Re: Occasional giant spikes in CPU load

Craig James <craig_james@emolecules.com> writes:
> On 6/25/10 7:47 AM, Tom Lane wrote:
>> Any chance of going to 8.4?  If this is what I suspect, you really need
>> this 8.4 fix:
>> http://archives.postgresql.org/pgsql-committers/2008-06/msg00227.php
>> which eliminated the thundering-herd behavior that previous releases
>> exhibit when the sinval queue overflows.

> Yes, there is a chance of upgrading to 8.4.4.  I just bought a new server and it has 8.4.4 on it, but it won't be
onlinefor a while so I can't compare yet.  This may motivate me to upgrade the current servers to 8.4.4 too.  I was
pleasedto see that 8.4 has a new upgrade-in-place feature that means we don't have to dump/restore.  That really helps
alot. 

I wouldn't put a lot of faith in pg_migrator for an 8.3 to 8.4
conversion ... it might work, but test it on a copy of your DB first.
Possibly it'll actually be recommendable in 9.0.

> A question about 8.4.4: I've been having problems with bloat.  I thought I'd adjusted the FSM parameters correctly
basedon advice I got here, but apparently not.  8.4.4 has removed the configurable FSM parameters completely, which is
verycool.  But ... if I upgrade a bloated database using the upgrade-in-place feature, will 8.4.4 recover the bloat and
returnit to the OS, or do I still have to recover the space manually (like vacuum-full/reindex, or cluster, or
copy/dropa table)? 

No, an in-place upgrade to 8.4 isn't magically going to fix that.  This
might actually be sufficient reason to stick with the tried&true dump
and reload method, since you're going to have to do something fairly
expensive anyway to clean out the bloat.

            regards, tom lane