Michail Nikolaev <michail.nikol...@gmail.com> wrote: > Hello, Antonin. > > > I'm trying to review the patch, but not sure if I understand this problem, > > please see my comment below. > > Thanks a lot for your attention. It is strongly recommended to look at > version N3 (1) because it is a much more elegant, easy, and reliable > solution :) But the minRecoveryPoint-related issue affects it anyway.
Indeed I'm reviewing (1), but I wanted to discuss this particular question in context, so I replied here. > > Why doesn't minRecoveryPoint get updated to 20? IMO that should happen by > > replaying the commit record. And if the standby happens to crash before the > > commit record could be replayed, no query should see the deletion and thus > > no > > hint bit should be set in the index. > > minRecoveryPoint is not affected by replaying the commit record in > most cases. It is updated in a lazy way, something like this: > minRecoveryPoint = max LSN of flushed page. Version 3 of a patch > contains a code_optional.patch to move minRecoveryPoint more > aggressively to get additional performance on standby (based on > Peter’s answer in (2). > So, “minRecoveryPoint will go here” is not because of “STANDBY INSERTS > NEW ROW IN INDEX” it is just a random event. > Michail. Sorry, I missed the fact that your example can be executed inside BEGIN - END block, in which case minRecoveryPoint won't advance after each command. I'll continue my review by replying to (1) > [1]: > https://www.postgresql.org/message-id/CANtu0ohHu1r1xQfTzEJuxeaOMYncG7xRxUQWdH%3DcMXZSf%2Bnzvg%40mail.gmail.com > [2]: > https://www.postgresql.org/message-id/CAH2-WzkSUcuFukhJdSxHFgtL6zEQgNhgOzNBiTbP_4u%3Dk6igAg%40mail.gmail.com > (“Also, btw, do you know any reason to keep minRecoveryPoint at a low > value?”) I'm not an expert in this area (I'm reviewing this patch also to learn more about recovery and replication), but after a breif research I think that postgres tries not to update the control file too frequently, see comments in UpdateMinRecoveryPoint(). I don't know if what you do in code_optional.patch would be a problem. Actually I think that a commit record should be replayed more often than XLOG_RUNNING_XACTS, shouldn't it? -- Antonin Houska Web: https://www.cybertec-postgresql.com
