[Pacemaker] proper "dampen" value for ping resource

[Andrew Beekhof]

On Fri, Mar 11, 2011 at 1:59 PM, Klaus Darilion
<klaus.mailinglists at pernau.at> wrote:
> Hi!
>
> I wonder what a proper value for "dampen" would be. Dampen is documented as:
>
> # attrd_updater --help|grep dampen
>  -d, --delay=value      The time to wait (dampening) in seconds further
> changes occur
>
>
> So, I would read this as the delay to forward changes, e.g. to not
> trigger fail-over on the first failed ping, but only after multiple
> failures.
>
> Now, the default values (and examples have):
>
> primitive pingtest ocf:pacemaker:ping \
>        params host_list="..." dampen="5s" \
>        op monitor interval="10s"
>
> This means, that the host is pinged 5 attempts (default), then 10
> seconds pause, then another 5 pings , then again 10 seconds pause.
>
> Thus, I would think that if pinging fails (5 of 5 fails), then this is
> an "error", but failvoer happens 5 seconds later (dampen). Is this
> correct? If yes, then it would make more sense to adapt the examples and
> increase the dampen value to cover at least 2 failed ping attempts (5*2s
> + 10s + 5*2s = 30s) or shorten the attempts and interval, e.g.:
> attempts=1, interval=2s, dampen=5.

Both are sensible ideas, _however_ there is a bug that makes this
inadvisable in pacemaker <= 1.0.10.
For those versions interval must be greater than dampen.

This might seem to make dampen useless, but its primary purpose was to
allow other nodes a chance to also detect connectivity changes.
This is unaffected by the above bug.

Bug fix is:
   http://hg.clusterlabs.org/pacemaker/devel/rev/f7b4c065a75c

>
> If I am completely wrong, what behavior is really caused by "dampen"?
>
> Thanks
> Klaus
>
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