 432                                 }
 433                         }
 434                 }
 435
 436                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 437                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 438
 439                 if ( $result == -1 || is_null( $result ) ) {
 440                         # Timed out waiting for slave, use master instead
 441                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 442                         return false;
 443                 } else {
 444                         wfDebug( __METHOD__.": Done\n" );
 445                         return true;
 446                 }
 447         }
 448
 449         /**
 450          * Get a connection by index
 451          * This is the main entry point for this class.
 452          *
 453          * @param $i Integer: server index
 454          * @param $groups Array: query groups
 455          * @param $wiki String: wiki ID
 456          *
 457          * @return DatabaseBase
 458          */
 459         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 460                 wfProfileIn( __METHOD__ );
 461
 462                 if ( $i == DB_LAST ) {
 463                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 464                 } elseif ( $i === null || $i === false ) {
 465                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 466                 }
 467
 468                 if ( $wiki === wfWikiID() ) {
 469                         $wiki = false;
 470                 }
 471
 472                 # Query groups
 473                 if ( $i == DB_MASTER ) {
 474                         $i = $this->getWriterIndex();
 475                 } elseif ( !is_array( $groups ) ) {
 476                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 477                         if ( $groupIndex !== false ) {
 478                                 $serverName = $this->getServerName( $groupIndex );
 479                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 480                                 $i = $groupIndex;
 481                         }
 482                 } else {
 483                         foreach ( $groups as $group ) {
 484                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 485                                 if ( $groupIndex !== false ) {
 486                                         $serverName = $this->getServerName( $groupIndex );
 487                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 488                                         $i = $groupIndex;
 489                                         break;
 490                                 }
 491                         }
 492                 }
 493
 494                 # Operation-based index
 495                 if ( $i == DB_SLAVE ) {
 496                         $i = $this->getReaderIndex( false, $wiki );
 497                         # Couldn't find a working server in getReaderIndex()?
 498                         if ( $i === false ) {
 499                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 500                                 $this->reportConnectionError( $this->mErrorConnection );
 501                                 wfProfileOut( __METHOD__ );
 502                                 return false;
 503                         }
 504                 }
 505
 506                 # Now we have an explicit index into the servers array
 507                 $conn = $this->openConnection( $i, $wiki );
 508                 if ( !$conn ) {
 509                         $this->reportConnectionError( $this->mErrorConnection );
 510                 }
 511
 512                 wfProfileOut( __METHOD__ );
 513                 return $conn;
 514         }
 515
 516         /**
 517          * Mark a foreign connection as being available for reuse under a different
 518          * DB name or prefix. This mechanism is reference-counted, and must be called
 519          * the same number of times as getConnection() to work.
 520          *
 521          * @param DatabaseBase $conn
 522          */
 523         public function reuseConnection( $conn ) {
 524                 $serverIndex = $conn->getLBInfo('serverIndex');
 525                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 526                 $dbName = $conn->getDBname();
 527                 $prefix = $conn->tablePrefix();
 528                 if ( strval( $prefix ) !== '' ) {
 529                         $wiki = "$dbName-$prefix";
 530                 } else {
 531                         $wiki = $dbName;
 532                 }
 533                 if ( $serverIndex === null || $refCount === null ) {
 534                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 535                         /**
 536                          * This can happen in code like:
 537                          *   foreach ( $dbs as $db ) {
 538                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 539                          *     ...
 540                          *     $lb->reuseConnection( $conn );
 541                          *   }
 542                          * When a connection to the local DB is opened in this way, reuseConnection()
 543                          * should be ignored
 544                          */
 545                         return;
 546                 }
 547                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 548                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 549                 }
 550                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 551                 if ( $refCount <= 0 ) {
 552                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 553                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 554                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 555                 } else {
 556                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 557                 }
 558         }
 559
 560         /**
 561          * Open a connection to the server given by the specified index
 562          * Index must be an actual index into the array.
 563          * If the server is already open, returns it.
 564          *
 565          * On error, returns false, and the connection which caused the
 566          * error will be available via $this->mErrorConnection.
