| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Default setting for enable_hashagg_disk |
| Date: | 2020-06-10 17:39:08 |
| Message-ID: | 87a16031a58db0c4ba4bb506f2919dea8948d7b0.camel@j-davis.com |
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| Lists: | pgsql-docs pgsql-hackers |
On Tue, 2020-06-09 at 18:20 -0700, Melanie Plageman wrote:
> So, I was catching up on email and noticed the last email in this
> thread.
>
> I think I am not fully understanding what
> enable_groupingsets_hash_disk
> does. Is it only for testing?
It's mostly for testing. I could imagine cases where it would be useful
to force groupingsets to use the disk, but I mainly wanted the setting
there for testing the grouping sets hash disk code path.
> Using the tests you added to src/test/regress/sql/groupingsets.sql, I
> did get a plan that looks like hashagg is spilling to disk (goes
> through
I had something that worked as a test for a while, but then when I
tweaked the costing, it started using the Sort path (therefore not
testing my grouping sets hash disk code at all) and a bug crept in. So
I thought it would be best to have a more forceful knob.
Perhaps I should just get rid of that GUC and use the stats trick?
Regards,
Jeff Davis
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