includes/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing object
   4  *
   5  * @todo document
   6  */
   7 class LoadBalancer {
   8         /* private */ var $mServers, $mConns, $mLoads, $mGroupLoads;
   9         /* private */ var $mFailFunction, $mErrorConnection;
  10         /* private */ var $mReadIndex, $mLastIndex, $mAllowLagged;
  11         /* private */ var $mWaitForPos, $mWaitTimeout;
  12         /* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
  13         /* private */ var $mParentInfo, $mLagTimes;
  14
  15         function __construct( $servers, $failFunction = false, $waitTimeout = 10, $unused = false )
  16         {
  17                 $this->mServers = $servers;
  18                 $this->mFailFunction = $failFunction;
  19                 $this->mReadIndex = -1;
  20                 $this->mWriteIndex = -1;
  21                 $this->mConns = array(
  22                         'local' => array(),
  23                         'foreignUsed' => array(),
  24                         'foreignFree' => array() );
  25                 $this->mLastIndex = -1;
  26                 $this->mLoads = array();
  27                 $this->mWaitForPos = false;
  28                 $this->mWaitTimeout = $waitTimeout;
  29                 $this->mLaggedSlaveMode = false;
  30                 $this->mErrorConnection = false;
  31                 $this->mAllowLag = false;
  32
  33                 foreach( $servers as $i => $server ) {
  34                         $this->mLoads[$i] = $server['load'];
  35                         if ( isset( $server['groupLoads'] ) ) {
  36                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  37                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  38                                                 $this->mGroupLoads[$group] = array();
  39                                         }
  40                                         $this->mGroupLoads[$group][$i] = $ratio;
  41                                 }
  42                         }
  43                 }
  44         }
  45
  46         static function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
  47         {
  48                 return new LoadBalancer( $servers, $failFunction, $waitTimeout );
  49         }
  50
  51         /**
  52          * Get or set arbitrary data used by the parent object, usually an LBFactory
  53          */
  54         function parentInfo( $x = null ) {
  55                 return wfSetVar( $this->mParentInfo, $x );
  56         }
  57
  58         /**
  59          * Given an array of non-normalised probabilities, this function will select
  60          * an element and return the appropriate key
  61          */
  62         function pickRandom( $weights )
  63         {
  64                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  65                         return false;
  66                 }
  67
  68                 $sum = array_sum( $weights );
  69                 if ( $sum == 0 ) {
  70                         # No loads on any of them
  71                         # In previous versions, this triggered an unweighted random selection,
  72                         # but this feature has been removed as of April 2006 to allow for strict
  73                         # separation of query groups.
  74                         return false;
  75                 }
  76                 $max = mt_getrandmax();
  77                 $rand = mt_rand(0, $max) / $max * $sum;
  78
  79                 $sum = 0;
  80                 foreach ( $weights as $i => $w ) {
  81                         $sum += $w;
  82                         if ( $sum >= $rand ) {
  83                                 break;
  84                         }
  85                 }
  86                 return $i;
  87         }
  88
  89         function getRandomNonLagged( $loads ) {
  90                 # Unset excessively lagged servers
  91                 $lags = $this->getLagTimes();
  92                 foreach ( $lags as $i => $lag ) {
  93                         if ( $i != 0 && isset( $this->mServers[$i]['max lag'] ) ) {
  94                                 if ( $lag === false ) {
  95                                         wfDebug( "Server #$i is not replicating\n" );
  96                                         unset( $loads[$i] );
  97                                 } elseif ( $lag > $this->mServers[$i]['max lag'] ) {
  98                                         wfDebug( "Server #$i is excessively lagged ($lag seconds)\n" );
  99                                         unset( $loads[$i] );
 100                                 }
 101                         }
 102                 }
 103
 104                 # Find out if all the slaves with non-zero load are lagged
 105                 $sum = 0;
 106                 foreach ( $loads as $load ) {
 107                         $sum += $load;
 108                 }
 109                 if ( $sum == 0 ) {
 110                         # No appropriate DB servers except maybe the master and some slaves with zero load
 111                         # Do NOT use the master
 112                         # Instead, this function will return false, triggering read-only mode,
 113                         # and a lagged slave will be used instead.
