Re: Generate pg_stat_get_xact*() functions with Macros

Hi,

On 1/11/23 11:59 PM, Andres Freund wrote:
> 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.
>
>

Thanks for looking at it! Makes sense, will do.

>> 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?
>
>

Right, but the idea is to take the same approach that the one used in 8018ffbf58 (where placing the prefixes in the macro
would have been possible too).

>> , 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.
>

Yeah, makes sense. Let's proceed that way. I'll provide the "rename" patch.

> Probably should remove PgStat_BackendFunctionEntry.

I think that would be a 3rd patch, agree?

>> @@ -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.
>

Makes sense, will do.

>> @@ -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?
>

PG_STAT_GET_FUNCENTRY_FLOAT8_MS looks good by me. Waiting on what we'll decide for
the existing PG_STAT_GET_DBENTRY_FLOAT8 (so that I can align for the PG_STAT_GET_FUNCENTRY_FLOAT8).

>> +#define PG_STAT_GET_XACT_WITH_SUBTRANS_RELENTRY_INT64(stat) \
>
> How about PG_STAT_GET_XACT_PLUS_SUBTRANS_INT64?
>

Sounds, better, thanks!

> 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.

Yeah, I think that would be for a 4th patch, agree?

Regards,

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