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         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard slave lag as a factor in slave selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on slave lag to resolve */
  42         private $mWaitTimeout;
  43
  44         /** @var array LBFactory information */
  45         private $mParentInfo;
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50
  51         /** @var bool|DatabaseBase Database connection that caused a problem */
  52         private $mErrorConnection;
  53         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  54         private $mReadIndex;
  55         /** @var bool|DBMasterPos False if not set */
  56         private $mWaitForPos;
  57         /** @var bool Whether the generic reader fell back to a lagged slave */
  58         private $mLaggedSlaveMode;
  59         /** @var string The last DB selection or connection error */
  60         private $mLastError = 'Unknown error';
  61         /** @var integer Total connections opened */
  62         private $connsOpened = 0;
  63         /** @var ProcessCacheLRU */
  64         private $mProcCache;
  65
  66         /** @var integer Warn when this many connection are held */
  67         const CONN_HELD_WARN_THRESHOLD = 10;
  68
  69         /**
  70          * @param array $params Array with keys:
  71          *   servers           Required. Array of server info structures.
  72          *   loadMonitor       Name of a class used to fetch server lag and load.
  73          * @throws MWException
  74          */
  75         public function __construct( array $params ) {
  76                 if ( !isset( $params['servers'] ) ) {
  77                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  78                 }
  79                 $this->mServers = $params['servers'];
  80                 $this->mWaitTimeout = 10;
  81
  82                 $this->mReadIndex = -1;
  83                 $this->mWriteIndex = -1;
  84                 $this->mConns = array(
  85                         'local' => array(),
  86                         'foreignUsed' => array(),
  87                         'foreignFree' => array() );
  88                 $this->mLoads = array();
  89                 $this->mWaitForPos = false;
  90                 $this->mLaggedSlaveMode = false;
  91                 $this->mErrorConnection = false;
  92                 $this->mAllowLagged = false;
  93
  94                 if ( isset( $params['loadMonitor'] ) ) {
  95                         $this->mLoadMonitorClass = $params['loadMonitor'];
  96                 } else {
  97                         $master = reset( $params['servers'] );
  98                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  99                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 100                         } else {
 101                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 102                         }
 103                 }
 104
 105                 foreach ( $params['servers'] as $i => $server ) {
 106                         $this->mLoads[$i] = $server['load'];
 107                         if ( isset( $server['groupLoads'] ) ) {
 108                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 109                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 110                                                 $this->mGroupLoads[$group] = array();
 111                                         }
 112                                         $this->mGroupLoads[$group][$i] = $ratio;
 113                                 }
 114                         }
 115                 }
 116
 117                 $this->mProcCache = new ProcessCacheLRU( 30 );
 118         }
 119
 120         /**
 121          * Get a LoadMonitor instance
 122          *
 123          * @return LoadMonitor
 124          */
 125         private function getLoadMonitor() {
 126                 if ( !isset( $this->mLoadMonitor ) ) {
 127                         $class = $this->mLoadMonitorClass;
 128                         $this->mLoadMonitor = new $class( $this );
 129                 }
 130
 131                 return $this->mLoadMonitor;
 132         }
 133
 134         /**
 135          * Get or set arbitrary data used by the parent object, usually an LBFactory
 136          * @param mixed $x
 137          * @return mixed
 138          */
 139         public function parentInfo( $x = null ) {
 140                 return wfSetVar( $this->mParentInfo, $x );
 141         }
 142
 143         /**
 144          * Given an array of non-normalised probabilities, this function will select
 145          * an element and return the appropriate key
 146          *
 147          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 148          *
 149          * @param array $weights
 150          * @return bool|int|string
 151          */
 152         public function pickRandom( array $weights ) {
 153                 return ArrayUtils::pickRandom( $weights );
 154         }
 155
 156         /**
 157          * @param array $loads
 158          * @param bool|string $wiki Wiki to get non-lagged for
 159          * @param float $maxLag Restrict the maximum allowed lag to this many seconds
 160          * @return bool|int|string
 161          */
 162         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 163                 $lags = $this->getLagTimes( $wiki );
 164
 165                 # Unset excessively lagged servers
 166                 foreach ( $lags as $i => $lag ) {
 167                         if ( $i != 0 ) {
 168                                 $maxServerLag = $maxLag;
 169                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 170                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 171                                 }
 172                                 if ( $lag === false ) {
 173                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 174                                         unset( $loads[$i] );
 175                                 } elseif ( $lag > $maxServerLag ) {
 176                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 177                                         unset( $loads[$i] );
 178                                 }
 179                         }
 180                 }
 181
 182                 # Find out if all the slaves with non-zero load are lagged
 183                 $sum = 0;
 184                 foreach ( $loads as $load ) {
 185                         $sum += $load;
 186                 }
 187                 if ( $sum == 0 ) {
 188                         # No appropriate DB servers except maybe the master and some slaves with zero load
 189                         # Do NOT use the master
 190                         # Instead, this function will return false, triggering read-only mode,
 191                         # and a lagged slave will be used instead.
