| From: | Hannu Krosing <hannu(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: VACUUMs and WAL |
| Date: | 2008-10-28 12:19:04 |
| Message-ID: | 1225196344.7694.2.camel@huvostro |
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| Lists: | pgsql-hackers |
On Tue, 2008-10-28 at 10:10 +0000, Simon Riggs wrote:
> On Tue, 2008-10-28 at 11:45 +0200, Hannu Krosing wrote:
> > On Tue, 2008-10-28 at 08:49 +0000, Simon Riggs wrote:
> > > Looking at a VACUUM's WAL records makes me think twice about the way we
> > > issue a VACUUM.
> > >
> > > 1. First we scan the heap, issuing a HEAP2 clean record for every block
> > > that needs cleaning.
> >
> > IIRC the first heap pass just collects info and does nothing else.
> > Is this just an empty/do-nothing WAL record ?
>
> 8.3 changed that; it used to work that way. I guess I never looked at
> the amount of WAL being generated.
I can't see how it is safe to do anything more than just lookups on
first pass.
There will be dangling index pointers if the system crashes/is rebooted
or the vacuum is just interrupted after cleaning some heap pages but
before cleaning corresponding index pages.
---------------
Hannu
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