includes/LoadBalancer.php

   1 <?php
   2 /**
   3  *
   4  * @package MediaWiki
   5  */
   6
   7 /**
   8  * Depends on the database object
   9  */
  10 require_once( 'Database.php' );
  11
  12 # Valid database indexes
  13 # Operation-based indexes
  14 define( 'DB_SLAVE', -1 );     # Read from the slave (or only server)
  15 define( 'DB_MASTER', -2 );    # Write to master (or only server)
  16 define( 'DB_LAST', -3 );     # Whatever database was used last
  17
  18 # Obsolete aliases
  19 define( 'DB_READ', -1 );
  20 define( 'DB_WRITE', -2 );
  21
  22 /**
  23  * Database load balancing object
  24  *
  25  * @todo document
  26  * @package MediaWiki
  27  */
  28 class LoadBalancer {
  29         /* private */ var $mServers, $mConnections, $mLoads, $mGroupLoads;
  30         /* private */ var $mFailFunction;
  31         /* private */ var $mForce, $mReadIndex, $mLastIndex;
  32         /* private */ var $mWaitForFile, $mWaitForPos, $mWaitTimeout;
  33         /* private */ var $mLaggedSlaveMode;
  34
  35         function LoadBalancer()
  36         {
  37                 $this->mServers = array();
  38                 $this->mConnections = array();
  39                 $this->mFailFunction = false;
  40                 $this->mReadIndex = -1;
  41                 $this->mForce = -1;
  42                 $this->mLastIndex = -1;
  43         }
  44
  45         function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
  46         {
  47                 $lb = new LoadBalancer;
  48                 $lb->initialise( $servers, $failFunction = false );
  49                 return $lb;
  50         }
  51
  52         function initialise( $servers, $failFunction = false, $waitTimeout = 10 )
  53         {
  54                 $this->mServers = $servers;
  55                 $this->mFailFunction = $failFunction;
  56                 $this->mReadIndex = -1;
  57                 $this->mWriteIndex = -1;
  58                 $this->mForce = -1;
  59                 $this->mConnections = array();
  60                 $this->mLastIndex = 1;
  61                 $this->mLoads = array();
  62                 $this->mWaitForFile = false;
  63                 $this->mWaitForPos = false;
  64                 $this->mWaitTimeout = $waitTimeout;
  65                 $this->mLaggedSlaveMode = false;
  66
  67                 foreach( $servers as $i => $server ) {
  68                         $this->mLoads[$i] = $server['load'];
  69                         if ( isset( $server['groupLoads'] ) ) {
  70                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  71                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  72                                                 $this->mGroupLoads[$group] = array();
  73                                         }
  74                                         $this->mGroupLoads[$group][$i] = $ratio;
  75                                 }
  76                         }
  77                 }
  78         }
  79
  80         /**
  81          * Given an array of non-normalised probabilities, this function will select
  82          * an element and return the appropriate key
  83          */
  84         function pickRandom( $weights )
  85         {
  86                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  87                         return false;
  88                 }
  89
  90                 $sum = 0;
  91                 foreach ( $weights as $w ) {
  92                         $sum += $w;
  93                 }
  94                 $max = mt_getrandmax();
  95                 $rand = mt_rand(0, $max) / $max * $sum;
  96
  97                 $sum = 0;
  98                 foreach ( $weights as $i => $w ) {
  99                         $sum += $w;
 100                         if ( $sum >= $rand ) {
 101                                 break;
 102                         }
 103                 }
 104                 return $i;
 105         }
 106
 107         function getReaderIndex()
 108         {
 109                 $fname = 'LoadBalancer::getReaderIndex';
 110                 wfProfileIn( $fname );
 111
 112                 $i = false;
 113                 if ( $this->mForce >= 0 ) {
 114                         $i = $this->mForce;
 115                 } else {
 116                         if ( $this->mReadIndex >= 0 ) {
 117                                 $i = $this->mReadIndex;
 118                         } else {
 119                                 # $loads is $this->mLoads except with elements knocked out if they
 120                                 # don't work
 121                                 $loads = $this->mLoads;
 122                                 do {
 123                                         $i = $this->pickRandom( $loads );
 124                                         if ( $i !== false ) {
 125                                                 wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 126                                                 $this->openConnection( $i );
