On Sat, Apr 20, 2019 at 04:46:03PM -0400, Tom Lane wrote: > Tomas Vondra <tomas.vondra@xxxxxxxxxxxxxxx> 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
