| From: | Surafel Temesgen <surafel3000(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | vik(dot)fearing(at)2ndquadrant(dot)com, Mark Dilger <hornschnorter(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, andrew(at)tao11(dot)riddles(dot)org(dot)uk |
| Subject: | Re: FETCH FIRST clause PERCENT option |
| Date: | 2019-01-04 07:08:50 |
| Message-ID: | CALAY4q-T3tGY0kjAfreykOpqZHej0oKn7Bv3+XiDCLyfvPU_pw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 1, 2019 at 10:08 PM Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
wrote:
> The execution part of the patch seems to be working correctly, but I
> think there's an improvement - we don't need to execute the outer plan
> to completion before emitting the first row. For example, let's say the
> outer plan produces 10000 rows in total and we're supposed to return the
> first 1% of those rows. We can emit the first row after fetching the
> first 100 rows, we don't have to wait for fetching all 10k rows.
>
>
my other concern is in this case we are going to determine limit and safe
row to return on the fly
which have additional computation and i fair that it will not perform
better on most of the case
regards
Surafel
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