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
  35         /** @var bool|DBMasterPos False if not set */
  36         private $mWaitForPos;
  37
  38         private $mWaitTimeout;
  39         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  40         private $mParentInfo, $mLagTimes;
  41         private $mLoadMonitorClass, $mLoadMonitor;
  42
  43         /**
  44          * @param array $params with keys:
  45          *   servers           Required. Array of server info structures.
  46          *   masterWaitTimeout Replication lag wait timeout
  47          *   loadMonitor       Name of a class used to fetch server lag and load.
  48          * @throws MWException
  49          */
  50         function __construct( $params ) {
  51                 if ( !isset( $params['servers'] ) ) {
  52                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  53                 }
  54                 $this->mServers = $params['servers'];
  55
  56                 if ( isset( $params['waitTimeout'] ) ) {
  57                         $this->mWaitTimeout = $params['waitTimeout'];
  58                 } else {
  59                         $this->mWaitTimeout = 10;
  60                 }
  61
  62                 $this->mReadIndex = -1;
  63                 $this->mWriteIndex = -1;
  64                 $this->mConns = array(
  65                         'local' => array(),
  66                         'foreignUsed' => array(),
  67                         'foreignFree' => array() );
  68                 $this->mLoads = array();
  69                 $this->mWaitForPos = false;
  70                 $this->mLaggedSlaveMode = false;
  71                 $this->mErrorConnection = false;
  72                 $this->mAllowLagged = false;
  73
  74                 if ( isset( $params['loadMonitor'] ) ) {
  75                         $this->mLoadMonitorClass = $params['loadMonitor'];
  76                 } else {
  77                         $master = reset( $params['servers'] );
  78                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  79                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  80                         } else {
  81                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  82                         }
  83                 }
  84
  85                 foreach ( $params['servers'] as $i => $server ) {
  86                         $this->mLoads[$i] = $server['load'];
  87                         if ( isset( $server['groupLoads'] ) ) {
  88                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  89                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  90                                                 $this->mGroupLoads[$group] = array();
  91                                         }
  92                                         $this->mGroupLoads[$group][$i] = $ratio;
  93                                 }
  94                         }
  95                 }
  96         }
  97
  98         /**
  99          * Get a LoadMonitor instance
 100          *
 101          * @return LoadMonitor
 102          */
 103         function getLoadMonitor() {
 104                 if ( !isset( $this->mLoadMonitor ) ) {
 105                         $class = $this->mLoadMonitorClass;
 106                         $this->mLoadMonitor = new $class( $this );
 107                 }
 108
 109                 return $this->mLoadMonitor;
 110         }
 111
 112         /**
 113          * Get or set arbitrary data used by the parent object, usually an LBFactory
 114          * @param $x
 115          * @return mixed
 116          */
 117         function parentInfo( $x = null ) {
 118                 return wfSetVar( $this->mParentInfo, $x );
 119         }
 120
 121         /**
 122          * Given an array of non-normalised probabilities, this function will select
 123          * an element and return the appropriate key
 124          *
 125          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 126          *
 127          * @param array $weights
 128          * @return bool|int|string
 129          */
 130         function pickRandom( $weights ) {
 131                 return ArrayUtils::pickRandom( $weights );
 132         }
 133
 134         /**
 135          * @param array $loads
 136          * @param bool|string $wiki Wiki to get non-lagged for
 137          * @return bool|int|string
 138          */
 139         function getRandomNonLagged( $loads, $wiki = false ) {
 140                 # Unset excessively lagged servers
 141                 $lags = $this->getLagTimes( $wiki );
 142                 foreach ( $lags as $i => $lag ) {
 143                         if ( $i != 0 ) {
 144                                 if ( $lag === false ) {
 145                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 146                                         unset( $loads[$i] );
 147                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 148                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 149                                         unset( $loads[$i] );
 150                                 }
 151                         }
 152                 }
 153
 154                 # Find out if all the slaves with non-zero load are lagged
 155                 $sum = 0;
 156                 foreach ( $loads as $load ) {
 157                         $sum += $load;
 158                 }
 159                 if ( $sum == 0 ) {
 160                         # No appropriate DB servers except maybe the master and some slaves with zero load
 161                         # Do NOT use the master
 162                         # Instead, this function will return false, triggering read-only mode,
 163                         # and a lagged slave will be used instead.
