* Andres Freund (and...@anarazel.de) wrote: > 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.
For my 2c, at least, this certainly sounds like a potentially promising approach too and I tend to agree with Andres on it not really being an issue to have a more aggressive snapshot for the duration of the CIC. Thanks! Stephen
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