* Kind of like Hawking's [[Chronology Protection Agency]].
*/
class ChronologyProtector {
- var $startupPos;
- var $shutdownPos = array();
+ /** @var Array (DB master name => position) */
+ protected $startupPositions = array();
+ /** @var Array (DB master name => position) */
+ protected $shutdownPositions = array();
+
+ protected $initialized = false; // bool; whether the session data was loaded
/**
* Initialise a LoadBalancer to give it appropriate chronology protection.
*
+ * If the session has a previous master position recorded, this will try to
+ * make sure that the next query to a slave of that master will see changes up
+ * to that position by delaying execution. The delay may timeout and allow stale
+ * data if no non-lagged slaves are available.
+ *
* @param $lb LoadBalancer
+ * @return void
*/
- function initLB( $lb ) {
- if ( $this->startupPos === null ) {
- if ( !empty( $_SESSION[__CLASS__] ) ) {
- $this->startupPos = $_SESSION[__CLASS__];
- }
+ public function initLB( LoadBalancer $lb ) {
+ if ( $lb->getServerCount() <= 1 ) {
+ return; // non-replicated setup
}
- if ( !$this->startupPos ) {
- return;
+ if ( !$this->initialized ) {
+ $this->initialized = true;
+ if ( isset( $_SESSION[__CLASS__] ) && is_array( $_SESSION[__CLASS__] ) ) {
+ $this->startupPositions = $_SESSION[__CLASS__];
+ }
}
$masterName = $lb->getServerName( 0 );
-
- if ( $lb->getServerCount() > 1 && !empty( $this->startupPos[$masterName] ) ) {
+ if ( !empty( $this->startupPositions[$masterName] ) ) {
$info = $lb->parentInfo();
- $pos = $this->startupPos[$masterName];
+ $pos = $this->startupPositions[$masterName];
wfDebug( __METHOD__ . ": LB " . $info['id'] . " waiting for master pos $pos\n" );
- $lb->waitFor( $this->startupPos[$masterName] );
+ $lb->waitFor( $pos );
}
}
* down. Saves replication positions.
*
* @param $lb LoadBalancer
+ * @return void
*/
- function shutdownLB( $lb ) {
- // Don't start a session, don't bother with non-replicated setups
- if ( strval( session_id() ) == '' || $lb->getServerCount() <= 1 ) {
- return;
+ public function shutdownLB( LoadBalancer $lb ) {
+ if ( session_id() == '' || $lb->getServerCount() <= 1 ) {
+ return; // don't start a session; don't bother with non-replicated setups
}
$masterName = $lb->getServerName( 0 );
- if ( isset( $this->shutdownPos[$masterName] ) ) {
- // Already done
- return;
+ if ( isset( $this->shutdownPositions[$masterName] ) ) {
+ return; // already done
}
// Only save the position if writes have been done on the connection
$db = $lb->getAnyOpenConnection( 0 );
}
$pos = $db->getMasterPos();
wfDebug( __METHOD__ . ": LB {$info['id']} has master pos $pos\n" );
- $this->shutdownPos[$masterName] = $pos;
+ $this->shutdownPositions[$masterName] = $pos;
}
/**
* Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
* May commit chronology data to persistent storage.
+ *
+ * @return void
*/
- function shutdown() {
- if ( session_id() != '' && count( $this->shutdownPos ) ) {
+ public function shutdown() {
+ if ( session_id() != '' && count( $this->shutdownPositions ) ) {
wfDebug( __METHOD__ . ": saving master pos for " .
- count( $this->shutdownPos ) . " master(s)\n" );
- $_SESSION[__CLASS__] = $this->shutdownPos;
+ count( $this->shutdownPositions ) . " master(s)\n" );
+ $_SESSION[__CLASS__] = $this->shutdownPositions;
}
}
}