 164                         return false;
 165                 }
 166
 167                 if ( count( $loads ) == 0 ) {
 168                         return false;
 169                 }
 170
 171                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 172
 173                 # Return a random representative of the remainder
 174                 return ArrayUtils::pickRandom( $loads );
 175         }
 176
 177         /**
 178          * Get the index of the reader connection, which may be a slave
 179          * This takes into account load ratios and lag times. It should
 180          * always return a consistent index during a given invocation
 181          *
 182          * Side effect: opens connections to databases
 183          * @param bool|string $group
 184          * @param bool|string $wiki
 185          * @throws MWException
 186          * @return bool|int|string
 187          */
 188         function getReaderIndex( $group = false, $wiki = false ) {
 189                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 190
 191                 # @todo FIXME: For now, only go through all this for mysql databases
 192                 if ( $wgDBtype != 'mysql' ) {
 193                         return $this->getWriterIndex();
 194                 }
 195
 196                 if ( count( $this->mServers ) == 1 ) {
 197                         # Skip the load balancing if there's only one server
 198                         return 0;
 199                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 200                         # Shortcut if generic reader exists already
 201                         return $this->mReadIndex;
 202                 }
 203
 204                 wfProfileIn( __METHOD__ );
 205
 206                 $totalElapsed = 0;
 207
 208                 # convert from seconds to microseconds
 209                 $timeout = $wgDBClusterTimeout * 1e6;
 210
 211                 # Find the relevant load array
 212                 if ( $group !== false ) {
 213                         if ( isset( $this->mGroupLoads[$group] ) ) {
 214                                 $nonErrorLoads = $this->mGroupLoads[$group];
 215                         } else {
 216                                 # No loads for this group, return false and the caller can use some other group
 217                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 218                                 wfProfileOut( __METHOD__ );
 219
 220                                 return false;
 221                         }
 222                 } else {
 223                         $nonErrorLoads = $this->mLoads;
 224                 }
 225
 226                 if ( !$nonErrorLoads ) {
 227                         wfProfileOut( __METHOD__ );
 228                         throw new MWException( "Empty server array given to LoadBalancer" );
 229                 }
 230
 231                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 232                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 233
 234                 $laggedSlaveMode = false;
 235
 236                 # First try quickly looking through the available servers for a server that
 237                 # meets our criteria
 238                 do {
 239                         $totalThreadsConnected = 0;
 240                         $overloadedServers = 0;
 241                         $currentLoads = $nonErrorLoads;
 242                         while ( count( $currentLoads ) ) {
 243                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 244                                         $i = ArrayUtils::pickRandom( $currentLoads );
 245                                 } else {
 246                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 247                                         if ( $i === false && count( $currentLoads ) != 0 ) {
 248                                                 # All slaves lagged. Switch to read-only mode
 249                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 250                                                 $wgReadOnly = 'The database has been automatically locked ' .
 251                                                         'while the slave database servers catch up to the master';
 252                                                 $i = ArrayUtils::pickRandom( $currentLoads );
 253                                                 $laggedSlaveMode = true;
 254                                         }
 255                                 }
 256
 257                                 if ( $i === false ) {
 258                                         # pickRandom() returned false
 259                                         # This is permanent and means the configuration or the load monitor
 260                                         # wants us to return false.
 261                                         wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 262                                         wfProfileOut( __METHOD__ );
 263
 264                                         return false;
 265                                 }
 266
 267                                 wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 268                                 $conn = $this->openConnection( $i, $wiki );
 269
 270                                 if ( !$conn ) {
 271                                         wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 272                                         unset( $nonErrorLoads[$i] );
 273                                         unset( $currentLoads[$i] );
 274                                         continue;
 275                                 }
 276
 277                                 // Perform post-connection backoff
 278                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 279                                         ? $this->mServers[$i]['max threads'] : false;
 280                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 281
 282                                 // Decrement reference counter, we are finished with this connection.
 283                                 // It will be incremented for the caller later.
