We have a Postgres 13 open item for Disk-based hash aggregate, which is the only non-trivial open item. There is a general concern about how often we get disk-based hash aggregation when work_mem is particularly low, and recursion seems unavoidable. This is generally thought to be a problem in the costing.
Tomas Vondra did some testing of the patch which led to discussion of this on the hash agg GUC megathread, here: https://www.postgresql.org/message-id/20200724012248.y77rpqc73agrsvb3@development I am starting this new thread to deal with the open item. Any progress on this, Jeff? Please correct or expand on my summary of the open item if I got something wrong. Thanks -- Peter Geoghegan
