| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | David Rowley <dgrowleyml(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Default setting for enable_hashagg_disk |
| Date: | 2020-06-25 16:37:46 |
| Message-ID: | 20200625163746.laoepc7esanptvxt@alap3.anarazel.de |
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| Lists: | pgsql-docs pgsql-hackers |
On 2020-06-25 09:24:52 -0700, Jeff Davis wrote:
> On Wed, 2020-06-24 at 12:14 -0700, Andres Freund wrote:
> > E.g. if the plan isn't expected to spill,
> > only spill at 10 x work_mem or something like that.
>
> Let's say you have work_mem=32MB and a query that's expected to use
> 16MB of memory. In reality, it uses 64MB of memory. So you are saying
> this query would get to use all 64MB of memory, right?
>
> But then you run ANALYZE. Now the query is (correctly) expected to use
> 64MB of memory. Are you saying this query, executed again with better
> stats, would only get to use 32MB of memory, and therefore run slower?
Yes. I think that's ok, because it was taken into account from a costing
perspective int he second case.
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