 114                         return false;
 115                 }
 116
 117                 if ( count( $loads ) == 0 ) {
 118                         return false;
 119                 }
 120
 121                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 122
 123                 # Return a random representative of the remainder
 124                 return $this->pickRandom( $loads );
 125         }
 126
 127         /**
 128          * Get the index of the reader connection, which may be a slave
 129          * This takes into account load ratios and lag times. It should
 130          * always return a consistent index during a given invocation
 131          *
 132          * Side effect: opens connections to databases
 133          */
 134         function getReaderIndex( $group = false, $wiki = false ) {
 135                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 136
 137                 # FIXME: For now, only go through all this for mysql databases
 138                 if ($wgDBtype != 'mysql') {
 139                         return $this->getWriterIndex();
 140                 }
 141
 142                 if ( count( $this->mServers ) == 1 )  {
 143                         # Skip the load balancing if there's only one server
 144                         return 0;
 145                 } elseif ( $this->mReadIndex >= 0 ) {
 146                         return $this->mReadIndex;
 147                 }
 148
 149                 wfProfileIn( __METHOD__ );
 150
 151                 $totalElapsed = 0;
 152
 153                 # convert from seconds to microseconds
 154                 $timeout = $wgDBClusterTimeout * 1e6;
 155
 156                 # Find the relevant load array
 157                 if ( $group !== false ) {
 158                         if ( isset( $this->mGroupLoads[$group] ) ) {
 159                                 $nonErrorLoads = $this->mGroupLoads[$group];
 160                         } else {
 161                                 # No loads for this group, return false and the caller can use some other group
 162                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 163                                 wfProfileOut( __METHOD__ );
 164                                 return false;
 165                         }
 166                 } else {
 167                         $nonErrorLoads = $this->mLoads;
 168                 }
 169
 170                 if ( !$nonErrorLoads ) {
 171                         throw new MWException( "Empty server array given to LoadBalancer" );
 172                 }
 173
 174                 $i = false;
 175                 $found = false;
 176                 $laggedSlaveMode = false;
 177
 178                 # First try quickly looking through the available servers for a server that
 179                 # meets our criteria
 180                 do {
 181                         $totalThreadsConnected = 0;
 182                         $overloadedServers = 0;
 183                         $currentLoads = $nonErrorLoads;
 184                         while ( count( $currentLoads ) ) {
 185                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 186                                         $i = $this->pickRandom( $currentLoads );
 187                                 } else {
 188                                         $i = $this->getRandomNonLagged( $currentLoads );
 189                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 190                                                 # All slaves lagged. Switch to read-only mode
 191                                                 $wgReadOnly = wfMsgNoDBForContent( 'readonly_lag' );
 192                                                 $i = $this->pickRandom( $currentLoads );
 193                                                 $laggedSlaveMode = true;
 194                                         }
 195                                 }
 196
 197                                 if ( $i === false ) {
 198                                         # pickRandom() returned false
 199                                         # This is permanent and means the configuration wants us to return false
 200                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 201                                         wfProfileOut( __METHOD__ );
 202                                         return false;
 203                                 }
 204
 205                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 206                                 $conn = $this->openConnection( $i, $wiki );
 207
 208                                 if ( !$conn ) {
 209                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 210                                         unset( $nonErrorLoads[$i] );
 211                                         unset( $currentLoads[$i] );
 212                                         continue;
 213                                 }
 214
 215                                 if ( isset( $this->mServers[$i]['max threads'] ) ) {
 216                                         $status = $conn->getStatus("Thread%");
 217                                         if ( $wiki !== false ) {
 218                                                 $this->reuseConnection( $conn );
 219                                         }
 220                                         if ( $status['Threads_running'] > $this->mServers[$i]['max threads'] ) {
 221                                                 $totalThreadsConnected += $status['Threads_connected'];
 222                                                 $overloadedServers++;
 223                                                 unset( $currentLoads[$i] );
 224                                         } else {
 225                                                 # Max threads satisfied, return this server