 567          *
 568          * @param $i Integer server index
 569          * @param $wiki String wiki ID to open
 570          * @return DatabaseBase
 571          *
 572          * @access private
 573          */
 574         function openConnection( $i, $wiki = false ) {
 575                 wfProfileIn( __METHOD__ );
 576                 if ( $wiki !== false ) {
 577                         $conn = $this->openForeignConnection( $i, $wiki );
 578                         wfProfileOut( __METHOD__);
 579                         return $conn;
 580                 }
 581                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 582                         $conn = $this->mConns['local'][$i][0];
 583                 } else {
 584                         $server = $this->mServers[$i];
 585                         $server['serverIndex'] = $i;
 586                         $conn = $this->reallyOpenConnection( $server, false );
 587                         if ( $conn->isOpen() ) {
 588                                 $this->mConns['local'][$i][0] = $conn;
 589                         } else {
 590                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 591                                 $this->mErrorConnection = $conn;
 592                                 $conn = false;
 593                         }
 594                 }
 595                 wfProfileOut( __METHOD__ );
 596                 return $conn;
 597         }
 598
 599         /**
 600          * Open a connection to a foreign DB, or return one if it is already open.
 601          *
 602          * Increments a reference count on the returned connection which locks the
 603          * connection to the requested wiki. This reference count can be
 604          * decremented by calling reuseConnection().
 605          *
 606          * If a connection is open to the appropriate server already, but with the wrong
 607          * database, it will be switched to the right database and returned, as long as
 608          * it has been freed first with reuseConnection().
 609          *
 610          * On error, returns false, and the connection which caused the
 611          * error will be available via $this->mErrorConnection.
 612          *
 613          * @param $i Integer: server index
 614          * @param $wiki String: wiki ID to open
 615          * @return DatabaseBase
 616          */
 617         function openForeignConnection( $i, $wiki ) {
 618                 wfProfileIn(__METHOD__);
 619                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 620                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 621                         // Reuse an already-used connection
 622                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 623                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 624                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 625                         // Reuse a free connection for the same wiki
 626                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 627                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 628                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 629                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 630                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 631                         // Reuse a connection from another wiki
 632                         $conn = reset( $this->mConns['foreignFree'][$i] );
 633                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 634
 635                         if ( !$conn->selectDB( $dbName ) ) {
 636                                 $this->mLastError = "Error selecting database $dbName on server " .
 637                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 638                                 $this->mErrorConnection = $conn;
 639                                 $conn = false;
 640                         } else {
 641                                 $conn->tablePrefix( $prefix );
 642                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 643                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 644                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 645                         }
 646                 } else {
 647                         // Open a new connection
 648                         $server = $this->mServers[$i];
 649                         $server['serverIndex'] = $i;
 650                         $server['foreignPoolRefCount'] = 0;
 651                         $conn = $this->reallyOpenConnection( $server, $dbName );
 652                         if ( !$conn->isOpen() ) {
 653                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 654                                 $this->mErrorConnection = $conn;
 655                                 $conn = false;
 656                         } else {
 657                                 $conn->tablePrefix( $prefix );
 658                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 659                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 660                         }
 661                 }
 662
 663                 // Increment reference count
 664                 if ( $conn ) {
 665                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 666                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 667                 }
 668                 wfProfileOut(__METHOD__);
 669                 return $conn;
 670         }
 671
 672         /**
 673          * Test if the specified index represents an open connection
 674          *
 675          * @param $index Integer: server index
 676          * @access private
 677          * @return bool
 678          */
 679         function isOpen( $index ) {
 680                 if( !is_integer( $index ) ) {
 681                         return false;
 682                 }
 683                 return (bool)$this->getAnyOpenConnection( $index );
 684         }
 685
 686         /**
 687          * Really opens a connection. Uncached.
 688          * Returns a Database object whether or not the connection was successful.
 689          * @access private
 690          *
 691          * @param $server
 692          * @param $dbNameOverride bool
 693          * @return DatabaseBase
 694          */
 695         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 696                 if( !is_array( $server ) ) {
 697                         throw new MWException( 'You must update your load-balancing configuration. ' .
