| From: | Justin Pryzby <pryzby(at)telsasoft(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Gunther <raj(at)gusw(dot)net>, pgsql-performance(at)lists(dot)postgresql(dot)org, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| Subject: | Re: Out of Memory errors are frustrating as heck! |
| Date: | 2019-04-20 21:45:41 |
| Message-ID: | 20190420214541.GD4323@telsasoft.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-performance |
On Sat, Apr 20, 2019 at 04:46:03PM -0400, Tom Lane wrote:
> Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> > I think it's really a matter of underestimate, which convinces the planner
> > to hash the larger table. In this case, the table is 42GB, so it's
> > possible it actually works as expected. With work_mem = 4MB I've seen 32k
> > batches, and that's not that far off, I'd day. Maybe there are more common
> > values, but it does not seem like a very contrived data set.
>
> Maybe we just need to account for the per-batch buffers while estimating
> the amount of memory used during planning. That would force this case
> into a mergejoin instead, given that work_mem is set so small.
Do you mean by adding disable_cost if work_mem is so small that it's estimated
to be exceeded ?
Justin
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Tom Lane | 2019-04-20 22:20:15 | Re: Out of Memory errors are frustrating as heck! |
| Previous Message | Tomas Vondra | 2019-04-20 21:13:20 | Re: Out of Memory errors are frustrating as heck! |