includes/LoadBalancer.php

   1 <?php
   2 /**
   3  *
   4  */
   5
   6 /**
   7  * Depends on the database object
   8  */
   9 require_once( 'Database.php' );
  10
  11 # Valid database indexes
  12 # Operation-based indexes
  13 define( 'DB_SLAVE', -1 );     # Read from the slave (or only server)
  14 define( 'DB_MASTER', -2 );    # Write to master (or only server)
  15 define( 'DB_LAST', -3 );     # Whatever database was used last
  16
  17 # Obsolete aliases
  18 define( 'DB_READ', -1 );
  19 define( 'DB_WRITE', -2 );
  20
  21 # Task-based indexes
  22 # ***NOT USED YET, EXPERIMENTAL***
  23 # These may be defined in $wgDBservers. If they aren't, the default reader or writer will be used
  24 # Even numbers are always readers, odd numbers are writers
  25 define( 'DB_TASK_FIRST', 1000 );  # First in list
  26 define( 'DB_SEARCH_R', 1000 );    # Search read
  27 define( 'DB_SEARCH_W', 1001 );    # Search write
  28 define( 'DB_ASKSQL_R', 1002 );    # Special:Asksql read
  29 define( 'DB_WATCHLIST_R', 1004 ); # Watchlist read
  30 define( 'DB_TASK_LAST', 1004) ;   # Last in list
  31
  32 define( 'MASTER_WAIT_TIMEOUT', 15 ); # Time to wait for a slave to synchronise
  33
  34 /**
  35  * Database load balancing object
  36  * @todo document
  37  */
  38 class LoadBalancer {
  39         /* private */ var $mServers, $mConnections, $mLoads;
  40         /* private */ var $mFailFunction;
  41         /* private */ var $mForce, $mReadIndex, $mLastIndex;
  42         /* private */ var $mWaitForFile, $mWaitForPos;
  43
  44         function LoadBalancer()
  45         {
  46                 $this->mServers = array();
  47                 $this->mConnections = array();
  48                 $this->mFailFunction = false;
  49                 $this->mReadIndex = -1;
  50                 $this->mForce = -1;
  51                 $this->mLastIndex = -1;
  52         }
  53
  54         function newFromParams( $servers, $failFunction = false )
  55         {
  56                 $lb = new LoadBalancer;
  57                 $lb->initialise( $servers, $failFunction = false );
  58                 return $lb;
  59         }
  60
  61         function initialise( $servers, $failFunction = false )
  62         {
  63                 $this->mServers = $servers;
  64                 $this->mFailFunction = $failFunction;
  65                 $this->mReadIndex = -1;
  66                 $this->mWriteIndex = -1;
  67                 $this->mForce = -1;
  68                 $this->mConnections = array();
  69                 $this->mLastIndex = 1;
  70                 $this->mLoads = array();
  71                 $this->mWaitForFile = false;
  72                 $this->mWaitForPos = false;
  73
  74                 foreach( $servers as $i => $server ) {
  75                         $this->mLoads[$i] = $server['load'];
  76                 }
  77         }
  78
  79         /**
  80          * Given an array of non-normalised probabilities, this function will select
  81          * an element and return the appropriate key
  82          */
  83         function pickRandom( $weights )
  84         {
  85                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  86                         return false;
  87                 }
  88
  89                 $sum = 0;
  90                 foreach ( $weights as $w ) {
  91                         $sum += $w;
  92                 }
  93                 $max = mt_getrandmax();
  94                 $rand = mt_rand(0, $max) / $max * $sum;
  95
  96                 $sum = 0;
  97                 foreach ( $weights as $i => $w ) {
  98                         $sum += $w;
  99                         if ( $sum >= $rand ) {
 100                                 break;
 101                         }
 102                 }
 103                 return $i;
 104         }
 105
 106         function getReaderIndex()
 107         {
 108                 $fname = 'LoadBalancer::getReaderIndex';
 109                 wfProfileIn( $fname );
 110
 111                 $i = false;
 112                 if ( $this->mForce >= 0 ) {
 113                         $i = $this->mForce;
 114                 } else {
 115                         if ( $this->mReadIndex >= 0 ) {
 116                                 $i = $this->mReadIndex;
 117                         } else {
 118                                 # $loads is $this->mLoads except with elements knocked out if they
 119                                 # don't work
 120                                 $loads = $this->mLoads;
 121                                 do {
 122                                         $i = $this->pickRandom( $loads );
 123                                         if ( $i !== false ) {
 124                                                 wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}\n" );
 125
 126                                                 $this->openConnection( $i );
 127
 128                                                 if ( !$this->isOpen( $i ) ) {
 129                                                         unset( $loads[$i] );
 130                                                 }
 131                                         }
 132                                 } while ( $i !== false && !$this->isOpen( $i ) );
 133
 134                                 if ( $this->isOpen( $i ) ) {
 135                                         $this->mReadIndex = $i;
 136                                 } else {
 137                                         $i = false;
 138                                 }
 139                         }
 140                 }
 141                 wfProfileOut( $fname );
 142                 return $i;
 143         }
 144
 145         /**
 146          * Set the master wait position
 147          * If a DB_SLAVE connection has been opened already, waits
