Remove some unused and seldom used fields from RelationAmInfo.

This saves some memory from each index relcache entry. At least on a 64-bit
machine, it saves just enough to shrink a typical relcache entry's memory
usage from 2k to 1k. That's nice if you have a lot of backends and a lot of
indexes.

src/backend/access/index/indexam.c

@@ -114,6 +114,13 @@ do { \
 	} \
 } while(0)
 
+#define GET_UNCACHED_REL_PROCEDURE(pname) \
+do { \
+	if (!RegProcedureIsValid(indexRelation->rd_am->pname)) \
+		elog(ERROR, "invalid %s regproc", CppAsString(pname)); \
+	fmgr_info(indexRelation->rd_am->pname, &procedure); \
+} while(0)
+
 #define GET_SCAN_PROCEDURE(pname) \
 do { \
 	procedure = &scan->indexRelation->rd_aminfo->pname; \
@@ -671,14 +678,14 @@ index_bulk_delete(IndexVacuumInfo *info,
 				  void *callback_state)
 {
 	Relation	indexRelation = info->index;
-	FmgrInfo   *procedure;
+	FmgrInfo	procedure;
 	IndexBulkDeleteResult *result;
 
 	RELATION_CHECKS;
-	GET_REL_PROCEDURE(ambulkdelete);
+	GET_UNCACHED_REL_PROCEDURE(ambulkdelete);
 
 	result = (IndexBulkDeleteResult *)
-		DatumGetPointer(FunctionCall4(procedure,
+		DatumGetPointer(FunctionCall4(&procedure,
 									  PointerGetDatum(info),
 									  PointerGetDatum(stats),
 									  PointerGetDatum((Pointer) callback),
@@ -698,14 +705,14 @@ index_vacuum_cleanup(IndexVacuumInfo *info,
 					 IndexBulkDeleteResult *stats)
 {
 	Relation	indexRelation = info->index;
-	FmgrInfo   *procedure;
+	FmgrInfo	procedure;
 	IndexBulkDeleteResult *result;
 
 	RELATION_CHECKS;
-	GET_REL_PROCEDURE(amvacuumcleanup);
+	GET_UNCACHED_REL_PROCEDURE(amvacuumcleanup);
 
 	result = (IndexBulkDeleteResult *)
-		DatumGetPointer(FunctionCall2(procedure,
+		DatumGetPointer(FunctionCall2(&procedure,
 									  PointerGetDatum(info),
 									  PointerGetDatum(stats)));
 

src/include/utils/rel.h

@@ -47,8 +47,8 @@ typedef LockInfoData *LockInfo;
 
 
 /*
- * Cached lookup information for the index access method functions defined
- * by the pg_am row associated with an index relation.
+ * Cached lookup information for the frequently used index access method
+ * functions, defined by the pg_am row associated with an index relation.
  */
 typedef struct RelationAmInfo
 {
@@ -60,13 +60,7 @@ typedef struct RelationAmInfo
 	FmgrInfo	amendscan;
 	FmgrInfo	ammarkpos;
 	FmgrInfo	amrestrpos;
-	FmgrInfo	ambuild;
-	FmgrInfo	ambuildempty;
-	FmgrInfo	ambulkdelete;
-	FmgrInfo	amvacuumcleanup;
 	FmgrInfo	amcanreturn;
-	FmgrInfo	amcostestimate;
-	FmgrInfo	amoptions;
 } RelationAmInfo;