PATCH: PR27092 debuginfod improve low-memory operations

[Mark Wielaard]

Hi,

Just for the list to have it archived.
We did briefly discuss this on irc.
The changes have already been pushed.

On Fri, 2021-02-05 at 18:24 +0100, Mark Wielaard wrote:
> On Thu, 2021-02-04 at 20:45 -0500, Frank Ch. Eigler via Elfutils-
> devel wrote:    
> >     - New prometheus metrics to track filesystem freespace, and more
> >       details about some errors.
> 
> This part looks fine.
> 
> Maybe this is a general question about exposing metrics. But does this
> help people who want to do denial of service attacks? I mean by seeing
> what effect some queries might have on freespace/errors?
> 
> Not a showstopper, but maybe something to think about before
> encouraging people to expose their metrics?

yeah hypothetically, and yet at the same time one needs that info more
to detect problems early

> >     - Frequent checking of $TMPDIR freespace, to trigger fdcache
> >       emergency flushes.
> 
> This too looks fine.
> 
> >     - Switch to floating point prometheus metrics, to communicate
> >       fractions - and short time intervals - accurately.
> 
> You move all metrics to use doubles. Including the metrics that use
> integral values using inc_metric (the threads, _total and _count ones).
> I cannot tell how that looks on the Prometheus side. Isn't it better to
> keep those as integrals? Aka maybe inc_metric shouldn't call through to
> add_metric? Or maybe have two metric maps, one for counts and one for
> values/durations?

doubles are the native type for prometheus consumers, the textual form
doesn't really matter (and ieee doubles propagate 40+bit integers
exactly so that's okay)
might tweak the formatting to add all the digits of precision rather
than the c++ default, easily

> All code changes look fine. Please feel free to push if you think my
> questions above are a little silly :) The actual changes seem to do
> what you intended.

Cheers,

Mark