Re: shared-memory based stats collector

On Fri, Jul 6, 2018 at 8:57 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:

> On 2018-07-06 14:49:53 -0400, Robert Haas wrote:
> > I think we also have to ask ourselves in general whether snapshots of
> > this data are worth what they cost. I don't think anyone would doubt
> > that a consistent snapshot of the data is better than an inconsistent
> > view of the data if the costs were equal. However, if we can avoid a
> > huge amount of memory usage and complexity on large systems with
> > hundreds of backends by ditching the snapshot requirement, then we
> > should ask ourselves how important we think the snapshot behavior
> > really is.
>
> Indeed. I don't think it's worthwhile major additional memory or code
> complexity in this situation. The likelihood of benefitting from more /
> better stats seems far higher than a more accurate view of the stats -
> which aren't particularly accurate themselves. They don't even survive
> crashes right now, so I don't think the current accuracy is very high.
>

Definitely agreed.

*If* we can provide the snapshots view of them without too much overhead I
think it's worth looking into that while *also* proviiding a lower overhead
interface for those that don't care about it.

If it ends up that keeping the snapshots become too much overhead in either
in performance or code-maintenance, then I agree can probably drop that.
But we should at least properly investigate the cost.

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>