-<?
-# Database load balancing object
+<?php
+/**
+ *
+ * @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
+
+define( 'MASTER_WAIT_TIMEOUT', 15 ); # Time to wait for a slave to synchronise
+
+/**
+ * Database load balancing object
+ *
+ * @todo document
+ * @package MediaWiki
+ */
class LoadBalancer {
/* private */ var $mServers, $mConnections, $mLoads;
- /* private */ var $mUser, $mPassword, $mDbName, $mFailFunction;
- /* private */ var $mForce, $mReadIndex;
+ /* private */ var $mFailFunction;
+ /* private */ var $mForce, $mReadIndex, $mLastIndex;
+ /* private */ var $mWaitForFile, $mWaitForPos;
function LoadBalancer()
{
$this->mServers = array();
- $this->mLoads = array();
$this->mConnections = array();
- $this->mUser = false;
- $this->mPassword = false;
- $this->mDbName = false;
$this->mFailFunction = false;
$this->mReadIndex = -1;
$this->mForce = -1;
+ $this->mLastIndex = -1;
}
- function newFromParams( $servers, $loads, $user, $password, $dbName, $failFunction = false )
+ function newFromParams( $servers, $failFunction = false )
{
$lb = new LoadBalancer;
- $lb->initialise( $servers, $loads, $user, $password, $dbName, $failFunction = false );
+ $lb->initialise( $servers, $failFunction = false );
return $lb;
}
- function initialise( $servers, $loads, $user, $password, $dbName, $failFunction = false )
+ function initialise( $servers, $failFunction = false )
{
$this->mServers = $servers;
- $this->mLoads = $loads;
- $this->mUser = $user;
- $this->mPassword = $password;
- $this->mDbName = $dbName;
$this->mFailFunction = $failFunction;
$this->mReadIndex = -1;
$this->mWriteIndex = -1;
$this->mForce = -1;
$this->mConnections = array();
- wfSeedRandom();
+ $this->mLastIndex = 1;
+ $this->mLoads = array();
+ $this->mWaitForFile = false;
+ $this->mWaitForPos = 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 ) {
foreach ( $weights as $w ) {
$sum += $w;
}
- $rand = mt_rand() / RAND_MAX * $sum;
+ $max = mt_getrandmax();
+ $rand = mt_rand(0, $max) / $max * $sum;
$sum = 0;
foreach ( $weights as $i => $w ) {
return $i;
}
- function &getReader()
+ function getReaderIndex()
{
+ $fname = 'LoadBalancer::getReaderIndex';
+ wfProfileIn( $fname );
+
+ $i = false;
if ( $this->mForce >= 0 ) {
- $conn =& $this->getConnection( $this->mForce );
+ $i = $this->mForce;
} else {
if ( $this->mReadIndex >= 0 ) {
- $conn =& $this->getConnection( $this->mReadIndex );
+ $i = $this->mReadIndex;
} else {
# $loads is $this->mLoads except with elements knocked out if they
# don't work
$loads = $this->mLoads;
do {
- $i = pickRandom( $loads );
+ $i = $this->pickRandom( $loads );
if ( $i !== false ) {
- $conn =& $this->getConnection( $i );
- if ( !$conn->isOpen() ) {
+ wfDebug( "Using reader #$i: {$this->mServers[$i]['host']}\n" );
+
+ $this->openConnection( $i );
+
+ if ( !$this->isOpen( $i ) ) {
unset( $loads[$i] );
}
}
- } while ( $i !== false && !$conn->isOpen() );
- if ( $conn->isOpen() ) {
+ } while ( $i !== false && !$this->isOpen( $i ) );
+
+ if ( $this->isOpen( $i ) ) {
$this->mReadIndex = $i;
+ } else {
+ $i = false;
}
}
}
- if ( $conn === false || !$conn->isOpen() ) {
- $this->reportConnectionError( $conn );
- $conn = false;
+ 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
+ */
+ 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 ) {
+ $this->mWaitForFile = $file;
+ $this->mWaitForPos = $pos;
+
+ if ( $this->mReadIndex > 0 ) {
+ if ( !$this->doWait( $this->mReadIndex ) ) {
+ # Use master instead
+ $this->mReadIndex = 0;
+ }
+ }
}
- return $conn;
+ wfProfileOut( $fname );
}
-
- function &getConnection( $i, $fail = false )
+
+ /**
+ * Wait for a given slave to catch up to the master pos stored in $this
