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
 105                 return $this->mLoadMonitor;
 106         }
 107
 108         /**
 109          * Get or set arbitrary data used by the parent object, usually an LBFactory
 110          * @param $x
 111          * @return Mixed
 112          */
 113         function parentInfo( $x = null ) {
 114                 return wfSetVar( $this->mParentInfo, $x );
 115         }
 116
 117         /**
 118          * Given an array of non-normalised probabilities, this function will select
 119          * an element and return the appropriate key
 120          *
 121          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 122          *
 123          * @param $weights array
 124          *
 125          * @return bool|int|string
 126          */
 127         function pickRandom( $weights ) {
 128                 return ArrayUtils::pickRandom( $weights );
 129         }
 130
 131         /**
 132          * @param $loads array
 133          * @param $wiki bool
 134          * @return bool|int|string
 135          */
 136         function getRandomNonLagged( $loads, $wiki = false ) {
 137                 # Unset excessively lagged servers
 138                 $lags = $this->getLagTimes( $wiki );
 139                 foreach ( $lags as $i => $lag ) {
 140                         if ( $i != 0 ) {
 141                                 if ( $lag === false ) {
 142                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 143                                         unset( $loads[$i] );
 144                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 145                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 146                                         unset( $loads[$i] );
 147                                 }
 148                         }
 149                 }
 150
 151                 # Find out if all the slaves with non-zero load are lagged
 152                 $sum = 0;
 153                 foreach ( $loads as $load ) {
 154                         $sum += $load;
 155                 }
 156                 if ( $sum == 0 ) {
 157                         # No appropriate DB servers except maybe the master and some slaves with zero load
 158                         # Do NOT use the master
 159                         # Instead, this function will return false, triggering read-only mode,
 160                         # and a lagged slave will be used instead.
 161                         return false;
 162                 }
 163
 164                 if ( count( $loads ) == 0 ) {
 165                         return false;
 166                 }
 167
 168                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 169
 170                 # Return a random representative of the remainder
 171                 return ArrayUtils::pickRandom( $loads );
 172         }
 173
 174         /**
 175          * Get the index of the reader connection, which may be a slave
 176          * This takes into account load ratios and lag times. It should
 177          * always return a consistent index during a given invocation
 178          *
 179          * Side effect: opens connections to databases
 180          * @param $group bool
 181          * @param $wiki bool
 182          * @throws MWException
 183          * @return bool|int|string
 184          */
 185         function getReaderIndex( $group = false, $wiki = false ) {
 186                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 187
 188                 # @todo FIXME: For now, only go through all this for mysql databases
 189                 if ( $wgDBtype != 'mysql' ) {
 190                         return $this->getWriterIndex();
 191                 }
 192
 193                 if ( count( $this->mServers ) == 1 ) {
 194                         # Skip the load balancing if there's only one server
 195                         return 0;
 196                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 197                         # Shortcut if generic reader exists already
 198                         return $this->mReadIndex;
 199                 }
 200
 201                 wfProfileIn( __METHOD__ );
 202
 203                 $totalElapsed = 0;
 204
 205                 # convert from seconds to microseconds
 206                 $timeout = $wgDBClusterTimeout * 1e6;
 207
 208                 # Find the relevant load array
 209                 if ( $group !== false ) {
 210                         if ( isset( $this->mGroupLoads[$group] ) ) {
 211                                 $nonErrorLoads = $this->mGroupLoads[$group];
 212                         } else {
 213                                 # No loads for this group, return false and the caller can use some other group
 214                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 215                                 wfProfileOut( __METHOD__ );
 216
 217                                 return false;
 218                         }
 219                 } else {
 220                         $nonErrorLoads = $this->mLoads;
 221                 }
 222
 223                 if ( !$nonErrorLoads ) {
 224                         wfProfileOut( __METHOD__ );
 225                         throw new MWException( "Empty server array given to LoadBalancer" );
 226                 }
 227
 228                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 229                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 230
 231                 $laggedSlaveMode = false;
 232
 233                 # First try quickly looking through the available servers for a server that
 234                 # meets our criteria
 235                 do {
 236                         $totalThreadsConnected = 0;
 237                         $overloadedServers = 0;
 238                         $currentLoads = $nonErrorLoads;
 239                         while ( count( $currentLoads ) ) {
 240                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 241                                         $i = ArrayUtils::pickRandom( $currentLoads );
 242                                 } else {
 243                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 244                                         if ( $i === false && count( $currentLoads ) != 0 ) {
 245                                                 # All slaves lagged. Switch to read-only mode
 246                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 247                                                 $wgReadOnly = 'The database has been automatically locked ' .