 284                                 if ( $wiki !== false ) {
 285                                         $this->reuseConnection( $conn );
 286                                 }
 287
 288                                 if ( $backoff ) {
 289                                         # Post-connection overload, don't use this server for now
 290                                         $totalThreadsConnected += $backoff;
 291                                         $overloadedServers++;
 292                                         unset( $currentLoads[$i] );
 293                                 } else {
 294                                         # Return this server
 295                                         break 2;
 296                                 }
 297                         }
 298
 299                         # No server found yet
 300                         $i = false;
 301
 302                         # If all servers were down, quit now
 303                         if ( !count( $nonErrorLoads ) ) {
 304                                 wfDebugLog( 'connect', "All servers down\n" );
 305                                 break;
 306                         }
 307
 308                         # Some servers must have been overloaded
 309                         if ( $overloadedServers == 0 ) {
 310                                 throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
 311                         }
 312                         # Back off for a while
 313                         # Scale the sleep time by the number of connected threads, to produce a
 314                         # roughly constant global poll rate
 315                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 316                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 317                 } while ( $totalElapsed < $timeout );
 318
 319                 if ( $totalElapsed >= $timeout ) {
 320                         wfDebugLog( 'connect', "All servers busy\n" );
 321                         $this->mErrorConnection = false;
 322                         $this->mLastError = 'All servers busy';
 323                 }
 324
 325                 if ( $i !== false ) {
 326                         # Slave connection successful
 327                         # Wait for the session master pos for a short time
 328                         if ( $this->mWaitForPos && $i > 0 ) {
 329                                 if ( !$this->doWait( $i ) ) {
 330                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 331                                 }
 332                         }
 333                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 334                                 $this->mReadIndex = $i;
 335                         }
 336                 }
 337                 wfProfileOut( __METHOD__ );
 338
 339                 return $i;
 340         }
 341
 342         /**
 343          * Wait for a specified number of microseconds, and return the period waited
 344          * @param int $t
 345          * @return int
 346          */
 347         function sleep( $t ) {
 348                 wfProfileIn( __METHOD__ );
 349                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 350                 usleep( $t );
 351                 wfProfileOut( __METHOD__ );
 352
 353                 return $t;
 354         }
 355
 356         /**
 357          * Set the master wait position
 358          * If a DB_SLAVE connection has been opened already, waits
 359          * Otherwise sets a variable telling it to wait if such a connection is opened
 360          * @param DBMasterPos $pos
 361          */
 362         public function waitFor( $pos ) {
 363                 wfProfileIn( __METHOD__ );
 364                 $this->mWaitForPos = $pos;
 365                 $i = $this->mReadIndex;
 366
 367                 if ( $i > 0 ) {
 368                         if ( !$this->doWait( $i ) ) {
 369                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 370                                 $this->mLaggedSlaveMode = true;
 371                         }
 372                 }
 373                 wfProfileOut( __METHOD__ );
 374         }
 375
 376         /**
 377          * Set the master wait position and wait for ALL slaves to catch up to it
 378          * @param DBMasterPos $pos
 379          */
 380         public function waitForAll( $pos ) {
 381                 wfProfileIn( __METHOD__ );
 382                 $this->mWaitForPos = $pos;
 383                 $serverCount = count( $this->mServers );
 384                 for ( $i = 1; $i < $serverCount; $i++ ) {
 385                         if ( $this->mLoads[$i] > 0 ) {
 386                                 $this->doWait( $i, true );
 387                         }
 388                 }
 389                 wfProfileOut( __METHOD__ );
 390         }
 391
 392         /**
 393          * Get any open connection to a given server index, local or foreign
 394          * Returns false if there is no connection open
 395          *
 396          * @param int $i
 397          * @return DatabaseBase|bool False on failure
 398          */
 399         function getAnyOpenConnection( $i ) {
 400                 foreach ( $this->mConns as $conns ) {
 401                         if ( !empty( $conns[$i] ) ) {
 402                                 return reset( $conns[$i] );
 403                         }
 404                 }
 405
 406                 return false;
 407         }
 408
 409         /**
 410          * Wait for a given slave to catch up to the master pos stored in $this
 411          * @param $index
 412          * @param $open bool
 413          * @return bool
 414          */
 415         protected function doWait( $index, $open = false ) {
 416                 # Find a connection to wait on
 417                 $conn = $this->getAnyOpenConnection( $index );
 418                 if ( !$conn ) {
 419                         if ( !$open ) {
 420                                 wfDebug( __METHOD__ . ": no connection open\n" );
 421
 422                                 return false;
 423                         } else {
 424                                 $conn = $this->openConnection( $index, '' );
 425                                 if ( !$conn ) {
 426                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 427
 428                                         return false;
 429                                 }
 430                         }
 431                 }
 432
 433                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 434                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 435
 436                 if ( $result == -1 || is_null( $result ) ) {
 437                         # Timed out waiting for slave, use master instead
 438                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 439
 440                         return false;
 441                 } else {
 442                         wfDebug( __METHOD__ . ": Done\n" );
 443
 444                         return true;
 445                 }
 446         }
 447
 448         /**
 449          * Get a connection by index
 450          * This is the main entry point for this class.
