| From: | "Zeugswetter Andreas DCP SD" <ZeugswetterA(at)spardat(dot)at> |
|---|---|
| To: | "Mark Woodward" <pgsql(at)mohawksoft(dot)com>, "Christopher Browne" <cbbrowne(at)acm(dot)org> |
| Cc: | <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: vacuum, performance, and MVCC |
| Date: | 2006-06-22 11:54:27 |
| Message-ID: | E1539E0ED7043848906A8FF995BDA579011EFDA7@m0143.s-mxs.net |
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| Thread: | |
| Lists: | pgsql-hackers |
> >> Each time the record is updated, a new version is created, thus
> >> lengthening the "correct" version search each time row is accessed,
> >> until, of course, the next vacuum comes along and corrects the
index
> >> to point to the latest version of the record.
> >>
> >> Is that a fair explanation?
> >
> > No, it's not.
> >
> > 1. The index points to all the versions, until they get vacuumed
out.
> it points to the last "current" version as updated by vacuum, or the
first version
> of the row.
no, the index has one entry for each version of the row.
This is why updating only non-indexed columns is relatively expensive
in pg.
Andreas
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