 248                                                         'while the slave database servers catch up to the master';
 249                                                 $i = ArrayUtils::pickRandom( $currentLoads );
 250                                                 $laggedSlaveMode = true;
 251                                         }
 252                                 }
 253
 254                                 if ( $i === false ) {
 255                                         # pickRandom() returned false
 256                                         # This is permanent and means the configuration or the load monitor
 257                                         # wants us to return false.
 258                                         wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 259                                         wfProfileOut( __METHOD__ );
 260
 261                                         return false;
 262                                 }
 263
 264                                 wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 265                                 $conn = $this->openConnection( $i, $wiki );
 266
 267                                 if ( !$conn ) {
 268                                         wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 269                                         unset( $nonErrorLoads[$i] );
 270                                         unset( $currentLoads[$i] );
 271                                         continue;
 272                                 }
 273
 274                                 // Perform post-connection backoff
 275                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 276                                         ? $this->mServers[$i]['max threads'] : false;
 277                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 278
 279                                 // Decrement reference counter, we are finished with this connection.
 280                                 // It will be incremented for the caller later.
 281                                 if ( $wiki !== false ) {
 282                                         $this->reuseConnection( $conn );
 283                                 }
 284
 285                                 if ( $backoff ) {
 286                                         # Post-connection overload, don't use this server for now
 287                                         $totalThreadsConnected += $backoff;
 288                                         $overloadedServers++;
 289                                         unset( $currentLoads[$i] );
 290                                 } else {
 291                                         # Return this server
 292                                         break 2;
 293                                 }
 294                         }
 295
 296                         # No server found yet
 297                         $i = false;
 298
 299                         # If all servers were down, quit now
 300                         if ( !count( $nonErrorLoads ) ) {
 301                                 wfDebugLog( 'connect', "All servers down\n" );
 302                                 break;
 303                         }
 304
 305                         # Some servers must have been overloaded
 306                         if ( $overloadedServers == 0 ) {
 307                                 throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
 308                         }
 309                         # Back off for a while
 310                         # Scale the sleep time by the number of connected threads, to produce a
 311                         # roughly constant global poll rate
 312                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 313                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 314                 } while ( $totalElapsed < $timeout );
 315
 316                 if ( $totalElapsed >= $timeout ) {
 317                         wfDebugLog( 'connect', "All servers busy\n" );
 318                         $this->mErrorConnection = false;
 319                         $this->mLastError = 'All servers busy';
 320                 }
 321
 322                 if ( $i !== false ) {
 323                         # Slave connection successful
 324                         # Wait for the session master pos for a short time
 325                         if ( $this->mWaitForPos && $i > 0 ) {
 326                                 if ( !$this->doWait( $i ) ) {
 327                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 328                                 }
 329                         }
 330                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 331                                 $this->mReadIndex = $i;
 332                         }
 333                 }
 334                 wfProfileOut( __METHOD__ );
 335
 336                 return $i;
 337         }
 338
 339         /**
 340          * Wait for a specified number of microseconds, and return the period waited
 341          * @param $t int
 342          * @return int
 343          */
 344         function sleep( $t ) {
 345                 wfProfileIn( __METHOD__ );
 346                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 347                 usleep( $t );
 348                 wfProfileOut( __METHOD__ );
 349
 350                 return $t;
 351         }
 352
 353         /**
 354          * Set the master wait position
 355          * If a DB_SLAVE connection has been opened already, waits
 356          * Otherwise sets a variable telling it to wait if such a connection is opened
 357          * @param $pos DBMasterPos
 358          */
 359         public function waitFor( $pos ) {
 360                 wfProfileIn( __METHOD__ );
 361                 $this->mWaitForPos = $pos;
