Jim C. Nasby wrote:
> On Thu, Jan 25, 2007 at 12:52:02AM -0300, Alvaro Herrera wrote:
>> Jim C. Nasby wrote:
>>
>>> I'll generally start with a cost delay of 20ms and adjust based on IO
>>> utilization.
>> I've been considering set a default autovacuum cost delay to 10ms; does
>> this sound reasonable?
The problem in here is that we can not easily find a direct relation
between Cost delay <-> CPU/IO utilization <--> real performance (response
time in peak hour)
It is very hard for any normal user to set this correctly. I think the
experience / trial-and-error approach is awful for the user, every DBA
need to be an expert of vacuum to keep the system stable. For vacuum is
still a big threat to the performance, a more intelligent way is needed.
A lot of efforts have contributed to make vacuum to be a more
lightweight operation, but I think we should still need more efforts on
how to make it can be used easily and safely.
So I have proposed the "vacuum in time" feature in previous; just let
vacuum know how long can it runs, and then it will minimize the impact
in the time span for you. Some argue that it should not have the
maintenance window assumption, but the most safely way is to run in the
maintenance window.