 698                                 'See DefaultSettings.php entry for $wgDBservers.' );
 699                 }
 700
 701                 $host = $server['host'];
 702                 $dbname = $server['dbname'];
 703
 704                 if ( $dbNameOverride !== false ) {
 705                         $server['dbname'] = $dbname = $dbNameOverride;
 706                 }
 707
 708                 # Create object
 709                 wfDebug( "Connecting to $host $dbname...\n" );
 710                 try {
 711                         $db = DatabaseBase::factory( $server['type'], $server );
 712                 } catch ( DBConnectionError $e ) {
 713                         // FIXME: This is probably the ugliest thing I have ever done to
 714                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 715                         $db = $e->db;
 716                 }
 717
 718                 if ( $db->isOpen() ) {
 719                         wfDebug( "Connected to $host $dbname.\n" );
 720                 } else {
 721                         wfDebug( "Connection failed to $host $dbname.\n" );
 722                 }
 723                 $db->setLBInfo( $server );
 724                 if ( isset( $server['fakeSlaveLag'] ) ) {
 725                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 726                 }
 727                 if ( isset( $server['fakeMaster'] ) ) {
 728                         $db->setFakeMaster( true );
 729                 }
 730                 return $db;
 731         }
 732
 733         /**
 734          * @param $conn
 735          * @throws DBConnectionError
 736          */
 737         function reportConnectionError( &$conn ) {
 738                 wfProfileIn( __METHOD__ );
 739
 740                 if ( !is_object( $conn ) ) {
 741                         // No last connection, probably due to all servers being too busy
 742                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 743                         $conn = new Database;
 744                         // If all servers were busy, mLastError will contain something sensible
 745                         throw new DBConnectionError( $conn, $this->mLastError );
 746                 } else {
 747                         $server = $conn->getProperty( 'mServer' );
 748                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 749                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 750                 }
 751                 wfProfileOut( __METHOD__ );
 752         }
 753
 754         /**
 755          * @return int
 756          */
 757         function getWriterIndex() {
 758                 return 0;
 759         }
 760
 761         /**
 762          * Returns true if the specified index is a valid server index
 763          *
 764          * @param $i
 765          * @return bool
 766          */
 767         function haveIndex( $i ) {
 768                 return array_key_exists( $i, $this->mServers );
 769         }
 770
 771         /**
 772          * Returns true if the specified index is valid and has non-zero load
 773          *
 774          * @param $i
 775          * @return bool
 776          */
 777         function isNonZeroLoad( $i ) {
 778                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 779         }
 780
 781         /**
 782          * Get the number of defined servers (not the number of open connections)
 783          *
 784          * @return int
 785          */
 786         function getServerCount() {
 787                 return count( $this->mServers );
 788         }
 789
 790         /**
 791          * Get the host name or IP address of the server with the specified index
 792          * Prefer a readable name if available.
 793          * @param $i
 794          * @return string
 795          */
 796         function getServerName( $i ) {
 797                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 798                         return $this->mServers[$i]['hostName'];
 799                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 800                         return $this->mServers[$i]['host'];
 801                 } else {
 802                         return '';
 803                 }
 804         }
 805
 806         /**
 807          * Return the server info structure for a given index, or false if the index is invalid.
 808          * @param $i
 809          * @return bool
 810          */
 811         function getServerInfo( $i ) {
 812                 if ( isset( $this->mServers[$i] ) ) {
 813                         return $this->mServers[$i];
 814                 } else {
 815                         return false;
 816                 }
 817         }
 818
 819         /**
 820          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 821          * @param $i
 822          * @param $serverInfo
 823          */
 824         function setServerInfo( $i, $serverInfo ) {
 825                 $this->mServers[$i] = $serverInfo;
 826         }
 827
 828         /**
 829          * Get the current master position for chronology control purposes
 830          * @return mixed
 831          */
 832         function getMasterPos() {
 833                 # If this entire request was served from a slave without opening a connection to the
 834                 # master (however unlikely that may be), then we can fetch the position from the slave.