 226                                                 break 2;
 227                                         }
 228                                 } else {
 229                                         # No maximum, return this server
 230                                         if ( $wiki !== false ) {
 231                                                 $this->reuseConnection( $conn );
 232                                         }
 233                                         $found = true;
 234                                         break 2;
 235                                 }
 236                         }
 237
 238                         # No server found yet
 239                         $i = false;
 240
 241                         # If all servers were down, quit now
 242                         if ( !count( $nonErrorLoads ) ) {
 243                                 wfDebugLog( 'connect', "All servers down\n" );
 244                                 break;
 245                         }
 246
 247                         # Some servers must have been overloaded
 248                         if ( $overloadedServers == 0 ) {
 249                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 250                         }
 251                         # Back off for a while
 252                         # Scale the sleep time by the number of connected threads, to produce a
 253                         # roughly constant global poll rate
 254                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 255                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 256                 } while ( $totalElapsed < $timeout );
 257
 258                 if ( $totalElapsed >= $timeout ) {
 259                         wfDebugLog( 'connect', "All servers busy\n" );
 260                         $this->mErrorConnection = false;
 261                         $this->mLastError = 'All servers busy';
 262                 }
 263
 264                 if ( $i !== false ) {
 265                         # Wait for the session master pos for a short time
 266                         if ( $this->mWaitForPos && $i > 0 ) {
 267                                 if ( !$this->doWait( $i ) ) {
 268                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 269                                 }
 270                         }
 271                         if ( $i !== false ) {
 272                                 $this->mReadIndex = $i;
 273                         }
 274                 }
 275                 wfProfileOut( __METHOD__ );
 276                 return $i;
 277         }
 278
 279         /**
 280          * Wait for a specified number of microseconds, and return the period waited
 281          */
 282         function sleep( $t ) {
 283                 wfProfileIn( __METHOD__ );
 284                 wfDebug( __METHOD__.": waiting $t us\n" );
 285                 usleep( $t );
 286                 wfProfileOut( __METHOD__ );
 287                 return $t;
 288         }
 289
 290         /**
 291          * Get a random server to use in a query group
 292          * @deprecated use getReaderIndex
 293          */
 294         function getGroupIndex( $group ) {
 295                 return $this->getReaderIndex( $group );
 296         }
 297
 298         /**
 299          * Set the master wait position
 300          * If a DB_SLAVE connection has been opened already, waits
 301          * Otherwise sets a variable telling it to wait if such a connection is opened
 302          */
 303         public function waitFor( $pos ) {
 304                 wfProfileIn( __METHOD__ );
 305                 $this->mWaitForPos = $pos;
 306                 $i = $this->mReadIndex;
 307
 308                 if ( $i > 0 ) {
 309                         if ( !$this->doWait( $i ) ) {
 310                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 311                                 $this->mLaggedSlaveMode = true;
 312                         }
 313                 }
 314                 wfProfileOut( __METHOD__ );
 315         }
 316
 317         /**
 318          * Get any open connection to a given server index, local or foreign
 319          * Returns false if there is no connection open
 320          */
 321         function getAnyOpenConnection( $i ) {
 322                 foreach ( $this->mConns as $type => $conns ) {
 323                         if ( !empty( $conns[$i] ) ) {
 324                                 return reset( $conns[$i] );
 325                         }
 326                 }
 327                 return false;
 328         }
 329
 330         /**
 331          * Wait for a given slave to catch up to the master pos stored in $this
 332          */
 333         function doWait( $index ) {
 334                 # Find a connection to wait on
 335                 $conn = $this->getAnyOpenConnection( $index );
 336                 if ( !$conn ) {
 337                         wfDebug( __METHOD__ . ": no connection open\n" );
 338                         return false;
 339                 }
 340
 341                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 342                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 343
 344                 if ( $result == -1 || is_null( $result ) ) {
 345                         # Timed out waiting for slave, use master instead
 346                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 347                         return false;
 348                 } else {
 349                         wfDebug( __METHOD__.": Done\n" );
 350                         return true;
 351                 }
 352         }
 353
 354         /**
 355          * Get a connection by index
 356          * This is the main entry point for this class.
