Re: [HACKERS] getting rid of SnapshotNow

On 2013-07-20 00:49:11 +0900, Hiroshi Inoue wrote:
> (2013/07/18 21:46), Robert Haas wrote:
> >There seems to be a consensus that we should try to get rid of
> >SnapshotNow entirely now that we have MVCC catalog scans, so I'm
> >attaching two patches that together come close to achieving that goal:
> 
> ...
> 
> >With that done, the only remaining uses of SnapshotNow in our code
> >base will be in currtid_byreloid() and currtid_byrelname().  So far no
> >one on this list has been able to understand clearly what the purpose
> >of those functions is, so I'm copying this email to pgsql-odbc in case
> >someone there can provide more insight.  If I were a betting man, I'd
> >bet that they are used in contexts where the difference between
> >SnapshotNow and SnapshotSelf wouldn't matter there, either.
> 
> Using SnapshotSelf instead of SnapshotNow for currtid_ () wouldn't
>  matter.

I think it actually might. You could get into dicey situations if you
use currtid_ in a query performing updates or inserts because it would
see the to-be-inserted tuple...

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
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