Avoid useless delay and master connections in wfWaitForSlaves() in runJobs.php

* Some jobs, like Parsoid ones, do not actually do master DB updates

Change-Id: I1a8830eafd7760d081df966bb423030dcdc96408

includes/GlobalFunctions.php

@@ -3798,11 +3798,14 @@ function wfGetNull() {
  * in maintenance scripts, to avoid causing too much lag.  Of course, this is
  * a no-op if there are no slaves.
  *
- * @param int|bool $maxLag (deprecated)
+ * @param float|null $ifWritesSince Only wait if writes were done since this UNIX timestamp
  * @param string|bool $wiki Wiki identifier accepted by wfGetLB
  * @param string|bool $cluster Cluster name accepted by LBFactory. Default: false.
  */
-function wfWaitForSlaves( $maxLag = false, $wiki = false, $cluster = false ) {
+function wfWaitForSlaves( $ifWritesSince = false, $wiki = false, $cluster = false ) {
+	// B/C: first argument used to be "max seconds of lag"; ignore such values
+	$ifWritesSince = ( $ifWritesSince > 1e9 ) ? $ifWritesSince : false;
+
 	if ( $cluster !== false ) {
 		$lb = wfGetLBFactory()->getExternalLB( $cluster );
 	} else {
@@ -3812,7 +3815,13 @@ function wfWaitForSlaves( $maxLag = false, $wiki = false, $cluster = false ) {
 	// bug 27975 - Don't try to wait for slaves if there are none
 	// Prevents permission error when getting master position
 	if ( $lb->getServerCount() > 1 ) {
+		if ( $ifWritesSince && !$lb->isOpen( DB_MASTER ) ) {
+			return; // assume no writes done
+		}
 		$dbw = $lb->getConnection( DB_MASTER, array(), $wiki );
+		if ( $ifWritesSince && $dbw->lastDoneWrites() < $ifWritesSince ) {
+			return; // no writes since the last wait
+		}
 		$pos = $dbw->getMasterPos();
 		// The DBMS may not support getMasterPos() or the whole
 		// load balancer might be fake (e.g. $wgAllDBsAreLocalhost).

includes/db/Database.php

@@ -600,7 +600,18 @@ abstract class DatabaseBase implements IDatabase, DatabaseType {
 	 * @return bool
 	 */
 	public function doneWrites() {
-		return $this->mDoneWrites;
+		return (bool)$this->mDoneWrites;
+	}
+
+	/**
+	 * Returns the last time the connection may have been used for write queries.
+	 * Should return a timestamp if unsure.
+	 *
+	 * @return int|float UNIX timestamp or false
+	 * @since 1.24
+	 */
+	public function lastDoneWrites() {
+		return $this->mDoneWrites ?: false;
 	}
 
 	/**
@@ -1020,10 +1031,10 @@ abstract class DatabaseBase implements IDatabase, DatabaseType {
 		global $wgUser, $wgDebugDBTransactions;
 
 		$this->mLastQuery = $sql;
-		if ( !$this->mDoneWrites && $this->isWriteQuery( $sql ) ) {
+		if ( $this->isWriteQuery( $sql ) ) {
 			# Set a flag indicating that writes have been done
 			wfDebug( __METHOD__ . ': Writes done: ' . DatabaseBase::generalizeSQL( $sql ) . "\n" );
-			$this->mDoneWrites = true;
+			$this->mDoneWrites = microtime( true );
 		}
 
 		# Add a comment for easy SHOW PROCESSLIST interpretation

maintenance/runJobs.php

@@ -86,7 +86,7 @@ class RunJobs extends Maintenance {
 
 		$jobsRun = 0; // counter
 		$flags = JobQueueGroup::USE_CACHE;
-		$lastTime = time(); // time since last slave check
+		$lastTime = microtime( true ); // time since last slave check
 		do {
 			$backoffs = array_filter( $backoffs, $backoffExpireFunc );
 			$blacklist = $noThrottle ? array() : array_keys( $backoffs );
@@ -146,10 +146,10 @@ class RunJobs extends Maintenance {
 				}
 
 				// Don't let any of the main DB slaves get backed up
-				$timePassed = time() - $lastTime;
+				$timePassed = microtime( true ) - $lastTime;
 				if ( $timePassed >= 5 || $timePassed < 0 ) {
-					wfWaitForSlaves();
+					wfWaitForSlaves( $lastTime );
-					$lastTime = time();
+					$lastTime = microtime( true );
 				}
 				// Don't let any queue slaves/backups fall behind
 				if ( $jobsRun > 0 && ( $jobsRun % 100 ) == 0 ) {