new object - basic DB load balancer

diff --git a/includes/LoadBalancer.php b/includes/LoadBalancer.php
new file mode 100644 (file)
index 0000000..a3116e2
--- /dev/null
+++ b/includes/LoadBalancer.php
@@ -0,0 +1,143 @@
+<?
+# Database load balancing object
+
+class LoadBalancer {
+       /* private */ var $mServers, $mConnections, $mLoads;
+       /* private */ var $mUser, $mPassword, $mDbName, $mFailFunction;
+       /* private */ var $mForce, $mReadIndex;
+
+       function LoadBalancer()
+       {
+               $this->mServers = array();
+               $this->mLoads = array();
+               $this->mConnections = array();
+               $this->mUser = false;
+               $this->mPassword = false;
+               $this->mDbName = false;
+               $this->mFailFunction = false;
+               $this->mReadIndex = -1;
+               $this->mForce = -1;
+       }
+
+       function newFromParams( $servers, $loads, $user, $password, $dbName, $failFunction = false )
+       {
+               $lb = new LoadBalancer;
+               $lb->initialise( $servers, $loads, $user, $password, $dbName, $failFunction = false );
+               return $lb;
+       }
+
+       function initialise( $servers, $loads, $user, $password, $dbName, $failFunction = false )
+       {
+               $this->mServers = $servers;
+               $this->mLoads = $loads;
+               $this->mUser = $user;
+               $this->mPassword = $password;
+               $this->mDbName = $dbName;
+               $this->mFailFunction = $failFunction;
+               $this->mReadIndex = -1;
+               $this->mWriteIndex = -1;
+               $this->mForce = -1;
+               $this->mConnections = array();
+               wfSeedRandom();
+       }
+       
+       # Given an array of non-normalised probabilities, this function will select
+       # an element and return the appropriate key
+       function pickRandom( $weights )
+       {
+               if ( !is_array( $weights ) || count( $weights ) == 0 ) {
+                       return false;
+               }
+
+               $sum = 0;
+               foreach ( $weights as $w ) {
+                       $sum += $w;
+               }
+               $rand = mt_rand() / RAND_MAX * $sum;
+               
+               $sum = 0;
+               foreach ( $weights as $i => $w ) {
+                       $sum += $w;
+                       if ( $sum >= $rand ) {
+                               break;
+                       }
+               }
+               return $i;
+       }
+
+       function &getReader()
+       {
+               if ( $this->mForce >= 0 ) {
+                       $conn =& $this->getConnection( $this->mForce );
+               } else {
+                       if ( $this->mReadIndex >= 0 ) {
+                               $conn =& $this->getConnection( $this->mReadIndex );
+                       } else {
+                               # $loads is $this->mLoads except with elements knocked out if they
+                               # don't work
+                               $loads = $this->mLoads;
+                               do {
+                                       $i = pickRandom( $loads );
+                                       if ( $i !== false ) {
+                                               $conn =& $this->getConnection( $i );
+                                               if ( !$conn->isOpen() ) {
+                                                       unset( $loads[$i] );
+                                               }
+                                       }
+                               } while ( $i !== false && !$conn->isOpen() );
+                               if ( $conn->isOpen() ) {
+                                       $this->mReadIndex = $i;
+                               }
+                       }
+               }
+               if ( $conn === false || !$conn->isOpen() ) {
+                       $this->reportConnectionError( $conn );
+                       $conn = false;
+               }
+               return $conn;
+       }
+       
+       function &getConnection( $i, $fail = false )
+       {
+               if ( !array_key_exists( $i, $this->mConnections) || !$this->mConnections[$i]->isOpen() ) {
+                       $this->mConnections[$i] = Database::newFromParams( $this->mServers[$i], $this->mUser, 
+                         $this->mPassword, $this->mDbName, 1 );
+               }
+               if ( !$this->mConnections[$i]->isOpen() ) {
+                       wfDebug( "Failed to connect to database $i at {$this->mServers[$i]}\n" );
+                       if ( $fail ) {
+                               $this->reportConnectionError( $this->mConnections[$i] );
+                       }
+                       $this->mConnections[$i] = false;
+               }
+               return $this->mConnections[$i];
+       }
+
+       function reportConnectionError( &$conn )
+       {
+               if ( !is_object( $conn ) ) {
+                       $conn = new Database;
+               }
+               if ( $this->mFailFunction ) {
+                       $conn->setFailFunction( $this->mFailFunction );
+               } else {
+                       $conn->setFailFunction( "wfEmergencyAbort" );
+               }
+               $conn->reportConnectionError();
+       }
+       
+       function &getWriter()
+       {
+               $c =& $this->getConnection( 0 );
+               if ( !$c->isOpen() ) {
+                       reportConnectionError( $conn );
+                       $c = false;
+               }
+               return $c;
+       }
+
+       function force( $i )
+       {
+               $this->mForce = $i;
+       }
+}