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                 $serverCount = count( $this->mServers );
 381                 for ( $i = 1; $i < $serverCount; $i++ ) {
 382                         if ( $this->mLoads[$i] > 0 ) {
 383                                 $this->doWait( $i, true );
 384                         }
 385                 }
 386                 wfProfileOut( __METHOD__ );
 387         }
 388
 389         /**
 390          * Get any open connection to a given server index, local or foreign
 391          * Returns false if there is no connection open
 392          *
 393          * @param $i int
 394          * @return DatabaseBase|bool False on failure
 395          */
 396         function getAnyOpenConnection( $i ) {
 397                 foreach ( $this->mConns as $conns ) {
 398                         if ( !empty( $conns[$i] ) ) {
 399                                 return reset( $conns[$i] );
 400                         }
 401                 }
 402
 403                 return false;
 404         }
 405
 406         /**
 407          * Wait for a given slave to catch up to the master pos stored in $this
 408          * @param $index
 409          * @param $open bool
 410          * @return bool
 411          */
 412         protected function doWait( $index, $open = false ) {
 413                 # Find a connection to wait on
 414                 $conn = $this->getAnyOpenConnection( $index );
 415                 if ( !$conn ) {
 416                         if ( !$open ) {
 417                                 wfDebug( __METHOD__ . ": no connection open\n" );
 418
 419                                 return false;
 420                         } else {
 421                                 $conn = $this->openConnection( $index, '' );
 422                                 if ( !$conn ) {
 423                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 424
 425                                         return false;
 426                                 }
 427                         }
 428                 }
 429
 430                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 431                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 432
 433                 if ( $result == -1 || is_null( $result ) ) {
 434                         # Timed out waiting for slave, use master instead
 435                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 436
 437                         return false;
 438                 } else {
 439                         wfDebug( __METHOD__ . ": Done\n" );
 440
 441                         return true;
 442                 }
 443         }
 444
 445         /**
 446          * Get a connection by index
 447          * This is the main entry point for this class.
 448          *
 449          * @param $i Integer: server index
 450          * @param array $groups query groups
 451          * @param bool|string $wiki Wiki ID
 452          *
 453          * @throws MWException
 454          * @return DatabaseBase
 455          */
 456         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 457                 wfProfileIn( __METHOD__ );
 458
 459                 if ( $i == DB_LAST ) {
 460                         wfProfileOut( __METHOD__ );
 461                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 462                                 ' with deprecated server index DB_LAST' );
 463                 } elseif ( $i === null || $i === false ) {
 464                         wfProfileOut( __METHOD__ );
 465                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 466                                 ' with invalid server index' );
 467                 }
 468
 469                 if ( $wiki === wfWikiID() ) {
 470                         $wiki = false;
 471                 }
 472
 473                 # Query groups
 474                 if ( $i == DB_MASTER ) {
 475                         $i = $this->getWriterIndex();
 476                 } elseif ( !is_array( $groups ) ) {
 477                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 478                         if ( $groupIndex !== false ) {
 479                                 $serverName = $this->getServerName( $groupIndex );
 480                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 481                                 $i = $groupIndex;
 482                         }
 483                 } else {
 484                         foreach ( $groups as $group ) {
 485                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 486                                 if ( $groupIndex !== false ) {
 487                                         $serverName = $this->getServerName( $groupIndex );
 488                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 489                                         $i = $groupIndex;
 490                                         break;
 491                                 }
 492                         }
 493                 }
 494
 495                 # Operation-based index
 496                 if ( $i == DB_SLAVE ) {
 497                         $this->mLastError = 'Unknown error'; // reset error string
 498                         $i = $this->getReaderIndex( false, $wiki );
 499                         # Couldn't find a working server in getReaderIndex()?