 127
 128                                                 if ( !$this->isOpen( $i ) ) {
 129                                                         wfDebug( "Failed\n" );
 130                                                         unset( $loads[$i] );
 131                                                 } elseif ( isset( $this->mServers[$i]['slave pos'] ) ) {
 132                                                         wfDebug( "Lagged slave\n" );
 133                                                         $this->mLaggedSlaveMode = true;
 134                                                 } else {
 135                                                         wfDebug( "OK\n" );
 136                                                 }
 137                                         }
 138                                 } while ( $i !== false && !$this->isOpen( $i ) );
 139
 140                                 if ( $this->isOpen( $i ) ) {
 141                                         $this->mReadIndex = $i;
 142                                 } else {
 143                                         $i = false;
 144                                 }
 145                         }
 146                 }
 147                 wfProfileOut( $fname );
 148                 return $i;
 149         }
 150
 151         /**
 152          * Get a random server to use in a query group
 153          */
 154         function getGroupIndex( $group ) {
 155                 if ( isset( $this->mGroupLoads[$group] ) ) {
 156                         $i = $this->pickRandom( $this->mGroupLoads[$group] );
 157                 } else {
 158                         $i = false;
 159                 }
 160                 wfDebug( "Query group $group => $i\n" );
 161                 return $i;
 162         }
 163
 164         /**
 165          * Set the master wait position
 166          * If a DB_SLAVE connection has been opened already, waits
 167          * Otherwise sets a variable telling it to wait if such a connection is opened
 168          */
 169         function waitFor( $file, $pos ) {
 170                 $fname = 'LoadBalancer::waitFor';
 171                 wfProfileIn( $fname );
 172
 173                 wfDebug( "User master pos: $file $pos\n" );
 174                 $this->mWaitForFile = false;
 175                 $this->mWaitForPos = false;
 176
 177                 if ( count( $this->mServers ) > 1 ) {
 178                         $this->mWaitForFile = $file;
 179                         $this->mWaitForPos = $pos;
 180                         $i = $this->mReadIndex;
 181
 182                         if ( $i > 0 ) {
 183                                 if ( !$this->doWait( $i ) ) {
 184                                         $this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
 185                                         $this->mLaggedSlaveMode = true;
 186                                 }
 187                         }
 188                 }
 189                 wfProfileOut( $fname );
 190         }
 191
 192         /**
 193          * Wait for a given slave to catch up to the master pos stored in $this
 194          */
 195         function doWait( $index ) {
 196                 global $wgMemc;
 197
 198                 $retVal = false;
 199
 200                 # Debugging hacks
 201                 if ( isset( $this->mServers[$index]['lagged slave'] ) ) {
 202                         return false;
 203                 } elseif ( isset( $this->mServers[$index]['fake slave'] ) ) {
 204                         return true;
 205                 }
 206
 207                 $key = 'masterpos:' . $index;
 208                 $memcPos = $wgMemc->get( $key );
 209                 if ( $memcPos ) {
 210                         list( $file, $pos ) = explode( ' ', $memcPos );
 211                         # If the saved position is later than the requested position, return now
 212                         if ( $file == $this->mWaitForFile && $this->mWaitForPos <= $pos ) {
 213                                 $retVal = true;
 214                         }
 215                 }
 216
 217                 if ( !$retVal && $this->isOpen( $index ) ) {
 218                         $conn =& $this->mConnections[$index];
 219                         wfDebug( "Waiting for slave #$index to catch up...\n" );
 220                         $result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, $this->mWaitTimeout );
 221
 222                         if ( $result == -1 || is_null( $result ) ) {
 223                                 # Timed out waiting for slave, use master instead
 224                                 wfDebug( "Timed out waiting for slave #$index pos {$this->mWaitForFile} {$this->mWaitForPos}\n" );
 225                                 $retVal = false;
 226                         } else {
 227                                 $retVal = true;
 228                                 wfDebug( "Done\n" );
