Hi po 22. 7. 2024 v 17:08 odesÃlatel Konstantin Knizhnik <knizh...@garret.ru> napsal:
> > On 16/01/2024 5:38 pm, Tomas Vondra wrote: > > By "broken" you mean that you prefetch items only from a single leaf > > page, so immediately after reading the next one nothing is prefetched. > Correct? > > > Yes, exactly. It means that reading first heap page from next leaf page > will be done without prefetch which in case of Neon means roundtrip with > page server (~0.2msec within one data center). > > > Yeah, I had this problem initially too, when I did the > prefetching in the index AM code. One of the reasons why it got moved to > the executor. > > Yeh, it works nice for vanilla Postgres. You call index_getnext_tid() and > when it reaches end of leaf page it reads next read page. Because of OS > read-ahead this read is expected to be fast even without prefetch. But not > in Neon case - we have to download this page from page server (see above). > So ideal solution for Neon will be to prefetch both leave pages and > referenced heap pages. And prefetch of last one should be initiated as soon > as leaf page is loaded. Unfortunately it is non-trivial to implement and > current index scan prefetch implementation for Neon is not doing it. > What is the current state of this patch - it is abandoned? It needs a rebase. Regards Pavel
