Thanks for the feedback. > On 8 Oct 2023, at 03:33, Andy Fan <zhihui.fan1...@gmail.com> wrote: > > > > On Sun, Oct 8, 2023 at 5:04 AM Michał Kłeczek <mic...@kleczek.org > <mailto:mic...@kleczek.org>> wrote: >> Hi All, >> >> Attached is a second version of the patch. >> >> The goal is to: >> 1. Apply LIMIT as early as possible - especially to apply LIMIT in partition >> scans > > For the patches for performance improvement, it is better to provide > an example to show how much benefits we can get. As for this case, > I'm doubtful it can work as an improvement. > >> 2. Enable LIMIT pushdown for FDW partitions. > > The same as above, some testing is helpful.
The idea came up from this e-mail thread from 2019: https://www.postgresql.org/message-id/CAFT%2BaqL1Tt0qfYqjHH%2BshwPoW8qdFjpJ8vBR5ABoXJDUcHyN1w%40mail.gmail.com FDW does not push down LIMIT & ORDER BY with sharding (partitions) postgresql.org While obviously permofmance testing is needed to confirm any real improvements I now (after your feedback) have second thoughts if it is worth pursuing at all. Could you elaborate a little why you think it won’t work as an improvement? Is it because in practice LIMIT _is_ pushed down already during execution? From what I understand postgres_fdw does indeed fetch on demand. OTOH pushing down LIMIT is considered an improvement (as witnessed in the postgres_fdw code itself after d50d172e51) Care to provide some more information? Thanks, -- Michal