 362                 $i = $this->mReadIndex;
 363
 364                 if ( $i > 0 ) {
 365                         if ( !$this->doWait( $i ) ) {
 366                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 367                                 $this->mLaggedSlaveMode = true;
 368                         }
 369                 }
 370                 wfProfileOut( __METHOD__ );
 371         }
 372
 373         /**
 374          * Set the master wait position and wait for ALL slaves to catch up to it
 375          * @param $pos DBMasterPos
 376          */
 377         public function waitForAll( $pos ) {
 378                 wfProfileIn( __METHOD__ );
 379                 $this->mWaitForPos = $pos;
 380                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 381                         if ( $this->mLoads[$i] > 0 ) {
 382                                 $this->doWait( $i, true );
 383                         }
 384                 }
 385                 wfProfileOut( __METHOD__ );
 386         }
 387
 388         /**
 389          * Get any open connection to a given server index, local or foreign
 390          * Returns false if there is no connection open
 391          *
 392          * @param $i int
 393          * @return DatabaseBase|bool False on failure
 394          */
 395         function getAnyOpenConnection( $i ) {
 396                 foreach ( $this->mConns as $conns ) {
 397                         if ( !empty( $conns[$i] ) ) {
 398                                 return reset( $conns[$i] );
 399                         }
 400                 }
 401
 402                 return false;
 403         }
 404
 405         /**
 406          * Wait for a given slave to catch up to the master pos stored in $this
 407          * @param $index
 408          * @param $open bool
 409          * @return bool
 410          */
 411         protected function doWait( $index, $open = false ) {
 412                 # Find a connection to wait on
 413                 $conn = $this->getAnyOpenConnection( $index );
 414                 if ( !$conn ) {
 415                         if ( !$open ) {
 416                                 wfDebug( __METHOD__ . ": no connection open\n" );
 417
 418                                 return false;
 419                         } else {
 420                                 $conn = $this->openConnection( $index, '' );
 421                                 if ( !$conn ) {
 422                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 423
 424                                         return false;
 425                                 }
 426                         }
 427                 }
 428
 429                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 430                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 431
 432                 if ( $result == -1 || is_null( $result ) ) {
 433                         # Timed out waiting for slave, use master instead
 434                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 435
 436                         return false;
 437                 } else {
 438                         wfDebug( __METHOD__ . ": Done\n" );
 439
 440                         return true;
 441                 }
 442         }
 443
 444         /**
 445          * Get a connection by index
 446          * This is the main entry point for this class.
 447          *
 448          * @param $i Integer: server index
 449          * @param array $groups query groups
 450          * @param bool|string $wiki Wiki ID
 451          *
 452          * @throws MWException
 453          * @return DatabaseBase
 454          */
 455         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 456                 wfProfileIn( __METHOD__ );
 457
 458                 if ( $i == DB_LAST ) {
 459                         wfProfileOut( __METHOD__ );
 460                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 461                 } elseif ( $i === null || $i === false ) {
 462                         wfProfileOut( __METHOD__ );
 463                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 464                 }
 465
 466                 if ( $wiki === wfWikiID() ) {
 467                         $wiki = false;
 468                 }
 469
 470                 # Query groups
 471                 if ( $i == DB_MASTER ) {
 472                         $i = $this->getWriterIndex();
 473                 } elseif ( !is_array( $groups ) ) {
 474                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 475                         if ( $groupIndex !== false ) {
 476                                 $serverName = $this->getServerName( $groupIndex );
 477                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 478                                 $i = $groupIndex;
 479                         }
 480                 } else {
 481                         foreach ( $groups as $group ) {
 482                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 483                                 if ( $groupIndex !== false ) {
 484                                         $serverName = $this->getServerName( $groupIndex );
 485                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 486                                         $i = $groupIndex;
 487                                         break;
 488                                 }
 489                         }
 490                 }
 491
 492                 # Operation-based index
 493                 if ( $i == DB_SLAVE ) {
 494                         $this->mLastError = 'Unknown error'; // reset error string
 495                         $i = $this->getReaderIndex( false, $wiki );
 496                         # Couldn't find a working server in getReaderIndex()?