 192                         return false;
 193                 }
 194
 195                 if ( count( $loads ) == 0 ) {
 196                         return false;
 197                 }
 198
 199                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 200
 201                 # Return a random representative of the remainder
 202                 return ArrayUtils::pickRandom( $loads );
 203         }
 204
 205         /**
 206          * Get the index of the reader connection, which may be a slave
 207          * This takes into account load ratios and lag times. It should
 208          * always return a consistent index during a given invocation
 209          *
 210          * Side effect: opens connections to databases
 211          * @param string|bool $group Query group, or false for the generic reader
 212          * @param string|bool $wiki Wiki ID, or false for the current wiki
 213          * @throws MWException
 214          * @return bool|int|string
 215          */
 216         public function getReaderIndex( $group = false, $wiki = false ) {
 217                 global $wgDBtype;
 218
 219                 # @todo FIXME: For now, only go through all this for mysql databases
 220                 if ( $wgDBtype != 'mysql' ) {
 221                         return $this->getWriterIndex();
 222                 }
 223
 224                 if ( count( $this->mServers ) == 1 ) {
 225                         # Skip the load balancing if there's only one server
 226                         return 0;
 227                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 228                         # Shortcut if generic reader exists already
 229                         return $this->mReadIndex;
 230                 }
 231
 232                 # Find the relevant load array
 233                 if ( $group !== false ) {
 234                         if ( isset( $this->mGroupLoads[$group] ) ) {
 235                                 $nonErrorLoads = $this->mGroupLoads[$group];
 236                         } else {
 237                                 # No loads for this group, return false and the caller can use some other group
 238                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 239
 240                                 return false;
 241                         }
 242                 } else {
 243                         $nonErrorLoads = $this->mLoads;
 244                 }
 245
 246                 if ( !count( $nonErrorLoads ) ) {
 247                         throw new MWException( "Empty server array given to LoadBalancer" );
 248                 }
 249
 250                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 251                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 252
 253                 $laggedSlaveMode = false;
 254
 255                 # No server found yet
 256                 $i = false;
 257                 # First try quickly looking through the available servers for a server that
 258                 # meets our criteria
 259                 $currentLoads = $nonErrorLoads;
 260                 while ( count( $currentLoads ) ) {
 261                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 262                                 $i = ArrayUtils::pickRandom( $currentLoads );
 263                         } else {
 264                                 $i = false;
 265                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 266                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 267                                         # This triggers doWait() after connect, so it's especially good to
 268                                         # avoid lagged servers so as to avoid just blocking in that method.
 269                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 270                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 271                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 272                                 }
 273                                 if ( $i === false ) {
 274                                         # Any server with less lag than it's 'max lag' param is preferable
 275                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 276                                 }
 277                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 278                                         # All slaves lagged. Switch to read-only mode
 279                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 280                                         $i = ArrayUtils::pickRandom( $currentLoads );
 281                                         $laggedSlaveMode = true;
 282                                 }
 283                         }
 284
 285                         if ( $i === false ) {
 286                                 # pickRandom() returned false
 287                                 # This is permanent and means the configuration or the load monitor
 288                                 # wants us to return false.
 289                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 290
 291                                 return false;
 292                         }
 293
 294                         $serverName = $this->getServerName( $i );
 295                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 296
 297                         $conn = $this->openConnection( $i, $wiki );
 298                         if ( !$conn ) {
 299                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 300                                 unset( $nonErrorLoads[$i] );
 301                                 unset( $currentLoads[$i] );
 302                                 $i = false;
 303                                 continue;
 304                         }
 305
 306                         // Decrement reference counter, we are finished with this connection.
 307                         // It will be incremented for the caller later.