 835                 $masterConn = $this->getAnyOpenConnection( 0 );
 836                 if ( !$masterConn ) {
 837                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 838                                 $conn = $this->getAnyOpenConnection( $i );
 839                                 if ( $conn ) {
 840                                         wfDebug( "Master pos fetched from slave\n" );
 841                                         return $conn->getSlavePos();
 842                                 }
 843                         }
 844                 } else {
 845                         wfDebug( "Master pos fetched from master\n" );
 846                         return $masterConn->getMasterPos();
 847                 }
 848                 return false;
 849         }
 850
 851         /**
 852          * Close all open connections
 853          */
 854         function closeAll() {
 855                 foreach ( $this->mConns as $conns2 ) {
 856                         foreach  ( $conns2 as $conns3 ) {
 857                                 foreach ( $conns3 as $conn ) {
 858                                         $conn->close();
 859                                 }
 860                         }
 861                 }
 862                 $this->mConns = array(
 863                         'local' => array(),
 864                         'foreignFree' => array(),
 865                         'foreignUsed' => array(),
 866                 );
 867         }
 868
 869         /**
 870          * Deprecated function, typo in function name
 871          *
 872          * @deprecated in 1.18
 873          * @param $conn
 874          */
 875         function closeConnecton( $conn ) {
 876                 wfDeprecated( __METHOD__, '1.18' );
 877                 $this->closeConnection( $conn );
 878         }
 879
 880         /**
 881          * Close a connection
 882          * Using this function makes sure the LoadBalancer knows the connection is closed.
 883          * If you use $conn->close() directly, the load balancer won't update its state.
 884          * @param $conn DatabaseBase
 885          */
 886         function closeConnection( $conn ) {
 887                 $done = false;
 888                 foreach ( $this->mConns as $i1 => $conns2 ) {
 889                         foreach ( $conns2 as $i2 => $conns3 ) {
 890                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 891                                         if ( $conn === $candidateConn ) {
 892                                                 $conn->close();
 893                                                 unset( $this->mConns[$i1][$i2][$i3] );
 894                                                 $done = true;
 895                                                 break;
 896                                         }
 897                                 }
 898                         }
 899                 }
 900                 if ( !$done ) {
 901                         $conn->close();
 902                 }
 903         }
 904
 905         /**
 906          * Commit transactions on all open connections
 907          */
 908         function commitAll() {
 909                 foreach ( $this->mConns as $conns2 ) {
 910                         foreach ( $conns2 as $conns3 ) {
 911                                 foreach ( $conns3 as $conn ) {
 912                                         $conn->commit( __METHOD__ );
 913                                 }
 914                         }
 915                 }
 916         }
 917
 918         /**
 919          *  Issue COMMIT only on master, only if queries were done on connection
 920          */
 921         function commitMasterChanges() {
 922                 // Always 0, but who knows.. :)
 923                 $masterIndex = $this->getWriterIndex();
 924                 foreach ( $this->mConns as $conns2 ) {
 925                         if ( empty( $conns2[$masterIndex] ) ) {
 926                                 continue;
 927                         }
 928                         foreach ( $conns2[$masterIndex] as $conn ) {
 929                                 if ( $conn->doneWrites() ) {
 930                                         $conn->commit( __METHOD__ );
 931                                 }
 932                         }
 933                 }
 934         }
 935
 936         /**
 937          * @param $value null
 938          * @return Mixed
 939          */
 940         function waitTimeout( $value = null ) {
 941                 return wfSetVar( $this->mWaitTimeout, $value );
 942         }
 943
 944         /**
 945          * @return bool
 946          */
 947         function getLaggedSlaveMode() {
 948                 return $this->mLaggedSlaveMode;
 949         }
 950
 951         /**
 952          * Disables/enables lag checks
 953          * @param $mode null
 954          * @return bool
 955          */
 956         function allowLagged( $mode = null ) {
 957                 if ( $mode === null) {
 958                         return $this->mAllowLagged;
 959                 }
 960                 $this->mAllowLagged = $mode;
 961         }
 962
 963         /**
 964          * @return bool
 965          */
 966         function pingAll() {
 967                 $success = true;
 968                 foreach ( $this->mConns as $conns2 ) {
 969                         foreach ( $conns2 as $conns3 ) {
 970                                 foreach ( $conns3 as $conn ) {
 971                                         if ( !$conn->ping() ) {
 972                                                 $success = false;
 973                                         }
 974                                 }
 975                         }
 976                 }
 977                 return $success;
 978         }
 979
 980         /**
 981          * Call a function with each open connection object
 982          * @param $callback
 983          * @param array $params
 984          */
 985         function forEachOpenConnection( $callback, $params = array() ) {
 986                 foreach ( $this->mConns as $conns2 ) {
 987                         foreach ( $conns2 as $conns3 ) {
 988                                 foreach ( $conns3 as $conn ) {
 989                                         $mergedParams = array_merge( array( $conn ), $params );
 990                                         call_user_func_array( $callback, $mergedParams );
 991                                 }
 992                         }
 993                 }
 994         }
 995
 996         /**
 997          * Get the hostname and lag time of the most-lagged slave.
