[check_postgres] [PATCH] Change autovac_freeze default warn/critical from 90%/95% to 105%/120%

[Robert Treat]

On Saturday 09 January 2010 14:15:28 Greg Sabino Mullane wrote:
> > I wrote a patch to do my suggested change to autovac_freeze defaults.
>
> Thanks, we've (finally) applied this, will be a part of 2.12.1

The logic behind this change is flawed. If your database reaches the 
autovac_max_freeze, you are susceptible to a large performance degradation due 
to increased i/o load from your database maxing out autovac workers whilst 
trying to catch up on vacuuming. For most people, advance notice of that 
threshold allows them flexibility to spread out the vacuuming over time, adjust 
the vacuum cost params, or schedule vacuuming for low server activity times; 
if you set your warning/critical above 100% it's already too late. 

If you are concerned that tables are not being vacuum in sufficient time, 
measure txn_wraparound. 

-- 
Robert Treat
Conjecture: http://www.xzilla.net
Consulting: http://www.omniti.com