Cache opaque handle for GUC option to avoid repeasted lookups.

When setting GUCs from proconfig, performance is important, and hash
lookups in the GUC table are significant.

Per suggestion from Robert Haas.

Discussion: https://postgr.es/m/CA+TgmoYpKxhR3HOD9syK2XwcAUVPa0+ba0XPnwWBcYxtKLkyxA@mail.gmail.com
Reviewed-by: John Naylor

src/backend/utils/fmgr/fmgr.c

@@ -613,6 +613,7 @@ struct fmgr_security_definer_cache
 	FmgrInfo	flinfo;			/* lookup info for target function */
 	Oid			userid;			/* userid to set, or InvalidOid */
 	List	   *configNames;	/* GUC names to set, or NIL */
+	List	   *configHandles;	/* GUC handles to set, or NIL */
 	List	   *configValues;	/* GUC values to set, or NIL */
 	Datum		arg;			/* passthrough argument for plugin modules */
 };
@@ -635,8 +636,9 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 	FmgrInfo   *save_flinfo;
 	Oid			save_userid;
 	int			save_sec_context;
-	ListCell   *lc1;
-	ListCell   *lc2;
+	ListCell   *lc1,
+			   *lc2,
+			   *lc3;
 	volatile int save_nestlevel;
 	PgStat_FunctionCallUsage fcusage;
 
@@ -670,11 +672,23 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 		if (!isnull)
 		{
 			ArrayType  *array;
+			ListCell   *lc;
 
 			oldcxt = MemoryContextSwitchTo(fcinfo->flinfo->fn_mcxt);
 			array = DatumGetArrayTypeP(datum);
 			TransformGUCArray(array, &fcache->configNames,
 							  &fcache->configValues);
+
+			/* transform names to config handles to avoid lookup cost */
+			fcache->configHandles = NIL;
+			foreach(lc, fcache->configNames)
+			{
+				char	   *name = (char *) lfirst(lc);
+
+				fcache->configHandles = lappend(fcache->configHandles,
+												get_config_handle(name));
+			}
+
 			MemoryContextSwitchTo(oldcxt);
 		}
 
@@ -696,17 +710,20 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 		SetUserIdAndSecContext(fcache->userid,
 							   save_sec_context | SECURITY_LOCAL_USERID_CHANGE);
 
-	forboth(lc1, fcache->configNames, lc2, fcache->configValues)
+	forthree(lc1, fcache->configNames,
+			 lc2, fcache->configHandles,
+			 lc3, fcache->configValues)
 	{
 		GucContext	context = superuser() ? PGC_SUSET : PGC_USERSET;
 		GucSource	source = PGC_S_SESSION;
 		GucAction	action = GUC_ACTION_SAVE;
 		char	   *name = lfirst(lc1);
-		char	   *value = lfirst(lc2);
+		config_handle *handle = lfirst(lc2);
+		char	   *value = lfirst(lc3);
 
-		(void) set_config_option(name, value,
-								 context, source,
-								 action, true, 0, false);
+		(void) set_config_with_handle(name, handle, value,
+									  context, source, GetUserId(),
+									  action, true, 0, false);
 	}
 
 	/* function manager hook */

src/backend/utils/misc/guc.c

@@ -3329,10 +3329,10 @@ set_config_option(const char *name, const char *value,
 	else
 		srole = BOOTSTRAP_SUPERUSERID;
 
-	return set_config_option_ext(name, value,
-								 context, source, srole,
-								 action, changeVal, elevel,
-								 is_reload);
+	return set_config_with_handle(name, NULL, value,
+								  context, source, srole,
+								  action, changeVal, elevel,
+								  is_reload);
 }
 
 /*
@@ -3355,6 +3355,27 @@ set_config_option_ext(const char *name, const char *value,
 					  GucContext context, GucSource source, Oid srole,
 					  GucAction action, bool changeVal, int elevel,
 					  bool is_reload)
+{
+	return set_config_with_handle(name, NULL, value,
+								  context, source, srole,
+								  action, changeVal, elevel,
+								  is_reload);
+}
+
+
+/*
+ * set_config_with_handle: takes an optional 'handle' argument, which can be
+ * obtained by the caller from get_config_handle().
+ *
+ * This should be used by callers which repeatedly set the same config
+ * option(s), and want to avoid the overhead of a hash lookup each time.
+ */
+int
+set_config_with_handle(const char *name, config_handle *handle,
+					   const char *value,
+					   GucContext context, GucSource source, Oid srole,
+					   GucAction action, bool changeVal, int elevel,
+					   bool is_reload)
 {
 	struct config_generic *record;
 	union config_var_val newval_union;
@@ -3395,9 +3416,15 @@ set_config_option_ext(const char *name, const char *value,
 				(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
 				 errmsg("cannot set parameters during a parallel operation")));
 
-	record = find_option(name, true, false, elevel);
-	if (record == NULL)
-		return 0;
+	/* if handle is specified, no need to look up option */
+	if (!handle)
+	{
+		record = find_option(name, true, false, elevel);
+		if (record == NULL)
+			return 0;
+	}
+	else
+		record = handle;
 
 	/*
 	 * Check if the option can be set at this time. See guc.h for the precise
@@ -4166,6 +4193,22 @@ set_config_option_ext(const char *name, const char *value,
 }
 
 
+/*
+ * Retrieve a config_handle for the given name, suitable for calling
+ * set_config_with_handle(). Only return handle to permanent GUC.
+ */
+config_handle *
+get_config_handle(const char *name)
+{
+	struct config_generic *gen = find_option(name, false, false, 0);
+
+	if (gen && ((gen->flags & GUC_CUSTOM_PLACEHOLDER) == 0))
+		return gen;
+
+	return NULL;
+}
+
+
 /*
  * Set the fields for source file and line number the setting came from.
  */

src/include/utils/guc.h

@@ -144,6 +144,8 @@ typedef struct ConfigVariable
 	struct ConfigVariable *next;
 } ConfigVariable;
 
+typedef struct config_generic config_handle;
+
 extern bool ParseConfigFile(const char *config_file, bool strict,
 							const char *calling_file, int calling_lineno,
 							int depth, int elevel,
@@ -387,6 +389,13 @@ extern int	set_config_option_ext(const char *name, const char *value,
 								  Oid srole,
 								  GucAction action, bool changeVal, int elevel,
 								  bool is_reload);
+extern int	set_config_with_handle(const char *name, config_handle *handle,
+								   const char *value,
+								   GucContext context, GucSource source,
+								   Oid srole,
+								   GucAction action, bool changeVal,
+								   int elevel, bool is_reload);
+extern config_handle *get_config_handle(const char *name);
 extern void AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt);
 extern char *GetConfigOptionByName(const char *name, const char **varname,
 								   bool missing_ok);

src/tools/pgindent/typedefs.list

@@ -3247,6 +3247,7 @@ collation_cache_entry
 color
 colormaprange
 compare_context
+config_handle
 config_var_value
 contain_aggs_of_level_context
 contain_placeholder_references_context