Allow Memoize to operate in binary comparison mode

Memoize would always use the hash equality operator for the cache key
types to determine if the current set of parameters were the same as some
previously cached set.  Certain types such as floating points where -0.0
and +0.0 differ in their binary representation but are classed as equal by
the hash equality operator may cause problems as unless the join uses the
same operator it's possible that whichever join operator is being used
would be able to distinguish the two values.  In which case we may
accidentally return in the incorrect rows out of the cache.

To fix this here we add a binary mode to Memoize to allow it to the
current set of parameters to previously cached values by comparing
bit-by-bit rather than logically using the hash equality operator.  This
binary mode is always used for LATERAL joins and it's used for normal
joins when any of the join operators are not hashable.

Reported-by: Tom Lane
Author: David Rowley
Discussion: https://postgr.es/m/3004308.1632952496@sss.pgh.pa.us
Backpatch-through: 14, where Memoize was added

1 files changed, 2 insertions, 0 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 105180764e1..8341c2b8a16 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -2108,6 +2108,8 @@ typedef struct MemoizeState
 								 * NULL if 'last_tuple' is NULL. */
 	bool		singlerow;		/* true if the cache entry is to be marked as
 								 * complete after caching the first tuple. */
+	bool		binary_mode;	/* true when cache key should be compared bit
+								 * by bit, false when using hash equality ops */
 	MemoizeInstrumentation stats;	/* execution statistics */
 	SharedMemoizeInfo *shared_info; /* statistics for parallel workers */
 } MemoizeState;