 357          */
 358         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 359                 global $wgDBtype;
 360                 wfProfileIn( __METHOD__ );
 361
 362                 if ( $wiki === wfWikiID() ) {
 363                         $wiki = false;
 364                 }
 365
 366                 # Query groups
 367                 if ( !is_array( $groups ) ) {
 368                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 369                         if ( $groupIndex !== false ) {
 370                                 $serverName = $this->getServerName( $groupIndex );
 371                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 372                                 $i = $groupIndex;
 373                         }
 374                 } else {
 375                         foreach ( $groups as $group ) {
 376                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 377                                 if ( $groupIndex !== false ) {
 378                                         $serverName = $this->getServerName( $groupIndex );
 379                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 380                                         $i = $groupIndex;
 381                                         break;
 382                                 }
 383                         }
 384                 }
 385
 386                 # Operation-based index
 387                 if ( $i == DB_SLAVE ) {
 388                         $i = $this->getReaderIndex( false, $wiki );
 389                 } elseif ( $i == DB_MASTER ) {
 390                         $i = $this->getWriterIndex();
 391                 } elseif ( $i == DB_LAST ) {
 392                         # Just use $this->mLastIndex, which should already be set
 393                         $i = $this->mLastIndex;
 394                         if ( $i === -1 ) {
 395                                 # Oh dear, not set, best to use the writer for safety
 396                                 wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
 397                                 $i = $this->getWriterIndex();
 398                         }
 399                 }
 400                 # Couldn't find a working server in getReaderIndex()?
 401                 if ( $i === false ) {
 402                         $this->reportConnectionError( $this->mErrorConnection );
 403                 }
 404
 405                 # Now we have an explicit index into the servers array
 406                 $conn = $this->openConnection( $i, $wiki );
 407                 if ( !$conn ) {
 408                         $this->reportConnectionError( $this->mErrorConnection );
 409                 }
 410
 411                 wfProfileOut( __METHOD__ );
 412                 return $conn;
 413         }
 414
 415         /**
 416          * Mark a foreign connection as being available for reuse under a different
 417          * DB name or prefix. This mechanism is reference-counted, and must be called
 418          * the same number of times as getConnection() to work.
 419          */
 420         public function reuseConnection( $conn ) {
 421                 $serverIndex = $conn->getLBInfo('serverIndex');
 422                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 423                 $dbName = $conn->getDBname();
 424                 $prefix = $conn->tablePrefix();
 425                 if ( strval( $prefix ) !== '' ) {
 426                         $wiki = "$dbName-$prefix";
 427                 } else {
 428                         $wiki = $dbName;
 429                 }
 430                 if ( $serverIndex === null || $refCount === null ) {
 431                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 432                         /**
 433                          * This can happen in code like:
 434                          *   foreach ( $dbs as $db ) {
 435                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 436                          *     ...
 437                          *     $lb->reuseConnection( $conn );
 438                          *   }
 439                          * When a connection to the local DB is opened in this way, reuseConnection()
 440                          * should be ignored
 441                          */
 442                         return;
 443                 }
 444                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 445                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 446                 }
 447                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 448                 if ( $refCount <= 0 ) {
 449                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 450                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 451                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 452                 } else {
 453                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 454                 }
 455         }
 456
 457         /**
 458          * Open a connection to the server given by the specified index
 459          * Index must be an actual index into the array.
 460          * If the server is already open, returns it.
 461          *
 462          * On error, returns false, and the connection which caused the
 463          * error will be available via $this->mErrorConnection.
 464          *
 465          * @param integer $i Server index
 466          * @param string $wiki Wiki ID to open
 467          * @return Database
 468          *
 469          * @access private
 470          */
 471         function openConnection( $i, $wiki = false ) {
 472                 wfProfileIn( __METHOD__ );
 473
 474                 if ( $wiki !== false ) {
 475                         return $this->openForeignConnection( $i, $wiki );
 476                 }
 477                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 478                         $conn = $this->mConns['local'][$i][0];
 479                 } else {
 480                         $server = $this->mServers[$i];
 481                         $server['serverIndex'] = $i;
 482                         $conn = $this->reallyOpenConnection( $server );
 483                         if ( $conn->isOpen() ) {
 484                                 $this->mConns['local'][$i][0] = $conn;
 485                         } else {
 486                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 487                                 $this->mErrorConnection = $conn;
 488                                 $conn = false;
 489                         }
 490                 }
 491                 $this->mLastIndex = $i;
 492                 wfProfileOut( __METHOD__ );
 493                 return $conn;
 494         }
 495
 496         /**
 497          * Open a connection to a foreign DB, or return one if it is already open.
