Update parallel BTree scan state when the scan keys can't be satisfied.

Amit Kapila · Amit Kapila · commit fcc3665a03a6 · 2020-09-17T15:59:42.000+05:30
For parallel btree scan to work for array of scan keys, it should reach BTPARALLEL_DONE state once for every distinct combination of array keys. This is required to ensure that the parallel workers don't try to seize blocks at the same time for different scan keys. We missed to update this state when we discovered that the scan keys can't be satisfied. Author: James Hunter Reviewed-by: Amit Kapila Tested-by: Justin Pryzby Backpatch-through: 10, where it was introduced Discussion: https://postgr.es/m/4248CABC-25E3-4809-B4D0-128E1BAABC3C@amazon.com
diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
@@ -568,7 +568,11 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 	 * never be satisfied (eg, x == 1 AND x > 2).
 	 */
 	if (!so->qual_ok)
+	{
+		/* Notify any other workers that we're done with this scan key. */
+		_bt_parallel_done(scan);
 		return false;
+	}
 
 	/*
 	 * For parallel scans, get the starting page from shared state. If the
