includes/LoadBalancer.php

   1 <?php
   2 # Database load balancing object
   3
   4 class LoadBalancer {
   5         /* private */ var $mServers, $mConnections, $mLoads;
   6         /* private */ var $mUser, $mPassword, $mDbName, $mFailFunction;
   7         /* private */ var $mForce, $mReadIndex;
   8
   9         function LoadBalancer()
  10         {
  11                 $this->mServers = array();
  12                 $this->mLoads = array();
  13                 $this->mConnections = array();
  14                 $this->mUser = false;
  15                 $this->mPassword = false;
  16                 $this->mDbName = false;
  17                 $this->mFailFunction = false;
  18                 $this->mReadIndex = -1;
  19                 $this->mForce = -1;
  20         }
  21
  22         function newFromParams( $servers, $loads, $user, $password, $dbName, $failFunction = false )
  23         {
  24                 $lb = new LoadBalancer;
  25                 $lb->initialise( $servers, $loads, $user, $password, $dbName, $failFunction = false );
  26                 return $lb;
  27         }
  28
  29         function initialise( $servers, $loads, $user, $password, $dbName, $failFunction = false )
  30         {
  31                 $this->mServers = $servers;
  32                 $this->mLoads = $loads;
  33                 $this->mUser = $user;
  34                 $this->mPassword = $password;
  35                 $this->mDbName = $dbName;
  36                 $this->mFailFunction = $failFunction;
  37                 $this->mReadIndex = -1;
  38                 $this->mWriteIndex = -1;
  39                 $this->mForce = -1;
  40                 $this->mConnections = array();
  41                 wfSeedRandom();
  42         }
  43
  44         # Given an array of non-normalised probabilities, this function will select
  45         # an element and return the appropriate key
  46         function pickRandom( $weights )
  47         {
  48                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  49                         return false;
  50                 }
  51
  52                 $sum = 0;
  53                 foreach ( $weights as $w ) {
  54                         $sum += $w;
  55                 }
  56                 $rand = mt_rand() / RAND_MAX * $sum;
  57
  58                 $sum = 0;
  59                 foreach ( $weights as $i => $w ) {
  60                         $sum += $w;
  61                         if ( $sum >= $rand ) {
  62                                 break;
  63                         }
  64                 }
  65                 return $i;
  66         }
  67
  68         function &getReader()
  69         {
  70                 if ( $this->mForce >= 0 ) {
  71                         $conn =& $this->getConnection( $this->mForce );
  72                 } else {
  73                         if ( $this->mReadIndex >= 0 ) {
  74                                 $conn =& $this->getConnection( $this->mReadIndex );
  75                         } else {
  76                                 # $loads is $this->mLoads except with elements knocked out if they
  77                                 # don't work
  78                                 $loads = $this->mLoads;
  79                                 do {
  80                                         $i = pickRandom( $loads );
  81                                         if ( $i !== false ) {
  82                                                 $conn =& $this->getConnection( $i );
  83                                                 if ( !$conn->isOpen() ) {
  84                                                         unset( $loads[$i] );
  85                                                 }
  86                                         }
  87                                 } while ( $i !== false && !$conn->isOpen() );
  88                                 if ( $conn->isOpen() ) {
  89                                         $this->mReadIndex = $i;
  90                                 }
  91                         }
  92                 }
  93                 if ( $conn === false || !$conn->isOpen() ) {
  94                         $this->reportConnectionError( $conn );
  95                         $conn = false;
  96                 }
  97                 return $conn;
  98         }
  99
 100         function &getConnection( $i, $fail = false )
 101         {
 102                 if ( !array_key_exists( $i, $this->mConnections) || !$this->mConnections[$i]->isOpen() ) {
 103                         $this->mConnections[$i] = Database::newFromParams( $this->mServers[$i], $this->mUser,
 104                           $this->mPassword, $this->mDbName, 1 );
 105                 }
 106                 if ( !$this->mConnections[$i]->isOpen() ) {
 107                         wfDebug( "Failed to connect to database $i at {$this->mServers[$i]}\n" );
 108                         if ( $fail ) {
 109                                 $this->reportConnectionError( $this->mConnections[$i] );
 110                         }
 111                         $this->mConnections[$i] = false;
 112                 }
 113                 return $this->mConnections[$i];
 114         }
 115
 116         function reportConnectionError( &$conn )
 117         {
 118                 if ( !is_object( $conn ) ) {
 119                         $conn = new Database;
 120                 }
 121                 if ( $this->mFailFunction ) {
 122                         $conn->setFailFunction( $this->mFailFunction );
 123                 } else {
 124                         $conn->setFailFunction( "wfEmergencyAbort" );
 125                 }
 126                 $conn->reportConnectionError();
 127         }
 128
 129         function &getWriter()
 130         {
 131                 $c =& $this->getConnection( 0 );
 132                 if ( !$c->isOpen() ) {
 133                         reportConnectionError( $conn );
 134                         $c = false;
 135                 }
 136                 return $c;
 137         }
 138
 139         function force( $i )
 140         {
 141                 $this->mForce = $i;
 142         }
 143 }