From 1231546be76f9dc56ddef14e34e087e431d4fefa Mon Sep 17 00:00:00 2001
From: Tim Starling <tstarling@users.mediawiki.org>
Date: Sun, 25 Jan 2004 13:27:53 +0000
Subject: [PATCH] new object - basic DB load balancer

---
 includes/LoadBalancer.php | 143 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)
 create mode 100644 includes/LoadBalancer.php

diff --git a/includes/LoadBalancer.php b/includes/LoadBalancer.php
new file mode 100644
index 0000000000..a3116e2ce1
--- /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;
+	}
+}
-- 
2.20.1