 308                         if ( $wiki !== false ) {
 309                                 $this->reuseConnection( $conn );
 310                         }
 311
 312                         # Return this server
 313                         break;
 314                 }
 315
 316                 # If all servers were down, quit now
 317                 if ( !count( $nonErrorLoads ) ) {
 318                         wfDebugLog( 'connect', "All servers down" );
 319                 }
 320
 321                 if ( $i !== false ) {
 322                         # Slave connection successful
 323                         # Wait for the session master pos for a short time
 324                         if ( $this->mWaitForPos && $i > 0 ) {
 325                                 if ( !$this->doWait( $i ) ) {
 326                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 327                                 }
 328                         }
 329                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 330                                 $this->mReadIndex = $i;
 331                                 # Record if the generic reader index is in "lagged slave" mode
 332                                 if ( $laggedSlaveMode ) {
 333                                         $this->mLaggedSlaveMode = true;
 334                                 }
 335                         }
 336                         $serverName = $this->getServerName( $i );
 337                         wfDebug( __METHOD__ . ": using server $serverName for group '$group'\n" );
 338                 }
 339
 340                 return $i;
 341         }
 342
 343         /**
 344          * Set the master wait position
 345          * If a DB_SLAVE connection has been opened already, waits
 346          * Otherwise sets a variable telling it to wait if such a connection is opened
 347          * @param DBMasterPos $pos
 348          */
 349         public function waitFor( $pos ) {
 350                 $this->mWaitForPos = $pos;
 351                 $i = $this->mReadIndex;
 352
 353                 if ( $i > 0 ) {
 354                         if ( !$this->doWait( $i ) ) {
 355                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 356                                 $this->mLaggedSlaveMode = true;
 357                         }
 358                 }
 359         }
 360
 361         /**
 362          * Set the master wait position and wait for a "generic" slave to catch up to it
 363          *
 364          * This can be used a faster proxy for waitForAll()
 365          *
 366          * @param DBMasterPos $pos
 367          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 368          * @return bool Success (able to connect and no timeouts reached)
 369          * @since 1.26
 370          */
 371         public function waitForOne( $pos, $timeout = null ) {
 372                 $this->mWaitForPos = $pos;
 373
 374                 $i = $this->mReadIndex;
 375                 if ( $i <= 0 ) {
 376                         // Pick a generic slave if there isn't one yet
 377                         $readLoads = $this->mLoads;
 378                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 379                         $readLoads = array_filter( $readLoads ); // with non-zero load
 380                         $i = ArrayUtils::pickRandom( $readLoads );
 381                 }
 382
 383                 if ( $i > 0 ) {
 384                         $ok = $this->doWait( $i, true, $timeout );
 385                 } else {
 386                         $ok = true; // no applicable loads
 387                 }
 388
 389                 return $ok;
 390         }
 391
 392         /**
 393          * Set the master wait position and wait for ALL slaves to catch up to it
 394          * @param DBMasterPos $pos
 395          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 396          * @return bool Success (able to connect and no timeouts reached)
 397          */
 398         public function waitForAll( $pos, $timeout = null ) {
 399                 $this->mWaitForPos = $pos;
 400                 $serverCount = count( $this->mServers );
 401
 402                 $ok = true;
 403                 for ( $i = 1; $i < $serverCount; $i++ ) {
 404                         if ( $this->mLoads[$i] > 0 ) {
 405                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 406                         }
 407                 }
 408
 409                 return $ok;
 410         }
 411
 412         /**
 413          * Get any open connection to a given server index, local or foreign
 414          * Returns false if there is no connection open
 415          *
 416          * @param int $i
 417          * @return DatabaseBase|bool False on failure
 418          */
 419         public function getAnyOpenConnection( $i ) {
 420                 foreach ( $this->mConns as $conns ) {
 421                         if ( !empty( $conns[$i] ) ) {
 422                                 return reset( $conns[$i] );
 423                         }
 424                 }
 425
 426                 return false;
 427         }
 428
 429         /**
 430          * Wait for a given slave to catch up to the master pos stored in $this
 431          * @param int $index Server index
 432          * @param bool $open Check the server even if a new connection has to be made
 433          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 434          * @return bool
 435          */
 436         protected function doWait( $index, $open = false, $timeout = null ) {
 437                 $close = false; // close the connection afterwards
 438
 439                 # Find a connection to wait on, creating one if needed and allowed
 440                 $conn = $this->getAnyOpenConnection( $index );
 441                 if ( !$conn ) {
 442                         if ( !$open ) {
 443                                 wfDebug( __METHOD__ . ": no connection open\n" );
 444
 445                                 return false;
 446                         } else {
 447                                 $conn = $this->openConnection( $index, '' );
 448                                 if ( !$conn ) {
 449                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 450
 451                                         return false;
 452                                 }
 453                                 // Avoid connection spam in waitForAll() when connections
 454                                 // are made just for the sake of doing this lag check.
 455                                 $close = true;
 456                         }
 457                 }
 458
 459                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 460                 $timeout = $timeout ?: $this->mWaitTimeout;
 461                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 462
 463                 if ( $result == -1 || is_null( $result ) ) {
 464                         # Timed out waiting for slave, use master instead
 465                         $server = $server = $this->getServerName( $index );
 466                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 467                         wfDebug( "$msg\n" );
 468                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 469                         $ok = false;
 470                 } else {
 471                         wfDebug( __METHOD__ . ": Done\n" );
 472                         $ok = true;
 473                 }
 474
 475                 if ( $close ) {
 476                         $this->closeConnection( $conn );
 477                 }
 478
 479                 return $ok;
 480         }
 481
 482         /**
 483          * Get a connection by index
 484          * This is the main entry point for this class.
