Use a replica dedicated to slow queries (if available)

Bug: T187880
Change-Id: I2987b5ae9446cb0bf503978ee62861f2f969b1df

maintenance/ULSCompactLinksDisablePref.php

@@ -31,7 +31,7 @@ class ULSCompactLinksDisablePref extends Maintenance {
 	}
 
 	public function execute() {
-		$dbr = wfGetDB( DB_REPLICA );
+		$dbr = wfGetDB( DB_REPLICA, 'vslow' );
 
 		$this->really = $this->hasOption( 'really' );