From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
---|---|
To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: is possible cache tupledesc templates in execution plan? significant performance issue, maybe bug? |
Date: | 2017-10-08 16:57:28 |
Message-ID: | CAFj8pRDq-m7cA_KUehkMbhF_x3ZzCKqGEoStc4z7ihRwzBdSnA@mail.gmail.com |
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Lists: | pgsql-hackers |
2017-10-08 18:44 GMT+02:00 Andres Freund <andres(at)anarazel(dot)de>:
> Hi,
>
> On 2017-10-08 18:36:23 +0200, Pavel Stehule wrote:
> > 2. Lot of used tables are pretty wide - 60, 120, .. columns
> >
> > Now, I am doing profiling, and I see so most time is related to
> >
> > ExecTypeFromTLInternal(List *targetList, bool hasoid, bool skipjunk)
>
> Yea, that's known - I've complained about this a couple times. You could
> try whether the following master branch helps:
> https://git.postgresql.org/gitweb/?p=users/andresfreund/
> postgres.git;a=shortlog;h=refs/heads/simple_statement_perf
>
> That's just micro-optimization though, not a more fundamental
> solution. But for me it yields pretty nice speedups for cases with long
> tlists.
>
>
it is just this patch
HeapTuple tup;
Form_pg_type typTup;
+ if (typid < FirstBootstrapObjectId)
+ break;
+
tup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typid));
if (!HeapTupleIsValid(tup))
elog(ERROR, "cache lookup failed for type %u", typid);
?
>
> > This function is executed in exec init time - in this case pretty often.
> > Although there are used few columns from the table, the target list is
> > build for columns (maybe it is bug)
>
> It's probably just the physical tlist "optimization".
>
>
> > 2. If is not possible to reduce the number of fields of target list, is
> > possible to store tupledesc template to plan?
>
> We should do that, but it's not a small change.
>
> Greetings,
>
> Andres Freund
>
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