 451          *
 452          * @param $i Integer: server index
 453          * @param array $groups query groups
 454          * @param bool|string $wiki Wiki ID
 455          *
 456          * @throws MWException
 457          * @return DatabaseBase
 458          */
 459         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 460                 wfProfileIn( __METHOD__ );
 461
 462                 if ( $i == DB_LAST ) {
 463                         wfProfileOut( __METHOD__ );
 464                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 465                                 ' with deprecated server index DB_LAST' );
 466                 } elseif ( $i === null || $i === false ) {
 467                         wfProfileOut( __METHOD__ );
 468                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 469                                 ' with invalid server index' );
 470                 }
 471
 472                 if ( $wiki === wfWikiID() ) {
 473                         $wiki = false;
 474                 }
 475
 476                 # Query groups
 477                 if ( $i == DB_MASTER ) {
 478                         $i = $this->getWriterIndex();
 479                 } elseif ( !is_array( $groups ) ) {
 480                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 481                         if ( $groupIndex !== false ) {
 482                                 $serverName = $this->getServerName( $groupIndex );
 483                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 484                                 $i = $groupIndex;
 485                         }
 486                 } else {
 487                         foreach ( $groups as $group ) {
 488                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 489                                 if ( $groupIndex !== false ) {
 490                                         $serverName = $this->getServerName( $groupIndex );
 491                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 492                                         $i = $groupIndex;
 493                                         break;
 494                                 }
 495                         }
 496                 }
 497
 498                 # Operation-based index
 499                 if ( $i == DB_SLAVE ) {
 500                         $this->mLastError = 'Unknown error'; // reset error string
 501                         $i = $this->getReaderIndex( false, $wiki );
 502                         # Couldn't find a working server in getReaderIndex()?
 503                         if ( $i === false ) {
 504                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 505                                 wfProfileOut( __METHOD__ );
 506
 507                                 return $this->reportConnectionError();
 508                         }
 509                 }
 510
 511                 # Now we have an explicit index into the servers array
 512                 $conn = $this->openConnection( $i, $wiki );
 513                 if ( !$conn ) {
 514                         wfProfileOut( __METHOD__ );
 515
 516                         return $this->reportConnectionError();
 517                 }
 518
 519                 wfProfileOut( __METHOD__ );
 520
 521                 return $conn;
 522         }
 523
 524         /**
 525          * Mark a foreign connection as being available for reuse under a different
 526          * DB name or prefix. This mechanism is reference-counted, and must be called
 527          * the same number of times as getConnection() to work.
 528          *
 529          * @param DatabaseBase $conn
 530          * @throws MWException
 531          */
 532         public function reuseConnection( $conn ) {
 533                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 534                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 535                 $dbName = $conn->getDBname();
 536                 $prefix = $conn->tablePrefix();
 537                 if ( strval( $prefix ) !== '' ) {
 538                         $wiki = "$dbName-$prefix";
 539                 } else {
 540                         $wiki = $dbName;
 541                 }
 542                 if ( $serverIndex === null || $refCount === null ) {
 543                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 544
 545                         /**
 546                          * This can happen in code like:
 547                          *   foreach ( $dbs as $db ) {
 548                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 549                          *     ...
 550                          *     $lb->reuseConnection( $conn );
 551                          *   }
 552                          * When a connection to the local DB is opened in this way, reuseConnection()
 553                          * should be ignored
 554                          */
 555
 556                         return;
 557                 }
 558                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 559                         throw new MWException( __METHOD__ . ": connection not found, has " .