 498          *
 499          * Increments a reference count on the returned connection which locks the
 500          * connection to the requested wiki. This reference count can be
 501          * decremented by calling reuseConnection().
 502          *
 503          * If a connection is open to the appropriate server already, but with the wrong
 504          * database, it will be switched to the right database and returned, as long as
 505          * it has been freed first with reuseConnection().
 506          *
 507          * On error, returns false, and the connection which caused the
 508          * error will be available via $this->mErrorConnection.
 509          *
 510          * @param integer $i Server index
 511          * @param string $wiki Wiki ID to open
 512          * @return Database
 513          */
 514         function openForeignConnection( $i, $wiki ) {
 515                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 516
 517                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 518                         // Reuse an already-used connection
 519                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 520                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 521                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 522                         // Reuse a free connection for the same wiki
 523                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 524                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 525                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 526                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 527                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 528                         // Reuse a connection from another wiki
 529                         $conn = reset( $this->mConns['foreignFree'][$i] );
 530                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 531
 532                         if ( !$conn->selectDB( $dbName ) ) {
 533                                 global $wguname;
 534                                 $this->mLastError = "Error selecting database $dbName on server " .
 535                                         $conn->getServer() . " from client host {$wguname['nodename']}\n";
 536                                 $this->mErrorConnection = $conn;
 537                                 $conn = false;
 538                         } else {
 539                                 $conn->tablePrefix( $prefix );
 540                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 541                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 542                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 543                         }
 544                 } else {
 545                         // Open a new connection
 546                         $server = $this->mServers[$i];
 547                         $server['serverIndex'] = $i;
 548                         $server['foreignPoolRefCount'] = 0;
 549                         $conn = $this->reallyOpenConnection( $server, $dbName );
 550                         if ( !$conn->isOpen() ) {
 551                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 552                                 $this->mErrorConnection = $conn;
 553                                 $conn = false;
 554                         } else {
 555                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 556                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 557                         }
 558                 }
 559
 560                 // Increment reference count
 561                 if ( $conn ) {
 562                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 563                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 564                 }
 565                 return $conn;
 566         }
 567
 568         /**
 569          * Test if the specified index represents an open connection
 570          * @access private
 571          */
 572         function isOpen( $index ) {
 573                 if( !is_integer( $index ) ) {
 574                         return false;
 575                 }
 576                 return (bool)$this->getAnyOpenConnection( $index );
 577         }
 578
 579         /**
 580          * Really opens a connection. Uncached.
 581          * Returns a Database object whether or not the connection was successful.
 582          * @access private
 583          */
 584         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 585                 if( !is_array( $server ) ) {
 586                         throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 587                 }
 588
 589                 extract( $server );
 590                 if ( $dbNameOverride !== false ) {
 591                         $dbname = $dbNameOverride;
 592                 }
 593
 594                 # Get class for this database type
 595                 $class = 'Database' . ucfirst( $type );
 596
 597                 # Create object
 598                 wfDebug( "Connecting to $host...\n" );
 599                 $db = new $class( $host, $user, $password, $dbname, 1, $flags );
 600                 if ( $db->isOpen() ) {
 601                         wfDebug( "Connected\n" );
 602                 } else {
 603                         wfDebug( "Failed\n" );
 604                 }
 605                 $db->setLBInfo( $server );
 606                 if ( isset( $server['fakeSlaveLag'] ) ) {
 607                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 608                 }
 609                 if ( isset( $server['fakeMaster'] ) ) {
 610                         $db->setFakeMaster( true );
 611                 }
 612                 return $db;
 613         }
 614
 615         function reportConnectionError( &$conn ) {
 616                 wfProfileIn( __METHOD__ );
 617                 # Prevent infinite recursion
 618
 619                 static $reporting = false;
