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 # Task-based indexes
  23 # ***NOT USED YET, EXPERIMENTAL***
  24 # These may be defined in $wgDBservers. If they aren't, the default reader or writer will be used
  25 # Even numbers are always readers, odd numbers are writers
  26 define( 'DB_TASK_FIRST', 1000 );  # First in list
  27 define( 'DB_SEARCH_R', 1000 );    # Search read
  28 define( 'DB_SEARCH_W', 1001 );    # Search write
  29 define( 'DB_ASKSQL_R', 1002 );    # Special:Asksql read
  30 define( 'DB_WATCHLIST_R', 1004 ); # Watchlist read
  31 define( 'DB_TASK_LAST', 1004) ;   # Last in list
  32
  33 /**
  34  * Database load balancing object
  35  *
  36  * @todo document
  37  * @package MediaWiki
  38  */
  39 class LoadBalancer {
  40         /* private */ var $mServers, $mConnections, $mLoads;
  41         /* private */ var $mFailFunction;
  42         /* private */ var $mForce, $mReadIndex, $mLastIndex;
  43         /* private */ var $mWaitForFile, $mWaitForPos, $mWaitTimeout;
  44         /* private */ var $mLaggedSlaveMode;
  45
  46         function LoadBalancer()
  47         {
  48                 $this->mServers = array();
  49                 $this->mConnections = array();
  50                 $this->mFailFunction = false;
  51                 $this->mReadIndex = -1;
  52                 $this->mForce = -1;
  53                 $this->mLastIndex = -1;
  54         }
  55
  56         function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
  57         {
  58                 $lb = new LoadBalancer;
  59                 $lb->initialise( $servers, $failFunction = false );
  60                 return $lb;
  61         }
  62
  63         function initialise( $servers, $failFunction = false, $waitTimeout = 10 )
  64         {
  65                 $this->mServers = $servers;
  66                 $this->mFailFunction = $failFunction;
  67                 $this->mReadIndex = -1;
  68                 $this->mWriteIndex = -1;
  69                 $this->mForce = -1;
  70                 $this->mConnections = array();
  71                 $this->mLastIndex = 1;
  72                 $this->mLoads = array();
  73                 $this->mWaitForFile = false;
  74                 $this->mWaitForPos = false;
  75                 $this->mWaitTimeout = $waitTimeout;
  76                 $this->mLaggedSlaveMode = false;
  77
  78                 foreach( $servers as $i => $server ) {
  79                         $this->mLoads[$i] = $server['load'];
  80                 }
  81         }
  82
  83         /**
  84          * Given an array of non-normalised probabilities, this function will select
  85          * an element and return the appropriate key
  86          */
  87         function pickRandom( $weights )
  88         {
  89                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  90                         return false;
  91                 }
  92
  93                 $sum = 0;
  94                 foreach ( $weights as $w ) {
  95                         $sum += $w;
  96                 }
  97                 $max = mt_getrandmax();
  98                 $rand = mt_rand(0, $max) / $max * $sum;
  99
 100                 $sum = 0;
 101                 foreach ( $weights as $i => $w ) {
 102                         $sum += $w;
 103                         if ( $sum >= $rand ) {
 104                                 break;
 105                         }
 106                 }
 107                 return $i;
 108         }
 109
 110         function getReaderIndex()
 111         {
 112                 $fname = 'LoadBalancer::getReaderIndex';
 113                 wfProfileIn( $fname );
 114
 115                 $i = false;
 116                 if ( $this->mForce >= 0 ) {
 117                         $i = $this->mForce;
 118                 } else {
 119                         if ( $this->mReadIndex >= 0 ) {
 120                                 $i = $this->mReadIndex;
 121                         } else {
 122                                 # $loads is $this->mLoads except with elements knocked out if they
 123                                 # don't work
 124                                 $loads = $this->mLoads;
 125                                 do {
 126                                         $i = $this->pickRandom( $loads );
 127                                         if ( $i !== false ) {
 128                                                 wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}\n" );
 129
 130                                                 $this->openConnection( $i );
 131
 132                                                 if ( !$this->isOpen( $i ) ) {
 133                                                         unset( $loads[$i] );
 134                                                 }
 135                                         }
 136                                 } while ( $i !== false && !$this->isOpen( $i ) );
 137
 138                                 if ( $this->isOpen( $i ) ) {
 139                                         $this->mReadIndex = $i;
 140                                 } else {
 141                                         $i = false;
 142                                 }
 143                         }
 144                 }
 145                 wfProfileOut( $fname );
 146                 return $i;
 147         }
 148
 149         /**
 150          * Set the master wait position
 151          * If a DB_SLAVE connection has been opened already, waits
 152          * Otherwise sets a variable telling it to wait if such a connection is opened
 153          */
 154         function waitFor( $file, $pos ) {
 155                 $fname = 'LoadBalancer::waitFor';
 156                 wfProfileIn( $fname );
 157
 158                 wfDebug( "User master pos: $file $pos\n" );
 159                 $this->mWaitForFile = false;
