Re: What is xmin ?

On Tue, Jan 18, 2005 at 02:43:09PM +0100, Karsten Hilbert wrote:
> > Can you guys tell me how to interpret this value. I want to convert
> > this to date format. Is it possible ?
> No.
>
> XMIN holds the id of the transaction which did the most recent
> change to a row as is visible from within the current
> transaction. Unless it wraps around (is that possible ?) older
> transactions should have XMIN values lower than younger
> transactions.

Correct. XMIN is a transaction ID and it can wraparound. To counter
this there is a special XMIN value which means "older than any
transaction". Which the reason you must run VACUUM at least once every
billion transactions or so. Hardly a difficult request :)

There is no way to convert it to a date, since it doesn't represent a
date or even a point in time. It represents a transaction and how it
relates to other transactions.

Hope this helps,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.