 148          * Otherwise sets a variable telling it to wait if such a connection is opened
 149          */
 150         function waitFor( $file, $pos ) {
 151                 $fname = 'LoadBalancer::waitFor';
 152                 wfProfileIn( $fname );
 153
 154                 wfDebug( "User master pos: $file $pos\n" );
 155                 $this->mWaitForFile = false;
 156                 $this->mWaitForPos = false;
 157
 158                 if ( count( $this->mServers ) > 1 ) {
 159                         $this->mWaitForFile = $file;
 160                         $this->mWaitForPos = $pos;
 161
 162                         if ( $this->mReadIndex > 0 ) {
 163                                 if ( !$this->doWait( $this->mReadIndex ) ) {
 164                                         # Use master instead
 165                                         $this->mReadIndex = 0;
 166                                 }
 167                         }
 168                 }
 169                 wfProfileOut( $fname );
 170         }
 171
 172         /**
 173          * Wait for a given slave to catch up to the master pos stored in $this
 174          */
 175         function doWait( $index ) {
 176                 global $wgMemc;
 177
 178                 $retVal = false;
 179
 180                 $key = 'masterpos:' . $index;
 181                 $memcPos = $wgMemc->get( $key );
 182                 if ( $memcPos ) {
 183                         list( $file, $pos ) = explode( ' ', $memcPos );
 184                         # If the saved position is later than the requested position, return now
 185                         if ( $file == $this->mWaitForFile && $this->mWaitForPos <= $pos ) {
 186                                 $retVal = true;
 187                         }
 188                 }
 189
 190                 if ( !$retVal && $this->isOpen( $index ) ) {
 191                         $conn =& $this->mConnections( $index );
 192                         wfDebug( "Waiting for slave #$index to catch up...\n" );
 193                         $result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, MASTER_WAIT_TIMEOUT );
 194
 195                         if ( $result == -1 || is_null( $result ) ) {
 196                                 # Timed out waiting for slave, use master instead
 197                                 wfDebug( "Timed out waiting for slave #$index pos {$this->mWaitForFile} {$this->mWaitForPos}\n" );
 198                                 $retVal = false;
 199                         } else {
 200                                 $retVal = true;
 201                                 wfDebug( "Done\n" );
 202                         }
 203                 }
 204                 return $retVal;
 205         }
 206
 207         /**
 208          * Get a connection by index
 209          */
 210         function &getConnection( $i, $fail = true )
 211         {
 212                 $fname = 'LoadBalancer::getConnection';
 213                 wfProfileIn( $fname );
 214                 /*
 215                 # Task-based index
 216                 if ( $i >= DB_TASK_FIRST && $i < DB_TASK_LAST ) {
 217                         if ( $i % 2 ) {
 218                                 # Odd index use writer
 219                                 $i = DB_MASTER;
 220                         } else {
 221                                 # Even index use reader
 222                                 $i = DB_SLAVE;
 223                         }
 224                 }*/
 225
 226                 # Operation-based index
 227                 if ( $i == DB_SLAVE ) {
 228                         $i = $this->getReaderIndex();
 229                 } elseif ( $i == DB_MASTER ) {
 230                         $i = $this->getWriterIndex();
 231                 } elseif ( $i == DB_LAST ) {
 232                         # Just use $this->mLastIndex, which should already be set
 233                         $i = $this->mLastIndex;
 234                         if ( $i === -1 ) {
 235                                 # Oh dear, not set, best to use the writer for safety
 236                                 wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
 237                                 $i = $this->getWriterIndex();
 238                         }
 239                 }
 240                 # Now we have an explicit index into the servers array
 241                 $this->openConnection( $i, $fail );
 242                 wfProfileOut( $fname );
 243                 return $this->mConnections[$i];
 244         }
 245
 246         /**
 247          * Open a connection to the server given by the specified index
 248          * Index must be an actual index into the array
 249          * @private
 250          */
 251         function openConnection( $i, $fail = false ) {
 252                 $fname = 'LoadBalancer::openConnection';
 253                 wfProfileIn( $fname );
 254
 255                 if ( !$this->isOpen( $i ) ) {
 256                         $this->mConnections[$i] = $this->reallyOpenConnection( $this->mServers[$i] );
 257
 258                         if ( $i != 0 && $this->mWaitForFile ) {
 259                                 if ( !$this->doWait( $i ) ) {
 260                                         # Error waiting for this slave, use master instead
 261                                         $this->mReadIndex = 0;
 262                                         $i = 0;
 263                                         if ( !$this->isOpen( 0 ) ) {
 264                                                 $this->mConnections[0] = $this->reallyOpenConnection( $this->mServers[0] );
 265                                         }
 266                                         wfDebug( "Failed over to {$this->mConnections[0]->mServer}\n" );
 267                                 }
 268                         }
 269                 }
