Re: Generate pg_stat_get_xact*() functions with Macros

Hi,

Michael, CCing you because of the point about PG_STAT_GET_DBENTRY_FLOAT8
below.

On 2023-01-05 14:48:39 +0100, Drouvot, Bertrand wrote:
> While at it, I also took the opportunity to create the macros for pg_stat_get_xact_function_total_time(),
> pg_stat_get_xact_function_self_time() and pg_stat_get_function_total_time(), pg_stat_get_function_self_time()
> (even if the same code pattern is only repeated two 2 times).

I'd split that up into a separate commit.

> Now that this patch renames some fields

I don't mind renaming the fields - the prefixes really don't provide anything
useful. But it's not clear why this is related to this patch? You could just
include the f_ prefix in the macro, no?

> , I think that, for consistency, those ones should be renamed too (aka remove the f_ and t_ prefixes):
>
> PgStat_FunctionCounts.f_numcalls
> PgStat_StatFuncEntry.f_numcalls
> PgStat_TableCounts.t_truncdropped
> PgStat_TableCounts.t_delta_live_tuples
> PgStat_TableCounts.t_delta_dead_tuples
> PgStat_TableCounts.t_changed_tuples

Yea, without that the result is profoundly weird.

> But I think it would be better to do it in a follow-up patch (once this one get committed).

I don't mind committing it in a separate commit, but I think it should be done
at least immediately following the other commit. I.e. developed together.

I probably would go the other way, and rename all of them first. That'd make
this commit a lot more focused, and the renaming commit purely mechanical.

Probably should remove PgStat_BackendFunctionEntry. PgStat_TableStatus has
reason to exist, but that's not true for PgStat_BackendFunctionEntry.

> @@ -168,19 +168,19 @@ pgstat_end_function_usage(PgStat_FunctionCallUsage *fcu, bool finalize)
> INSTR_TIME_ADD(total_func_time, f_self);
>
> /*
> - * Compute the new f_total_time as the total elapsed time added to the
> - * pre-call value of f_total_time. This is necessary to avoid
> + * Compute the new total_time as the total elapsed time added to the
> + * pre-call value of total_time. This is necessary to avoid
> * double-counting any time taken by recursive calls of myself. (We do
> * not need any similar kluge for self time, since that already excludes
> * any recursive calls.)
> */
> - INSTR_TIME_ADD(f_total, fcu->save_f_total_time);
> + INSTR_TIME_ADD(f_total, fcu->save_total_time);
>
> /* update counters in function stats table */
> if (finalize)
> fs->f_numcalls++;
> - fs->f_total_time = f_total;
> - INSTR_TIME_ADD(fs->f_self_time, f_self);
> + fs->total_time = f_total;
> + INSTR_TIME_ADD(fs->self_time, f_self);
> }

I'd also rename f_self etc.

> @@ -148,29 +148,24 @@ pg_stat_get_function_calls(PG_FUNCTION_ARGS)
> PG_RETURN_INT64(funcentry->f_numcalls);
> }
>
> -Datum
> -pg_stat_get_function_total_time(PG_FUNCTION_ARGS)
> -{
> - Oid funcid = PG_GETARG_OID(0);
> - PgStat_StatFuncEntry *funcentry;
> -
> - if ((funcentry = pgstat_fetch_stat_funcentry(funcid)) == NULL)
> - PG_RETURN_NULL();
> - /* convert counter from microsec to millisec for display */
> - PG_RETURN_FLOAT8(((double) funcentry->f_total_time) / 1000.0);
> +#define PG_STAT_GET_FUNCENTRY_FLOAT8(stat) \
> +Datum \
> +CppConcat(pg_stat_get_function_,stat)(PG_FUNCTION_ARGS) \
> +{ \
> + Oid funcid = PG_GETARG_OID(0); \
> + PgStat_StatFuncEntry *funcentry; \
> + \
> + if ((funcentry = pgstat_fetch_stat_funcentry(funcid)) == NULL) \
> + PG_RETURN_NULL(); \
> + /* convert counter from microsec to millisec for display */ \
> + PG_RETURN_FLOAT8(((double) funcentry->stat) / 1000.0); \
> }

Hm. Given the conversion with / 1000, is PG_STAT_GET_FUNCENTRY_FLOAT8 an
accurate name? Maybe PG_STAT_GET_FUNCENTRY_FLOAT8_MS?

I now see that PG_STAT_GET_DBENTRY_FLOAT8 already exists, defined the same
way. But the name fields misleading enough that I'd be inclined to rename it?

> +#define PG_STAT_GET_XACT_WITH_SUBTRANS_RELENTRY_INT64(stat) \

How about PG_STAT_GET_XACT_PLUS_SUBTRANS_INT64?

Although I suspect this actually hints at an architectural thing that could be
fixed better: Perhaps we should replace find_tabstat_entry() with a version
returning a fully "reconciled" PgStat_StatTabEntry? It feels quite wrong to
have that intimitate knowledge of the subtransaction stuff in pgstatfuncs.c
and about how the different counts get combined.

I think that'd allow us to move the definition of PgStat_TableStatus to
PgStat_TableXactStatus, PgStat_TableCounts to pgstat_internal.h. Which feels a
heck of a lot cleaner.

Greetings,

Andres Freund