On Fri, Apr 05, 2019 at 03:14:56PM +0300, Surafel Temesgen wrote:
On Tue, Mar 26, 2019 at 5:46 PM Tomas Vondra <tomas.von...@2ndquadrant.com>
wrote:
On Tue, Mar 26, 2019 at 03:06:52PM +0300, Surafel Temesgen wrote:
>On Thu, Feb 28, 2019 at 11:16 PM Tomas Vondra <
tomas.von...@2ndquadrant.com>
>wrote:
>
>>
>> To give you a (admittedly, somewhat contrived and artificial example):
>>
>> SELECT * FROM t1 WHERE id IN (
>> SELECT id FROM t2 ORDER BY x FETCH FIRST 10 PERCENT ROWS ONLY
>> );
>>
>> Maybe this example is bogus and/or does not really matter in practice. I
>> don't know, but I've been unable to convince myself that's the case.
>
>
>does this means we abandon incremental approach? and am not sure of
>calculating
>percentage after OFFSET clause is acceptable or not
>
I don't follow. I don't think I've suggested to abandon the incremental
approach - I've explained why I think it's what the patch should be doing,
and illustrated that with an example.
but it is more complex than the previous approach and it will be more
complex
in starting calculating percentage before offset row count. Doesn't
simplicity prefer?
Sure, simplicity has it's value. And often the simplest solution is the
best one. But in But in plenty of cases it's a tradeoff between simplicity
and efficiency, i.e. the simplest solution may perform poorly. I've tried
to explain why I think the incremental solution is the right approach
here - not having to always execute the subplan to completion. I still
haven't heard reasons why that argument is irrelevant (it may be).
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
