On Sat, Mar 2, 2019 at 5:45 AM Michael Banck <michael.ba...@credativ.de> wrote: > Am Freitag, den 01.03.2019, 18:03 -0500 schrieb Robert Haas: > > On Tue, Sep 18, 2018 at 10:37 AM Michael Banck > > <michael.ba...@credativ.de> wrote: > > > I have added a retry for this as well now, without a pg_sleep() as well. > > > This catches around 80% of the half-reads, but a few slip through. At > > > that point we bail out with exit(1), and the user can try again, which I > > > think is fine? > > > > Maybe I'm confused here, but catching 80% of torn pages doesn't sound > > robust at all. > > The chance that pg_verify_checksums hits a torn page (at least in my > tests, see below) is already pretty low, a couple of times per 1000 > runs. Maybe 4 out 5 times, the page is read fine on retry and we march > on. Otherwise, we now just issue a warning and skip the file (or so was > the idea, see below), do you think that is not acceptable?
Yeah. Consider a paranoid customer with 100 clusters who runs this every day on every cluster. They're going to see failures every day or three and go ballistic. I suspect that better retry logic might help here. I mean, I would guess that 10 retries at 1 second intervals or something of that sort would be enough to virtually eliminate false positives while still allowing us to report persistent -- and thus real -- problems. But if even that is going to produce false positives with any measurable probability different from zero, then I think we have a problem, because I neither like a verification tool that ignores possible signs of trouble nor one that "cries wolf" when things are fine. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
