Re: VACUUMs and WAL

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