Re: is possible cache tupledesc templates in execution plan? significant performance issue, maybe bug?

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.

> 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