Don't Memoize lateral joins with volatile join conditions

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

1 files changed, 17 insertions, 0 deletions

diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 4b58936fa4c..03b31859847 100644
--- 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,