 485          *
 486          * @param int $i Server index
 487          * @param array|string|bool $groups Query group(s), or false for the generic reader
 488          * @param string|bool $wiki Wiki ID, or false for the current wiki
 489          *
 490          * @throws MWException
 491          * @return DatabaseBase
 492          */
 493         public function getConnection( $i, $groups = array(), $wiki = false ) {
 494                 if ( $i === null || $i === false ) {
 495                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 496                                 ' with invalid server index' );
 497                 }
 498
 499                 if ( $wiki === wfWikiID() ) {
 500                         $wiki = false;
 501                 }
 502
 503                 $groups = ( $groups === false || $groups === array() )
 504                         ? array( false ) // check one "group": the generic pool
 505                         : (array)$groups;
 506
 507                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 508                 $oldConnsOpened = $this->connsOpened; // connections open now
 509
 510                 if ( $i == DB_MASTER ) {
 511                         $i = $this->getWriterIndex();
 512                 } else {
 513                         # Try to find an available server in any the query groups (in order)
 514                         foreach ( $groups as $group ) {
 515                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 516                                 if ( $groupIndex !== false ) {
 517                                         $i = $groupIndex;
 518                                         break;
 519                                 }
 520                         }
 521                 }
 522
 523                 # Operation-based index
 524                 if ( $i == DB_SLAVE ) {
 525                         $this->mLastError = 'Unknown error'; // reset error string
 526                         # Try the general server pool if $groups are unavailable.
 527                         $i = in_array( false, $groups, true )
 528                                 ? false // don't bother with this if that is what was tried above
 529                                 : $this->getReaderIndex( false, $wiki );
 530                         # Couldn't find a working server in getReaderIndex()?
 531                         if ( $i === false ) {
 532                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 533
 534                                 return $this->reportConnectionError();
 535                         }
 536                 }
 537
 538                 # Now we have an explicit index into the servers array
 539                 $conn = $this->openConnection( $i, $wiki );
 540                 if ( !$conn ) {
 541                         return $this->reportConnectionError();
 542                 }
 543
 544                 # Profile any new connections that happen
 545                 if ( $this->connsOpened > $oldConnsOpened ) {
 546                         $host = $conn->getServer();
 547                         $dbname = $conn->getDBname();
 548                         $trxProf = Profiler::instance()->getTransactionProfiler();
 549                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 550                 }
 551
 552                 return $conn;
 553         }
 554
 555         /**
 556          * Mark a foreign connection as being available for reuse under a different
 557          * DB name or prefix. This mechanism is reference-counted, and must be called
 558          * the same number of times as getConnection() to work.
 559          *
 560          * @param DatabaseBase $conn
 561          * @throws MWException
 562          */
 563         public function reuseConnection( $conn ) {
 564                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 565                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 566                 if ( $serverIndex === null || $refCount === null ) {
 567                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 568
 569                         /**
 570                          * This can happen in code like:
 571                          *   foreach ( $dbs as $db ) {
 572                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 573                          *     ...
 574                          *     $lb->reuseConnection( $conn );
 575                          *   }
 576                          * When a connection to the local DB is opened in this way, reuseConnection()
 577                          * should be ignored
 578                          */
 579
 580                         return;
 581                 }
 582
 583                 $dbName = $conn->getDBname();
 584                 $prefix = $conn->tablePrefix();
 585                 if ( strval( $prefix ) !== '' ) {
 586                         $wiki = "$dbName-$prefix";
 587                 } else {
 588                         $wiki = $dbName;
 589                 }
 590                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 591                         throw new MWException( __METHOD__ . ": connection not found, has " .
 592                                 "the connection been freed already?" );
 593                 }
 594                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 595                 if ( $refCount <= 0 ) {
 596                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 597                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 598                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 599                 } else {
 600                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 601                 }
 602         }
 603
 604         /**
 605          * Get a database connection handle reference
 606          *
 607          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 608          *
 609          * @see LoadBalancer::getConnection() for parameter information
 610          *
 611          * @param int $db
 612          * @param array|string|bool $groups Query group(s), or false for the generic reader
 613          * @param string|bool $wiki Wiki ID, or false for the current wiki
 614          * @return DBConnRef
 615          */
 616         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 617                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 618         }
 619
 620         /**
 621          * Get a database connection handle reference without connecting yet
 622          *
 623          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 624          *
 625          * @see LoadBalancer::getConnection() for parameter information
 626          *
 627          * @param int $db
 628          * @param array|string|bool $groups Query group(s), or false for the generic reader
 629          * @param string|bool $wiki Wiki ID, or false for the current wiki
 630          * @return DBConnRef
 631          */
 632         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 633                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 634         }
 635
 636         /**
 637          * Open a connection to the server given by the specified index
 638          * Index must be an actual index into the array.
 639          * If the server is already open, returns it.
 640          *
 641          * On error, returns false, and the connection which caused the
 642          * error will be available via $this->mErrorConnection.
