Re: Split index and table statistics into different types of stats

[Drouvot, Bertrand]

Hi,

On 11/16/22 9:12 PM, Andres Freund wrote:

Hi,

On 2022-11-15 10:48:40 +0100, Drouvot, Bertrand wrote:

diff --git a/src/backend/utils/adt/pgstatfuncs.c 
b/src/backend/utils/adt/pgstatfuncs.c
index ae3365d917..be7f175bf1 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -36,24 +36,34 @@

#define HAS_PGSTAT_PERMISSIONS(role) (has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS) || has_privs_of_role(GetUserId(), role)) +#define PGSTAT_FETCH_STAT_ENTRY(entry, stat_name) ((entry == NULL) ? 0 : (int64) (entry->stat_name))

+
  Datum
-pg_stat_get_numscans(PG_FUNCTION_ARGS)
+pg_stat_get_index_numscans(PG_FUNCTION_ARGS)
  {
        Oid                     relid = PG_GETARG_OID(0);
        int64           result;
-       PgStat_StatTabEntry *tabentry;
+       PgStat_StatIndEntry *indentry = pgstat_fetch_stat_indentry(relid);

- if ((tabentry = pgstat_fetch_stat_tabentry(relid)) == NULL)

-               result = 0;
-       else
-               result = (int64) (tabentry->numscans);
+       result = PGSTAT_FETCH_STAT_ENTRY(indentry, numscans);

PG_RETURN_INT64(result);

  }

This still leaves a fair bit of boilerplate. ISTM that the function body
really should just be a single line.

Might even be worth defining the whole function via a macro. Perhaps something 
like

PGSTAT_DEFINE_REL_FIELD_ACCESSOR(PGSTAT_KIND_INDEX, pg_stat_get_index, 
numscans);

Thanks for the feedback!

Right, what about something like the following?

"
#define PGSTAT_FETCH_STAT_ENTRY(pgstat_entry_kind, pgstat_fetch_stat_function, 
relid, stat_name) \
        do { \
                pgstat_entry_kind *entry = pgstat_fetch_stat_function(relid); \
                PG_RETURN_INT64(entry == NULL ? 0 : (int64) 
(entry->stat_name)); \
        } while (0)

Datum
pg_stat_get_index_numscans(PG_FUNCTION_ARGS)
{
        PGSTAT_FETCH_STAT_ENTRY(PgStat_StatIndEntry, 
pgstat_fetch_stat_indentry, PG_GETARG_OID(0), numscans);
}
"

I think the logic to infer which DB oid to use for a stats entry could be
shared between different kinds of stats. We don't need to duplicate it.

Agree, will provide a new patch version once [1] is committed.

Is there any reason to not replace the "double lookup" in
pgstat_fetch_stat_tabentry() with IsSharedRelation()?

Thanks for the suggestion!

This should probably be done in a preparatory commit.

Proposal submitted in [1].

[1]: 
https://www.postgresql.org/message-id/flat/2e4a0ae1-2696-9f0c-301c-2330e447133f%40gmail.com#e47bf5d2902121461b61ed47413628fc

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com