 500                         if ( $i === false ) {
 501                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 502                                 wfProfileOut( __METHOD__ );
 503
 504                                 return $this->reportConnectionError();
 505                         }
 506                 }
 507
 508                 # Now we have an explicit index into the servers array
 509                 $conn = $this->openConnection( $i, $wiki );
 510                 if ( !$conn ) {
 511                         wfProfileOut( __METHOD__ );
 512
 513                         return $this->reportConnectionError();
 514                 }
 515
 516                 wfProfileOut( __METHOD__ );
 517
 518                 return $conn;
 519         }
 520
 521         /**
 522          * Mark a foreign connection as being available for reuse under a different
 523          * DB name or prefix. This mechanism is reference-counted, and must be called
 524          * the same number of times as getConnection() to work.
 525          *
 526          * @param DatabaseBase $conn
 527          * @throws MWException
 528          */
 529         public function reuseConnection( $conn ) {
 530                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 531                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 532                 $dbName = $conn->getDBname();
 533                 $prefix = $conn->tablePrefix();
 534                 if ( strval( $prefix ) !== '' ) {
 535                         $wiki = "$dbName-$prefix";
 536                 } else {
 537                         $wiki = $dbName;
 538                 }
 539                 if ( $serverIndex === null || $refCount === null ) {
 540                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 541
 542                         /**
 543                          * This can happen in code like:
 544                          *   foreach ( $dbs as $db ) {
 545                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 546                          *     ...
 547                          *     $lb->reuseConnection( $conn );
 548                          *   }
 549                          * When a connection to the local DB is opened in this way, reuseConnection()
 550                          * should be ignored
 551                          */
 552
 553                         return;
 554                 }
 555                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 556                         throw new MWException( __METHOD__ . ": connection not found, has " .
 557                                 "the connection been freed already?" );
 558                 }
 559                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 560                 if ( $refCount <= 0 ) {
 561                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 562                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 563                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 564                 } else {
 565                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 566                 }
 567         }
 568
 569         /**
 570          * Get a database connection handle reference
 571          *
 572          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 573          *
 574          * @see LoadBalancer::getConnection() for parameter information
 575          *
 576          * @param integer $db
 577          * @param mixed $groups
 578          * @param string $wiki
 579          * @return DBConnRef
 580          */
 581         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 582                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 583         }
 584
 585         /**
 586          * Get a database connection handle reference without connecting yet
 587          *
 588          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 589          *
 590          * @see LoadBalancer::getConnection() for parameter information
 591          *
 592          * @param integer $db
 593          * @param mixed $groups
 594          * @param string $wiki
 595          * @return DBConnRef
 596          */
 597         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 598                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 599         }
 600
 601         /**
 602          * Open a connection to the server given by the specified index
 603          * Index must be an actual index into the array.
 604          * If the server is already open, returns it.
 605          *
 606          * On error, returns false, and the connection which caused the
 607          * error will be available via $this->mErrorConnection.
 608          *
 609          * @param $i Integer server index
 610          * @param string $wiki wiki ID to open
 611          * @return DatabaseBase
 612          *
 613          * @access private
 614          */
 615         function openConnection( $i, $wiki = false ) {
 616                 wfProfileIn( __METHOD__ );
 617                 if ( $wiki !== false ) {
 618                         $conn = $this->openForeignConnection( $i, $wiki );
 619                         wfProfileOut( __METHOD__ );
 620
 621                         return $conn;
 622                 }
 623                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 624                         $conn = $this->mConns['local'][$i][0];
 625                 } else {
 626                         $server = $this->mServers[$i];
 627                         $server['serverIndex'] = $i;
 628                         $conn = $this->reallyOpenConnection( $server, false );
 629                         if ( $conn->isOpen() ) {
 630                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 631                                 $this->mConns['local'][$i][0] = $conn;
 632                         } else {
 633                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 634                                 $this->mErrorConnection = $conn;
 635                                 $conn = false;
 636                         }
 637                 }
 638                 wfProfileOut( __METHOD__ );
 639
 640                 return $conn;
 641         }
 642
 643         /**
 644          * Open a connection to a foreign DB, or return one if it is already open.
 645          *
 646          * Increments a reference count on the returned connection which locks the
 647          * connection to the requested wiki. This reference count can be
 648          * decremented by calling reuseConnection().