 643          *
 644          * @param int $i Server index
 645          * @param string|bool $wiki Wiki ID, or false for the current wiki
 646          * @return DatabaseBase
 647          *
 648          * @access private
 649          */
 650         public function openConnection( $i, $wiki = false ) {
 651                 if ( $wiki !== false ) {
 652                         $conn = $this->openForeignConnection( $i, $wiki );
 653                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 654                         $conn = $this->mConns['local'][$i][0];
 655                 } else {
 656                         $server = $this->mServers[$i];
 657                         $server['serverIndex'] = $i;
 658                         $conn = $this->reallyOpenConnection( $server, false );
 659                         $serverName = $this->getServerName( $i );
 660                         if ( $conn->isOpen() ) {
 661                                 wfDebug( "Connected to database $i at $serverName\n" );
 662                                 $this->mConns['local'][$i][0] = $conn;
 663                         } else {
 664                                 wfDebug( "Failed to connect to database $i at $serverName\n" );
 665                                 $this->mErrorConnection = $conn;
 666                                 $conn = false;
 667                         }
 668                 }
 669
 670                 if ( $conn && !$conn->isOpen() ) {
 671                         // Connection was made but later unrecoverably lost for some reason.
 672                         // Do not return a handle that will just throw exceptions on use,
 673                         // but let the calling code (e.g. getReaderIndex) try another server.
 674                         // See DatabaseMyslBase::ping() for how this can happen.
 675                         $this->mErrorConnection = $conn;
 676                         $conn = false;
 677                 }
 678
 679                 return $conn;
 680         }
 681
 682         /**
 683          * Open a connection to a foreign DB, or return one if it is already open.
 684          *
 685          * Increments a reference count on the returned connection which locks the
 686          * connection to the requested wiki. This reference count can be
 687          * decremented by calling reuseConnection().
 688          *
 689          * If a connection is open to the appropriate server already, but with the wrong
 690          * database, it will be switched to the right database and returned, as long as
 691          * it has been freed first with reuseConnection().
 692          *
 693          * On error, returns false, and the connection which caused the
 694          * error will be available via $this->mErrorConnection.
 695          *
 696          * @param int $i Server index
 697          * @param string $wiki Wiki ID to open
 698          * @return DatabaseBase
 699          */
 700         private function openForeignConnection( $i, $wiki ) {
 701                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 702                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 703                         // Reuse an already-used connection
 704                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 705                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 706                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 707                         // Reuse a free connection for the same wiki
 708                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 709                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 710                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 711                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 712                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 713                         // Reuse a connection from another wiki
 714                         $conn = reset( $this->mConns['foreignFree'][$i] );
 715                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 716
 717                         // The empty string as a DB name means "don't care".
 718                         // DatabaseMysqlBase::open() already handle this on connection.
 719                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 720                                 $this->mLastError = "Error selecting database $dbName on server " .
 721                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 722                                 $this->mErrorConnection = $conn;
 723                                 $conn = false;
 724                         } else {
 725                                 $conn->tablePrefix( $prefix );
 726                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 727                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 728                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 729                         }
 730                 } else {
 731                         // Open a new connection
 732                         $server = $this->mServers[$i];
 733                         $server['serverIndex'] = $i;
 734                         $server['foreignPoolRefCount'] = 0;
 735                         $server['foreign'] = true;
 736                         $conn = $this->reallyOpenConnection( $server, $dbName );
 737                         if ( !$conn->isOpen() ) {
 738                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 739                                 $this->mErrorConnection = $conn;
 740                                 $conn = false;
 741                         } else {
 742                                 $conn->tablePrefix( $prefix );
 743                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 744                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 745                         }
 746                 }
 747
 748                 // Increment reference count
 749                 if ( $conn ) {
 750                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 751                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 752                 }
 753
 754                 return $conn;
 755         }
 756
 757         /**
 758          * Test if the specified index represents an open connection
 759          *
 760          * @param int $index Server index
 761          * @access private
 762          * @return bool
 763          */
 764         private function isOpen( $index ) {
 765                 if ( !is_integer( $index ) ) {
 766                         return false;
 767                 }
 768
 769                 return (bool)$this->getAnyOpenConnection( $index );
 770         }
 771
 772         /**
 773          * Really opens a connection. Uncached.
 774          * Returns a Database object whether or not the connection was successful.
 775          * @access private
 776          *
 777          * @param array $server
 778          * @param bool $dbNameOverride
 779          * @throws MWException
 780          * @return DatabaseBase
 781          */
 782         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 783                 if ( !is_array( $server ) ) {
 784                         throw new MWException( 'You must update your load-balancing configuration. ' .
