Re: PATCH: generate fractional cheapest paths in generate_orderedappend_path

Hi,

On 6/3/21 7:17 PM, Arne Roland wrote:
> Hi,
>
>
> I haven't tested the parallel case, but I think we should sort out (3)
> get_cheapest_fractional_path_for_pathkeys as mentioned above.
>

Not sure what you refer to by "above" - it's probably better to reply
in-line to existing message, which makes it much cleared.

>
> I am lost about the comment regarding startup_new_fractional. Could you
> elaborate what you mean by that?
>

Not sure what this refers to either - there's no startup_new_fractional
in my message and 'git grep startup_new_fractional' returns nothing.

>
> Apart from that, I'd argue for a small test case. I attached a slimmed
> down case of what we were trying to fix. It might be worth to integrate
> that with an existing test, since more than a third of the time seems to
> be consumed by the creation and attachment of partitions.
>

Maybe, if there's a suitable table to reuse, we can do that. But I don't
think it matters it takes ~1/3 of the time to attach the partitions.
What's more important is whether it measurably slows down the test
suite, and I don't think that's an issue.

In any case, this seems a bit premature - we need something to test the
patch etc. We can worry about how expensive the test is much later.

regards

--
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

src/backend/optimizer/path/pathkeys.c: * get_cheapest_fractional_path_for_pathkeys
src/backend/optimizer/path/pathkeys.c:get_cheapest_fractional_path_for_pathkeys(List *paths,
src/backend/optimizer/plan/planagg.c:           get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,