| From: | Manfred Koizar <mkoi-pg(at)aon(dot)at> |
|---|---|
| To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)lab(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Remove xmin and cmin from frozen tuples |
| Date: | 2005-09-02 23:25:06 |
| Message-ID: | qcmhh1lgk5udc2qiq4tapqrhh7nsdinnlg@4ax.com |
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| Lists: | pgsql-hackers |
On Fri, 2 Sep 2005 15:51:15 -0400 (EDT), Bruce Momjian
<pgman(at)candle(dot)pha(dot)pa(dot)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
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