Accommodate very large dshash tables.

If a dshash table grows very large (e.g., the dshash table for
cumulative statistics when there are millions of tables), resizing
it may fail with an error like:

	ERROR: invalid DSA memory alloc request size 1073741824

To fix, permit dshash resizing to allocate more than 1 GB by
providing the DSA_ALLOC_HUGE flag.

Reported-by: Andreas Scherbaum
Author: Matthias van de Meent
Reviewed-by: Cédric Villemain, Michael Paquier, Andres Freund
Discussion: https://postgr.es/m/80a12d59-0d5e-4c54-866c-e69cd6536471%40pgug.de
Backpatch-through: 13

src/backend/lib/dshash.c

@@ -844,8 +844,10 @@ resize(dshash_table *hash_table, size_t new_size_log2)
 	Assert(new_size_log2 == hash_table->control->size_log2 + 1);
 
 	/* Allocate the space for the new table. */
-	new_buckets_shared = dsa_allocate0(hash_table->area,
-									   sizeof(dsa_pointer) * new_size);
+	new_buckets_shared =
+		dsa_allocate_extended(hash_table->area,
+							  sizeof(dsa_pointer) * new_size,
+							  DSA_ALLOC_HUGE | DSA_ALLOC_ZERO);
 	new_buckets = dsa_get_address(hash_table->area, new_buckets_shared);
 
 	/*