 497                         if ( $i === false ) {
 498                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 499                                 wfProfileOut( __METHOD__ );
 500
 501                                 return $this->reportConnectionError();
 502                         }
 503                 }
 504
 505                 # Now we have an explicit index into the servers array
 506                 $conn = $this->openConnection( $i, $wiki );
 507                 if ( !$conn ) {
 508                         wfProfileOut( __METHOD__ );
 509
 510                         return $this->reportConnectionError();
 511                 }
 512
 513                 wfProfileOut( __METHOD__ );
 514
 515                 return $conn;
 516         }
 517
 518         /**
 519          * Mark a foreign connection as being available for reuse under a different
 520          * DB name or prefix. This mechanism is reference-counted, and must be called
 521          * the same number of times as getConnection() to work.
 522          *
 523          * @param DatabaseBase $conn
 524          * @throws MWException
 525          */
 526         public function reuseConnection( $conn ) {
 527                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 528                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 529                 $dbName = $conn->getDBname();
 530                 $prefix = $conn->tablePrefix();
 531                 if ( strval( $prefix ) !== '' ) {
 532                         $wiki = "$dbName-$prefix";
 533                 } else {
 534                         $wiki = $dbName;
 535                 }
 536                 if ( $serverIndex === null || $refCount === null ) {
 537                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 538
 539                         /**
 540                          * This can happen in code like:
 541                          *   foreach ( $dbs as $db ) {
 542                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 543                          *     ...
 544                          *     $lb->reuseConnection( $conn );
 545                          *   }
 546                          * When a connection to the local DB is opened in this way, reuseConnection()
 547                          * should be ignored
 548                          */
 549
 550                         return;
 551                 }
 552                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 553                         throw new MWException( __METHOD__ . ": connection not found, has the connection been freed already?" );
 554                 }
 555                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 556                 if ( $refCount <= 0 ) {
 557                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 558                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 559                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 560                 } else {
 561                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 562                 }
 563         }
 564
 565         /**
 566          * Get a database connection handle reference
 567          *
 568          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 569          *
 570          * @see LoadBalancer::getConnection() for parameter information
 571          *
 572          * @param integer $db
 573          * @param mixed $groups
 574          * @param string $wiki
 575          * @return DBConnRef
 576          */
 577         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 578                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 579         }
 580
 581         /**
 582          * Get a database connection handle reference without connecting yet
 583          *
 584          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 585          *
 586          * @see LoadBalancer::getConnection() for parameter information
 587          *
 588          * @param integer $db
 589          * @param mixed $groups
 590          * @param string $wiki
 591          * @return DBConnRef
 592          */
 593         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 594                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 595         }
 596
 597         /**
 598          * Open a connection to the server given by the specified index
 599          * Index must be an actual index into the array.
 600          * If the server is already open, returns it.
 601          *
 602          * On error, returns false, and the connection which caused the
 603          * error will be available via $this->mErrorConnection.
 604          *
 605          * @param $i Integer server index
 606          * @param string $wiki wiki ID to open
 607          * @return DatabaseBase
 608          *
 609          * @access private
 610          */
 611         function openConnection( $i, $wiki = false ) {
 612                 wfProfileIn( __METHOD__ );
 613                 if ( $wiki !== false ) {
 614                         $conn = $this->openForeignConnection( $i, $wiki );
 615                         wfProfileOut( __METHOD__ );
 616
 617                         return $conn;
 618                 }
 619                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 620                         $conn = $this->mConns['local'][$i][0];
 621                 } else {
 622                         $server = $this->mServers[$i];
 623                         $server['serverIndex'] = $i;
 624                         $conn = $this->reallyOpenConnection( $server, false );
 625                         if ( $conn->isOpen() ) {
 626                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 627                                 $this->mConns['local'][$i][0] = $conn;
 628                         } else {
 629                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 630                                 $this->mErrorConnection = $conn;
 631                                 $conn = false;
 632                         }
 633                 }
 634                 wfProfileOut( __METHOD__ );
 635
 636                 return $conn;
 637         }
 638
 639         /**
 640          * Open a connection to a foreign DB, or return one if it is already open.
