X-Git-Url: https://git.heureux-cyclage.org/?a=blobdiff_plain;f=includes%2FLoadBalancer.php;h=396ef865be4fc280c2edb0a440db14b526c42ccc;hb=75a2ed9ffaa4c1a71f4fb29b85008b1d9d0499da;hp=8c9aa64f551a2e874346d6f1018654b2ea8e163d;hpb=ef3b9225fd9e3416da471824d9f6d5f57a6642dd;p=lhc%2Fweb%2Fwiklou.git

diff --git a/includes/LoadBalancer.php b/includes/LoadBalancer.php
index 8c9aa64f55..396ef865be 100644
--- a/includes/LoadBalancer.php
+++ b/includes/LoadBalancer.php
@@ -4,31 +4,6 @@
  * @package MediaWiki
  */
 
-/**
- * Depends on the database object
- */
-require_once( 'Database.php' );
-
-# Valid database indexes
-# Operation-based indexes
-define( 'DB_SLAVE', -1 );     # Read from the slave (or only server)
-define( 'DB_MASTER', -2 );    # Write to master (or only server)
-define( 'DB_LAST', -3 );     # Whatever database was used last
-
-# Obsolete aliases
-define( 'DB_READ', -1 );
-define( 'DB_WRITE', -2 );
-
-# Task-based indexes
-# ***NOT USED YET, EXPERIMENTAL***
-# These may be defined in $wgDBservers. If they aren't, the default reader or writer will be used
-# Even numbers are always readers, odd numbers are writers
-define( 'DB_TASK_FIRST', 1000 );  # First in list
-define( 'DB_SEARCH_R', 1000 );    # Search read
-define( 'DB_SEARCH_W', 1001 );    # Search write
-define( 'DB_ASKSQL_R', 1002 );    # Special:Asksql read
-define( 'DB_WATCHLIST_R', 1004 ); # Watchlist read
-define( 'DB_TASK_LAST', 1004) ;   # Last in list
 
 /**
  * Database load balancing object
@@ -37,30 +12,19 @@ define( 'DB_TASK_LAST', 1004) ;   # Last in list
  * @package MediaWiki
  */
 class LoadBalancer {
-	/* private */ var $mServers, $mConnections, $mLoads;
-	/* private */ var $mFailFunction;
-	/* private */ var $mForce, $mReadIndex, $mLastIndex;
+	/* private */ var $mServers, $mConnections, $mLoads, $mGroupLoads;
+	/* private */ var $mFailFunction, $mErrorConnection;
+	/* private */ var $mForce, $mReadIndex, $mLastIndex, $mAllowLagged;
 	/* private */ var $mWaitForFile, $mWaitForPos, $mWaitTimeout;
-	/* private */ var $mLaggedSlaveMode;
+	/* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
 
-	function LoadBalancer()
-	{
-		$this->mServers = array();
-		$this->mConnections = array();
-		$this->mFailFunction = false;
-		$this->mReadIndex = -1;
-		$this->mForce = -1;
-		$this->mLastIndex = -1;
-	}
-
-	function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
-	{
-		$lb = new LoadBalancer;
-		$lb->initialise( $servers, $failFunction = false );
-		return $lb;
-	}
+	/**
+	 * Scale polling time so that under overload conditions, the database server
+	 * receives a SHOW STATUS query at an average interval of this many microseconds
+	 */
+	const AVG_STATUS_POLL = 2000;
 
-	function initialise( $servers, $failFunction = false, $waitTimeout = 10 )
+	function LoadBalancer( $servers, $failFunction = false, $waitTimeout = 10, $waitForMasterNow = false )
 	{
 		$this->mServers = $servers;
 		$this->mFailFunction = $failFunction;
@@ -74,12 +38,30 @@ class LoadBalancer {
 		$this->mWaitForPos = false;
 		$this->mWaitTimeout = $waitTimeout;
 		$this->mLaggedSlaveMode = false;
+		$this->mErrorConnection = false;
+		$this->mAllowLag = false;
 
