Re: Per table autovacuum vacuum cost limit behaviour strange

On Wed, Aug 27, 2014 at 8:27 AM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> Alvaro Herrera wrote:
>
>> So my proposal is a bit more complicated.  First we introduce the notion
>> of a single number, to enable sorting and computations: the "delay
>> equivalent", which is the cost_limit divided by cost_delay.
>
> Here's a patch that implements this idea.  As you see this is quite a
> bit more complicated that Haribabu's proposal.
>
> There are two holes in this:
>
> 1. if you ALTER DATABASE to change vacuum delay for a database, those
> values are not considered in the global equiv delay.  I don't think this
> is very important and anyway we haven't considered this very much, so
> it's okay if we don't handle it.

In the attached patch, I changed the balance_cost function to get the
global cost values.
With this change the above problem can be addressed.

> 2. If you have a "fast worker" that's only slightly faster than regular
> workers, it will become slower in some cases.  This is explained in a
> FIXME comment in the patch.

I changed as follows to handle these scenarios,

If fast workers equiv_delay is more than double global equiv_delay then the
global equiv_delay is decreased from fast workers equiv_delay and distribute
the same among fast workers.

If the difference delay between fast workers equiv_delay to global equiv_delay
is less than global equiv_delay, the fast workers equiv_delay along with
global equiv_delay is changed as below.

fast_equiv_delay -= (diff_equiv_delay) / num_fast_workers

global_equiv_delay -= (diff_equiv_delay) / num_regular_workers

Sorry for the late reply. Please let me know your comments.

Regards,
Hari Babu
Fujitsu Australia