Fix comments in heapam.c.

Amit Kapila · Amit Kapila · commit 0d32511eca5a · 2020-09-18T09:50:44.000+05:30
After commits 85f6b49 and 3ba59cc, we can allow parallel inserts which was earlier not possible as parallel group members won't conflict for relation extension and page lock. In those commits, we forgot to update comments at few places. Author: Amit Kapila Reviewed-by: Robert Haas and Dilip Kumar Backpatch-through: 13 Discussion: https://postgr.es/m/CAFiTN-tMrQh5FFMPx5aWJ+1gi1H6JxktEhq5mDwCHgnEO5oBkA@mail.gmail.com
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -2044,12 +2044,10 @@ heap_prepare_insert(Relation relation, HeapTuple tup, TransactionId xid,
 					CommandId cid, int options)
 {
 	/*
-	 * Parallel operations are required to be strictly read-only in a parallel
-	 * worker.  Parallel inserts are not safe even in the leader in the
-	 * general case, because group locking means that heavyweight locks for
-	 * relation extension or GIN page locks will not conflict between members
-	 * of a lock group, but we don't prohibit that case here because there are
-	 * useful special cases that we can safely allow, such as CREATE TABLE AS.
+	 * To allow parallel inserts, we need to ensure that they are safe to be
+	 * performed in workers. We have the infrastructure to allow parallel
+	 * inserts in general except for the cases where inserts generate a new
+	 * CommandId (eg. inserts into a table having a foreign key column).
 	 */
 	if (IsParallelWorker())
 		ereport(ERROR,
@@ -5725,10 +5723,10 @@ heap_inplace_update(Relation relation, HeapTuple tuple)
 	uint32		newlen;
 
 	/*
-	 * For now, parallel operations are required to be strictly read-only.
-	 * Unlike a regular update, this should never create a combo CID, so it
-	 * might be possible to relax this restriction, but not without more
-	 * thought and testing.  It's not clear that it would be useful, anyway.
+	 * For now, we don't allow parallel updates.  Unlike a regular update,
+	 * this should never create a combo CID, so it might be possible to relax
+	 * this restriction, but not without more thought and testing.  It's not
+	 * clear that it would be useful, anyway.
 	 */
 	if (IsInParallelMode())
 		ereport(ERROR,