 		foreach( $servers as $i => $server ) {
 			$this->mLoads[$i] = $server['load'];
+			if ( isset( $server['groupLoads'] ) ) {
+				foreach ( $server['groupLoads'] as $group => $ratio ) {
+					if ( !isset( $this->mGroupLoads[$group] ) ) {
+						$this->mGroupLoads[$group] = array();
+					}
+					$this->mGroupLoads[$group][$i] = $ratio;
+				}
+			}
 		}
+		if ( $waitForMasterNow ) {
+			$this->loadMasterPos();
+		}
+	}
+
+	static function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
+	{
+		return new LoadBalancer( $servers, $failFunction, $waitTimeout );
 	}
-	
+
 	/**
 	 * Given an array of non-normalised probabilities, this function will select
 	 * an element and return the appropriate key
@@ -90,13 +72,17 @@ class LoadBalancer {
 			return false;
 		}
 
-		$sum = 0;
-		foreach ( $weights as $w ) {
-			$sum += $w;
+		$sum = array_sum( $weights );
+		if ( $sum == 0 ) {
+			# No loads on any of them
+			# In previous versions, this triggered an unweighted random selection,
+			# but this feature has been removed as of April 2006 to allow for strict 
+			# separation of query groups. 
+			return false;
 		}
 		$max = mt_getrandmax();
 		$rand = mt_rand(0, $max) / $max * $sum;
-		
+
 		$sum = 0;
 		foreach ( $weights as $i => $w ) {
 			$sum += $w;
@@ -107,14 +93,57 @@ class LoadBalancer {
 		return $i;
 	}
 
-	function getReaderIndex()
-	{
+	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.
+			return false;
+		}
+
+		if ( count( $loads ) == 0 ) {
+			return false;
+		}
+
+		#wfDebugLog( 'connect', var_export( $loads, true ) );
+
+		# Return a random representative of the remainder
+		return $this->pickRandom( $loads );
+	}
+
+	/**
+	 * 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 = false;
 		if ( $this->mForce >= 0 ) {
 			$i = $this->mForce;
+		} elseif ( count( $this->mServers ) == 1 )  {
+			# Skip the load balancing if there's only one server
+			$i = 0;
 		} else {
 			if ( $this->mReadIndex >= 0 ) {
 				$i = $this->mReadIndex;
@@ -122,21 +151,75 @@ class LoadBalancer {
 				# $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 or $this->mAllowLagged ) {
+						$i = $this->pickRandom( $loads );
+					} else {
+						$i = $this->getRandomNonLagged( $loads );
+						if ( $i === false && count( $loads ) != 0 )  {
+							# All slaves lagged. Switch to read-only mode
+							$wgReadOnly = wfMsgNoDBForContent( 'readonly_lag' );
+							$i = $this->pickRandom( $loads );
+						}
+					}
+					$serverIndex = $i;
 					if ( $i !== false ) {
-						wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}\n" );
-
+						wfDebugLog( 'connect', "$fname: Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 						$this->openConnection( $i );
 
 						if ( !$this->isOpen( $i ) ) {
+							wfDebug( "$fname: Failed\n" );
 							unset( $loads[$i] );
+							$sleepTime = 0;
+						} else {
+							if ( isset( $this->mServers[$i]['max threads'] ) ) {
+							    $status = $this->mConnections[$i]->getStatus("Thread%");
+							    if ( $status['Threads_running'] > $this->mServers[$i]['max threads'] ) {
+								# Too much load, back off and wait for a while.
+								# The sleep time is scaled by the number of threads connected,
+								# to produce a roughly constant global poll rate.
+								$sleepTime = self::AVG_STATUS_POLL * $status['Threads_connected'];
+
+								# If we reach the timeout and exit the loop, don't use it
+								$i = false;
+							    } else {
+								$done = true;
+								$sleepTime = 0;
+							    }
+							} else {
+							    $done = true;
+							    $sleepTime = 0;
+							}
 						}
+					} else {
+						$sleepTime = 500000;
 					}
-				} while ( $i !== false && !$this->isOpen( $i ) );
+					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 < $wgDBClusterTimeout );
+
+				if ( $totalElapsed / 1e6 >= $wgDBClusterTimeout ) {
+					$this->mErrorConnection = false;
+					$this->mLastError = 'All servers busy';
+				}
 
