From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Regina Obe <lr(at)pcorp(dot)us> |
Cc: | 'Robert Haas' <robertmhaas(at)gmail(dot)com>, 'PostgreSQL Hackers' <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: CTE Changes in PostgreSQL 12, can we have a GUC to get old behavior |
Date: | 2019-02-22 21:32:09 |
Message-ID: | 20190222213209.ojylrztgbesybz7g@alap3.anarazel.de |
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Lists: | pgsql-hackers |
Hi,
On 2019-02-22 16:27:28 -0500, Regina Obe wrote:
> > I think there are probably other ways of fixing this query that won't have
> > such dramatic effects; it doesn't really seem to need to use WITH, and I bet
> > you could also tweak the WITH query to prevent inlining.
>
> Yes I know I can change THIS QUERY. I've changed other ones to work around this.
> Normally I just use a LATERAL for this.
>
> My point is lots of people use CTEs intentionally for this kind of thing because they know they are materialized.
>
> It's going to make a lot of people hesitant to upgrade if they think they need to revisit every CTE (that they intentionally wrote cause they thought it would be materialized) to throw in a MATERIALIZED keyword.
This was extensively discussed, in several threads about inlining
CTEs. But realistically, it doesn't actually solve the problem to offer
a GUC, because we'd not be able to remove it anytime soon. I see
benefit in discussing how we can address regressions like your example
query here, but I don't feel there's any benefit in re-opening the whole
discussion about GUCs, defaults, and whatnot.
Greetings,
Andres Freund
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