From: | "Regina Obe" <lr(at)pcorp(dot)us> |
---|---|
To: | "'Robert Haas'" <robertmhaas(at)gmail(dot)com> |
Cc: | "'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 21:27:28 |
Message-ID: | 000801d4caf5$6a129cf0$3e37d6d0$@pcorp.us |
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Lists: | pgsql-hackers |
> 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.
> I also think
> Andres's question about why this gets inlined in the first place is a good one;
> the (m).* seems like it ought to be counted as a multiple reference.
>
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL
> Company
Well if we can at least prevent the multiple reference thing from inlining that might be good enough to solve most performance regression issues that arise.
Thanks,
Regina
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