 649          *
 650          * If a connection is open to the appropriate server already, but with the wrong
 651          * database, it will be switched to the right database and returned, as long as
 652          * it has been freed first with reuseConnection().
 653          *
 654          * On error, returns false, and the connection which caused the
 655          * error will be available via $this->mErrorConnection.
 656          *
 657          * @param $i Integer: server index
 658          * @param string $wiki wiki ID to open
 659          * @return DatabaseBase
 660          */
 661         function openForeignConnection( $i, $wiki ) {
 662                 wfProfileIn( __METHOD__ );
 663                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 664                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 665                         // Reuse an already-used connection
 666                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 667                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 668                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 669                         // Reuse a free connection for the same wiki
 670                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 671                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 672                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 673                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 674                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 675                         // Reuse a connection from another wiki
 676                         $conn = reset( $this->mConns['foreignFree'][$i] );
 677                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 678
 679                         if ( !$conn->selectDB( $dbName ) ) {
 680                                 $this->mLastError = "Error selecting database $dbName on server " .
 681                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 682                                 $this->mErrorConnection = $conn;
 683                                 $conn = false;
 684                         } else {
 685                                 $conn->tablePrefix( $prefix );
 686                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 687                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 688                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 689                         }
 690                 } else {
 691                         // Open a new connection
 692                         $server = $this->mServers[$i];
 693                         $server['serverIndex'] = $i;
 694                         $server['foreignPoolRefCount'] = 0;
 695                         $server['foreign'] = true;
 696                         $conn = $this->reallyOpenConnection( $server, $dbName );
 697                         if ( !$conn->isOpen() ) {
 698                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 699                                 $this->mErrorConnection = $conn;
 700                                 $conn = false;
 701                         } else {
 702                                 $conn->tablePrefix( $prefix );
 703                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 704                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 705                         }
 706                 }
 707
 708                 // Increment reference count
 709                 if ( $conn ) {
 710                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 711                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 712                 }
 713                 wfProfileOut( __METHOD__ );
 714
 715                 return $conn;
 716         }
 717
 718         /**
 719          * Test if the specified index represents an open connection
 720          *
 721          * @param $index Integer: server index
 722          * @access private
 723          * @return bool
 724          */
 725         function isOpen( $index ) {
 726                 if ( !is_integer( $index ) ) {
 727                         return false;
 728                 }
 729
 730                 return (bool)$this->getAnyOpenConnection( $index );
 731         }
 732
 733         /**
 734          * Really opens a connection. Uncached.
 735          * Returns a Database object whether or not the connection was successful.
 736          * @access private
 737          *
 738          * @param $server
 739          * @param $dbNameOverride bool
 740          * @throws MWException
 741          * @return DatabaseBase
 742          */
 743         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 744                 if ( !is_array( $server ) ) {
 745                         throw new MWException( 'You must update your load-balancing configuration. ' .
 746                                 'See DefaultSettings.php entry for $wgDBservers.' );
 747                 }
 748
 749                 if ( $dbNameOverride !== false ) {
 750                         $server['dbname'] = $dbNameOverride;
 751                 }
 752
 753                 # Create object
 754                 try {
 755                         $db = DatabaseBase::factory( $server['type'], $server );
 756                 } catch ( DBConnectionError $e ) {
 757                         // FIXME: This is probably the ugliest thing I have ever done to
 758                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 759                         $db = $e->db;
 760                 }
 761
 762                 $db->setLBInfo( $server );
 763                 if ( isset( $server['fakeSlaveLag'] ) ) {
 764                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 765                 }
 766                 if ( isset( $server['fakeMaster'] ) ) {
 767                         $db->setFakeMaster( true );
 768                 }
 769
 770                 return $db;
 771         }
 772
 773         /**
 774          * @throws DBConnectionError
 775          * @return bool
 776          */
 777         private function reportConnectionError() {
 778                 $conn = $this->mErrorConnection; // The connection which caused the error
 779
 780                 if ( !is_object( $conn ) ) {
 781                         // No last connection, probably due to all servers being too busy
 782                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 783
 784                         // If all servers were busy, mLastError will contain something sensible
 785                         throw new DBConnectionError( null, $this->mLastError );
 786                 } else {
 787                         $server = $conn->getProperty( 'mServer' );
 788                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 789                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 790                 }
 791
 792                 return false; /* not reached */
 793         }
 794
 795         /**
 796          * @return int
 797          */
 798         function getWriterIndex() {
 799                 return 0;
 800         }
 801
 802         /**
 803          * Returns true if the specified index is a valid server index
 804          *
 805          * @param $i
 806          * @return bool
 807          */
 808         function haveIndex( $i ) {
 809                 return array_key_exists( $i, $this->mServers );
 810         }
 811
 812         /**
 813          * Returns true if the specified index is valid and has non-zero load
 814          *
 815          * @param $i
 816          * @return bool
 817          */
 818         function isNonZeroLoad( $i ) {
 819                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 820         }
 821
 822         /**
 823          * Get the number of defined servers (not the number of open connections)
 824          *
 825          * @return int
 826          */
 827         function getServerCount() {
 828                 return count( $this->mServers );
 829         }
 830
 831         /**
 832          * Get the host name or IP address of the server with the specified index
 833          * Prefer a readable name if available.