 785                                 'See DefaultSettings.php entry for $wgDBservers.' );
 786                 }
 787
 788                 if ( $dbNameOverride !== false ) {
 789                         $server['dbname'] = $dbNameOverride;
 790                 }
 791
 792                 // Log when many connection are made on requests
 793                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 794                         $masterAddr = $this->getServerName( 0 );
 795                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 796                                 "{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
 797                                 wfBacktrace( true ) );
 798                 }
 799
 800                 # Create object
 801                 try {
 802                         $db = DatabaseBase::factory( $server['type'], $server );
 803                 } catch ( DBConnectionError $e ) {
 804                         // FIXME: This is probably the ugliest thing I have ever done to
 805                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 806                         $db = $e->db;
 807                 }
 808
 809                 $db->setLBInfo( $server );
 810                 if ( isset( $server['fakeSlaveLag'] ) ) {
 811                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 812                 }
 813                 if ( isset( $server['fakeMaster'] ) ) {
 814                         $db->setFakeMaster( true );
 815                 }
 816
 817                 return $db;
 818         }
 819
 820         /**
 821          * @throws DBConnectionError
 822          * @return bool
 823          */
 824         private function reportConnectionError() {
 825                 $conn = $this->mErrorConnection; // The connection which caused the error
 826                 $context = array(
 827                         'method' => __METHOD__,
 828                         'last_error' => $this->mLastError,
 829                 );
 830
 831                 if ( !is_object( $conn ) ) {
 832                         // No last connection, probably due to all servers being too busy
 833                         wfLogDBError(
 834                                 "LB failure with no last connection. Connection error: {last_error}",
 835                                 $context
 836                         );
 837
 838                         // If all servers were busy, mLastError will contain something sensible
 839                         throw new DBConnectionError( null, $this->mLastError );
 840                 } else {
 841                         $context['db_server'] = $conn->getProperty( 'mServer' );
 842                         wfLogDBError(
 843                                 "Connection error: {last_error} ({db_server})",
 844                                 $context
 845                         );
 846                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 847                 }
 848
 849                 return false; /* not reached */
 850         }
 851
 852         /**
 853          * @return int
 854          * @since 1.26
 855          */
 856         public function getWriterIndex() {
 857                 return 0;
 858         }
 859
 860         /**
 861          * Returns true if the specified index is a valid server index
 862          *
 863          * @param string $i
 864          * @return bool
 865          */
 866         public function haveIndex( $i ) {
 867                 return array_key_exists( $i, $this->mServers );
 868         }
 869
 870         /**
 871          * Returns true if the specified index is valid and has non-zero load
 872          *
 873          * @param string $i
 874          * @return bool
 875          */
 876         public function isNonZeroLoad( $i ) {
 877                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 878         }
 879
 880         /**
 881          * Get the number of defined servers (not the number of open connections)
 882          *
 883          * @return int
 884          */
 885         public function getServerCount() {
 886                 return count( $this->mServers );
 887         }
 888
 889         /**
 890          * Get the host name or IP address of the server with the specified index
 891          * Prefer a readable name if available.
 892          * @param string $i
 893          * @return string
 894          */
 895         public function getServerName( $i ) {
 896                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 897                         $name = $this->mServers[$i]['hostName'];
 898                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 899                         $name = $this->mServers[$i]['host'];
 900                 } else {
 901                         $name = '';
 902                 }
 903
 904                 return ( $name != '' ) ? $name : 'localhost';
 905         }
 906
 907         /**
 908          * Return the server info structure for a given index, or false if the index is invalid.
 909          * @param int $i
 910          * @return array|bool
 911          */
 912         public function getServerInfo( $i ) {
 913                 if ( isset( $this->mServers[$i] ) ) {
 914                         return $this->mServers[$i];
 915                 } else {
 916                         return false;
 917                 }
 918         }
 919
 920         /**
 921          * Sets the server info structure for the given index. Entry at index $i
 922          * is created if it doesn't exist
 923          * @param int $i
 924          * @param array $serverInfo
 925          */
 926         public function setServerInfo( $i, array $serverInfo ) {
 927                 $this->mServers[$i] = $serverInfo;
 928         }
 929
 930         /**
 931          * Get the current master position for chronology control purposes
 932          * @return mixed
 933          */
 934         public function getMasterPos() {
 935                 # If this entire request was served from a slave without opening a connection to the
 936                 # master (however unlikely that may be), then we can fetch the position from the slave.
 937                 $masterConn = $this->getAnyOpenConnection( 0 );
 938                 if ( !$masterConn ) {
 939                         $serverCount = count( $this->mServers );
 940                         for ( $i = 1; $i < $serverCount; $i++ ) {
 941                                 $conn = $this->getAnyOpenConnection( $i );
 942                                 if ( $conn ) {
 943                                         wfDebug( "Master pos fetched from slave\n" );
 944
 945                                         return $conn->getSlavePos();
 946                                 }
 947                         }
 948                 } else {
 949                         wfDebug( "Master pos fetched from master\n" );
 950
 951                         return $masterConn->getMasterPos();
 952                 }
 953
 954                 return false;
 955         }
 956
 957         /**
 958          * Close all open connections
 959          */
 960         public function closeAll() {
 961                 foreach ( $this->mConns as $conns2 ) {
 962                         foreach ( $conns2 as $conns3 ) {
 963                                 /** @var DatabaseBase $conn */
 964                                 foreach ( $conns3 as $conn ) {
 965                                         $conn->close();
 966                                 }
 967                         }
 968                 }
 969                 $this->mConns = array(
 970                         'local' => array(),
 971                         'foreignFree' => array(),
 972                         'foreignUsed' => array(),
 973                 );
 974                 $this->connsOpened = 0;
 975         }
 976
 977         /**
 978          * Close a connection
 979          * Using this function makes sure the LoadBalancer knows the connection is closed.
