<?php
-# Database load balancing object
+/**
+ *
+ * @package MediaWiki
+ */
-require_once( "Database.php" );
+/**
+ * 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
+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 );
+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
-
-define( "MASTER_WAIT_TIMEOUT", 15 ); # Time to wait for a slave to synchronise
-
+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
+ *
+ * @todo document
+ * @package MediaWiki
+ */
class LoadBalancer {
/* private */ var $mServers, $mConnections, $mLoads;
/* private */ var $mFailFunction;
/* private */ var $mForce, $mReadIndex, $mLastIndex;
- /* private */ var $mWaitForFile, $mWaitForPos;
+ /* private */ var $mWaitForFile, $mWaitForPos, $mWaitTimeout;
+ /* private */ var $mLaggedSlaveMode;
function LoadBalancer()
{
$this->mLastIndex = -1;
}
- function newFromParams( $servers, $failFunction = false )
+ function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
{
$lb = new LoadBalancer;
$lb->initialise( $servers, $failFunction = false );
return $lb;
}
- function initialise( $servers, $failFunction = false )
+ function initialise( $servers, $failFunction = false, $waitTimeout = 10 )
{
$this->mServers = $servers;
$this->mFailFunction = $failFunction;
$this->mLoads = array();
$this->mWaitForFile = false;
$this->mWaitForPos = false;
+ $this->mWaitTimeout = $waitTimeout;
+ $this->mLaggedSlaveMode = false;
foreach( $servers as $i => $server ) {
$this->mLoads[$i] = $server['load'];
}
}
- # Given an array of non-normalised probabilities, this function will select
- # an element and return the appropriate key
+ /**
+ * 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 ) {
function getReaderIndex()
{
+ $fname = 'LoadBalancer::getReaderIndex';
+ wfProfileIn( $fname );
+
$i = false;
if ( $this->mForce >= 0 ) {
$i = $this->mForce;
if ( $i !== false ) {
wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}\n" );
- $this->getConnection( $i );
+ $this->openConnection( $i );
if ( !$this->isOpen( $i ) ) {
unset( $loads[$i] );
}
}
}
+ wfProfileOut( $fname );
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
+ /**
+ * 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 );
+
wfDebug( "User master pos: $file $pos\n" );
$this->mWaitForFile = false;
$this->mWaitForPos = false;
- if ( count( $this->mServers ) == 1 ) {
- return;
- }
-
- $this->mWaitForFile = $file;
- $this->mWaitForPos = $pos;
+ if ( count( $this->mServers ) > 1 ) {
+ $this->mWaitForFile = $file;
+ $this->mWaitForPos = $pos;
- if ( $this->mReadIndex > 0 ) {
- if ( !$this->doWait( $this->mReadIndex ) ) {
- # Use master instead
- $this->mReadIndex = 0;
- }
- }
+ if ( $this->mReadIndex > 0 ) {
+ if ( !$this->doWait( $this->mReadIndex ) ) {
+ $this->mLaggedSlaveMode = true;
+ }
+ }
+ }
+ wfProfileOut( $fname );
}
- # Wait for a given slave to catch up to the master pos stored in $this
+ /**
+ * Wait for a given slave to catch up to the master pos stored in $this
+ */
function doWait( $index ) {
global $wgMemc;
- $key = "masterpos:" . $index;
+ $retVal = false;
+
+ $key = 'masterpos:' . $index;
$memcPos = $wgMemc->get( $key );
if ( $memcPos ) {
list( $file, $pos ) = explode( ' ', $memcPos );
# If the saved position is later than the requested position, return now
if ( $file == $this->mWaitForFile && $this->mWaitForPos <= $pos ) {
- return true;
+ $retVal = true;
}
}
- $conn =& $this->getConnection( $index );
- wfDebug( "Waiting for slave #$index to catch up...\n" );
- $result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, MASTER_WAIT_TIMEOUT );
+ if ( !$retVal && $this->isOpen( $index ) ) {
+ $conn =& $this->mConnections[$index];
+ wfDebug( "Waiting for slave #$index to catch up...\n" );
+ $result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, $this->mWaitTimeout );
- if ( $result == -1 || is_null( $result ) ) {
- # Timed out waiting for slave, use master instead
- wfDebug( "Timed out waiting for slave #$index pos {$this->mWaitForFile} {$this->mWaitForPos}\n" );
- $retVal = false;
- } else {
- $retVal = true;
- wfDebug( "Done\n" );
+ if ( $result == -1 || is_null( $result ) ) {
+ # Timed out waiting for slave, use master instead
+ wfDebug( "Timed out waiting for slave #$index pos {$this->mWaitForFile} {$this->mWaitForPos}\n" );
+ $retVal = false;
+ } else {
+ $retVal = true;
+ wfDebug( "Done\n" );
+ }
}
return $retVal;
}
- # Get a connection by index
- function &getConnection( $i, $fail = false )
+ /**