 560                                 "the connection been freed already?" );
 561                 }
 562                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 563                 if ( $refCount <= 0 ) {
 564                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 565                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 566                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 567                 } else {
 568                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 569                 }
 570         }
 571
 572         /**
 573          * Get a database connection handle reference
 574          *
 575          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 576          *
 577          * @see LoadBalancer::getConnection() for parameter information
 578          *
 579          * @param integer $db
 580          * @param mixed $groups
 581          * @param bool|string $wiki
 582          * @return DBConnRef
 583          */
 584         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 585                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 586         }
 587
 588         /**
 589          * Get a database connection handle reference without connecting yet
 590          *
 591          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 592          *
 593          * @see LoadBalancer::getConnection() for parameter information
 594          *
 595          * @param integer $db
 596          * @param mixed $groups
 597          * @param bool|string $wiki
 598          * @return DBConnRef
 599          */
 600         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 601                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 602         }
 603
 604         /**
 605          * Open a connection to the server given by the specified index
 606          * Index must be an actual index into the array.
 607          * If the server is already open, returns it.
 608          *
 609          * On error, returns false, and the connection which caused the
 610          * error will be available via $this->mErrorConnection.
 611          *
 612          * @param $i Integer server index
 613          * @param bool|string $wiki wiki ID to open
 614          * @return DatabaseBase
 615          *
 616          * @access private
 617          */
 618         function openConnection( $i, $wiki = false ) {
 619                 wfProfileIn( __METHOD__ );
 620                 if ( $wiki !== false ) {
 621                         $conn = $this->openForeignConnection( $i, $wiki );
 622                         wfProfileOut( __METHOD__ );
 623
 624                         return $conn;
 625                 }
 626                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 627                         $conn = $this->mConns['local'][$i][0];
 628                 } else {
 629                         $server = $this->mServers[$i];
 630                         $server['serverIndex'] = $i;
 631                         $conn = $this->reallyOpenConnection( $server, false );
 632                         if ( $conn->isOpen() ) {
 633                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 634                                 $this->mConns['local'][$i][0] = $conn;
 635                         } else {
 636                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 637                                 $this->mErrorConnection = $conn;
 638                                 $conn = false;
 639                         }
 640                 }
 641                 wfProfileOut( __METHOD__ );
 642
 643                 return $conn;
 644         }
 645
 646         /**
 647          * Open a connection to a foreign DB, or return one if it is already open.
 648          *
 649          * Increments a reference count on the returned connection which locks the
 650          * connection to the requested wiki. This reference count can be
 651          * decremented by calling reuseConnection().
 652          *
 653          * If a connection is open to the appropriate server already, but with the wrong
 654          * database, it will be switched to the right database and returned, as long as
 655          * it has been freed first with reuseConnection().
 656          *
 657          * On error, returns false, and the connection which caused the
 658          * error will be available via $this->mErrorConnection.
 659          *
 660          * @param $i Integer: server index
 661          * @param string $wiki wiki ID to open
 662          * @return DatabaseBase
 663          */
 664         function openForeignConnection( $i, $wiki ) {
 665                 wfProfileIn( __METHOD__ );
 666                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 667                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 668                         // Reuse an already-used connection
 669                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 670                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 671                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 672                         // Reuse a free connection for the same wiki
 673                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 674                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 675                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 676                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 677                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 678                         // Reuse a connection from another wiki
 679                         $conn = reset( $this->mConns['foreignFree'][$i] );
 680                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 681
 682                         if ( !$conn->selectDB( $dbName ) ) {
 683                                 $this->mLastError = "Error selecting database $dbName on server " .
 684                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 685                                 $this->mErrorConnection = $conn;
 686                                 $conn = false;
 687                         } else {
 688                                 $conn->tablePrefix( $prefix );
 689                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 690                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 691                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 692                         }
 693                 } else {
 694                         // Open a new connection
 695                         $server = $this->mServers[$i];
 696                         $server['serverIndex'] = $i;
 697                         $server['foreignPoolRefCount'] = 0;
 698                         $server['foreign'] = true;
 699                         $conn = $this->reallyOpenConnection( $server, $dbName );
 700                         if ( !$conn->isOpen() ) {
 701                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 702                                 $this->mErrorConnection = $conn;
 703                                 $conn = false;
 704                         } else {
 705                                 $conn->tablePrefix( $prefix );
 706                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 707                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 708                         }
 709                 }
 710
 711                 // Increment reference count
 712                 if ( $conn ) {
 713                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 714                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 715                 }
 716                 wfProfileOut( __METHOD__ );
 717
 718                 return $conn;
 719         }
 720
 721         /**
 722          * Test if the specified index represents an open connection
 723          *
 724          * @param $index Integer: server index
 725          * @access private
 726          * @return bool
 727          */
 728         function isOpen( $index ) {
 729                 if ( !is_integer( $index ) ) {
 730                         return false;
 731                 }
 732
 733                 return (bool)$this->getAnyOpenConnection( $index );
 734         }
 735
 736         /**
 737          * Really opens a connection. Uncached.