 229                         }
 230                 }
 231                 return $retVal;
 232         }
 233
 234         /**
 235          * Get a connection by index
 236          */
 237         function &getConnection( $i, $fail = true, $groups = array() )
 238         {
 239                 $fname = 'LoadBalancer::getConnection';
 240                 wfProfileIn( $fname );
 241
 242                 # Query groups
 243                 $groupIndex = false;
 244                 foreach ( $groups as $group ) {
 245                         $groupIndex = $this->getGroupIndex( $group );
 246                         if ( $groupIndex !== false ) {
 247                                 $i = $groupIndex;
 248                                 break;
 249                         }
 250                 }
 251
 252                 # Operation-based index
 253                 if ( $i == DB_SLAVE ) {
 254                         $i = $this->getReaderIndex();
 255                 } elseif ( $i == DB_MASTER ) {
 256                         $i = $this->getWriterIndex();
 257                 } elseif ( $i == DB_LAST ) {
 258                         # Just use $this->mLastIndex, which should already be set
 259                         $i = $this->mLastIndex;
 260                         if ( $i === -1 ) {
 261                                 # Oh dear, not set, best to use the writer for safety
 262                                 wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
 263                                 $i = $this->getWriterIndex();
 264                         }
 265                 }
 266                 # Now we have an explicit index into the servers array
 267                 $this->openConnection( $i, $fail );
 268
 269                 wfProfileOut( $fname );
 270                 return $this->mConnections[$i];
 271         }
 272
 273         /**
 274          * Open a connection to the server given by the specified index
 275          * Index must be an actual index into the array
 276          * Returns success
 277          * @private
 278          */
 279         function openConnection( $i, $fail = false ) {
 280                 $fname = 'LoadBalancer::openConnection';
 281                 wfProfileIn( $fname );
 282                 $success = true;
 283
 284                 if ( !$this->isOpen( $i ) ) {
 285                         $this->mConnections[$i] = $this->reallyOpenConnection( $this->mServers[$i] );
 286
 287                         if ( $this->isOpen( $i ) && $i != 0 && $this->mWaitForFile ) {
 288                                 if ( !$this->doWait( $i ) ) {
 289                                         $this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
 290                                         $success = false;
 291                                 }
 292                         }
 293                 }
 294                 if ( !$this->isOpen( $i ) ) {
 295                         wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 296                         if ( $fail ) {
 297                                 $this->reportConnectionError( $this->mConnections[$i] );
 298                         }
 299                         $this->mConnections[$i] = false;
 300                         $success = false;
 301                 }
 302                 $this->mLastIndex = $i;
 303                 wfProfileOut( $fname );
 304                 return $success;
 305         }
 306
 307         /**
 308          * Test if the specified index represents an open connection
 309          * @private
 310          */
 311         function isOpen( $index ) {
 312                 if( !is_integer( $index ) ) {
 313                         return false;
 314                 }
 315                 if ( array_key_exists( $index, $this->mConnections ) && is_object( $this->mConnections[$index] ) &&
 316                   $this->mConnections[$index]->isOpen() )
 317                 {
 318                         return true;
 319                 } else {
 320                         return false;
 321                 }
 322         }
 323
 324         /**
 325          * Really opens a connection
 326          * @private
 327          */
 328         function reallyOpenConnection( &$server ) {
 329                 if( !is_array( $server ) ) {
 330                         wfDebugDieBacktrace( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 331                 }
 332
 333                 extract( $server );
 334                 # Get class for this database type
 335                 $class = 'Database' . ucfirst( $type );
 336                 if ( !class_exists( $class ) ) {
 337                         require_once( "$class.php" );
 338                 }
 339
 340                 # Create object
 341                 return new $class( $host, $user, $password, $dbname, 1, $flags );
 342         }
 343
 344         function reportConnectionError( &$conn )
 345         {