 641          *
 642          * Increments a reference count on the returned connection which locks the
 643          * connection to the requested wiki. This reference count can be
 644          * decremented by calling reuseConnection().
 645          *
 646          * If a connection is open to the appropriate server already, but with the wrong
 647          * database, it will be switched to the right database and returned, as long as
 648          * it has been freed first with reuseConnection().
 649          *
 650          * On error, returns false, and the connection which caused the
 651          * error will be available via $this->mErrorConnection.
 652          *
 653          * @param $i Integer: server index
 654          * @param string $wiki wiki ID to open
 655          * @return DatabaseBase
 656          */
 657         function openForeignConnection( $i, $wiki ) {
 658                 wfProfileIn( __METHOD__ );
 659                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 660                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 661                         // Reuse an already-used connection
 662                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 663                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 664                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 665                         // Reuse a free connection for the same wiki
 666                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 667                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 668                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 669                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 670                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 671                         // Reuse a connection from another wiki
 672                         $conn = reset( $this->mConns['foreignFree'][$i] );
 673                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 674
 675                         if ( !$conn->selectDB( $dbName ) ) {
 676                                 $this->mLastError = "Error selecting database $dbName on server " .
 677                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 678                                 $this->mErrorConnection = $conn;
 679                                 $conn = false;
 680                         } else {
 681                                 $conn->tablePrefix( $prefix );
 682                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 683                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 684                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 685                         }
 686                 } else {
 687                         // Open a new connection
 688                         $server = $this->mServers[$i];
 689                         $server['serverIndex'] = $i;
 690                         $server['foreignPoolRefCount'] = 0;
 691                         $server['foreign'] = true;
 692                         $conn = $this->reallyOpenConnection( $server, $dbName );
 693                         if ( !$conn->isOpen() ) {
 694                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 695                                 $this->mErrorConnection = $conn;
 696                                 $conn = false;
 697                         } else {
 698                                 $conn->tablePrefix( $prefix );
 699                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 700                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 701                         }
 702                 }
 703
 704                 // Increment reference count
 705                 if ( $conn ) {
 706                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 707                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 708                 }
 709                 wfProfileOut( __METHOD__ );
 710
 711                 return $conn;
 712         }
 713
 714         /**
 715          * Test if the specified index represents an open connection
 716          *
 717          * @param $index Integer: server index
 718          * @access private
 719          * @return bool
 720          */
 721         function isOpen( $index ) {
 722                 if ( !is_integer( $index ) ) {
 723                         return false;
 724                 }
 725
 726                 return (bool)$this->getAnyOpenConnection( $index );
 727         }
 728
 729         /**
 730          * Really opens a connection. Uncached.
 731          * Returns a Database object whether or not the connection was successful.
 732          * @access private
 733          *
 734          * @param $server
 735          * @param $dbNameOverride bool
 736          * @throws MWException
 737          * @return DatabaseBase
 738          */
 739         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 740                 if ( !is_array( $server ) ) {
 741                         throw new MWException( 'You must update your load-balancing configuration. ' .
