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