define( 'DB_READ', -1 );
define( 'DB_WRITE', -2 );
+
+# Scale polling time so that under overload conditions, the database server
+# receives a SHOW STATUS query at an average interval of this many microseconds
+define( 'AVG_STATUS_POLL', 2000 );
+
+
/**
* Database load balancing object
*
*/
class LoadBalancer {
/* private */ var $mServers, $mConnections, $mLoads, $mGroupLoads;
- /* private */ var $mFailFunction;
+ /* private */ var $mFailFunction, $mErrorConnection;
/* private */ var $mForce, $mReadIndex, $mLastIndex;
/* private */ var $mWaitForFile, $mWaitForPos, $mWaitTimeout;
- /* private */ var $mLaggedSlaveMode;
+ /* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
function LoadBalancer()
{
$this->mReadIndex = -1;
$this->mForce = -1;
$this->mLastIndex = -1;
+ $this->mErrorConnection = false;
}
function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
$this->mGroupLoads[$group][$i] = $ratio;
}
}
- }
+ }
}
-
+
/**
* Given an array of non-normalised probabilities, this function will select
* an element and return the appropriate key
}
$max = mt_getrandmax();
$rand = mt_rand(0, $max) / $max * $sum;
-
+
$sum = 0;
foreach ( $weights as $i => $w ) {
$sum += $w;
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,
+ # Instead, this function will return false, triggering read-only mode,
# and a lagged slave will be used instead.
unset ( $loads[0] );
}
return false;
}
- #wfDebug( var_export( $loads, true ) );
+ #wfDebugLog( 'connect', var_export( $loads, true ) );
# Return a random representative of the remainder
return $this->pickRandom( $loads );
}
-
- function getReaderIndex()
- {
- global $wgMaxLag, $wgReadOnly;
+ /**
+ * Get the index of the reader connection, which may be a slave
+ * This takes into account load ratios and lag times. It should
+ * always return a consistent index during a given invocation
+ *
+ * Side effect: opens connections to databases
+ */
+ function getReaderIndex() {
+ global $wgReadOnly, $wgDBClusterTimeout;
$fname = 'LoadBalancer::getReaderIndex';
wfProfileIn( $fname );
$i = $this->pickRandom( $loads );
}
}
+ $serverIndex = $i;
if ( $i !== false ) {
- wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}...\n" );
+ wfDebugLog( 'connect', "Using reader #$i: {$this->mServers[$i]['host']}...\n" );
$this->openConnection( $i );
-
+
if ( !$this->isOpen( $i ) ) {
wfDebug( "Failed\n" );
unset( $loads[$i] );
$sleepTime = 0;
} else {
$status = $this->mConnections[$i]->getStatus();
- if ( isset( $this->mServers[$i]['max threads'] ) &&
- $status['Threads_running'] > $this->mServers[$i]['max threads'] )
+ 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'];
+ $sleepTime = AVG_STATUS_POLL * $status['Threads_connected'];
# If we reach the timeout and exit the loop, don't use it
$i = false;
}
if ( $sleepTime ) {
$totalElapsed += $sleepTime;
+ $x = "{$this->mServers[$serverIndex]['host']} [$serverIndex]";
+ wfProfileIn( "$fname-sleep $x" );
usleep( $sleepTime );
+ wfProfileOut( "$fname-sleep $x" );
}
- } while ( count( $loads ) && !$done && $totalElapsed / 1e6 < $this->mWaitTimeout );
+ } while ( count( $loads ) && !$done && $totalElapsed / 1e6 < $wgDBClusterTimeout );
+ if ( $totalElapsed / 1e6 >= $wgDBClusterTimeout ) {
+ $this->mErrorConnection = false;
+ $this->mLastError = 'All servers busy';
+ }
+
if ( $i !== false && $this->isOpen( $i ) ) {
- $this->mReadIndex = $i;
+ # Wait for the session master pos for a short time
+ if ( $this->mWaitForFile ) {
+ if ( !$this->doWait( $i ) ) {
+ $this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
+ }
+ }
+ if ( $i !== false ) {
+ $this->mReadIndex = $i;
+ }
} else {
$i = false;
}
wfProfileOut( $fname );
return $i;
}
-
+
/**
* Get a random server to use in a query group
*/
wfDebug( "Query group $group => $i\n" );
return $i;
}
-
+
/**
* Set the master wait position
* If a DB_SLAVE connection has been opened already, waits
* Otherwise sets a variable telling it to wait if such a connection is opened
*/
function waitFor( $file, $pos ) {
- /*
$fname = 'LoadBalancer::waitFor';
wfProfileIn( $fname );
$this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
$this->mLaggedSlaveMode = true;
}
- }
+ }
}
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;
# Debugging hacks
wfDebug( "Done\n" );
}
}
- return $retVal;*/
- }
+ return $retVal;
+ }
/**
* Get a connection by index
{
$fname = 'LoadBalancer::getConnection';
wfProfileIn( $fname );
-
+
# Query groups
$groupIndex = false;
foreach ( $groups as $group ) {
break;
}
}
-
+
# Operation-based index
- if ( $i == DB_SLAVE ) {
+ if ( $i == DB_SLAVE ) {
$i = $this->getReaderIndex();
} elseif ( $i == DB_MASTER ) {
$i = $this->getWriterIndex();
$i = $this->getWriterIndex();
}
}
+ # Couldn't find a working server in getReaderIndex()?
