From 703ddd56fb484692c84101d1731e60f9ea81193f Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Wed, 13 Sep 2017 19:43:02 -0700
Subject: [PATCH 5/8] Replace binary search in fmgr_isbuiltin with hashtable.

Turns out we have enough functions that the binary search is quite
noticeable in profiles.

It'd be nice if there were a better place to build the hashtable than
the first pass through fmgr_isbuiltin() but there's currently none.
---
 src/backend/utils/fmgr/fmgr.c | 63 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 47 insertions(+), 16 deletions(-)

diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
index a7b07827e0..87867f2183 100644
--- a/src/backend/utils/fmgr/fmgr.c
+++ b/src/backend/utils/fmgr/fmgr.c
@@ -26,6 +26,7 @@
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/fmgrtab.h"
+#include "utils/hashutils.h"
 #include "utils/guc.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
@@ -36,6 +37,30 @@
 PGDLLIMPORT needs_fmgr_hook_type needs_fmgr_hook = NULL;
 PGDLLIMPORT fmgr_hook_type fmgr_hook = NULL;
 
+/*
+ * Hashtable for fast lookup builtin functions.
+ */
+typedef struct BuiltinOidLookupEntry
+{
+	Oid foid;
+	int status;
+	const FmgrBuiltin *builtin;
+} BuiltinOidLookupEntry;
+
+/* define hashtable mapping block numbers to PagetableEntry's */
+#define SH_PREFIX oid2builtins
+#define SH_ELEMENT_TYPE BuiltinOidLookupEntry
+#define SH_KEY_TYPE Oid
+#define SH_KEY foid
+#define SH_HASH_KEY(tb, key) murmurhash32(key)
+#define SH_EQUAL(tb, a, b) a == b
+#define SH_SCOPE static inline
+#define SH_DEFINE
+#define SH_DECLARE
+#include "lib/simplehash.h"
+
+static oid2builtins_hash *oid2builtins = 0;
+
 /*
  * Hashtable for fast lookup of external C functions
  */
@@ -70,26 +95,32 @@ static Datum fmgr_security_definer(PG_FUNCTION_ARGS);
 static const FmgrBuiltin *
 fmgr_isbuiltin(Oid id)
 {
-	int			low = 0;
-	int			high = fmgr_nbuiltins - 1;
+	BuiltinOidLookupEntry *entry;
 
-	/*
-	 * Loop invariant: low is the first index that could contain target entry,
-	 * and high is the last index that could contain it.
-	 */
-	while (low <= high)
+	/* TODO: it'd be better if this were done separately */
+	if (unlikely(oid2builtins == NULL))
 	{
-		int			i = (high + low) / 2;
-		const FmgrBuiltin *ptr = &fmgr_builtins[i];
+		int i;
 
-		if (id == ptr->foid)
-			return ptr;
-		else if (id > ptr->foid)
-			low = i + 1;
-		else
-			high = i - 1;
+		oid2builtins = oid2builtins_create(TopMemoryContext,
+										   fmgr_nbuiltins,
+										   NULL);
+		for (i = 0; i < fmgr_nbuiltins; i++)
+		{
+			const FmgrBuiltin *ptr = &fmgr_builtins[i];
+			bool found;
+
+			entry = oid2builtins_insert(oid2builtins, ptr->foid, &found);
+			Assert(!found);
+			entry->builtin = ptr;
+		}
 	}
-	return NULL;
+
+	entry = oid2builtins_lookup(oid2builtins, id);
+	if (entry)
+		return entry->builtin;
+	else
+		return NULL;
 }
 
 /*
-- 
2.14.1.536.g6867272d5b.dirty