Hi, On 08/31/2017 02:56 AM, Peter Geoghegan wrote: > On Wed, Aug 30, 2017 at 5:38 PM, Robert Haas <robertmh...@gmail.com> wrote: >> Wow. Just to be clear, I am looking for the BEST case for replacement >> selection, not the worst case. But I would have expected that case to >> be a win for replacement selection, and it clearly isn't. I can >> reproduce your results here. > > But I *was* trying to get a best case. That's why it isn't even worse. > That's what the docs say the best case is, after all. > > This is the kind of thing that replacement selection actually did do > better with on 9.6. I clearly remember Tomas Vondra doing lots of > benchmarking, showing some benefit with RS with a work_mem of 8MB or > less. As I said in my introduction on this thread, we weren't wrong to > add replacement_sort_tuples to 9.6, given where things were with > merging at the time. But, it does very much appear to create less than > zero benefit these days. The picture changed. >
Do we need/want to repeat some of that benchmarking on these patches? I don't recall how much this code changed since those benchmarks were done in the 9.6 cycle. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
