2017-09-19 20:49 GMT+02:00 Merlin Moncure <mmonc...@gmail.com>:
> On Tue, Sep 19, 2017 at 1:37 PM, Robert Haas <robertmh...@gmail.com>
> wrote:
> > On Tue, Sep 19, 2017 at 12:45 PM, Pavel Stehule <pavel.steh...@gmail.com>
> wrote:
> >>> You can already set a GUC with function scope. I'm not getting your
> >>> point.
> >>
> >> yes, it is true. But implementation of #option is limited to PLpgSQL -
> so
> >> there is not any too much questions - GUC is global - there is lot of
> >> points:
> >>
> >> * what is correct impact on PREPARE
> >> * what is correct impact on EXECUTE
> >> * what should be done if this GUC is changed ..
> >
> > For better or for worse, as a project we've settled on GUCs as a way
> > to control behavior. I think it makes more sense to try to apply that
> > option to new behaviors we want to control than to invent some new
> > system.
>
> This seems very sensible.
>
> We also have infrastructure at the SQL level (SET) to manage the GUC.
> Tom upthread (for pretty good reasons) extending SET to pl/pgsql
> specific scoping but TBH I'm struggling as to why we need to implement
> new syntax for this; the only thing missing is being able to scope SET
> statements to a code block FWICT.
>
>
here is a GUC based patch for plancache controlling. Looks so this code is
working.
It is hard to create regress tests. Any ideas?
Regards
Pavel
> merlin
>
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index ad8a82f1e3..cc99cf6dcc 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -106,6 +106,8 @@ static void PlanCacheRelCallback(Datum arg, Oid relid);
static void PlanCacheFuncCallback(Datum arg, int cacheid, uint32 hashvalue);
static void PlanCacheSysCallback(Datum arg, int cacheid, uint32 hashvalue);
+/* GUC parameter */
+int plancache_mode;
/*
* InitPlanCache: initialize module during InitPostgres.
@@ -1031,6 +1033,12 @@ choose_custom_plan(CachedPlanSource *plansource, ParamListInfo boundParams)
if (IsTransactionStmtPlan(plansource))
return false;
+ /* See if settings wants to force the decision */
+ if (plancache_mode & PLANCACHE_FORCE_GENERIC_PLAN)
+ return false;
+ if (plancache_mode & PLANCACHE_FORCE_CUSTOM_PLAN)
+ return true;
+
/* See if caller wants to force the decision */
if (plansource->cursor_options & CURSOR_OPT_GENERIC_PLAN)
return false;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index ae22185fbd..4ce275e39d 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -403,6 +403,13 @@ static const struct config_enum_entry force_parallel_mode_options[] = {
{NULL, 0, false}
};
+static const struct config_enum_entry plancache_mode_options[] = {
+ {"default", PLANCACHE_DEFAULT, false},
+ {"force_generic_plan", PLANCACHE_FORCE_GENERIC_PLAN, false},
+ {"force_custom_plan", PLANCACHE_FORCE_CUSTOM_PLAN, false},
+ {NULL, 0, false}
+};
+
/*
* password_encryption used to be a boolean, so accept all the likely
* variants of "on", too. "off" used to store passwords in plaintext,
@@ -3916,6 +3923,16 @@ static struct config_enum ConfigureNamesEnum[] =
NULL, NULL, NULL
},
+ {
+ {"plancache_mode", PGC_USERSET, QUERY_TUNING_OTHER,
+ gettext_noop("Forces use of custom or generic plans."),
+ gettext_noop("It can control query plan cache.")
+ },
+ &plancache_mode,
+ PLANCACHE_DEFAULT, plancache_mode_options,
+ NULL, NULL, NULL
+ },
+
/* End-of-list marker */
{
{NULL, 0, 0, NULL, NULL}, NULL, 0, NULL, NULL, NULL, NULL
diff --git a/src/include/utils/plancache.h b/src/include/utils/plancache.h
index 87fab19f3c..962895cc1a 100644
--- a/src/include/utils/plancache.h
+++ b/src/include/utils/plancache.h
@@ -143,7 +143,6 @@ typedef struct CachedPlan
MemoryContext context; /* context containing this CachedPlan */
} CachedPlan;
-
extern void InitPlanCache(void);
extern void ResetPlanCache(void);
@@ -182,4 +181,16 @@ extern CachedPlan *GetCachedPlan(CachedPlanSource *plansource,
QueryEnvironment *queryEnv);
extern void ReleaseCachedPlan(CachedPlan *plan, bool useResOwner);
+/* possible values for plancache_mode */
+typedef enum
+{
+ PLANCACHE_DEFAULT,
+ PLANCACHE_FORCE_GENERIC_PLAN,
+ PLANCACHE_FORCE_CUSTOM_PLAN
+} PlanCacheMode;
+
+
+/* GUC parameter */
+extern int plancache_mode;
+
#endif /* PLANCACHE_H */
--
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