Revert "Fix an O(N^2) problem in foreign key references".

Commit 5ddc7288 does not actually work
because it will happily blow away ri_constraint_cache entries that are
in active use in outer call levels.  In any case, it's a very ugly,
brute-force solution to the problem of limiting the cache size.
Revert until it can be redesigned.

src/backend/utils/adt/ri_triggers.c

@@ -183,7 +183,6 @@ typedef struct RI_CompareHashEntry
  * ----------
  */
 static HTAB *ri_constraint_cache = NULL;
-static long  ri_constraint_cache_seq_count = 0;
 static HTAB *ri_query_cache = NULL;
 static HTAB *ri_compare_cache = NULL;
 
@@ -216,7 +215,6 @@ static bool ri_KeysEqual(Relation rel, HeapTuple oldtup, HeapTuple newtup,
 static bool ri_AttributesEqual(Oid eq_opr, Oid typeid,
 				   Datum oldvalue, Datum newvalue);
 
-static void ri_InitConstraintCache(void);
 static void ri_InitHashTables(void);
 static void InvalidateConstraintCacheCallBack(Datum arg, int cacheid, uint32 hashvalue);
 static SPIPlanPtr ri_FetchPreparedPlan(RI_QueryKey *key);
@@ -2947,20 +2945,6 @@ InvalidateConstraintCacheCallBack(Datum arg, int cacheid, uint32 hashvalue)
 
 	Assert(ri_constraint_cache != NULL);
 
-	/*
-	 * Prevent an O(N^2) problem when creating large amounts of foreign
-	 * key constraints with ALTER TABLE, like it happens at the end of
-	 * a pg_dump with hundred-thousands of tables having references.
-	 */
-	ri_constraint_cache_seq_count += hash_get_num_entries(ri_constraint_cache);
-	if (ri_constraint_cache_seq_count > 1000000)
-	{
-		hash_destroy(ri_constraint_cache);
-		ri_InitConstraintCache();
-		ri_constraint_cache_seq_count = 0;
-		return;
-	}
-
 	hash_seq_init(&status, ri_constraint_cache);
 	while ((hentry = (RI_ConstraintInfo *) hash_seq_search(&status)) != NULL)
 	{
@@ -3380,15 +3364,13 @@ ri_NullCheck(HeapTuple tup,
 
 
 /* ----------
- * ri_InitConstraintCache
- *
- * Initialize ri_constraint_cache when new or being rebuilt.
+ * ri_InitHashTables -
  *
- * This needs to be done from two places, so split it out to prevent drift.
+ *	Initialize our internal hash tables.
  * ----------
  */
 static void
-ri_InitConstraintCache(void)
+ri_InitHashTables(void)
 {
 	HASHCTL		ctl;
 
@@ -3398,20 +3380,6 @@ ri_InitConstraintCache(void)
 	ri_constraint_cache = hash_create("RI constraint cache",
 									  RI_INIT_CONSTRAINTHASHSIZE,
 									  &ctl, HASH_ELEM | HASH_BLOBS);
-}
-
-/* ----------
- * ri_InitHashTables -
- *
- *	Initialize our internal hash tables.
- * ----------
- */
-static void
-ri_InitHashTables(void)
-{
-	HASHCTL		ctl;
-
-	ri_InitConstraintCache();
 
 	/* Arrange to flush cache on pg_constraint changes */
 	CacheRegisterSyscacheCallback(CONSTROID,