On 11/01/2018 10:06 PM, Thomas Munro wrote: > On Fri, Nov 2, 2018 at 9:23 AM Jim Finnerty <jfinn...@amazon.com> wrote: >> I'm very interested in this patch, and particularly in possible >> extensions to push the Bloom filter down on the probe side of the join. I >> made a few small edits to the patch to enable it to compile on PG11, and can >> send it to you if you're interested. > > Hi Jim, > > Would you compute the hash for the outer tuples in the scan, and then > again in the Hash Join when probing, or would you want to (somehow) > attach the hash to emitted tuples for later reuse by the higher node? > Someone pointed out to me off-list that a popular RDBMS emanating from > the bicycle capital of the North-West pushes down Bloom filters to > scans, but only when the key is a non-nullable integer; I wonder if > that is because they hash in both places, but consider that OK only > when it's really cheap to do so. (Along the same lines, if we could > attach extra data to tuples, I wonder if it would make sense to > transmit sort support information to higher nodes, so that (for > example) GatherMerge could use it to avoid full key comparison when > dealing with subplans that already did a sort and computed integers > for fast inequality checks.) > >> It is currently in the list of patches for the current commitfest, but >> based on your previous post I'm not sure if you're planning to get back to >> this patch just now. If you plan to resume work on it, I'll sign up as a >> reviewer. > > I'm also signed up to review. >
I haven't really planned to work on this anytime soon, unfortunately, which is why I proposed to mark it as RwF at the end of the last CF. I already have a couple other patches there, and (more importantly) I don't have a very clear idea how to implement the filter pushdown. That being said I still think it'd be an interesting improvement, and if someone wants to take over I'm available as a reviewer / tester ... regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