 738          * Returns a Database object whether or not the connection was successful.
 739          * @access private
 740          *
 741          * @param $server
 742          * @param $dbNameOverride bool
 743          * @throws MWException
 744          * @return DatabaseBase
 745          */
 746         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 747                 if ( !is_array( $server ) ) {
 748                         throw new MWException( 'You must update your load-balancing configuration. ' .
 749                                 'See DefaultSettings.php entry for $wgDBservers.' );
 750                 }
 751
 752                 if ( $dbNameOverride !== false ) {
 753                         $server['dbname'] = $dbNameOverride;
 754                 }
 755
 756                 # Create object
 757                 try {
 758                         $db = DatabaseBase::factory( $server['type'], $server );
 759                 } catch ( DBConnectionError $e ) {
 760                         // FIXME: This is probably the ugliest thing I have ever done to
 761                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 762                         $db = $e->db;
 763                 }
 764
 765                 $db->setLBInfo( $server );
 766                 if ( isset( $server['fakeSlaveLag'] ) ) {
 767                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 768                 }
 769                 if ( isset( $server['fakeMaster'] ) ) {
 770                         $db->setFakeMaster( true );
 771                 }
 772
 773                 return $db;
 774         }
 775
 776         /**
 777          * @throws DBConnectionError
 778          * @return bool
 779          */
 780         private function reportConnectionError() {
 781                 $conn = $this->mErrorConnection; // The connection which caused the error
 782
 783                 if ( !is_object( $conn ) ) {
 784                         // No last connection, probably due to all servers being too busy
 785                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 786
 787                         // If all servers were busy, mLastError will contain something sensible
 788                         throw new DBConnectionError( null, $this->mLastError );
 789                 } else {
 790                         $server = $conn->getProperty( 'mServer' );
 791                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 792                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 793                 }
 794
 795                 return false; /* not reached */
 796         }
 797
 798         /**
 799          * @return int
 800          */
 801         function getWriterIndex() {
 802                 return 0;
 803         }
 804
 805         /**
 806          * Returns true if the specified index is a valid server index
 807          *
 808          * @param $i
 809          * @return bool
 810          */
 811         function haveIndex( $i ) {
 812                 return array_key_exists( $i, $this->mServers );
 813         }
 814
 815         /**
 816          * Returns true if the specified index is valid and has non-zero load
 817          *
 818          * @param $i
 819          * @return bool
 820          */
 821         function isNonZeroLoad( $i ) {
 822                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 823         }
 824
 825         /**
 826          * Get the number of defined servers (not the number of open connections)
 827          *
 828          * @return int
 829          */
 830         function getServerCount() {
 831                 return count( $this->mServers );
 832         }
 833
 834         /**
 835          * Get the host name or IP address of the server with the specified index
 836          * Prefer a readable name if available.
 837          * @param $i
 838          * @return string
 839          */
 840         function getServerName( $i ) {
 841                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 842                         return $this->mServers[$i]['hostName'];
 843                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 844                         return $this->mServers[$i]['host'];
 845                 } else {
 846                         return '';
 847                 }
 848         }
 849
 850         /**
 851          * Return the server info structure for a given index, or false if the index is invalid.
 852          * @param $i
 853          * @return bool
 854          */
 855         function getServerInfo( $i ) {
 856                 if ( isset( $this->mServers[$i] ) ) {
 857                         return $this->mServers[$i];
 858                 } else {
 859                         return false;
 860                 }
 861         }
 862
 863         /**
 864          * Sets the server info structure for the given index. Entry at index $i
 865          * is created if it doesn't exist
 866          * @param $i
 867          * @param $serverInfo
 868          */
 869         function setServerInfo( $i, $serverInfo ) {
 870                 $this->mServers[$i] = $serverInfo;
 871         }
 872
 873         /**
 874          * Get the current master position for chronology control purposes
 875          * @return mixed
 876          */
 877         function getMasterPos() {
 878                 # If this entire request was served from a slave without opening a connection to the
 879                 # master (however unlikely that may be), then we can fetch the position from the slave.
