On 2017-03-07 21:38:40 -0500, Robert Haas wrote: > > I wonder however, if careful snapshot managment couldn't solve this as > > well. I have *not* thought a lot about this, but afaics we can easily > > prevent all-visible from being set in cases it'd bother us by having an > > "appropriate" xmin / registered snapshot. > > Yeah, but that's a tax on the whole system.
I'm not sure I can buy that argument. CIC *already* holds a snapshot during each of the two scans. By reducing the amount of time that's held in the second scan, the systemwide impact is reduced, because it's held for a shorter amount of time. We need to hold a slightly "more aggressive" snapshot, that's true, but if you have high xid throughput those effects should roughly balance each other. Greetings, Andres Freund -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