 620                 if ( !$reporting ) {
 621                         $reporting = true;
 622                         if ( !is_object( $conn ) ) {
 623                                 // No last connection, probably due to all servers being too busy
 624                                 $conn = new Database;
 625                                 if ( $this->mFailFunction ) {
 626                                         $conn->failFunction( $this->mFailFunction );
 627                                         $conn->reportConnectionError( $this->mLastError );
 628                                 } else {
 629                                         // If all servers were busy, mLastError will contain something sensible
 630                                         throw new DBConnectionError( $conn, $this->mLastError );
 631                                 }
 632                         } else {
 633                                 if ( $this->mFailFunction ) {
 634                                         $conn->failFunction( $this->mFailFunction );
 635                                 } else {
 636                                         $conn->failFunction( false );
 637                                 }
 638                                 $server = $conn->getProperty( 'mServer' );
 639                                 $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 640                         }
 641                         $reporting = false;
 642                 }
 643                 wfProfileOut( __METHOD__ );
 644         }
 645
 646         function getWriterIndex() {
 647                 return 0;
 648         }
 649
 650         /**
 651          * Returns true if the specified index is a valid server index
 652          */
 653         function haveIndex( $i ) {
 654                 return array_key_exists( $i, $this->mServers );
 655         }
 656
 657         /**
 658          * Returns true if the specified index is valid and has non-zero load
 659          */
 660         function isNonZeroLoad( $i ) {
 661                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 662         }
 663
 664         /**
 665          * Get the number of defined servers (not the number of open connections)
 666          */
 667         function getServerCount() {
 668                 return count( $this->mServers );
 669         }
 670
 671         /**
 672          * Get the host name or IP address of the server with the specified index
 673          */
 674         function getServerName( $i ) {
 675                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 676                         return $this->mServers[$i]['hostName'];
 677                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 678                         return $this->mServers[$i]['host'];
 679                 } else {
 680                         return '';
 681                 }
 682         }
 683
 684         /**
 685          * Get the current master position for chronology control purposes
 686          * @return mixed
 687          */
 688         function getMasterPos() {
 689                 # If this entire request was served from a slave without opening a connection to the
 690                 # master (however unlikely that may be), then we can fetch the position from the slave.
 691                 $masterConn = $this->getAnyOpenConnection( 0 );
 692                 if ( !$masterConn ) {
 693                         $conn = $this->getConnection( DB_SLAVE );
 694                         $pos = $conn->getSlavePos();
 695                         wfDebug( "Master pos fetched from slave\n" );
 696                 } else {
 697                         $pos = $masterConn->getMasterPos();
 698                         wfDebug( "Master pos fetched from master\n" );
 699                 }
 700                 return $pos;
 701         }
 702
 703         /**
 704          * Close all open connections
 705          */
 706         function closeAll() {
 707                 foreach ( $this->mConns as $conns2 ) {
 708                         foreach  ( $conns2 as $conns3 ) {
 709                                 foreach ( $conns3 as $conn ) {
 710                                         $conn->close();
 711                                 }
 712                         }
 713                 }
 714                 $this->mConns = array(
 715                         'local' => array(),
 716                         'foreignFree' => array(),
 717                         'foreignUsed' => array(),
 718                 );
 719         }
 720
 721         /**
 722          * Close a connection
 723          * Using this function makes sure the LoadBalancer knows the connection is closed.
 724          * If you use $conn->close() directly, the load balancer won't update its state.
 725          */
 726         function closeConnecton( $conn ) {
 727                 $done = false;
 728                 foreach ( $this->mConns as $i1 => $conns2 ) {
 729                         foreach ( $conns2 as $i2 => $conns3 ) {
 730                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 731                                         if ( $conn === $candidateConn ) {
 732                                                 $conn->close();
 733                                                 unset( $this->mConns[$i1][$i2][$i3] );
 734                                                 $done = true;
 735                                                 break;
 736                                         }
 737                                 }
 738                         }
 739                 }
 740                 if ( !$done ) {
 741                         $conn->close();
 742                 }
 743         }
 744
 745         /**
 746          * Commit transactions on all open connections
 747          */
 748         function commitAll() {
 749                 foreach ( $this->mConns as $conns2 ) {
 750                         foreach ( $conns2 as $conns3 ) {
