Re: [HACKERS] [PATCH] Push limit to sort through a subquery
| От | Douglas Doole |
|---|---|
| Тема | Re: [HACKERS] [PATCH] Push limit to sort through a subquery |
| Дата | |
| Msg-id | CADE5jYJWROLd-wnMFcYqtTsyo3bNto9PECx_r+xvzf844yrGJQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: [HACKERS] [PATCH] Push limit to sort through a subquery (Robert Haas <robertmhaas@gmail.com>) |
| Ответы |
Re: [HACKERS] [PATCH] Push limit to sort through a subquery
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| Список | pgsql-hackers |
Thanks for the feedback on my original patch Robert. Here's an updated patch that will tunnel through multiple SubqueryScanStates.
- Doug
Salesforce
On Thu, Aug 17, 2017 at 6:33 PM Robert Haas <robertmhaas@gmail.com> wrote:
On Thu, Aug 17, 2017 at 11:36 AM, Douglas Doole <dougdoole@gmail.com> wrote:I completely agree. The further a limit can be pushed down, the better.The patch looks good to me.It seems like a somewhat ad-hoc approach; it supposes that we can take any query produced by deparseSelectStmtForRel() and stick a LIMIT clause onto the very end and all will be well. Maybe that's not a problematic assumption, not sure. The grammar happens to allow both FOR UPDATE LIMIT n and LIMIT n FOR UPDATE even though only the latter syntax is documented.Regarding the other patch on this thread, you mentioned upthread that "If it is possible to get more than one SubqueryScanState and/or ResultState between the limit and sort, then the first block of code could be placed in a while loop." I think that's not possible for a ResultState, but I think it *is* possible for a SubqueryScanState.
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