ac549401d4
* DB_WRITE now called DB_MASTER, DB_READ now called DB_SLAVE * Converted to use SQL wrapper functions instead of direct SQL in various places * Experimental method for preserving the chronological order of events when slave servers are used. Untested. * Fixes to the new post-parse existence test feature * Some.. other stuff
295 lines
8 KiB
PHP
295 lines
8 KiB
PHP
<?php
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# Database load balancing object
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require_once( "Database.php" );
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# Valid database indexes
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# Operation-based indexes
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define( "DB_SLAVE", -1 ); # Read from the slave (or only server)
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define( "DB_MASTER", -2 ); # Write to master (or only server)
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define( "DB_LAST", -3 ); # Whatever database was used last
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# Obsolete aliases
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define( "DB_READ", -1 );
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define( "DB_WRITE", -2 );
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# Task-based indexes
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# ***NOT USED YET, EXPERIMENTAL***
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# These may be defined in $wgDBservers. If they aren't, the default reader or writer will be used
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# Even numbers are always readers, odd numbers are writers
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define( "DB_TASK_FIRST", 1000 ); # First in list
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define( "DB_SEARCH_R", 1000 ); # Search read
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define( "DB_SEARCH_W", 1001 ); # Search write
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define( "DB_ASKSQL_R", 1002 ); # Special:Asksql read
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define( "DB_WATCHLIST_R", 1004 ); # Watchlist read
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define( "DB_TASK_LAST", 1004) ; # Last in list
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define( "MASTER_WAIT_TIMEOUT", 15 ); # Time to wait for a slave to synchronise
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class LoadBalancer {
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/* private */ var $mServers, $mConnections, $mLoads;
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/* private */ var $mFailFunction;
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/* private */ var $mForce, $mReadIndex, $mLastConn;
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/* private */ var $mWaitForFile, $mWaitForPos;
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function LoadBalancer()
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{
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$this->mServers = array();
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$this->mConnections = array();
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$this->mFailFunction = false;
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$this->mReadIndex = -1;
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$this->mForce = -1;
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$this->mLastConn = false;
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}
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function newFromParams( $servers, $failFunction = false )
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{
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$lb = new LoadBalancer;
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$lb->initialise( $servers, $failFunction = false );
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return $lb;
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}
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function initialise( $servers, $failFunction = false )
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{
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$this->mServers = $servers;
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$this->mFailFunction = $failFunction;
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$this->mReadIndex = -1;
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$this->mWriteIndex = -1;
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$this->mForce = -1;
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$this->mConnections = array();
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$this->mLastConn = false;
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$this->mLoads = array();
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$this->mWaitForFile = false;
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$this->mWaitForPos = false;
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foreach( $servers as $i => $server ) {
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$this->mLoads[$i] = $server['load'];
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}
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}
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# Given an array of non-normalised probabilities, this function will select
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# an element and return the appropriate key
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function pickRandom( $weights )
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{
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if ( !is_array( $weights ) || count( $weights ) == 0 ) {
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return false;
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}
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$sum = 0;
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foreach ( $weights as $w ) {
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$sum += $w;
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}
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$max = mt_getrandmax();
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$rand = mt_rand(0, $max) / $max * $sum;
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$sum = 0;
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foreach ( $weights as $i => $w ) {
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$sum += $w;
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if ( $sum >= $rand ) {
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break;
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}
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}
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return $i;
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}
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function &getReader()
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{
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if ( $this->mForce >= 0 ) {
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$conn =& $this->getConnection( $this->mForce );
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} else {
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if ( $this->mReadIndex >= 0 ) {
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$conn =& $this->getConnection( $this->mReadIndex );
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} else {
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# $loads is $this->mLoads except with elements knocked out if they
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# don't work
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$loads = $this->mLoads;
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do {
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$i = $this->pickRandom( $loads );
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if ( $i !== false ) {
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wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}\n" );
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$conn =& $this->getConnection( $i );
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if ( !$conn->isOpen() ) {
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unset( $loads[$i] );
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}
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}
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} while ( $i !== false && !$conn->isOpen() );
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if ( $conn->isOpen() ) {
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$this->mReadIndex = $i;
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}
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}
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}
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if ( $conn === false || !$conn->isOpen() ) {
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$this->reportConnectionError( $conn );
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$conn = false;
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}
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return $conn;
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}
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# Set the master wait position
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# If a DB_SLAVE connection has been opened already, waits
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# Otherwise sets a variable telling it to wait if such a connection is opened
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function waitFor( $file, $pos ) {
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$this->mWaitForFile = false;
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$this->mWaitForPos = false;
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if ( count( $this->mServers ) == 1 ) {
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return;
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}
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$this->mWaitForFile = $file;
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$this->mWaitForPos = $pos;
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if ( $this->mReadIndex > 0 ) {
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$this->doWait( $this->mReadIndex );
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}
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}
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# Wait for a given slave to catch up to the master pos stored in $this
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function doWait( $index ) {
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global $wgMemc;
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$key = "masterpos:" . $index;
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$memcPos = $wgMemc->get( $key );
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if ( $memcPos ) {
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list( $file, $pos ) = explode( ' ', $memcPos );
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# If the saved position is later than the requested position, return now
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if ( $file == $this->mWaitForFile && $this->mWaitForPos <= $pos ) {
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return;
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}
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}
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$conn =& $this->getConnection( $index );
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$result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, MASTER_WAIT_TIMEOUT );
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if ( $result == -1 ) {
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# Timed out waiting for slave, use master instead
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# This is not the ideal solution. If there are a large number of slaves, a slow
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# replicated write query will cause the master to be swamped with reads. However
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# that's a relatively graceful failure mode, so it will do for now.