 834          * @param $i
 835          * @return string
 836          */
 837         function getServerName( $i ) {
 838                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 839                         return $this->mServers[$i]['hostName'];
 840                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 841                         return $this->mServers[$i]['host'];
 842                 } else {
 843                         return '';
 844                 }
 845         }
 846
 847         /**
 848          * Return the server info structure for a given index, or false if the index is invalid.
 849          * @param $i
 850          * @return bool
 851          */
 852         function getServerInfo( $i ) {
 853                 if ( isset( $this->mServers[$i] ) ) {
 854                         return $this->mServers[$i];
 855                 } else {
 856                         return false;
 857                 }
 858         }
 859
 860         /**
 861          * Sets the server info structure for the given index. Entry at index $i
 862          * is created if it doesn't exist
 863          * @param $i
 864          * @param $serverInfo
 865          */
 866         function setServerInfo( $i, $serverInfo ) {
 867                 $this->mServers[$i] = $serverInfo;
 868         }
 869
 870         /**
 871          * Get the current master position for chronology control purposes
 872          * @return mixed
 873          */
 874         function getMasterPos() {
 875                 # If this entire request was served from a slave without opening a connection to the
 876                 # master (however unlikely that may be), then we can fetch the position from the slave.
 877                 $masterConn = $this->getAnyOpenConnection( 0 );
 878                 if ( !$masterConn ) {
 879                         $serverCount = count( $this->mServers );
 880                         for ( $i = 1; $i < $serverCount; $i++ ) {
 881                                 $conn = $this->getAnyOpenConnection( $i );
 882                                 if ( $conn ) {
 883                                         wfDebug( "Master pos fetched from slave\n" );
 884
 885                                         return $conn->getSlavePos();
 886                                 }
 887                         }
 888                 } else {
 889                         wfDebug( "Master pos fetched from master\n" );
 890
 891                         return $masterConn->getMasterPos();
 892                 }
 893
 894                 return false;
 895         }
 896
 897         /**
 898          * Close all open connections
 899          */
 900         function closeAll() {
 901                 foreach ( $this->mConns as $conns2 ) {
 902                         foreach ( $conns2 as $conns3 ) {
 903                                 foreach ( $conns3 as $conn ) {
 904                                         $conn->close();
 905                                 }
 906                         }
 907                 }
 908                 $this->mConns = array(
 909                         'local' => array(),
 910                         'foreignFree' => array(),
 911                         'foreignUsed' => array(),
 912                 );
 913         }
 914
 915         /**
 916          * Deprecated function, typo in function name
 917          *
 918          * @deprecated in 1.18
 919          * @param $conn
 920          */
 921         function closeConnecton( $conn ) {
 922                 wfDeprecated( __METHOD__, '1.18' );
 923                 $this->closeConnection( $conn );
 924         }
 925
 926         /**
 927          * Close a connection
 928          * Using this function makes sure the LoadBalancer knows the connection is closed.
