Re: Per table autovacuum vacuum cost limit behaviour strange

On Thu, Oct 2, 2014 at 9:54 AM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
> Alvaro Herrera wrote:
>> So in essence what we're going to do is that the balance mechanism
>> considers only tables that don't have per-table configuration options;
>> for those that do, we will use the values configured there without any
>> changes.
>>
>> I'll see about implementing this and making sure it finds its way to
>> 9.4beta3.
>
> Here's a patch that makes it work as proposed.
>
> How do people feel about back-patching this? On one hand it seems
> there's a lot of fear of changing autovacuum behavior in back branches,
> because for many production systems it has carefully been tuned; on the
> other hand, it seems hard to believe that anyone has tuned the system to
> work sanely given how insanely per-table options behave in the current
> code.

I agree with both of those arguments. I have run into very few
customers who have used the autovacuum settings to customize behavior
for particular tables, and anyone who hasn't should see no change
(right?), so my guess is that the practical impact of the change will
be pretty limited. On the other hand, it's a clear behavior change.
Someone could have set the per-table limit to something enormous and
never suffered from that setting because it has basically no effect as
things stand right now today; and that person might get an unpleasant
surprise when they update.

I would at least back-patch it to 9.4. I could go either way on
whether to back-patch into older branches. I lean mildly in favor of
it at the moment, but with considerable trepidation.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company