 346                 $fname = 'LoadBalancer::reportConnectionError';
 347                 wfProfileIn( $fname );
 348                 # Prevent infinite recursion
 349
 350                 static $reporting = false;
 351                 if ( !$reporting ) {
 352                         $reporting = true;
 353                         if ( !is_object( $conn ) ) {
 354                                 $conn = new Database;
 355                         }
 356                         if ( $this->mFailFunction ) {
 357                                 $conn->failFunction( $this->mFailFunction );
 358                         } else {
 359                                 $conn->failFunction( 'wfEmergencyAbort' );
 360                         }
 361                         $conn->reportConnectionError();
 362                         $reporting = false;
 363                 }
 364                 wfProfileOut( $fname );
 365         }
 366
 367         function getWriterIndex()
 368         {
 369                 return 0;
 370         }
 371
 372         function force( $i )
 373         {
 374                 $this->mForce = $i;
 375         }
 376
 377         function haveIndex( $i )
 378         {
 379                 return array_key_exists( $i, $this->mServers );
 380         }
 381
 382         /**
 383          * Get the number of defined servers (not the number of open connections)
 384          */
 385         function getServerCount() {
 386                 return count( $this->mServers );
 387         }
 388
 389         /**
 390          * Save master pos to the session and to memcached, if the session exists
 391          */
 392         function saveMasterPos() {
 393                 global $wgSessionStarted;
 394                 if ( $wgSessionStarted && count( $this->mServers ) > 1 ) {
 395                         # If this entire request was served from a slave without opening a connection to the
 396                         # master (however unlikely that may be), then we can fetch the position from the slave.
 397                         if ( empty( $this->mConnections[0] ) ) {
 398                                 $conn =& $this->getConnection( DB_SLAVE );
 399                                 list( $file, $pos ) = $conn->getSlavePos();
 400                                 wfDebug( "Saving master pos fetched from slave: $file $pos\n" );
 401                         } else {
 402                                 $conn =& $this->getConnection( 0 );
 403                                 list( $file, $pos ) = $conn->getMasterPos();
 404                                 wfDebug( "Saving master pos: $file $pos\n" );
 405                         }
 406                         if ( $file !== false ) {
 407                                 $_SESSION['master_log_file'] = $file;
 408                                 $_SESSION['master_pos'] = $pos;
 409                         }
 410                 }
 411         }
 412
 413         /**
 414          * Loads the master pos from the session, waits for it if necessary
 415          */
 416         function loadMasterPos() {
 417                 if ( isset( $_SESSION['master_log_file'] ) && isset( $_SESSION['master_pos'] ) ) {
 418                         $this->waitFor( $_SESSION['master_log_file'], $_SESSION['master_pos'] );
 419                 }
 420         }
 421
 422         /**
 423          * Close all open connections
 424          */
 425         function closeAll() {
 426                 foreach( $this->mConnections as $i => $conn ) {
 427                         if ( $this->isOpen( $i ) ) {
 428                                 // Need to use this syntax because $conn is a copy not a reference
 429                                 $this->mConnections[$i]->close();
 430                         }
 431                 }
 432         }
 433
 434         function commitAll() {
 435                 foreach( $this->mConnections as $i => $conn ) {
 436                         if ( $this->isOpen( $i ) ) {
 437                                 // Need to use this syntax because $conn is a copy not a reference
 438                                 $this->mConnections[$i]->immediateCommit();
 439                         }
 440                 }
 441         }
 442
 443         function waitTimeout( $value = NULL ) {
 444                 return wfSetVar( $this->mWaitTimeout, $value );
 445         }
 446
 447         function getLaggedSlaveMode() {
 448                 return $this->mLaggedSlaveMode;
 449         }
 450
 451         function pingAll() {
 452                 $success = true;
 453                 foreach ( $this->mConnections as $i => $conn ) {
 454                         if ( $this->isOpen( $i ) ) {
 455                                 if ( !$this->mConnections[$i]->ping() ) {
 456                                         $success = false;
 457                                 }
 458                         }
 459                 }
 460                 return $success;
 461         }
 462 }
 463
 464 ?>