+ */
+ function doWait( $index ) {
+ global $wgMemc;
+
+ $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 ) {
+ $retVal = true;
+ }
+ }
+
+ if ( !$retVal && $this->isOpen( $index ) ) {
+ $conn =& $this->mConnections( $index );
+ wfDebug( "Waiting for slave #$index to catch up...\n" );
+ $result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, MASTER_WAIT_TIMEOUT );
+
+ 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 = true )
{
- if ( !array_key_exists( $i, $this->mConnections) || !$this->mConnections[$i]->isOpen() ) {
- $this->mConnections[$i] = Database::newFromParams( $this->mServers[$i], $this->mUser,
- $this->mPassword, $this->mDbName, 1 );
+ $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;
+ }
+ }*/
+
+ # Operation-based index
+ if ( $i == DB_SLAVE ) {
+ $i = $this->getReaderIndex();
+ } elseif ( $i == DB_MASTER ) {
+ $i = $this->getWriterIndex();
+ } elseif ( $i == DB_LAST ) {
+ # Just use $this->mLastIndex, which should already be set
+ $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 = $this->getWriterIndex();
+ }
}
- if ( !$this->mConnections[$i]->isOpen() ) {
- wfDebug( "Failed to connect to database $i at {$this->mServers[$i]}\n" );
+ # 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->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] );
}
$this->mConnections[$i] = false;
}
- return $this->mConnections[$i];
+ $this->mLastIndex = $i;
+ wfProfileOut( $fname );
}
- function reportConnectionError( &$conn )
- {
- if ( !is_object( $conn ) ) {
- $conn = new Database;
+ /**
+ * Test if the specified index represents an open connection
+ * @private
+ */
+ function isOpen( $index ) {
+ if( !is_integer( $index ) ) {
+ return false;
}
- if ( $this->mFailFunction ) {
- $conn->setFailFunction( $this->mFailFunction );
+ if ( array_key_exists( $index, $this->mConnections ) && is_object( $this->mConnections[$index] ) &&
+ $this->mConnections[$index]->isOpen() )
+ {
+ return true;
} else {
- $conn->setFailFunction( "wfEmergencyAbort" );
+ return false;
}
- $conn->reportConnectionError();
}
- function &getWriter()
+ /**
+ * Really opens a connection
+ * @private
+ */
+ function reallyOpenConnection( &$server ) {
+ 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, $flags );
+ }
+
+ function reportConnectionError( &$conn )
{
- $c =& $this->getConnection( 0 );
- if ( !$c->isOpen() ) {
- reportConnectionError( $conn );
- $c = false;
+ $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;
}
- return $c;
+ wfProfileOut( $fname );
+ }
+
+ function getWriterIndex()
+ {
+ return 0;
}
function force( $i )
{
$this->mForce = $i;
}
+
+ function haveIndex( $i )
+ {
+ return array_key_exists( $i, $this->mServers );
+ }
+
+ /**
+ * 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
+ */
+ 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
+ # 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 );
+ list( $file, $pos ) = $conn->getSlavePos();
+ wfDebug( "Saving master pos fetched from slave: $file $pos\n" );
+ } else {
+ $conn =& $this->getConnection( 0 );
+ list( $file, $pos ) = $conn->getMasterPos();
+ wfDebug( "Saving master pos: $file $pos\n" );
+ }
+ if ( $file !== false ) {
+ $_SESSION['master_log_file'] = $file;
+ $_SESSION['master_pos'] = $pos;
+ }
+ }
+ }
+
+ /**
+ * 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
+ */
+ function closeAll() {
+ foreach( $this->mConnections as $i => $conn ) {
+ if ( $this->isOpen( $i ) ) {
+ $conn->close();
+ }
+ }
+ }
+
+ function commitAll() {
+ foreach( $this->mConnections as $i => $conn ) {
+ if ( $this->isOpen( $i ) ) {
+ $conn->immediateCommit();
+ }
+ }
+ }
}
dépôts / lhc / web / wiklou.git / blobdiff