Re: shared-memory based stats collector

On 2018-07-06 12:02:39 -0700, Joshua D. Drake wrote:
> On 07/06/2018 11:57 AM, Andres Freund 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.
>
>
> Will stats, if we move toward the suggested changes be "less" accurate than
> they are now? We already know that stats are generally not accurate but they
> are close enough. If we move toward this change will it still be close
> enough?

I don't think there's a meaningful difference to before. And at the same
time less duplication / hardcoded structure will allow us to increase
the amount of stats we keep.

Greetings,

Andres Freund