-				if ( $this->isOpen( $i ) ) {
-					$this->mReadIndex = $i;
+				if ( $i !== false && $this->isOpen( $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;
 				}
@@ -146,6 +229,19 @@ class LoadBalancer {
 		return $i;
 	}
 
+	/**
+	 * Get a random server to use in a query group
+	 */
+	function getGroupIndex( $group ) {
+		if ( isset( $this->mGroupLoads[$group] ) ) {
+			$i = $this->pickRandom( $this->mGroupLoads[$group] );
+		} else {
+			$i = false;
+		}
+		wfDebug( "Query group $group => $i\n" );
+		return $i;
+	}
+
 	/**
 	 * Set the master wait position
 	 * If a DB_SLAVE connection has been opened already, waits
@@ -162,12 +258,14 @@ class LoadBalancer {
 		if ( count( $this->mServers ) > 1 ) {
 			$this->mWaitForFile = $file;
 			$this->mWaitForPos = $pos;
+			$i = $this->mReadIndex;
 
-			if ( $this->mReadIndex > 0 ) {
-				if ( !$this->doWait( $this->mReadIndex ) ) {
+			if ( $i > 0 ) {
+				if ( !$this->doWait( $i ) ) {
+					$this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
 					$this->mLaggedSlaveMode = true;
 				}
-			} 
+			}
 		}
 		wfProfileOut( $fname );
 	}
@@ -177,9 +275,16 @@ class LoadBalancer {
 	 */
 	function doWait( $index ) {
 		global $wgMemc;
-		
+
 		$retVal = false;
 
+		# Debugging hacks
+		if ( isset( $this->mServers[$index]['lagged slave'] ) ) {
+			return false;
+		} elseif ( isset( $this->mServers[$index]['fake slave'] ) ) {
+			return true;
+		}
+
 		$key = 'masterpos:' . $index;
 		$memcPos = $wgMemc->get( $key );
 		if ( $memcPos ) {
@@ -205,29 +310,40 @@ class LoadBalancer {
 			}
 		}
 		return $retVal;
-	}		
+	}
 
 	/**
 	 * Get a connection by index
 	 */
-	function &getConnection( $i, $fail = true )
+	function &getConnection( $i, $fail = true, $groups = array() )
 	{
+		global $wgDBtype;
 		$fname = 'LoadBalancer::getConnection';
 		wfProfileIn( $fname );
-		/*
-		# Task-based index
-		if ( $i >= DB_TASK_FIRST && $i < DB_TASK_LAST ) {
-			if ( $i % 2 ) {
-				# Odd index use writer
-				$i = DB_MASTER;
-			} else {
-				# Even index use reader
-				$i = DB_SLAVE;
+
+
+		# Query groups
+		if ( !is_array( $groups ) ) {
+			$groupIndex = $this->getGroupIndex( $groups, $i );
+			if ( $groupIndex !== false ) {
+				$i = $groupIndex;
+			}
+		} else {
+			foreach ( $groups as $group ) {
+				$groupIndex = $this->getGroupIndex( $group, $i );
+				if ( $groupIndex !== false ) {
+					$i = $groupIndex;
+					break;
+				}
 			}
-		}*/
+		}
 
+		# For now, only go through all this for mysql databases
+		if ($wgDBtype != 'mysql') {
+			$i = $this->getWriterIndex();
+		}
 		# Operation-based index
-		if ( $i == DB_SLAVE ) {	
+		elseif ( $i == DB_SLAVE ) {
 			$i = $this->getReaderIndex();
 		} elseif ( $i == DB_MASTER ) {
 			$i = $this->getWriterIndex();
@@ -240,8 +356,13 @@ class LoadBalancer {
 				$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];
 	}
@@ -249,113 +370,129 @@ class LoadBalancer {
 	/**
 	 * Open a connection to the server given by the specified index
 	 * Index must be an actual index into the array
-	 * @private
+	 * Returns success
+	 * @access private
 	 */
 	function openConnection( $i, $fail = false ) {
 		$fname = 'LoadBalancer::openConnection';
 		wfProfileIn( $fname );
+		$success = true;
 
 		if ( !$this->isOpen( $i ) ) {
 			$this->mConnections[$i] = $this->reallyOpenConnection( $this->mServers[$i] );
-			
-			if ( $i != 0 && $this->mWaitForFile ) {
-				if ( !$this->doWait( $i ) ) {
-					# Error waiting for this slave, use master instead
-					$this->mReadIndex = 0;
-					$i = 0;
-					if ( !$this->isOpen( 0 ) ) {
-						$this->mConnections[0] = $this->reallyOpenConnection( $this->mServers[0] );
-					}
-					wfDebug( "Failed over to {$this->mConnections[0]->mServer}\n" );
-				}
-			}
 		}
+
 		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;
 		}
 		$this->mLastIndex = $i;
 		wfProfileOut( $fname );
+		return $success;
 	}
 
