On Thu, Aug 27, 2020 at 2:51 PM Stephen Frost <sfr...@snowman.net> wrote: > > Hm? At least earlier versions didn't do prefetching for records with an > > fpw, and only for subsequent records affecting the same or if not in s_b > > anymore. > > We don't actually read the page when we're replaying an FPW though..? > If we don't read it, and we entirely write the page from the FPW, how is > pre-fetching helping..?
Suppose there is a checkpoint. Then we replay a record with an FPW, pre-fetching nothing. Then the buffer gets evicted from shared_buffers, and maybe the OS cache too. Then, before the next checkpoint, we again replay a record for the same page. At this point, pre-fetching should be helpful. Admittedly, I don't quite understand whether that is what is happening in this test case, or why SDD vs. HDD should make any difference. But there doesn't seem to be any reason why it doesn't make sense in theory. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
