includes/LoadBalancer.php

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