Disable anonymous record hash support except in special cases

Commit 01e658fa74 added hash support for row types.  This also added
support for hashing anonymous record types, using the same approach
that the type cache uses for comparison support for record types: It
just reports that it works, but it might fail at run time if a
component type doesn't actually support the operation.  We get away
with that for comparison because most types support that.  But some
types don't support hashing, so the current state can result in
failures at run time where the planner chooses hashing over sorting,
whereas that previously worked if only sorting was an option.

We do, however, want the record hashing support for path tracking in
recursive unions, and the SEARCH and CYCLE clauses built on that.  In
that case, hashing is the only plan option.  So enable that, this
commit implements the following approach: The type cache does not
report that hashing is available for the record type.  This undoes
that part of 01e658fa74.  Instead, callers that require hashing no
matter what can override that result themselves.  This patch only
touches the callers to make the aforementioned recursive query cases
work, namely the parse analysis of unions, as well as the hash_array()
function.

Reported-by: Sait Talha Nisanci <sait.nisanci@microsoft.com>
Bug: #17158
Discussion: https://www.postgresql.org/message-id/flat/17158-8a2ba823982537a4%40postgresql.org

1 files changed, 35 insertions, 1 deletions

diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index 04d487c5442..bc2f30bae15 100644
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -29,6 +29,7 @@
 #include "utils/arrayaccess.h"
 #include "utils/builtins.h"
 #include "utils/datum.h"
+#include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/selfuncs.h"
@@ -3973,13 +3974,46 @@ hash_array(PG_FUNCTION_ARGS)
 	{
 		typentry = lookup_type_cache(element_type,
 									 TYPECACHE_HASH_PROC_FINFO);
-		if (!OidIsValid(typentry->hash_proc_finfo.fn_oid))
+		if (!OidIsValid(typentry->hash_proc_finfo.fn_oid) && element_type != RECORDOID)
 			ereport(ERROR,
 					(errcode(ERRCODE_UNDEFINED_FUNCTION),
 					 errmsg("could not identify a hash function for type %s",
 							format_type_be(element_type))));
+
+		/*
+		 * The type cache doesn't believe that record is hashable (see
+		 * cache_record_field_properties()), but since we're here, we're
+		 * committed to hashing, so we can assume it does.  Worst case, if any
+		 * components of the record don't support hashing, we will fail at
+		 * execution.
+		 */
+		if (element_type == RECORDOID)
+		{
+			MemoryContext oldcontext;
+			TypeCacheEntry *record_typentry;
+
+			oldcontext = MemoryContextSwitchTo(CacheMemoryContext);
+
+			/*
+			 * Make fake type cache entry structure.  Note that we can't just
+			 * modify typentry, since that points directly into the type cache.
+			 */
+			record_typentry = palloc(sizeof(*record_typentry));
+
+			/* fill in what we need below */
+			record_typentry->typlen = typentry->typlen;
+			record_typentry->typbyval = typentry->typbyval;
+			record_typentry->typalign = typentry->typalign;
+			fmgr_info(F_HASH_RECORD, &record_typentry->hash_proc_finfo);
+
+			MemoryContextSwitchTo(oldcontext);
+
+			typentry = record_typentry;
+		}
+
 		fcinfo->flinfo->fn_extra = (void *) typentry;
 	}
+
 	typlen = typentry->typlen;
 	typbyval = typentry->typbyval;
 	typalign = typentry->typalign;