Don't Memoize lateral joins with volatile join conditions

david-rowley · david-rowley · commit 990c3650c535 · 2023-08-07T22:14:21.000+12:00
The use of Memoize was already disabled in normal joins when the join conditions had volatile functions per the code in match_opclause_to_indexcol(). Ordinarily, the parameterization for the inner side of a nested loop will be an Index Scan or at least eventually lead to an index scan (perhaps nested several joins deep). However, for lateral joins, that's not the case and seq scans can be parameterized too, so we can't rely on match_opclause_to_indexcol(). Here we explicitly check the parameterization for volatile functions and don't consider the generation of a Memoize path when such functions are present. Author: Richard Guo Discussion: https://postgr.es/m/CAMbWs49nHFnHbpepLsv_yF3qkpCS4BdB-v8HoJVv8_=Oat0u_w@mail.gmail.com Backpatch-through: 14, where Memoize was introduced
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
@@ -667,6 +667,23 @@ get_memoize_path(PlannerInfo *root, RelOptInfo *innerrel,
 			return NULL;
 	}
 
+	/*
+	 * Also check the parameterized path restrictinfos for volatile functions.
+	 * Indexed functions must be immutable so shouldn't have any volatile
+	 * functions, however, with a lateral join the inner scan may not be an
+	 * index scan.
+	 */
+	if (inner_path->param_info != NULL)
+	{
+		foreach(lc, inner_path->param_info->ppi_clauses)
+		{
+			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+			if (contain_volatile_functions((Node *) rinfo))
+				return NULL;
+		}
+	}
+
 	/* Check if we have hash ops for each parameter to the path */
 	if (paraminfo_get_equal_hashops(root,
 									inner_path->param_info,
