| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Cc: | Jan Wieck <JanWieck(at)Yahoo(dot)com>, Hannu Krosing <hannu(at)skype(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Mark Woodward <pgsql(at)mohawksoft(dot)com>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, Christopher Browne <cbbrowne(at)acm(dot)org>, postgres hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: vacuum, performance, and MVCC |
| Date: | 2006-06-26 10:39:45 |
| Message-ID: | 200606261039.k5QAdjZ27014@momjian.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera wrote:
> Jan Wieck wrote:
> > On 6/25/2006 10:12 PM, Bruce Momjian wrote:
> > >When you are using the update chaining, you can't mark that index row as
> > >dead because it actually points to more than one row on the page, some
> > >are non-visible, some are visible.
> >
> > Back up the truck ... you mean in the current code base we have heap
> > tuples that are visible in index scans because of heap tuple chaining
> > but without index tuples pointing directly at them?
>
> I don't know where this idea came from, but it's not true. All heap
> tuples, dead or otherwise, have index entries. Unless the idea is to
> extend update chaining to mean something different from the current
> meaning.
It does mean something different. Single-Index-Tuple Chain (CITC) is a
special type of update chaining where the updates are all on the same
row, and a single index entry points to the entire chain.
--
Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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