> > StartUpID counts database startups and so has timestamp characteristics.
> > Actually, idea is to use SUI in future to allow reusing XIDs after startup: seeing
> > old SUI in data pages we'll know that all transaction on this page was committed
> > "long ago" (ie visible from MVCC POV). This requires UNDO, of course.
>
> First thanx for the description, but db startup would only count to 5-7 per year :-),
> is that sufficient ? It hardly sounds like anything useful to include in page header.
It will be sufficient if DB will not use all 2^32 XIDs without shutdown.
Removing pg_log *segments* for old XIDs is another story.
> What about the xlog id, that is also used for xlog file name, but I still think a xid would
> be the best candidate.
logid would be ok too, xid is not - we have to shorten xids lifetime in near future.
Vadim