+ * Get a connection by index
+ */
+ function &getConnection( $i, $fail = true )
{
+ $fname = 'LoadBalancer::getConnection';
+ wfProfileIn( $fname );
/*
# Task-based index
if ( $i >= DB_TASK_FIRST && $i < DB_TASK_LAST ) {
# Operation-based index
if ( $i == DB_SLAVE ) {
- # Note: re-entrant
$i = $this->getReaderIndex();
} elseif ( $i == DB_MASTER ) {
$i = $this->getWriterIndex();
$i = $this->mLastIndex;
if ( $i === -1 ) {
# Oh dear, not set, best to use the writer for safety
+ wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
$i = $this->getWriterIndex();
}
- }
+ }
# Now we have an explicit index into the servers array
+ $this->openConnection( $i, $fail );
+ wfProfileOut( $fname );
+ return $this->mConnections[$i];
+ }
+
+ /**
+ * Open a connection to the server given by the specified index
+ * Index must be an actual index into the array
+ * @private
+ */
+ function openConnection( $i, $fail = false ) {
+ $fname = 'LoadBalancer::openConnection';
+ wfProfileIn( $fname );
+
if ( !$this->isOpen( $i ) ) {
- $this->mConnections[$i] = $this->makeConnection( $this->mServers[$i] );
+ $this->mConnections[$i] = $this->reallyOpenConnection( $this->mServers[$i] );
if ( $i != 0 && $this->mWaitForFile ) {
if ( !$this->doWait( $i ) ) {
$this->mReadIndex = 0;
$i = 0;
if ( !$this->isOpen( 0 ) ) {
- $this->mConnections[0] = $this->makeConnection( $this->mServers[0] );
+ $this->mConnections[0] = $this->reallyOpenConnection( $this->mServers[0] );
}
wfDebug( "Failed over to {$this->mConnections[0]->mServer}\n" );
}
$this->mConnections[$i] = false;
}
$this->mLastIndex = $i;
-
- return $this->mConnections[$i];
+ wfProfileOut( $fname );
}
- /* private */ function isOpen( $index ) {
+ /**
+ * Test if the specified index represents an open connection
+ * @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() )
{
}
}
- /* private */ function makeConnection( &$server ) {
- extract( $server );
- # Get class for this database type
- $class = 'Database' . ucfirst( $type );
- if ( !class_exists( $class ) ) {
- require_once( "$class.php" );
- }
+ /**
+ * Really opens a connection
+ * @private
+ */
+ function reallyOpenConnection( &$server ) {
+ 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 );
+ if ( !class_exists( $class ) ) {
+ require_once( "$class.php" );
+ }
- # Create object
- return new $class( $host, $user, $password, $dbname, 1, $flags );
+ # Create object
+ return new $class( $host, $user, $password, $dbname, 1, $flags );
}
function reportConnectionError( &$conn )
{
- if ( !is_object( $conn ) ) {
- $conn = new Database;
- }
- if ( $this->mFailFunction ) {
- $conn->setFailFunction( $this->mFailFunction );
- } else {
- $conn->setFailFunction( "wfEmergencyAbort" );
+ $fname = 'LoadBalancer::reportConnectionError';
+ wfProfileIn( $fname );
+ # Prevent infinite recursion
+
+ static $reporting = false;
+ if ( !$reporting ) {
+ $reporting = true;
+ if ( !is_object( $conn ) ) {
+ $conn = new Database;
+ }
+ if ( $this->mFailFunction ) {
+ $conn->failFunction( $this->mFailFunction );
+ } else {
+ $conn->failFunction( 'wfEmergencyAbort' );
+ }
+ $conn->reportConnectionError();
+ $reporting = false;
}
- $conn->reportConnectionError();
+ wfProfileOut( $fname );
}
function getWriterIndex()
return array_key_exists( $i, $this->mServers );
}
- # Get the number of defined servers (not the number of open connections)
+ /**
+ * Get the number of defined servers (not the number of open connections)
+ */
function getServerCount() {
return count( $this->mServers );
}
- # Save master pos to the session and to memcached, if the session exists
+ /**
+ * Save master pos to the session and to memcached, if the session exists
+ */
function saveMasterPos() {
global $wgSessionStarted;
if ( $wgSessionStarted && count( $this->mServers ) > 1 ) {
}
}
- # Loads the master pos from the session, waits for it if necessary
+ /**
+ * Loads the master pos from the session, waits for it if necessary
+ */
function loadMasterPos() {
if ( isset( $_SESSION['master_log_file'] ) && isset( $_SESSION['master_pos'] ) ) {
$this->waitFor( $_SESSION['master_log_file'], $_SESSION['master_pos'] );
}
}
- # Close all open connections
+ /**
+ * Close all open connections
+ */
function closeAll() {
foreach( $this->mConnections as $i => $conn ) {
if ( $this->isOpen( $i ) ) {
}
}
}
+
+ function waitTimeout( $value = NULL ) {
+ return wfSetVar( $this->mWaitTimeout, $value );
+ }
+
+ function getLaggedSlaveMode() {
+ return $this->mLaggedSlaveMode;
+ }
}