Re: scheduler in core

On Sun, Feb 21, 2010 at 1:05 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Sun, Feb 21, 2010 at 10:17 AM, Lucas <lucas75@gmail.com> wrote:
>>> I wonder if the scheduler already existed before the
>>>  implementation of the autovacuum, its implementation would
>>>  not be a function executed by the in-core scheduler?
>
>> The real genius of autovacuum is that it works out when there has been
>> enough activity in particular tables that they need to be vacuumed.
>> We might be able to use an in-core scheduler to wake it up every
>> minute to look at the stats, or whatever it is that we do, but that's
>> not all that exciting.
>
> The wake-up-every-N-seconds part of it is actually the weakest part
> (search the archives for questions about autovacuum_naptime).  To my
> mind, the killer reason why autovac needed to be integrated is so that
> the system itself could trigger autovac runs in response to threatened
> XID wraparound conditions.  A facility for scheduling user jobs, almost
> by definition, won't have any system-internal trigger conditions.

Right.  Without prejudice to my earlier statements that I think this
might possibly be a good thing to do anyway, the case for it would be
a lot stronger if it provided some genuine additional functionality.

...Robert