 160                 $this->mWaitForPos = false;
 161
 162                 if ( count( $this->mServers ) > 1 ) {
 163                         $this->mWaitForFile = $file;
 164                         $this->mWaitForPos = $pos;
 165
 166                         if ( $this->mReadIndex > 0 ) {
 167                                 if ( !$this->doWait( $this->mReadIndex ) ) {
 168                                         $this->mLaggedSlaveMode = true;
 169                                 }
 170                         }
 171                 }
 172                 wfProfileOut( $fname );
 173         }
 174
 175         /**
 176          * Wait for a given slave to catch up to the master pos stored in $this
 177          */
 178         function doWait( $index ) {
 179                 global $wgMemc;
 180
 181                 $retVal = false;
 182
 183                 $key = 'masterpos:' . $index;
 184                 $memcPos = $wgMemc->get( $key );
 185                 if ( $memcPos ) {
 186                         list( $file, $pos ) = explode( ' ', $memcPos );
 187                         # If the saved position is later than the requested position, return now
 188                         if ( $file == $this->mWaitForFile && $this->mWaitForPos <= $pos ) {
 189                                 $retVal = true;
 190                         }
 191                 }
 192
 193                 if ( !$retVal && $this->isOpen( $index ) ) {
 194                         $conn =& $this->mConnections[$index];
 195                         wfDebug( "Waiting for slave #$index to catch up...\n" );
 196                         $result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, $this->mWaitTimeout );
 197
 198                         if ( $result == -1 || is_null( $result ) ) {
 199                                 # Timed out waiting for slave, use master instead
 200                                 wfDebug( "Timed out waiting for slave #$index pos {$this->mWaitForFile} {$this->mWaitForPos}\n" );
 201                                 $retVal = false;
 202                         } else {
 203                                 $retVal = true;
 204                                 wfDebug( "Done\n" );
 205                         }
 206                 }
 207                 return $retVal;
 208         }
 209
 210         /**
 211          * Get a connection by index
 212          */
 213         function &getConnection( $i, $fail = true )
 214         {
 215                 $fname = 'LoadBalancer::getConnection';
 216                 wfProfileIn( $fname );
 217                 /*
 218                 # Task-based index
 219                 if ( $i >= DB_TASK_FIRST && $i < DB_TASK_LAST ) {
 220                         if ( $i % 2 ) {
 221                                 # Odd index use writer
 222                                 $i = DB_MASTER;
 223                         } else {
 224                                 # Even index use reader
 225                                 $i = DB_SLAVE;
 226                         }
 227                 }*/
 228
 229                 # Operation-based index
 230                 if ( $i == DB_SLAVE ) {
 231                         $i = $this->getReaderIndex();
 232                 } elseif ( $i == DB_MASTER ) {
 233                         $i = $this->getWriterIndex();
 234                 } elseif ( $i == DB_LAST ) {
 235                         # Just use $this->mLastIndex, which should already be set
 236                         $i = $this->mLastIndex;
 237                         if ( $i === -1 ) {
 238                                 # Oh dear, not set, best to use the writer for safety
 239                                 wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
 240                                 $i = $this->getWriterIndex();
 241                         }
 242                 }
 243                 # Now we have an explicit index into the servers array
 244                 $this->openConnection( $i, $fail );
 245                 wfProfileOut( $fname );
 246                 return $this->mConnections[$i];
 247         }
 248
 249         /**
 250          * Open a connection to the server given by the specified index
 251          * Index must be an actual index into the array
 252          * @private
 253          */
 254         function openConnection( $i, $fail = false ) {
 255                 $fname = 'LoadBalancer::openConnection';
 256                 wfProfileIn( $fname );
 257
 258                 if ( !$this->isOpen( $i ) ) {
 259                         $this->mConnections[$i] = $this->reallyOpenConnection( $this->mServers[$i] );
 260
 261                         if ( $i != 0 && $this->mWaitForFile ) {
 262                                 if ( !$this->doWait( $i ) ) {
 263                                         # Error waiting for this slave, use master instead
 264                                         $this->mReadIndex = 0;
 265                                         $i = 0;
 266                                         if ( !$this->isOpen( 0 ) ) {
 267                                                 $this->mConnections[0] = $this->reallyOpenConnection( $this->mServers[0] );
 268                                         }
 269                                         wfDebug( "Failed over to {$this->mConnections[0]->mServer}\n" );
 270                                 }
 271                         }
 272                 }
 273                 if ( !$this->isOpen( $i ) ) {
 274                         wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 275                         if ( $fail ) {
 276                                 $this->reportConnectionError( $this->mConnections[$i] );
 277                         }
 278                         $this->mConnections[$i] = false;
 279                 }