 929          * If you use $conn->close() directly, the load balancer won't update its state.
 930          * @param $conn DatabaseBase
 931          */
 932         function closeConnection( $conn ) {
 933                 $done = false;
 934                 foreach ( $this->mConns as $i1 => $conns2 ) {
 935                         foreach ( $conns2 as $i2 => $conns3 ) {
 936                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 937                                         if ( $conn === $candidateConn ) {
 938                                                 $conn->close();
 939                                                 unset( $this->mConns[$i1][$i2][$i3] );
 940                                                 $done = true;
 941                                                 break;
 942                                         }
 943                                 }
 944                         }
 945                 }
 946                 if ( !$done ) {
 947                         $conn->close();
 948                 }
 949         }
 950
 951         /**
 952          * Commit transactions on all open connections
 953          */
 954         function commitAll() {
 955                 foreach ( $this->mConns as $conns2 ) {
 956                         foreach ( $conns2 as $conns3 ) {
 957                                 foreach ( $conns3 as $conn ) {
 958                                         if ( $conn->trxLevel() ) {
 959                                                 $conn->commit( __METHOD__, 'flush' );
 960                                         }
 961                                 }
 962                         }
 963                 }
 964         }
 965
 966         /**
 967          *  Issue COMMIT only on master, only if queries were done on connection
 968          */
 969         function commitMasterChanges() {
 970                 // Always 0, but who knows.. :)
 971                 $masterIndex = $this->getWriterIndex();
 972                 foreach ( $this->mConns as $conns2 ) {
 973                         if ( empty( $conns2[$masterIndex] ) ) {
 974                                 continue;
 975                         }
 976                         foreach ( $conns2[$masterIndex] as $conn ) {
 977                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 978                                         $conn->commit( __METHOD__, 'flush' );
 979                                 }
 980                         }
 981                 }
 982         }
 983
 984         /**
 985          * @param $value null
 986          * @return Mixed
 987          */
 988         function waitTimeout( $value = null ) {
 989                 return wfSetVar( $this->mWaitTimeout, $value );
 990         }
 991
 992         /**
 993          * @return bool
 994          */
 995         function getLaggedSlaveMode() {
 996                 return $this->mLaggedSlaveMode;
 997         }
 998
 999         /**
1000          * Disables/enables lag checks
1001          * @param $mode null
1002          * @return bool
1003          */
1004         function allowLagged( $mode = null ) {
1005                 if ( $mode === null ) {
1006                         return $this->mAllowLagged;
1007                 }
1008                 $this->mAllowLagged = $mode;
1009
1010                 return $this->mAllowLagged;
1011         }
1012
1013         /**
1014          * @return bool
1015          */
1016         function pingAll() {
1017                 $success = true;
1018                 foreach ( $this->mConns as $conns2 ) {
1019                         foreach ( $conns2 as $conns3 ) {
1020                                 foreach ( $conns3 as $conn ) {
1021                                         if ( !$conn->ping() ) {
1022                                                 $success = false;
1023                                         }
1024                                 }
1025                         }
1026                 }
1027
1028                 return $success;
1029         }
1030
1031         /**
1032          * Call a function with each open connection object
1033          * @param $callback
1034          * @param array $params
1035          */
1036         function forEachOpenConnection( $callback, $params = array() ) {
1037                 foreach ( $this->mConns as $conns2 ) {
1038                         foreach ( $conns2 as $conns3 ) {
1039                                 foreach ( $conns3 as $conn ) {
1040                                         $mergedParams = array_merge( array( $conn ), $params );
1041                                         call_user_func_array( $callback, $mergedParams );
1042                                 }
1043                         }
1044                 }
1045         }
1046
1047         /**
1048          * Get the hostname and lag time of the most-lagged slave.
1049          * This is useful for maintenance scripts that need to throttle their updates.
1050          * May attempt to open connections to slaves on the default DB. If there is
1051          * no lag, the maximum lag will be reported as -1.