 742                                 'See DefaultSettings.php entry for $wgDBservers.' );
 743                 }
 744
 745                 if ( $dbNameOverride !== false ) {
 746                         $server['dbname'] = $dbNameOverride;
 747                 }
 748
 749                 # Create object
 750                 try {
 751                         $db = DatabaseBase::factory( $server['type'], $server );
 752                 } catch ( DBConnectionError $e ) {
 753                         // FIXME: This is probably the ugliest thing I have ever done to
 754                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 755                         $db = $e->db;
 756                 }
 757
 758                 $db->setLBInfo( $server );
 759                 if ( isset( $server['fakeSlaveLag'] ) ) {
 760                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 761                 }
 762                 if ( isset( $server['fakeMaster'] ) ) {
 763                         $db->setFakeMaster( true );
 764                 }
 765
 766                 return $db;
 767         }
 768
 769         /**
 770          * @throws DBConnectionError
 771          * @return bool
 772          */
 773         private function reportConnectionError() {
 774                 $conn = $this->mErrorConnection; // The connection which caused the error
 775
 776                 if ( !is_object( $conn ) ) {
 777                         // No last connection, probably due to all servers being too busy
 778                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 779
 780                         // If all servers were busy, mLastError will contain something sensible
 781                         throw new DBConnectionError( null, $this->mLastError );
 782                 } else {
 783                         $server = $conn->getProperty( 'mServer' );
 784                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 785                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 786                 }
 787
 788                 return false; /* not reached */
 789         }
 790
 791         /**
 792          * @return int
 793          */
 794         function getWriterIndex() {
 795                 return 0;
 796         }
 797
 798         /**
 799          * Returns true if the specified index is a valid server index
 800          *
 801          * @param $i
 802          * @return bool
 803          */
 804         function haveIndex( $i ) {
 805                 return array_key_exists( $i, $this->mServers );
 806         }
 807
 808         /**
 809          * Returns true if the specified index is valid and has non-zero load
 810          *
 811          * @param $i
 812          * @return bool
 813          */
 814         function isNonZeroLoad( $i ) {
 815                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 816         }
 817
 818         /**
 819          * Get the number of defined servers (not the number of open connections)
 820          *
 821          * @return int
 822          */
 823         function getServerCount() {
 824                 return count( $this->mServers );
 825         }
 826
 827         /**
 828          * Get the host name or IP address of the server with the specified index
 829          * Prefer a readable name if available.
 830          * @param $i
 831          * @return string
 832          */
 833         function getServerName( $i ) {
 834                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 835                         return $this->mServers[$i]['hostName'];
 836                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 837                         return $this->mServers[$i]['host'];
 838                 } else {
 839                         return '';
 840                 }
 841         }
 842
 843         /**
 844          * Return the server info structure for a given index, or false if the index is invalid.
 845          * @param $i
 846          * @return bool
 847          */
 848         function getServerInfo( $i ) {
 849                 if ( isset( $this->mServers[$i] ) ) {
 850                         return $this->mServers[$i];
 851                 } else {
 852                         return false;
 853                 }
 854         }
 855
 856         /**
 857          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 858          * @param $i
 859          * @param $serverInfo
 860          */
 861         function setServerInfo( $i, $serverInfo ) {
 862                 $this->mServers[$i] = $serverInfo;
 863         }
 864
 865         /**
 866          * Get the current master position for chronology control purposes
 867          * @return mixed
 868          */
 869         function getMasterPos() {
 870                 # If this entire request was served from a slave without opening a connection to the
 871                 # master (however unlikely that may be), then we can fetch the position from the slave.
 872                 $masterConn = $this->getAnyOpenConnection( 0 );
 873                 if ( !$masterConn ) {
 874                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 875                                 $conn = $this->getAnyOpenConnection( $i );
 876                                 if ( $conn ) {
 877                                         wfDebug( "Master pos fetched from slave\n" );
 878
 879                                         return $conn->getSlavePos();
 880                                 }
 881                         }
 882                 } else {
 883                         wfDebug( "Master pos fetched from master\n" );
 884
 885                         return $masterConn->getMasterPos();
 886                 }
 887
 888                 return false;
 889         }
 890
 891         /**
 892          * Close all open connections
 893          */
 894         function closeAll() {
 895                 foreach ( $this->mConns as $conns2 ) {
 896                         foreach ( $conns2 as $conns3 ) {
 897                                 foreach ( $conns3 as $conn ) {
 898                                         $conn->close();
 899                                 }
 900                         }
 901                 }
 902                 $this->mConns = array(
 903                         'local' => array(),
 904                         'foreignFree' => array(),
 905                         'foreignUsed' => array(),
 906                 );
 907         }
 908
 909         /**
 910          * Deprecated function, typo in function name
 911          *
 912          * @deprecated in 1.18
 913          * @param $conn
 914          */
 915         function closeConnecton( $conn ) {
 916                 wfDeprecated( __METHOD__, '1.18' );
 917                 $this->closeConnection( $conn );
 918         }
 919
 920         /**
 921          * Close a connection
 922          * Using this function makes sure the LoadBalancer knows the connection is closed.
