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

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);

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.

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

This should probably be done in a preparatory commit.

Greetings,

Andres Freund