 880                 $masterConn = $this->getAnyOpenConnection( 0 );
 881                 if ( !$masterConn ) {
 882                         $serverCount = count( $this->mServers );
 883                         for ( $i = 1; $i < $serverCount; $i++ ) {
 884                                 $conn = $this->getAnyOpenConnection( $i );
 885                                 if ( $conn ) {
 886                                         wfDebug( "Master pos fetched from slave\n" );
 887
 888                                         return $conn->getSlavePos();
 889                                 }
 890                         }
 891                 } else {
 892                         wfDebug( "Master pos fetched from master\n" );
 893
 894                         return $masterConn->getMasterPos();
 895                 }
 896
 897                 return false;
 898         }
 899
 900         /**
 901          * Close all open connections
 902          */
 903         function closeAll() {
 904                 foreach ( $this->mConns as $conns2 ) {
 905                         foreach ( $conns2 as $conns3 ) {
 906                                 foreach ( $conns3 as $conn ) {
 907                                         $conn->close();
 908                                 }
 909                         }
 910                 }
 911                 $this->mConns = array(
 912                         'local' => array(),
 913                         'foreignFree' => array(),
 914                         'foreignUsed' => array(),
 915                 );
 916         }
 917
 918         /**
 919          * Deprecated function, typo in function name
 920          *
 921          * @deprecated in 1.18
 922          * @param $conn
 923          */
 924         function closeConnecton( $conn ) {
 925                 wfDeprecated( __METHOD__, '1.18' );
 926                 $this->closeConnection( $conn );
 927         }
 928
 929         /**
 930          * Close a connection
 931          * Using this function makes sure the LoadBalancer knows the connection is closed.
 932          * If you use $conn->close() directly, the load balancer won't update its state.
 933          * @param $conn DatabaseBase
 934          */
 935         function closeConnection( $conn ) {
 936                 $done = false;
 937                 foreach ( $this->mConns as $i1 => $conns2 ) {
 938                         foreach ( $conns2 as $i2 => $conns3 ) {
 939                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 940                                         if ( $conn === $candidateConn ) {
 941                                                 $conn->close();
 942                                                 unset( $this->mConns[$i1][$i2][$i3] );
 943                                                 $done = true;
 944                                                 break;
 945                                         }
 946                                 }
 947                         }
 948                 }
 949                 if ( !$done ) {
 950                         $conn->close();
 951                 }
 952         }
 953
 954         /**
 955          * Commit transactions on all open connections
 956          */
 957         function commitAll() {
 958                 foreach ( $this->mConns as $conns2 ) {
 959                         foreach ( $conns2 as $conns3 ) {
 960                                 foreach ( $conns3 as $conn ) {
 961                                         if ( $conn->trxLevel() ) {
 962                                                 $conn->commit( __METHOD__, 'flush' );
 963                                         }
 964                                 }
 965                         }
 966                 }
 967         }
 968
 969         /**
 970          *  Issue COMMIT only on master, only if queries were done on connection
 971          */
 972         function commitMasterChanges() {
 973                 // Always 0, but who knows.. :)
 974                 $masterIndex = $this->getWriterIndex();
 975                 foreach ( $this->mConns as $conns2 ) {
 976                         if ( empty( $conns2[$masterIndex] ) ) {
 977                                 continue;
 978                         }
 979                         foreach ( $conns2[$masterIndex] as $conn ) {
 980                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 981                                         $conn->commit( __METHOD__, 'flush' );
 982                                 }
 983                         }
 984                 }
 985         }
 986
 987         /**
 988          * @param $value null
 989          * @return Mixed
 990          */
 991         function waitTimeout( $value = null ) {
 992                 return wfSetVar( $this->mWaitTimeout, $value );
 993         }
 994
 995         /**
 996          * @return bool
 997          */
 998         function getLaggedSlaveMode() {
 999                 return $this->mLaggedSlaveMode;
1000         }
1001
1002         /**
1003          * Disables/enables lag checks
1004          * @param null|bool $mode
1005          * @return bool
1006          */
1007         function allowLagged( $mode = null ) {
1008                 if ( $mode === null ) {
1009                         return $this->mAllowLagged;
1010                 }
1011                 $this->mAllowLagged = $mode;
1012
1013                 return $this->mAllowLagged;
1014         }
1015
1016         /**
1017          * @return bool
1018          */
1019         function pingAll() {
1020                 $success = true;
1021                 foreach ( $this->mConns as $conns2 ) {
1022                         foreach ( $conns2 as $conns3 ) {
1023                                 foreach ( $conns3 as $conn ) {
1024                                         if ( !$conn->ping() ) {
1025                                                 $success = false;
1026                                         }
1027                                 }
1028                         }
1029                 }
1030
1031                 return $success;
1032         }
1033
1034         /**
1035          * Call a function with each open connection object
1036          * @param callable $callback
1037          * @param array $params
1038          */
1039         function forEachOpenConnection( $callback, $params = array() ) {
1040                 foreach ( $this->mConns as $conns2 ) {
1041                         foreach ( $conns2 as $conns3 ) {
1042                                 foreach ( $conns3 as $conn ) {
1043                                         $mergedParams = array_merge( array( $conn ), $params );
1044                                         call_user_func_array( $callback, $mergedParams );
1045                                 }
1046                         }
1047                 }
1048         }
1049
1050         /**
1051          * Get the hostname and lag time of the most-lagged slave.