 923          * If you use $conn->close() directly, the load balancer won't update its state.
 924          * @param $conn DatabaseBase
 925          */
 926         function closeConnection( $conn ) {
 927                 $done = false;
 928                 foreach ( $this->mConns as $i1 => $conns2 ) {
 929                         foreach ( $conns2 as $i2 => $conns3 ) {
 930                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 931                                         if ( $conn === $candidateConn ) {
 932                                                 $conn->close();
 933                                                 unset( $this->mConns[$i1][$i2][$i3] );
 934                                                 $done = true;
 935                                                 break;
 936                                         }
 937                                 }
 938                         }
 939                 }
 940                 if ( !$done ) {
 941                         $conn->close();
 942                 }
 943         }
 944
 945         /**
 946          * Commit transactions on all open connections
 947          */
 948         function commitAll() {
 949                 foreach ( $this->mConns as $conns2 ) {
 950                         foreach ( $conns2 as $conns3 ) {
 951                                 foreach ( $conns3 as $conn ) {
 952                                         if ( $conn->trxLevel() ) {
 953                                                 $conn->commit( __METHOD__, 'flush' );
 954                                         }
 955                                 }
 956                         }
 957                 }
 958         }
 959
 960         /**
 961          *  Issue COMMIT only on master, only if queries were done on connection
 962          */
 963         function commitMasterChanges() {
 964                 // Always 0, but who knows.. :)
 965                 $masterIndex = $this->getWriterIndex();
 966                 foreach ( $this->mConns as $conns2 ) {
 967                         if ( empty( $conns2[$masterIndex] ) ) {
 968                                 continue;
 969                         }
 970                         foreach ( $conns2[$masterIndex] as $conn ) {
 971                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 972                                         $conn->commit( __METHOD__, 'flush' );
 973                                 }
 974                         }
 975                 }
 976         }
 977
 978         /**
 979          * @param $value null
 980          * @return Mixed
 981          */
 982         function waitTimeout( $value = null ) {
 983                 return wfSetVar( $this->mWaitTimeout, $value );
 984         }
 985
 986         /**
 987          * @return bool
 988          */
 989         function getLaggedSlaveMode() {
 990                 return $this->mLaggedSlaveMode;
 991         }
 992
 993         /**
 994          * Disables/enables lag checks
 995          * @param $mode null
 996          * @return bool
 997          */
 998         function allowLagged( $mode = null ) {
 999                 if ( $mode === null ) {
1000                         return $this->mAllowLagged;
1001                 }
1002                 $this->mAllowLagged = $mode;
1003
1004                 return $this->mAllowLagged;
1005         }
1006
1007         /**
1008          * @return bool
1009          */
1010         function pingAll() {
1011                 $success = true;
1012                 foreach ( $this->mConns as $conns2 ) {
1013                         foreach ( $conns2 as $conns3 ) {
1014                                 foreach ( $conns3 as $conn ) {
1015                                         if ( !$conn->ping() ) {
1016                                                 $success = false;
1017                                         }
1018                                 }
1019                         }
1020                 }
1021
1022                 return $success;
1023         }
1024
1025         /**
1026          * Call a function with each open connection object
1027          * @param $callback
1028          * @param array $params
1029          */
1030         function forEachOpenConnection( $callback, $params = array() ) {
1031                 foreach ( $this->mConns as $conns2 ) {
1032                         foreach ( $conns2 as $conns3 ) {
1033                                 foreach ( $conns3 as $conn ) {
1034                                         $mergedParams = array_merge( array( $conn ), $params );
1035                                         call_user_func_array( $callback, $mergedParams );
1036                                 }
1037                         }
1038                 }
1039         }
1040
1041         /**
1042          * Get the hostname and lag time of the most-lagged slave.
1043          * This is useful for maintenance scripts that need to throttle their updates.
1044          * May attempt to open connections to slaves on the default DB. If there is
1045          * no lag, the maximum lag will be reported as -1.