 270                 if ( !$this->isOpen( $i ) ) {
 271                         wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 272                         if ( $fail ) {
 273                                 $this->reportConnectionError( $this->mConnections[$i] );
 274                         }
 275                         $this->mConnections[$i] = false;
 276                 }
 277                 $this->mLastIndex = $i;
 278                 wfProfileOut( $fname );
 279         }
 280
 281         /**
 282          * Test if the specified index represents an open connection
 283          * @private
 284          */
 285         function isOpen( $index ) {
 286                 if( !is_integer( $index ) ) {
 287                         return false;
 288                 }
 289                 if ( array_key_exists( $index, $this->mConnections ) && is_object( $this->mConnections[$index] ) &&
 290                   $this->mConnections[$index]->isOpen() )
 291                 {
 292                         return true;
 293                 } else {
 294                         return false;
 295                 }
 296         }
 297
 298         /**
 299          * Really opens a connection
 300          * @private
 301          */
 302         function reallyOpenConnection( &$server ) {
 303                         extract( $server );
 304                         # Get class for this database type
 305                         $class = 'Database' . ucfirst( $type );
 306                         if ( !class_exists( $class ) ) {
 307                                 require_once( "$class.php" );
 308                         }
 309
 310                         # Create object
 311                         return new $class( $host, $user, $password, $dbname, 1, $flags );
 312         }
 313
 314         function reportConnectionError( &$conn )
 315         {
 316                 $fname = 'LoadBalancer::reportConnectionError';
 317                 wfProfileIn( $fname );
 318                 # Prevent infinite recursion
 319
 320                 static $reporting = false;
 321                 if ( !$reporting ) {
 322                         $reporting = true;
 323                         if ( !is_object( $conn ) ) {
 324                                 $conn = new Database;
 325                         }
 326                         if ( $this->mFailFunction ) {
 327                                 $conn->failFunction( $this->mFailFunction );
 328                         } else {
 329                                 $conn->failFunction( 'wfEmergencyAbort' );
 330                         }
 331                         $conn->reportConnectionError();
 332                         $reporting = false;
 333                 }
 334                 wfProfileOut( $fname );
 335         }
 336
 337         function getWriterIndex()
 338         {
 339                 return 0;
 340         }
 341
 342         function force( $i )
 343         {
 344                 $this->mForce = $i;
 345         }
 346
 347         function haveIndex( $i )
 348         {
 349                 return array_key_exists( $i, $this->mServers );
 350         }
 351
 352         /**
 353          * Get the number of defined servers (not the number of open connections)
 354          */
 355         function getServerCount() {
 356                 return count( $this->mServers );
 357         }
 358
 359         /**
 360          * Save master pos to the session and to memcached, if the session exists
 361          */
 362         function saveMasterPos() {
 363                 global $wgSessionStarted;
 364                 if ( $wgSessionStarted && count( $this->mServers ) > 1 ) {
 365                         # If this entire request was served from a slave without opening a connection to the
 366                         # master (however unlikely that may be), then we can fetch the position from the slave.
 367                         if ( empty( $this->mConnections[0] ) ) {
 368                                 $conn =& $this->getConnection( DB_SLAVE );
 369                                 list( $file, $pos ) = $conn->getSlavePos();
 370                                 wfDebug( "Saving master pos fetched from slave: $file $pos\n" );
 371                         } else {
 372                                 $conn =& $this->getConnection( 0 );
 373                                 list( $file, $pos ) = $conn->getMasterPos();
 374                                 wfDebug( "Saving master pos: $file $pos\n" );
 375                         }
 376                         if ( $file !== false ) {
 377                                 $_SESSION['master_log_file'] = $file;
 378                                 $_SESSION['master_pos'] = $pos;
 379                         }
 380                 }
 381         }
 382
 383         /**
 384          * Loads the master pos from the session, waits for it if necessary
 385          */
 386         function loadMasterPos() {
 387                 if ( isset( $_SESSION['master_log_file'] ) && isset( $_SESSION['master_pos'] ) ) {
 388                         $this->waitFor( $_SESSION['master_log_file'], $_SESSION['master_pos'] );
 389                 }
 390         }
 391
 392         /**
 393          * Close all open connections
 394          */
 395         function closeAll() {
 396                 foreach( $this->mConnections as $i => $conn ) {
 397                         if ( $this->isOpen( $i ) ) {
 398                                 $conn->close();
 399                         }
 400                 }
 401         }
 402
 403         function commitAll() {
 404                 foreach( $this->mConnections as $i => $conn ) {
 405                         if ( $this->isOpen( $i ) ) {
 406                                 $conn->immediateCommit();
 407                         }
 408                 }
 409         }
 410 }