 	/**
 	 * Test if the specified index represents an open connection
-	 * @private
+	 * @access private
 	 */
 	function isOpen( $index ) {
 		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
+	 * @access private
 	 */
 	function reallyOpenConnection( &$server ) {
 		if( !is_array( $server ) ) {
-			wfDebugDieBacktrace( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
+			throw new MWException( '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 );
-		if ( !class_exists( $class ) ) {
-			require_once( "$class.php" );
-		}
 
 		# 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
+					throw new DBConnectionError( $conn, $this->mLastError );
+				}
 			} else {
-				$conn->failFunction( 'wfEmergencyAbort' );
+				if ( $this->mFailFunction ) {
+					$conn->failFunction( $this->mFailFunction );
+				} else {
+					$conn->failFunction( false );
+				}
+				$server = $conn->getProperty( 'mServer' );
+				$conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 			}
-			$conn->reportConnectionError();
 			$reporting = false;
 		}
 		wfProfileOut( $fname );
 	}
-	
-	function getWriterIndex()
-	{
+
+	function getWriterIndex() {
 		return 0;
 	}
 
-	function force( $i )
-	{
+	/**
+	 * Force subsequent calls to getConnection(DB_SLAVE) to return the 
+	 * given index. Set to -1 to restore the original load balancing
+	 * behaviour. I thought this was a good idea when I originally 
+	 * wrote this class, but it has never been used.
+	 */
+	function force( $i ) {
 		$this->mForce = $i;
 	}
 
-	function haveIndex( $i )
-	{
+	/**
+	 * Returns true if the specified index is a valid server index
+	 */
+	function haveIndex( $i ) {
 		return array_key_exists( $i, $this->mServers );
 	}
 
+	/**
+	 * Returns true if the specified index is valid and has non-zero load
+	 */
+	function isNonZeroLoad( $i ) {
+		return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
+	}
+
 	/**
 	 * Get the number of defined servers (not the number of open connections)
 	 */
@@ -369,7 +506,7 @@ class LoadBalancer {
 	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 );
@@ -424,4 +561,90 @@ class LoadBalancer {
 	function getLaggedSlaveMode() {
 		return $this->mLaggedSlaveMode;
 	}
+
+	/* Disables/enables lag checks */
+	function allowLagged($mode=null) {
+		if ($mode===null)
+			return $this->mAllowLagged;
+		$this->mAllowLagged=$mode;
+	}
+
+	function pingAll() {
+		$success = true;
+		foreach ( $this->mConnections as $i => $conn ) {
+			if ( $this->isOpen( $i ) ) {
+				if ( !$this->mConnections[$i]->ping() ) {
+					$success = false;
+				}
+			}
+		}
+		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() {
+		wfProfileIn( __METHOD__ );
+		$expiry = 5;
+		$requestRate = 10;
+
+		global $wgMemc;
+		$times = $wgMemc->get( wfMemcKey( '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'] );
+				wfProfileOut( __METHOD__ );
+				return $times;
+			}
+			wfIncrStats( 'lag_cache_miss_expired' );
+		} else {
+			wfIncrStats( 'lag_cache_miss_absent' );
+		}
+
+		# Cache key missing or expired
+
+		$times = array();
+		foreach ( $this->mServers as $i => $conn ) {
+			if ($i==0) { # Master
+				$times[$i] = 0;
+			} elseif ( $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( wfMemcKey( 'lag_times' ), $times, $expiry );
+
+		# But don't give the timestamp to the caller
+		unset($times['timestamp']);
+		wfProfileOut( __METHOD__ );
+		return $times;
+	}
 }
+
+?>