 980          * If you use $conn->close() directly, the load balancer won't update its state.
 981          * @param DatabaseBase $conn
 982          */
 983         public function closeConnection( $conn ) {
 984                 $done = false;
 985                 foreach ( $this->mConns as $i1 => $conns2 ) {
 986                         foreach ( $conns2 as $i2 => $conns3 ) {
 987                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 988                                         if ( $conn === $candidateConn ) {
 989                                                 $conn->close();
 990                                                 unset( $this->mConns[$i1][$i2][$i3] );
 991                                                 --$this->connsOpened;
 992                                                 $done = true;
 993                                                 break;
 994                                         }
 995                                 }
 996                         }
 997                 }
 998                 if ( !$done ) {
 999                         $conn->close();
1000                 }
1001         }
1002
1003         /**
1004          * Commit transactions on all open connections
1005          */
1006         public function commitAll() {
1007                 foreach ( $this->mConns as $conns2 ) {
1008                         foreach ( $conns2 as $conns3 ) {
1009                                 /** @var DatabaseBase[] $conns3 */
1010                                 foreach ( $conns3 as $conn ) {
1011                                         if ( $conn->trxLevel() ) {
1012                                                 $conn->commit( __METHOD__, 'flush' );
1013                                         }
1014                                 }
1015                         }
1016                 }
1017         }
1018
1019         /**
1020          *  Issue COMMIT only on master, only if queries were done on connection
1021          */
1022         public function commitMasterChanges() {
1023                 $masterIndex = $this->getWriterIndex();
1024                 foreach ( $this->mConns as $conns2 ) {
1025                         if ( empty( $conns2[$masterIndex] ) ) {
1026                                 continue;
1027                         }
1028                         /** @var DatabaseBase $conn */
1029                         foreach ( $conns2[$masterIndex] as $conn ) {
1030                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1031                                         $conn->commit( __METHOD__, 'flush' );
1032                                 }
1033                         }
1034                 }
1035         }
1036
1037         /**
1038          * Issue ROLLBACK only on master, only if queries were done on connection
1039          * @since 1.23
1040          */
1041         public function rollbackMasterChanges() {
1042                 $failedServers = array();
1043
1044                 $masterIndex = $this->getWriterIndex();
1045                 foreach ( $this->mConns as $conns2 ) {
1046                         if ( empty( $conns2[$masterIndex] ) ) {
1047                                 continue;
1048                         }
1049                         /** @var DatabaseBase $conn */
1050                         foreach ( $conns2[$masterIndex] as $conn ) {
1051                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1052                                         try {
1053                                                 $conn->rollback( __METHOD__, 'flush' );
1054                                         } catch ( DBError $e ) {
1055                                                 MWExceptionHandler::logException( $e );
1056                                                 $failedServers[] = $conn->getServer();
1057                                         }
1058                                 }
1059                         }
1060                 }
1061
1062                 if ( $failedServers ) {
1063                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1064                                 implode( ', ', array_unique( $failedServers ) ) );
1065                 }
1066         }
1067
1068         /**
1069          * @return bool Whether a master connection is already open
1070          * @since 1.24
1071          */
1072         public function hasMasterConnection() {
1073                 return $this->isOpen( $this->getWriterIndex() );
1074         }
1075
1076         /**
1077          * Determine if there are pending changes in a transaction by this thread
1078          * @since 1.23
1079          * @return bool
1080          */
1081         public function hasMasterChanges() {
1082                 $masterIndex = $this->getWriterIndex();
1083                 foreach ( $this->mConns as $conns2 ) {
1084                         if ( empty( $conns2[$masterIndex] ) ) {
1085                                 continue;
1086                         }
1087                         /** @var DatabaseBase $conn */
1088                         foreach ( $conns2[$masterIndex] as $conn ) {
1089                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1090                                         return true;
1091                                 }
1092                         }
1093                 }
1094                 return false;
1095         }
1096
1097         /**
1098          * Get the timestamp of the latest write query done by this thread
1099          * @since 1.25
1100          * @return float|bool UNIX timestamp or false
1101          */
1102         public function lastMasterChangeTimestamp() {
1103                 $lastTime = false;
1104                 $masterIndex = $this->getWriterIndex();
1105                 foreach ( $this->mConns as $conns2 ) {
1106                         if ( empty( $conns2[$masterIndex] ) ) {
1107                                 continue;
1108                         }
1109                         /** @var DatabaseBase $conn */
1110                         foreach ( $conns2[$masterIndex] as $conn ) {
1111                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1112                         }
1113                 }
1114                 return $lastTime;
1115         }
1116
1117         /**
1118          * Check if this load balancer object had any recent or still
1119          * pending writes issued against it by this PHP thread
1120          *
