/**
* @param array $loads
* @param bool|string $wiki Wiki to get non-lagged for
+ * @param float $maxLag Restrict the maximum allowed lag to this many seconds
* @return bool|int|string
*/
- private function getRandomNonLagged( array $loads, $wiki = false ) {
- # Unset excessively lagged servers
+ private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
$lags = $this->getLagTimes( $wiki );
+
+ # Unset excessively lagged servers
foreach ( $lags as $i => $lag ) {
if ( $i != 0 ) {
+ $maxServerLag = $maxLag;
+ if ( isset( $this->mServers[$i]['max lag'] ) ) {
+ $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
+ }
if ( $lag === false ) {
wfDebugLog( 'replication', "Server #$i is not replicating" );
unset( $loads[$i] );
- } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
+ } elseif ( $lag > $maxServerLag ) {
wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
unset( $loads[$i] );
}
if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
$i = ArrayUtils::pickRandom( $currentLoads );
} else {
- $i = $this->getRandomNonLagged( $currentLoads, $wiki );
+ $i = false;
+ if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
+ # ChronologyProtecter causes mWaitForPos to be set via sessions.
+ # This triggers doWait() after connect, so it's especially good to
+ # avoid lagged servers so as to avoid just blocking in that method.
+ $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
+ # Aim for <= 1 second of waiting (being too picky can backfire)
+ $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
+ }
+ if ( $i === false ) {
+ # Any server with less lag than it's 'max lag' param is preferable
+ $i = $this->getRandomNonLagged( $currentLoads, $wiki );
+ }
if ( $i === false && count( $currentLoads ) != 0 ) {
# All slaves lagged. Switch to read-only mode
wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
* @throws MWException
* @return DatabaseBase
*/
- public function &getConnection( $i, $groups = array(), $wiki = false ) {
+ public function getConnection( $i, $groups = array(), $wiki = false ) {
wfProfileIn( __METHOD__ );
if ( $i === null || $i === false ) {
$wiki = false;
}
- # Query groups
+ $groups = ( $groups === false || $groups === array() )
+ ? array( false ) // check one "group": the generic pool
+ : (array)$groups;
+
if ( $i == DB_MASTER ) {
$i = $this->getWriterIndex();
- } elseif ( !is_array( $groups ) ) {
- $groupIndex = $this->getReaderIndex( $groups, $wiki );
- if ( $groupIndex !== false ) {
- $serverName = $this->getServerName( $groupIndex );
- wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
- $i = $groupIndex;
- }
} else {
+ # Try to find an available server in any the query groups (in order)
foreach ( $groups as $group ) {
$groupIndex = $this->getReaderIndex( $group, $wiki );
if ( $groupIndex !== false ) {
# Operation-based index
if ( $i == DB_SLAVE ) {
$this->mLastError = 'Unknown error'; // reset error string
- $i = $this->getReaderIndex( false, $wiki );
+ # Try the general server pool if $groups are unavailable.
+ $i = in_array( false, $groups, true )
+ ? false // don't bother with this if that is what was tried above
+ : $this->getReaderIndex( false, $wiki );
# Couldn't find a working server in getReaderIndex()?
if ( $i === false ) {
$this->mLastError = 'No working slave server: ' . $this->mLastError;