[Gnumed-devel] address@hidden: Re: [GENERAL] XMIN semantic at peril ?]

[Karsten Hilbert]

I'd think this settles things for now:

----- Forwarded message from Tom Lane <address@hidden> -----

> Subject: Re: [GENERAL] XMIN semantic at peril ? 
> 
> Karsten Hilbert <address@hidden> writes:
> >   How likely is XMIN (or equivalent) to become invisible to
> >   SQL level user space ?
> 
> No one has suggested this.  I suppose the argument could be made that
> the system columns are an unwarranted intrusion on users' column
> namespace, but we'd probably handle that by demoting them to
> second-class citizens, not hiding them entirely --- there are far too
> many apps that rely on ctid, for instance, and I think some that are
> doing like you do with xmin.  So as long as you don't create a user
> column named xmin in your tables, you could expect to access the system
> column.
> 
> >   How likely is XMIN (or equivalent) to NOT change on each
> >   successful (write) transaction commit anymore ?
> 
> No chance of that, unless we abandon MVCC for something else, which
> again seems highly unlikely.
> 
> One question I'd have though is whether "freezing" of old tuples is
> likely to confuse your app.  That process might get more aggressive
> in the future (it already is more aggressive in 8.2 than before,
> depending on where vacuum_freeze_min_age is set).
> 
> The only argument you cited that seems impressive to me is the one
> about it being a Postgres-ism.  Are you willing to have GNUmed tied
> tightly to Postgres?
> 
>                       regards, tom lane

----- End forwarded message -----

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