foreach ( $weights as $w ) {
$sum += $w;
}
+
+ if ( $sum == 0 ) {
+ # No loads on any of them
+ # Just pick one at random
+ foreach ( $weights as $i => $w ) {
+ $weights[$i] = 1;
+ }
+ }
$max = mt_getrandmax();
$rand = mt_rand(0, $max) / $max * $sum;
return $i;
}
+ function getRandomNonLagged( $loads ) {
+ # Unset excessively lagged servers
+ $lags = $this->getLagTimes();
+ foreach ( $lags as $i => $lag ) {
+ if ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
+ unset( $loads[$i] );
+ }
+ }
+
+
+ # Find out if all the slaves with non-zero load are lagged
+ $sum = 0;
+ foreach ( $loads as $load ) {
+ $sum += $load;
+ }
+ if ( $sum == 0 ) {
+ # No appropriate DB servers except maybe the master and some slaves with zero load
+ # Do NOT use the master
+ # Instead, this function will return false, triggering read-only mode,
+ # and a lagged slave will be used instead.
+ unset ( $loads[0] );
+ }
+
+ if ( count( $loads ) == 0 ) {
+ return false;
+ }
+
+ wfDebug( var_export( $loads, true ) );
+
+ # Return a random representative of the remainder
+ return $this->pickRandom( $loads );
+ }
+
+
function getReaderIndex()
{
+ global $wgMaxLag, $wgReadOnly;
+
$fname = 'LoadBalancer::getReaderIndex';
wfProfileIn( $fname );
# $loads is $this->mLoads except with elements knocked out if they
# don't work
$loads = $this->mLoads;
+ $done = false;
+ $totalElapsed = 0;
do {
- $i = $this->pickRandom( $loads );
+ if ( $wgReadOnly ) {
+ $i = $this->pickRandom( $loads );
+ } else {
+ $i = $this->getRandomNonLagged( $loads );
+ if ( $i === false && count( $loads ) != 0 ) {
+ # All slaves lagged. Switch to read-only mode
+ $wgReadOnly = wfMsgNoDB( 'readonly_lag' );
+ $i = $this->pickRandom( $loads );
+ }
+ }
if ( $i !== false ) {
wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}...\n" );
$this->openConnection( $i );
if ( !$this->isOpen( $i ) ) {
wfDebug( "Failed\n" );
unset( $loads[$i] );
- } elseif ( isset( $this->mServers[$i]['slave pos'] ) ) {
- wfDebug( "Lagged slave\n" );
- $this->mLaggedSlaveMode = true;
+ $sleepTime = 0;
} else {
- wfDebug( "OK\n" );
+ $status = $this->mConnections[$i]->getStatus();
+ if ( isset( $this->mServers[$i]['max threads'] ) &&
+ $status['Threads_running'] > $this->mServers[$i]['max threads'] )
+ {
+ # Slave is lagged, wait for a while
+ $sleepTime = 5000 * $status['Threads_connected'];
+
+ # If we reach the timeout and exit the loop, don't use it
+ $i = false;
+ } else {
+ $done = true;
+ $sleepTime = 0;
+ }
}
+ } else {
+ $sleepTime = 500000;
+ }
+ if ( $sleepTime ) {
+ $totalElapsed += $sleepTime;
+ usleep( $sleepTime );
}
- } while ( $i !== false && !$this->isOpen( $i ) );
+ } while ( count( $loads ) && !$done && $totalElapsed / 1e6 < $this->mWaitTimeout );
- if ( $this->isOpen( $i ) ) {
+ if ( $i !== false && $this->isOpen( $i ) ) {
$this->mReadIndex = $i;
} else {
$i = false;
* Otherwise sets a variable telling it to wait if such a connection is opened
*/
function waitFor( $file, $pos ) {
+ /*
$fname = 'LoadBalancer::waitFor';
wfProfileIn( $fname );
}
}
wfProfileOut( $fname );
+ */
}
/**
* Wait for a given slave to catch up to the master pos stored in $this
*/
function doWait( $index ) {
+ return true;
+ /*
global $wgMemc;
$retVal = false;
wfDebug( "Done\n" );
}
}
- return $retVal;
+ return $retVal;*/
}
/**
}
return $success;
}
+
+ /**
+ * Get the hostname and lag time of the most-lagged slave
+ * This is useful for maintenance scripts that need to throttle their updates
+ */
+ function getMaxLag() {
+ $maxLag = -1;
+ $host = '';
+ foreach ( $this->mServers as $i => $conn ) {
+ if ( $this->openConnection( $i ) ) {
+ $lag = $this->mConnections[$i]->getLag();
+ if ( $lag > $maxLag ) {
+ $maxLag = $lag;
+ $host = $this->mServers[$i]['host'];
+ }
+ }
+ }
+ return array( $host, $maxLag );
+ }
+
+ /**
+ * Get lag time for each DB
+ * Results are cached for a short time in memcached
+ */
+ function getLagTimes() {
+ $expiry = 5;
+ $requestRate = 10;
+
+ global $wgMemc;
+ $times = $wgMemc->get( 'lag_times' );
+ if ( $times ) {
+ # Randomly recache with probability rising over $expiry
+ $elapsed = time() - $times['timestamp'];
+ $chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
+ if ( mt_rand( 0, $chance ) != 0 ) {
+ unset( $times['timestamp'] );
+ return $times;
+ }
+ }
+
+ # Cache key missing or expired
+
+ $times = array();
+ foreach ( $this->mServers as $i => $conn ) {
+ if ( $this->openConnection( $i ) ) {
+ $times[$i] = $this->mConnections[$i]->getLag();
+ }
+ }
+
+ # Add a timestamp key so we know when it was cached
+ $times['timestamp'] = time();
+ $wgMemc->set( 'lag_times', $times, $expiry );
+
+ # But don't give the timestamp to the caller
+ unset($times['timestamp']);
+ return $times;
+ }
}
?>
dépôts / lhc / web / wiklou.git / commitdiff