Re: Out of Memory errors are frustrating as heck!
Tomas Vondra <[email protected]>
| Newsgroups | gmane.comp.db.postgresql.performance |
|---|---|
| Message-ID | <20190420205356.ksmdm7wlbtwazse2@development> |
On Sat, Apr 20, 2019 at 04:46:03PM -0400, Tom Lane wrote: >Tomas Vondra <[email protected]> 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. > How would that solve the issue of underestimates like this one? regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services