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$this->mReadIndex = 0;
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}
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}
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function &getConnection( $i, $fail = false )
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{
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/*
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# Task-based index
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if ( $i >= DB_TASK_FIRST && $i < DB_TASK_LAST ) {
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if ( $i % 2 ) {
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# Odd index use writer
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$i = DB_MASTER;
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} else {
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# Even index use reader
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$i = DB_SLAVE;
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}
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}*/
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# Operation-based index
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# Note, getReader() and getWriter() will re-enter this function
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if ( $i == DB_SLAVE ) {
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$this->mLastConn =& $this->getReader();
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} elseif ( $i == DB_MASTER ) {
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$this->mLastConn =& $this->getWriter();
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} elseif ( $i == DB_LAST ) {
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# Just use $this->mLastConn, which should already be set
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if ( $this->mLastConn === false ) {
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# Oh dear, not set, best to use the writer for safety
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$this->mLastConn =& $this->getWriter();
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}
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} else {
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# Explicit index
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if ( !array_key_exists( $i, $this->mConnections ) || !$this->mConnections[$i]->isOpen() ) {
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$this->mConnections[$i] = $this->makeConnection( $this->mServers[$i] );
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if ( $i != 0 && $this->mWaitForFile ) {
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$this->doWait( $i );
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}
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}
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if ( !$this->mConnections[$i]->isOpen() ) {
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wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
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if ( $fail ) {
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$this->reportConnectionError( $this->mConnections[$i] );
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}
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$this->mConnections[$i] = false;
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}
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$this->mLastConn =& $this->mConnections[$i];
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}
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return $this->mLastConn;
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}
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/* private */ function makeConnection( &$server ) {
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extract( $server );
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# Get class for this database type
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$class = 'Database' . ucfirst( $type );
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if ( !class_exists( $class ) ) {
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require_once( "$class.php" );
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}
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# Create object
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return new $class( $host, $user, $password, $dbname, 1 );
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}
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function reportConnectionError( &$conn )
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{
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if ( !is_object( $conn ) ) {
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$conn = new Database;
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}
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if ( $this->mFailFunction ) {
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$conn->setFailFunction( $this->mFailFunction );
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} else {
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$conn->setFailFunction( "wfEmergencyAbort" );
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}
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$conn->reportConnectionError();
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}
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function &getWriter()
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{
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$c =& $this->getConnection( 0 );
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if ( $c === false || !$c->isOpen() ) {
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$this->reportConnectionError( $c );
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$c = false;
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}
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return $c;
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}
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function force( $i )
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{
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$this->mForce = $i;
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}
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function haveIndex( $i )
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{
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return array_key_exists( $i, $this->mServers );
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}
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# Get the number of defined servers (not the number of open connections)
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function getServerCount() {
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return count( $this->mServers );
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}
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# Save master pos to the session and to memcached, if the session exists
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function saveMasterPos() {
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global $wgSessionStarted;
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if ( $wgSessionStarted && count( $this->mServers ) > 1 ) {
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# If this entire request was served from a slave without opening a connection to the
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# master (however unlikely that may be), then we can fetch the position from the slave.
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if ( empty( $this->mConnections[0] ) ) {
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$conn =& $this->getConnection( DB_SLAVE );
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list( $file, $pos ) = $conn->getSlavePos();
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} else {
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$conn =& $this->getConnection( 0 );
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list( $file, $pos ) = $conn->getMasterPos();
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}
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if ( $file !== false ) {
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$_SESSION['master_log_file'] = $file;
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$_SESSION['master_pos'] = $pos;
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}
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}
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}
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# Loads the master pos from the session, waits for it if necessary
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function loadMasterPos() {
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if ( isset( $_SESSION['master_log_file'] ) && isset( $_SESSION['master_pos'] ) ) {
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$this->waitFor( $_SESSION['master_log_file'], $_SESSION['master_pos'] );
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}
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}
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}
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