 998          * This is useful for maintenance scripts that need to throttle their updates.
 999          * May attempt to open connections to slaves on the default DB. If there is
1000          * no lag, the maximum lag will be reported as -1.
1001          *
1002          * @param $wiki string Wiki ID, or false for the default database
1003          *
1004          * @return array ( host, max lag, index of max lagged host )
1005          */
1006         function getMaxLag( $wiki = false ) {
1007                 $maxLag = -1;
1008                 $host = '';
1009                 $maxIndex = 0;
1010                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1011                         foreach ( $this->mServers as $i => $conn ) {
1012                                 $conn = false;
1013                                 if ( $wiki === false ) {
1014                                         $conn = $this->getAnyOpenConnection( $i );
1015                                 }
1016                                 if ( !$conn ) {
1017                                         $conn = $this->openConnection( $i, $wiki );
1018                                 }
1019                                 if ( !$conn ) {
1020                                         continue;
1021                                 }
1022                                 $lag = $conn->getLag();
1023                                 if ( $lag > $maxLag ) {
1024                                         $maxLag = $lag;
1025                                         $host = $this->mServers[$i]['host'];
1026                                         $maxIndex = $i;
1027                                 }
1028                         }
1029                 }
1030                 return array( $host, $maxLag, $maxIndex );
1031         }
1032
1033         /**
1034          * Get lag time for each server
1035          * Results are cached for a short time in memcached, and indefinitely in the process cache
1036          *
1037          * @param $wiki
1038          *
1039          * @return array
1040          */
1041         function getLagTimes( $wiki = false ) {
1042                 # Try process cache
1043                 if ( isset( $this->mLagTimes ) ) {
1044                         return $this->mLagTimes;
1045                 }
1046                 if ( $this->getServerCount() == 1 ) {
1047                         # No replication
1048                         $this->mLagTimes = array( 0 => 0 );
1049                 } else {
1050                         # Send the request to the load monitor
1051                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1052                                 array_keys( $this->mServers ), $wiki );
1053                 }
1054                 return $this->mLagTimes;
1055         }
1056
1057         /**
1058          * Get the lag in seconds for a given connection, or zero if this load
1059          * balancer does not have replication enabled.
1060          *
1061          * This should be used in preference to Database::getLag() in cases where
1062          * replication may not be in use, since there is no way to determine if
1063          * replication is in use at the connection level without running
1064          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1065          * function instead of Database::getLag() avoids a fatal error in this
1066          * case on many installations.
1067          *
1068          * @param $conn DatabaseBase
1069          *
1070          * @return int
1071          */
1072         function safeGetLag( $conn ) {
1073                 if ( $this->getServerCount() == 1 ) {
1074                         return 0;
1075                 } else {
1076                         return $conn->getLag();
1077                 }
1078         }
1079
1080         /**
1081          * Clear the cache for getLagTimes
1082          */
1083         function clearLagTimeCache() {
1084                 $this->mLagTimes = null;
1085         }
1086 }