1052          *
1053          * @param string $wiki Wiki ID, or false for the default database
1054          *
1055          * @return array ( host, max lag, index of max lagged host )
1056          */
1057         function getMaxLag( $wiki = false ) {
1058                 $maxLag = -1;
1059                 $host = '';
1060                 $maxIndex = 0;
1061                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1062                         foreach ( $this->mServers as $i => $conn ) {
1063                                 $conn = false;
1064                                 if ( $wiki === false ) {
1065                                         $conn = $this->getAnyOpenConnection( $i );
1066                                 }
1067                                 if ( !$conn ) {
1068                                         $conn = $this->openConnection( $i, $wiki );
1069                                 }
1070                                 if ( !$conn ) {
1071                                         continue;
1072                                 }
1073                                 $lag = $conn->getLag();
1074                                 if ( $lag > $maxLag ) {
1075                                         $maxLag = $lag;
1076                                         $host = $this->mServers[$i]['host'];
1077                                         $maxIndex = $i;
1078                                 }
1079                         }
1080                 }
1081
1082                 return array( $host, $maxLag, $maxIndex );
1083         }
1084
1085         /**
1086          * Get lag time for each server
1087          * Results are cached for a short time in memcached, and indefinitely in the process cache
1088          *
1089          * @param $wiki
1090          *
1091          * @return array
1092          */
1093         function getLagTimes( $wiki = false ) {
1094                 # Try process cache
1095                 if ( isset( $this->mLagTimes ) ) {
1096                         return $this->mLagTimes;
1097                 }
1098                 if ( $this->getServerCount() == 1 ) {
1099                         # No replication
1100                         $this->mLagTimes = array( 0 => 0 );
1101                 } else {
1102                         # Send the request to the load monitor
1103                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1104                                 array_keys( $this->mServers ), $wiki );
1105                 }
1106
1107                 return $this->mLagTimes;
1108         }
1109
1110         /**
1111          * Get the lag in seconds for a given connection, or zero if this load
1112          * balancer does not have replication enabled.
1113          *
1114          * This should be used in preference to Database::getLag() in cases where
1115          * replication may not be in use, since there is no way to determine if
1116          * replication is in use at the connection level without running
1117          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1118          * function instead of Database::getLag() avoids a fatal error in this
1119          * case on many installations.
1120          *
1121          * @param $conn DatabaseBase
1122          *
1123          * @return int
1124          */
1125         function safeGetLag( $conn ) {
1126                 if ( $this->getServerCount() == 1 ) {
1127                         return 0;
1128                 } else {
1129                         return $conn->getLag();
1130                 }
1131         }
1132
1133         /**
1134          * Clear the cache for getLagTimes
1135          */
1136         function clearLagTimeCache() {
1137                 $this->mLagTimes = null;
1138         }
1139 }
1140
1141 /**
1142  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1143  * as well handling deferring the actual network connection until the handle is used
1144  *
1145  * @ingroup Database
1146  * @since 1.22
1147  */
1148 class DBConnRef implements IDatabase {
1149         /** @var LoadBalancer */
1150         protected $lb;
1151         /** @var DatabaseBase|null */
1152         protected $conn;
1153         /** @var Array|null */
1154         protected $params;
1155
1156         /**
1157          * @param $lb LoadBalancer
1158          * @param $conn DatabaseBase|array Connection or (server index, group, wiki ID) array
1159          */
1160         public function __construct( LoadBalancer $lb, $conn ) {
1161                 $this->lb = $lb;
1162                 if ( $conn instanceof DatabaseBase ) {
1163                         $this->conn = $conn;
1164                 } else {
1165                         $this->params = $conn;
1166                 }
1167         }
1168
1169         public function __call( $name, $arguments ) {
1170                 if ( $this->conn === null ) {
1171                         list( $db, $groups, $wiki ) = $this->params;
1172                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1173                 }
1174
1175                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1176         }
1177
1178         function __destruct() {
1179                 if ( $this->conn !== null ) {
1180                         $this->lb->reuseConnection( $this->conn );
1181                 }
1182         }
1183 }