From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Marko Tiikkaja <marko(at)joh(dot)to> |
Cc: | Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com>, pgsql-bugs <pgsql-bugs(at)postgresql(dot)org> |
Subject: | Re: BUG #13528: LATERAL vs. correlated scalar subquery |
Date: | 2015-07-30 17:44:58 |
Message-ID: | 28691.1438278298@sss.pgh.pa.us |
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Lists: | pgsql-bugs |
Marko Tiikkaja <marko(at)joh(dot)to> writes:
> On 7/30/15 1:48 PM, Maxim Boguk wrote:
>> You could see that the new plan have lower total cost than the old plan
>> (cost=1867.28..1873.03 vs cost=0.00..125498.75).
>> I think it's primary reason why it been selected (planner could produce the
>> old plan but new plan wins on the cost basis).
> I'll have to admit I could've put more time into the original report,
> but I don't think that's accurate.
Yeah. It would be nice if we could produce a more accurate rowcount
estimate for unnest(array[...]); that's something that's been a pain
for Salesforce so I've been considering ways to fix it. But it's
not the killer problem here.
> which to me suggests that the planner just doesn't realize that it can
> push the condition on counts.a into the view.
It can't. We'd need parameterized paths for subqueries, which we don't
have (yet).
regards, tom lane
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