Re: PoC: Partial sort
| От | Alexander Korotkov |
|---|---|
| Тема | Re: PoC: Partial sort |
| Дата | |
| Msg-id | CAPpHfdvrhbv+gGbLDsDFJY9Ln1ei4M2WiGnRzuZUnGGW_cfKZQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: PoC: Partial sort (Marti Raudsepp <marti@juffo.org>) |
| Список | pgsql-hackers |
On Thu, Feb 13, 2014 at 1:54 AM, Marti Raudsepp <marti@juffo.org> wrote:
------
With best regards,
Alexander Korotkov.
I think the 1st patch now has a bug in initial_cost_mergejoin; you
still pass the "presorted_keys" argument to cost_sort, making it
calculate a partial sort cost, but generated plans never use partial
sort. I think 0 should be passed instead. Patch attached, needs to be
applied on top of partial-sort-basic-1 and then reverse-applied on
partial-sort-merge-1.
It doesn't look so for me. Merge join doesn't find partial sort especially. But if path with some presorted pathkeys will be accidentally selected then partial sort will be used. See create_mergejoin_plan function. So, I think this cost_sort call is relevant to create_mergejoin_plan. If we don't want partial sort to be used in such rare cases then we should revert it from both places. However, I doubt that it does any overhead, so we can leave it as is.
------
With best regards,
Alexander Korotkov.
В списке pgsql-hackers по дате отправления: