On Thu, Oct 20, 2011 at 08:48:36AM -0600, Alan Robertson wrote:
> On 10/20/2011 03:41 AM, Philipp Marek wrote:
> > Hello,
> >
> > when constantly sending new data via attrd the changes are never used.
> >
> >
> > Example:
> > while sleep 1
> > do attrd_updater -l reboot -d 5 -n rep_chg -U try$SECONDS
> > cibadmin -Ql | grep rep_chg
> > done
> >
> > This always returns the same value - the one that was given with more than 5
> > seconds delay afterwards, so that the dampen interval wasn't broken by the
> > next change.
> >
> >
> > I've attached two draft patches; one for allowing the _first_ value in a
> > dampen interval to be used (effectively ignoring changes until this value is
> > written), and one for using the _last_ value in the dampen interval (by not
> > changing the dampen timer). [1]
> >
> >
> > *** Note: they are for discussion only!
> > *** I didn't test them, not even for compilation.
> > What is the correct way to handle multiple updates within the dampen
> > interval?
> Personally, I'd vote for the last value. I agree with you about this
> being a bug.
If the attribute is used to check connectivity changes (ping resource
agent), or similar, and we have a "flaky", "flapping" connectivity,
it would be useful to have a "max" or "min" consolidation function
for incoming values during a dampen interval.
Otherwise, I get + + - + + -|+ + + +
and if the dampen interval just "happened" to expire
where I put the | above, it would have pushed a - to the cib,
where I'd rather kept it at +.
We likely want to add an option to attrd_updater (and to the ipc
messages it sends to attrd, and to the rest of the chain involved),
which can specify the consolidation function to be used.
The initial set I suggest would be
generic:
oldest
latest (default?)
for values assumed to be numeric:
max (also a candidate for default behaviour)
min
avg (with a printf like template for rounding, %.2f or similar,
so we could even average "boolean" values)
I suggest this behaviour:
* If different updates request a different consolidation function,
the last one (within the respective dampen interval) wins.
* update with the _same_ value: Do not start or modify any timer.
If a timer is pending, still add the value to the list of values to
be processed by the consolidation function (relevant for avg,
possibly not yet listed others).
* update with a different value:
Start a new timer, unless one is pending already.
Do not restart/modify an already pending timer.
Add to the list of values for the consolidation function.
* Flush message received: expire timer. See below.
* Timer expires:
Apply consolidation function to list of values. If list is empty
(probably flush message without pending timer), use current value.
Send that result to the cib.
--
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com
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