Re: Review remove {join, from}_collapse_limit, add enable_join_ordering

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Subject: Re: Review remove {join, from}_collapse_limit, add enable_join_ordering
Date: 2009-07-16 13:13:02
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Andres Freund <andres(at)anarazel(dot)de> writes:
> The queries on the second reporting schema unfortunately are different. Its the
> one were I copied the crazy example I attached in the original thread.
> With geqo=off a good part of the queries used daily use too much memory to plan
> sensibly and geqo=on outright fails with:
> "Error: Failed to make a valid plan"
> on some.

We're not going to be able to fix this unless you show us examples.

> Noticeable even some plans which were plannable in reasonable time before now
> are problematic with enable_join_ordering=false!

And this even more so --- it doesn't make any sense at all.

> So, while I think the changes are principally a good idea, as
> {from,join}_collapse_limit are a bit confusing options, I personally! do not
> think geqo is ready for it today, especially as the benefit is relatively
> small.

In general I think that any such bugs are there anyway and need to be
fixed anyway.

regards, tom lane

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