 280                 $this->mLastIndex = $i;
 281                 wfProfileOut( $fname );
 282         }
 283
 284         /**
 285          * Test if the specified index represents an open connection
 286          * @private
 287          */
 288         function isOpen( $index ) {
 289                 if( !is_integer( $index ) ) {
 290                         return false;
 291                 }
 292                 if ( array_key_exists( $index, $this->mConnections ) && is_object( $this->mConnections[$index] ) &&
 293                   $this->mConnections[$index]->isOpen() )
 294                 {
 295                         return true;
 296                 } else {
 297                         return false;
 298                 }
 299         }
 300
 301         /**
 302          * Really opens a connection
 303          * @private
 304          */
 305         function reallyOpenConnection( &$server ) {
 306                 if( !is_array( $server ) ) {
 307                         wfDebugDieBacktrace( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 308                 }
 309
 310                 extract( $server );
 311                 # Get class for this database type
 312                 $class = 'Database' . ucfirst( $type );
 313                 if ( !class_exists( $class ) ) {
 314                         require_once( "$class.php" );
 315                 }
 316
 317                 # Create object
 318                 return new $class( $host, $user, $password, $dbname, 1, $flags );
 319         }
 320
 321         function reportConnectionError( &$conn )
 322         {
 323                 $fname = 'LoadBalancer::reportConnectionError';
 324                 wfProfileIn( $fname );
 325                 # Prevent infinite recursion
 326
 327                 static $reporting = false;
 328                 if ( !$reporting ) {
 329                         $reporting = true;
 330                         if ( !is_object( $conn ) ) {
 331                                 $conn = new Database;
 332                         }
 333                         if ( $this->mFailFunction ) {
 334                                 $conn->failFunction( $this->mFailFunction );
 335                         } else {
 336                                 $conn->failFunction( 'wfEmergencyAbort' );
 337                         }
 338                         $conn->reportConnectionError();
 339                         $reporting = false;
 340                 }
 341                 wfProfileOut( $fname );
 342         }
 343
 344         function getWriterIndex()
 345         {
 346                 return 0;
 347         }
 348
 349         function force( $i )
 350         {
 351                 $this->mForce = $i;
 352         }
 353
 354         function haveIndex( $i )
 355         {
 356                 return array_key_exists( $i, $this->mServers );
 357         }
 358
 359         /**
 360          * Get the number of defined servers (not the number of open connections)
 361          */
 362         function getServerCount() {
 363                 return count( $this->mServers );
 364         }
 365
 366         /**
 367          * Save master pos to the session and to memcached, if the session exists
 368          */
 369         function saveMasterPos() {
 370                 global $wgSessionStarted;
 371                 if ( $wgSessionStarted && count( $this->mServers ) > 1 ) {
 372                         # If this entire request was served from a slave without opening a connection to the
 373                         # master (however unlikely that may be), then we can fetch the position from the slave.
 374                         if ( empty( $this->mConnections[0] ) ) {
 375                                 $conn =& $this->getConnection( DB_SLAVE );
 376                                 list( $file, $pos ) = $conn->getSlavePos();
 377                                 wfDebug( "Saving master pos fetched from slave: $file $pos\n" );
 378                         } else {
 379                                 $conn =& $this->getConnection( 0 );
 380                                 list( $file, $pos ) = $conn->getMasterPos();
 381                                 wfDebug( "Saving master pos: $file $pos\n" );
 382                         }
 383                         if ( $file !== false ) {
 384                                 $_SESSION['master_log_file'] = $file;
 385                                 $_SESSION['master_pos'] = $pos;
 386                         }
 387                 }
 388         }
 389
 390         /**
 391          * Loads the master pos from the session, waits for it if necessary
 392          */
 393         function loadMasterPos() {
 394                 if ( isset( $_SESSION['master_log_file'] ) && isset( $_SESSION['master_pos'] ) ) {
 395                         $this->waitFor( $_SESSION['master_log_file'], $_SESSION['master_pos'] );
 396                 }
 397         }
 398
 399         /**
 400          * Close all open connections
 401          */
 402         function closeAll() {
 403                 foreach( $this->mConnections as $i => $conn ) {
 404                         if ( $this->isOpen( $i ) ) {
 405                                 $conn->close();
 406                         }
 407                 }
 408         }
 409
 410         function commitAll() {
 411                 foreach( $this->mConnections as $i => $conn ) {
 412                         if ( $this->isOpen( $i ) ) {
 413                                 $conn->immediateCommit();
 414                         }
 415                 }
 416         }
 417
 418         function waitTimeout( $value = NULL ) {
 419                 return wfSetVar( $this->mWaitTimeout, $value );
 420         }
 421
 422         function getLaggedSlaveMode() {
 423                 return $this->mLaggedSlaveMode;
 424         }
 425 }