| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Jan Wieck <JanWieck(at)Yahoo(dot)com> |
| Cc: | 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 10:38:00 |
| Message-ID: | 200606261038.k5QAc0726546@momjian.us |
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| Lists: | pgsql-hackers |
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?
No, this would be new code added. The basic idea is with the new
same-page update chaining, a single index points to the head of a chain,
not to a single tuple, so you can't mark a tuple as pointing to dead
rows if any of the tuples in the chain are visible.
--
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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