1052          * This is useful for maintenance scripts that need to throttle their updates.
1053          * May attempt to open connections to slaves on the default DB. If there is
1054          * no lag, the maximum lag will be reported as -1.
1055          *
1056          * @param bool|string $wiki Wiki ID, or false for the default database
1057          * @return array ( host, max lag, index of max lagged host )
1058          */
1059         function getMaxLag( $wiki = false ) {
1060                 $maxLag = -1;
1061                 $host = '';
1062                 $maxIndex = 0;
1063                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1064                         foreach ( $this->mServers as $i => $conn ) {
1065                                 $conn = false;
1066                                 if ( $wiki === false ) {
1067                                         $conn = $this->getAnyOpenConnection( $i );
1068                                 }
1069                                 if ( !$conn ) {
1070                                         $conn = $this->openConnection( $i, $wiki );
1071                                 }
1072                                 if ( !$conn ) {
1073                                         continue;
1074                                 }
1075                                 $lag = $conn->getLag();
1076                                 if ( $lag > $maxLag ) {
1077                                         $maxLag = $lag;
1078                                         $host = $this->mServers[$i]['host'];
1079                                         $maxIndex = $i;
1080                                 }
1081                         }
1082                 }
1083
1084                 return array( $host, $maxLag, $maxIndex );
1085         }
1086
1087         /**
1088          * Get lag time for each server
1089          * Results are cached for a short time in memcached, and indefinitely in the process cache
1090          *
1091          * @param string|bool $wiki
1092          * @return array
1093          */
1094         function getLagTimes( $wiki = false ) {
1095                 # Try process cache
1096                 if ( isset( $this->mLagTimes ) ) {
1097                         return $this->mLagTimes;
1098                 }
1099                 if ( $this->getServerCount() == 1 ) {
1100                         # No replication
1101                         $this->mLagTimes = array( 0 => 0 );
1102                 } else {
1103                         # Send the request to the load monitor
1104                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1105                                 array_keys( $this->mServers ), $wiki );
1106                 }
1107
1108                 return $this->mLagTimes;
1109         }
1110
1111         /**
1112          * Get the lag in seconds for a given connection, or zero if this load
1113          * balancer does not have replication enabled.
1114          *
1115          * This should be used in preference to Database::getLag() in cases where
1116          * replication may not be in use, since there is no way to determine if
1117          * replication is in use at the connection level without running
1118          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1119          * function instead of Database::getLag() avoids a fatal error in this
1120          * case on many installations.
1121          *
1122          * @param DatabaseBase $conn
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
1152         /** @var DatabaseBase|null */
1153         protected $conn;
1154
1155         /** @var array|null */
1156         protected $params;
1157
1158         /**
1159          * @param LoadBalancer $lb
1160          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1161          */
1162         public function __construct( LoadBalancer $lb, $conn ) {
1163                 $this->lb = $lb;
1164                 if ( $conn instanceof DatabaseBase ) {
1165                         $this->conn = $conn;
1166                 } else {
1167                         $this->params = $conn;
1168                 }
1169         }
1170
1171         public function __call( $name, $arguments ) {
1172                 if ( $this->conn === null ) {
1173                         list( $db, $groups, $wiki ) = $this->params;
1174                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1175                 }
1176
1177                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1178         }
1179
1180         function __destruct() {
1181                 if ( $this->conn !== null ) {
1182                         $this->lb->reuseConnection( $this->conn );
1183                 }
1184         }
1185 }