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Date: Thu, 8 Jan 2026 17:55:06 +1300
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Subject: Re: Unexpected planner choice in simple JOIN
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <dgrowleyml@gmail.com>,
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From: Mark Kirkwood <mark.kirkwood@gmail.com>
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Right makes sense - as I noted...the 'wrong' plan is still pretty fast...

On 08/01/2026 17:51, Tom Lane wrote:
> Mark Kirkwood <mark.kirkwood@gmail.com> writes:
>> A point comes to mind - this is not a particularly unusual setup (i.e
>> relatively small parent table with big child one), so maybe the defaults
>> are not ideal here?
> Very probably.  To my mind, the default costs for parallel query and
> JIT are both unduly optimistic and tend to drive the planner to use
> those features when you'd be better off without.  The reason there's
> not been more argument about them is that the downside of using those
> features on a too-small query is bounded, while the upside of using
> them on very-big queries isn't.  So nobody's invested the effort to
> gather enough evidence to back choosing a different set of defaults.
>
> 			regards, tom lane