Re: Out of Memory errors are frustrating as heck!
Tomas Vondra <[email protected]>
| Newsgroups | gmane.comp.db.postgresql.performance |
|---|---|
| Message-ID | <20190420203650.7kiausfmiv3hixg6@development> |
On Sat, Apr 20, 2019 at 04:26:34PM -0400, Tom Lane wrote: >Tomas Vondra <[email protected]> writes: >> Considering how rare this issue likely is, we need to be looking for a >> solution that does not break the common case. > >Agreed. What I think we need to focus on next is why the code keeps >increasing the number of batches. It seems like there must be an undue >amount of data all falling into the same bucket ... but if it were simply >a matter of a lot of duplicate hash keys, the growEnabled shutoff >heuristic ought to trigger. > 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. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services