1046          *
1047          * @param string $wiki Wiki ID, or false for the default database
1048          *
1049          * @return array ( host, max lag, index of max lagged host )
1050          */
1051         function getMaxLag( $wiki = false ) {
1052                 $maxLag = -1;
1053                 $host = '';
1054                 $maxIndex = 0;
1055                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1056                         foreach ( $this->mServers as $i => $conn ) {
1057                                 $conn = false;
1058                                 if ( $wiki === false ) {
1059                                         $conn = $this->getAnyOpenConnection( $i );
1060                                 }
1061                                 if ( !$conn ) {
1062                                         $conn = $this->openConnection( $i, $wiki );
1063                                 }
1064                                 if ( !$conn ) {
1065                                         continue;
1066                                 }
1067                                 $lag = $conn->getLag();
1068                                 if ( $lag > $maxLag ) {
1069                                         $maxLag = $lag;
1070                                         $host = $this->mServers[$i]['host'];
1071                                         $maxIndex = $i;
1072                                 }
1073                         }
1074                 }
1075
1076                 return array( $host, $maxLag, $maxIndex );
1077         }
1078
1079         /**
1080          * Get lag time for each server
1081          * Results are cached for a short time in memcached, and indefinitely in the process cache
1082          *
1083          * @param $wiki
1084          *
1085          * @return array
1086          */
1087         function getLagTimes( $wiki = false ) {
1088                 # Try process cache
1089                 if ( isset( $this->mLagTimes ) ) {
1090                         return $this->mLagTimes;
1091                 }
1092                 if ( $this->getServerCount() == 1 ) {
1093                         # No replication
1094                         $this->mLagTimes = array( 0 => 0 );
1095                 } else {
1096                         # Send the request to the load monitor
1097                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1098                                 array_keys( $this->mServers ), $wiki );
1099                 }
1100
1101                 return $this->mLagTimes;
1102         }
1103
1104         /**
1105          * Get the lag in seconds for a given connection, or zero if this load
1106          * balancer does not have replication enabled.
1107          *
1108          * This should be used in preference to Database::getLag() in cases where
1109          * replication may not be in use, since there is no way to determine if
1110          * replication is in use at the connection level without running
1111          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1112          * function instead of Database::getLag() avoids a fatal error in this
1113          * case on many installations.
1114          *
1115          * @param $conn DatabaseBase
1116          *
1117          * @return int
1118          */
1119         function safeGetLag( $conn ) {
1120                 if ( $this->getServerCount() == 1 ) {
1121                         return 0;
1122                 } else {
1123                         return $conn->getLag();
1124                 }
1125         }
1126
1127         /**
1128          * Clear the cache for getLagTimes
1129          */
1130         function clearLagTimeCache() {
1131                 $this->mLagTimes = null;
1132         }
1133 }
1134
1135 /**
1136  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1137  * as well handling deferring the actual network connection until the handle is used
1138  *
1139  * @ingroup Database
1140  * @since 1.22
1141  */
1142 class DBConnRef implements IDatabase {
1143         /** @var LoadBalancer */
1144         protected $lb;
1145         /** @var DatabaseBase|null */
1146         protected $conn;
1147         /** @var Array|null */
1148         protected $params;
1149
1150         /**
1151          * @param $lb LoadBalancer
1152          * @param $conn DatabaseBase|array Connection or (server index, group, wiki ID) array
1153          */
1154         public function __construct( LoadBalancer $lb, $conn ) {
1155                 $this->lb = $lb;
1156                 if ( $conn instanceof DatabaseBase ) {
1157                         $this->conn = $conn;
1158                 } else {
1159                         $this->params = $conn;
1160                 }
1161         }
1162
1163         public function __call( $name, $arguments ) {
1164                 if ( $this->conn === null ) {
1165                         list( $db, $groups, $wiki ) = $this->params;
1166                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1167                 }
1168
1169                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1170         }
1171
1172         function __destruct() {
1173                 if ( $this->conn !== null ) {
1174                         $this->lb->reuseConnection( $this->conn );
1175                 }
1176         }
1177 }