Re: Remove xmin and cmin from frozen tuples

On Fri, 2 Sep 2005 15:51:15 -0400 (EDT), Bruce Momjian
<pgman@candle.pha.pa.us> wrote:
>	* Merge xmin/xmax/cmin/cmax back into three header fields

And don't forget xvac, please.
	
>	  Before subtransactions, there used to be only three fields needed to
>	  store these four values.

... five values.

> This was possible because only the current
> transaction looks at the cmin/cmax values.

Which is a reason to get rid of cmin/cmax in tuple headers entirely.
Once I had a patch based on 7.4 that stored cmin and cmax in
backend-local memory.  It passed make check and some volume tests, but
I felt it was not ready to be applied without any spill-to-disk
mechanism.  Development stalled when I tried to eliminate xvac as
well, which would have required deep cuts into VACUUM code :-(

Servus
 Manfred