Re: Avoiding second heap scan in VACUUM

On Fri, May 30, 2008 at 2:41 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>
>  What I still
> don't accept is that an unconstrained wait is justifiable. You've just
> said its a minor detail, but that's not the way I see it. It might be a
> second, but it might be an hour or more.
>

I am suggesting a timed wait. May be say between 60-300 seconds.
That's the maximum VACUUM would get delayed. If exiting transactions
don't finish within that time, VACUUM just works as it does today. So
it can't certainly be much worse than what it is today.

> A non-waiting solution seems like the only way to proceed.
>

Yeah, but we don't have a simple solution yet which would work in all
cases and is not too complicated.

> Is this a non-issue anyway, with DSM?
>

I thought about that. DSM would certainly reduce the cost of heap
scans. But still the second pass would be required and it would
re-dirty all the pages again,

Thanks,
Pavan


-- 
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com