+ if ( $i === false ) {
+ $this->reportConnectionError( $this->mErrorConnection );
+ }
# Now we have an explicit index into the servers array
$this->openConnection( $i, $fail );
-
+
wfProfileOut( $fname );
return $this->mConnections[$i];
}
if ( !$this->isOpen( $i ) ) {
$this->mConnections[$i] = $this->reallyOpenConnection( $this->mServers[$i] );
-
- if ( $this->isOpen( $i ) && $i != 0 && $this->mWaitForFile ) {
- if ( !$this->doWait( $i ) ) {
- $this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
- $success = false;
- }
- }
}
+
if ( !$this->isOpen( $i ) ) {
wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
if ( $fail ) {
$this->reportConnectionError( $this->mConnections[$i] );
}
+ $this->mErrorConnection = $this->mConnections[$i];
$this->mConnections[$i] = false;
$success = false;
}
if( !is_integer( $index ) ) {
return false;
}
- if ( array_key_exists( $index, $this->mConnections ) && is_object( $this->mConnections[$index] ) &&
- $this->mConnections[$index]->isOpen() )
+ if ( array_key_exists( $index, $this->mConnections ) && is_object( $this->mConnections[$index] ) &&
+ $this->mConnections[$index]->isOpen() )
{
return true;
} else {
return false;
}
}
-
+
/**
* Really opens a connection
* @private
if( !is_array( $server ) ) {
wfDebugDieBacktrace( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
}
-
+
extract( $server );
# Get class for this database type
$class = 'Database' . ucfirst( $type );
}
# Create object
- return new $class( $host, $user, $password, $dbname, 1, $flags );
+ $db = new $class( $host, $user, $password, $dbname, 1, $flags );
+ $db->setLBInfo( $server );
+ return $db;
}
-
+
function reportConnectionError( &$conn )
{
$fname = 'LoadBalancer::reportConnectionError';
wfProfileIn( $fname );
# Prevent infinite recursion
-
+
static $reporting = false;
if ( !$reporting ) {
$reporting = true;
if ( !is_object( $conn ) ) {
+ // No last connection, probably due to all servers being too busy
$conn = new Database;
- }
- if ( $this->mFailFunction ) {
- $conn->failFunction( $this->mFailFunction );
+ if ( $this->mFailFunction ) {
+ $conn->failFunction( $this->mFailFunction );
+ $conn->reportConnectionError( $this->mLastError );
+ } else {
+ // If all servers were busy, mLastError will contain something sensible
+ wfEmergencyAbort( $conn, $this->mLastError );
+ }
} else {
- $conn->failFunction( 'wfEmergencyAbort' );
+ if ( $this->mFailFunction ) {
+ $conn->failFunction( $this->mFailFunction );
+ } else {
+ $conn->failFunction( false );
+ }
+ $conn->reportConnectionError( "{$this->mLastError} ({$conn->mServer})" );
}
- $conn->reportConnectionError();
$reporting = false;
}
wfProfileOut( $fname );
}
-
+
function getWriterIndex()
{
return 0;
function saveMasterPos() {
global $wgSessionStarted;
if ( $wgSessionStarted && count( $this->mServers ) > 1 ) {
- # If this entire request was served from a slave without opening a connection to the
+ # If this entire request was served from a slave without opening a connection to the
# master (however unlikely that may be), then we can fetch the position from the slave.
if ( empty( $this->mConnections[0] ) ) {
$conn =& $this->getConnection( DB_SLAVE );
}
return array( $host, $maxLag );
}
-
+
/**
* Get lag time for each DB
* Results are cached for a short time in memcached
*/
function getLagTimes() {
+ global $wgDBname;
+
$expiry = 5;
$requestRate = 10;
global $wgMemc;
- $times = $wgMemc->get( 'lag_times' );
+ $times = $wgMemc->get( "$wgDBname:lag_times" );
if ( $times ) {
# Randomly recache with probability rising over $expiry
$elapsed = time() - $times['timestamp'];
# Add a timestamp key so we know when it was cached
$times['timestamp'] = time();
- $wgMemc->set( 'lag_times', $times, $expiry );
+ $wgMemc->set( "$wgDBname:lag_times", $times, $expiry );
# But don't give the timestamp to the caller
unset($times['timestamp']);
dépôts / lhc / web / wiklou.git / blobdiff