| 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: | 2005-09-03 08:59:31 |
| Message-ID: | m8oih1lhv7khm953bpfpf5vp5v4mp7r0db@4ax.com |
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On Fri, 2 Sep 2005 20:41:48 -0400 (EDT), Bruce Momjian
<pgman(at)candle(dot)pha(dot)pa(dot)us> wrote:
>> Once I had a patch based on 7.4 that stored cmin and cmax in
>> backend-local memory.
>Interesting idea, but how would you record the cmin/xmin values without
>requiring unlimited memory?
That's exactly the reason for not sending it to -patches. Without
spilling to disk this is just not ready for real life. The problem is
that -- unlike other data structures that build up during a
transaction, e.g. trigger queues -- cmin/cmax lookup requires random
access, so we'd need some form of tree or hash. Unfornunately I never
got beyond brainstorming :-(
BTW, is there anything else that'd need spilling to disk during long
transactions?
Servus
Manfred
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