Re: Consider parallel for lateral subqueries with limit

From: David Steele <david(at)pgmasters(dot)net>
To: James Coleman <jtc331(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Cc: brian(at)brianlikespostgres(dot)com
Subject: Re: Consider parallel for lateral subqueries with limit
Date: 2021-03-10 17:31:36
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On 12/7/20 6:45 PM, James Coleman wrote:
> On Sun, Dec 6, 2020 at 7:34 PM Brian Davis <brian(at)brianlikespostgres(dot)com> wrote:
>> Played around with this a bit, here's a non-correlated subquery that gets us to that if statement
> While I haven't actually tracked down to guarantee this is handled
> elsewhere, a thought experiment -- I think -- shows it must be so.
> Here's why: suppose we don't have a limit here, but the query return
> order is different in different backends. Then we would have the same
> problem you bring up. In that case this code is already setting
> consider_parallel=true on the rel. So I don't think we're changing any
> behavior here.

So it looks like you and Brian are satisfied that this change is not
allowing bad behavior.

Seems like an obvious win. Hopefully we can get some other concurring


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