1121          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1122          * @return bool
1123          * @since 1.25
1124          */
1125         public function hasOrMadeRecentMasterChanges( $age = null ) {
1126                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1127
1128                 return ( $this->hasMasterChanges()
1129                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1130         }
1131
1132         /**
1133          * @param mixed $value
1134          * @return mixed
1135          */
1136         public function waitTimeout( $value = null ) {
1137                 return wfSetVar( $this->mWaitTimeout, $value );
1138         }
1139
1140         /**
1141          * @return bool Whether the generic connection for reads is highly "lagged"
1142          */
1143         public function getLaggedSlaveMode() {
1144                 # Get a generic reader connection
1145                 $this->getConnection( DB_SLAVE );
1146
1147                 return $this->mLaggedSlaveMode;
1148         }
1149
1150         /**
1151          * Disables/enables lag checks
1152          * @param null|bool $mode
1153          * @return bool
1154          */
1155         public function allowLagged( $mode = null ) {
1156                 if ( $mode === null ) {
1157                         return $this->mAllowLagged;
1158                 }
1159                 $this->mAllowLagged = $mode;
1160
1161                 return $this->mAllowLagged;
1162         }
1163
1164         /**
1165          * @return bool
1166          */
1167         public function pingAll() {
1168                 $success = true;
1169                 foreach ( $this->mConns as $conns2 ) {
1170                         foreach ( $conns2 as $conns3 ) {
1171                                 /** @var DatabaseBase[] $conns3 */
1172                                 foreach ( $conns3 as $conn ) {
1173                                         if ( !$conn->ping() ) {
1174                                                 $success = false;
1175                                         }
1176                                 }
1177                         }
1178                 }
1179
1180                 return $success;
1181         }
1182
1183         /**
1184          * Call a function with each open connection object
1185          * @param callable $callback
1186          * @param array $params
1187          */
1188         public function forEachOpenConnection( $callback, array $params = array() ) {
1189                 foreach ( $this->mConns as $conns2 ) {
1190                         foreach ( $conns2 as $conns3 ) {
1191                                 foreach ( $conns3 as $conn ) {
1192                                         $mergedParams = array_merge( array( $conn ), $params );
1193                                         call_user_func_array( $callback, $mergedParams );
1194                                 }
1195                         }
1196                 }
1197         }
1198
1199         /**
1200          * Get the hostname and lag time of the most-lagged slave
1201          *
1202          * This is useful for maintenance scripts that need to throttle their updates.
1203          * May attempt to open connections to slaves on the default DB. If there is
1204          * no lag, the maximum lag will be reported as -1.
1205          *
1206          * @param bool|string $wiki Wiki ID, or false for the default database
1207          * @return array ( host, max lag, index of max lagged host )
1208          */
1209         public function getMaxLag( $wiki = false ) {
1210                 $maxLag = -1;
1211                 $host = '';
1212                 $maxIndex = 0;
1213
1214                 if ( $this->getServerCount() <= 1 ) {
1215                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1216                 }
1217
1218                 $lagTimes = $this->getLagTimes( $wiki );
1219                 foreach ( $lagTimes as $i => $lag ) {
1220                         if ( $lag > $maxLag ) {
1221                                 $maxLag = $lag;
1222                                 $host = $this->mServers[$i]['host'];
1223                                 $maxIndex = $i;
1224                         }
1225                 }
1226
1227                 return array( $host, $maxLag, $maxIndex );
1228         }
1229
1230         /**
1231          * Get lag time for each server
1232          *
1233          * Results are cached for a short time in memcached/process cache
1234          *
1235          * @param string|bool $wiki
1236          * @return int[] Map of (server index => seconds)
1237          */
1238         public function getLagTimes( $wiki = false ) {
1239                 if ( $this->getServerCount() <= 1 ) {
1240                         return array( 0 => 0 ); // no replication = no lag
1241                 }
1242
1243                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1244                         return $this->mProcCache->get( 'slave_lag', 'times' );
1245                 }
1246
1247                 # Send the request to the load monitor
1248                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1249
1250                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1251
1252                 return $times;
1253         }
1254
1255         /**
1256          * Get the lag in seconds for a given connection, or zero if this load
1257          * balancer does not have replication enabled.
1258          *
1259          * This should be used in preference to Database::getLag() in cases where
1260          * replication may not be in use, since there is no way to determine if
1261          * replication is in use at the connection level without running
1262          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1263          * function instead of Database::getLag() avoids a fatal error in this
1264          * case on many installations.
1265          *
1266          * @param DatabaseBase $conn
1267          * @return int
1268          */
1269         public function safeGetLag( $conn ) {
1270                 if ( $this->getServerCount() == 1 ) {
1271                         return 0;
1272                 } else {
1273                         return $conn->getLag();
1274                 }
1275         }
1276
1277         /**
1278          * Clear the cache for slag lag delay times
1279          */
1280         public function clearLagTimeCache() {
1281                 $this->mProcCache->clear( 'slave_lag' );
1282         }
1283 }