 751                                 foreach ( $conns3 as $conn ) {
 752                                         $conn->immediateCommit();
 753                                 }
 754                         }
 755                 }
 756         }
 757
 758         /* Issue COMMIT only on master, only if queries were done on connection */
 759         function commitMasterChanges() {
 760                 // Always 0, but who knows.. :)
 761                 $masterIndex = $this->getWriterIndex();
 762                 foreach ( $this->mConns as $type => $conns2 ) {
 763                         if ( empty( $conns2[$masterIndex] ) ) {
 764                                 continue;
 765                         }
 766                         foreach ( $conns2[$masterIndex] as $conn ) {
 767                                 if ( $conn->lastQuery() != '' ) {
 768                                         $conn->commit();
 769                                 }
 770                         }
 771                 }
 772         }
 773
 774         function waitTimeout( $value = NULL ) {
 775                 return wfSetVar( $this->mWaitTimeout, $value );
 776         }
 777
 778         function getLaggedSlaveMode() {
 779                 return $this->mLaggedSlaveMode;
 780         }
 781
 782         /* Disables/enables lag checks */
 783         function allowLagged($mode=null) {
 784                 if ($mode===null)
 785                         return $this->mAllowLagged;
 786                 $this->mAllowLagged=$mode;
 787         }
 788
 789         function pingAll() {
 790                 $success = true;
 791                 foreach ( $this->mConns as $conns2 ) {
 792                         foreach ( $conns2 as $conns3 ) {
 793                                 foreach ( $conns3 as $conn ) {
 794                                         if ( !$conn->ping() ) {
 795                                                 $success = false;
 796                                         }
 797                                 }
 798                         }
 799                 }
 800                 return $success;
 801         }
 802
 803         /**
 804          * Get the hostname and lag time of the most-lagged slave
 805          * This is useful for maintenance scripts that need to throttle their updates
 806          */
 807         function getMaxLag() {
 808                 $maxLag = -1;
 809                 $host = '';
 810                 foreach ( $this->mServers as $i => $conn ) {
 811                         $conn = $this->getAnyOpenConnection( $i );
 812                         if ( !$conn ) {
 813                                 $conn = $this->openConnection( $i );
 814                         }
 815                         if ( !$conn ) {
 816                                 continue;
 817                         }
 818                         $lag = $conn->getLag();
 819                         if ( $lag > $maxLag ) {
 820                                 $maxLag = $lag;
 821                                 $host = $this->mServers[$i]['host'];
 822                         }
 823                 }
 824                 return array( $host, $maxLag );
 825         }
 826
 827         /**
 828          * Get lag time for each server
 829          * Results are cached for a short time in memcached, and indefinitely in the process cache
 830          */
 831         function getLagTimes() {
 832                 wfProfileIn( __METHOD__ );
 833
 834                 if ( !isset( $this->mLagTimes ) ) {
 835                         $expiry = 5;
 836                         $requestRate = 10;
 837
 838                         global $wgMemc;
 839                         $masterName = $this->getServerName( 0 );
 840                         $memcKey = wfMemcKey( 'lag_times', $masterName );
 841                         $times = $wgMemc->get( $memcKey );
 842                         if ( $times ) {
 843                                 # Randomly recache with probability rising over $expiry
 844                                 $elapsed = time() - $times['timestamp'];
 845                                 $chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
 846                                 if ( mt_rand( 0, $chance ) != 0 ) {
 847                                         unset( $times['timestamp'] );
 848                                         wfProfileOut( __METHOD__ );
 849                                         return $times;
 850                                 }
 851                                 wfIncrStats( 'lag_cache_miss_expired' );
 852                         } else {
 853                                 wfIncrStats( 'lag_cache_miss_absent' );
 854                         }
 855
 856                         # Cache key missing or expired
 857
 858                         $times = array();
 859                         foreach ( $this->mServers as $i => $conn ) {
 860                                 if ($i == 0) { # Master
 861                                         $times[$i] = 0;
 862                                 } elseif ( false !== ( $conn = $this->getAnyOpenConnection( $i ) ) ) {
 863                                         $times[$i] = $conn->getLag();
 864                                 } elseif ( false !== ( $conn = $this->openConnection( $i ) ) ) {
 865                                         $times[$i] = $conn->getLag();
 866                                 }
 867                         }
 868
 869                         # Add a timestamp key so we know when it was cached
 870                         $times['timestamp'] = time();
 871                         $wgMemc->set( $memcKey, $times, $expiry );
 872
 873                         # But don't give the timestamp to the caller
 874                         unset($times['timestamp']);
 875                         $this->mLagTimes = $times;
 876                 }
 877                 wfProfileOut( __METHOD__ );
 878                 return $this->mLagTimes;
 879         }
 880 }
 881
 882