Re: [HACKERS] A design for amcheck heapam verification

On Fri, Apr 28, 2017 at 6:02 PM, Peter Geoghegan <pg@bowt.ie> wrote:
>  - Is committed, and committed before RecentGlobalXmin.

Actually, I guess amcheck would need to use its own scan's snapshot
xmin instead. This is true because it cares about visibility in a way
that's "backwards" relative to existing code that tests something
against RecentGlobalXmin. Is there any existing thing that works that
way?

If it's not clear what I mean: existing code that cares about
RecentGlobalXmin is using it as a *conservative* point before which
every snapshot sees every transaction as committed/aborted (and
therefore nobody can care if that other backend hot prunes dead tuples
from before then, or whatever it is). Whereas, amcheck needs to care
about the possibility that *anyone else* decided that pruning or
whatever is okay, based on generic criteria, and not what amcheck
happened to see as RecentGlobalXmin during snapshot acquisition.

-- 
Peter Geoghegan

VMware vCenter Server
https://www.vmware.com/