On 10 Sep 2014, at 6:43 pm, Lars Ellenberg <lars.ellenb...@linbit.com> wrote:
> On Wed, Sep 10, 2014 at 03:00:15PM +1000, Andrew Beekhof wrote: >>>>>>> What are the precise semantics of "dampening" (attrd_updater -d)? > >>> Basic idea of "attr_updater -d delay" is in fact >>> "wait for the dust to settle", >>> especially for attribute based constraints, >>> as used with the ping RA. >>> >>> Current behaviour (afai understand it): >>> >>> If a new update comes in while a previous update is still "pending", >>> the timer of the new update is *ignored*, >>> the new value is queued instead, and >>> the original timer is restarted. >> >> I think thats what I wrote but longer :) > > Absolutely :) > >>> (UNLESS the "new" value is the same as the currently pending value. >>> Otherwise values would never reach the cib if the update interval >>> is shorter than the dampening interval.) >>> >>> Value is put into the cib only if the original timer actually expires, >>> or attrd "flushes out" all current values for some other reason. >>> >>> ----- >>> >>> Problem: >>> for "flapping" or otherwise continually changing values, >>> new values won't make it into the cib for "a long time". >> >> Do we have many attributes like that? > > I've seen it once for ping attributes with a dieing switch. > I guess that qualifies as "Not around here.". That would surely converge on 0 though right? > >>> Workaround: >>> use a dampening interval shorter than the update interval. >>> >>> Problem with that workaround: you may still hit the same undesired >>> situations you could reach with immediately updating the values, you >>> did not wait for "the dust to settle". >>> >>> >>> Proposal: >>> >>> add a "update deadline" along with the dampening, which would normally >>> be sufficiently larger, and count from the original update (this timer >>> would not be restarted). >>> >>> Optionally feed all updates into an aggregate function. >>> Default aggregate function may be "latest value". >>> >>> Once the "update deadline" is reached, >>> (submitted values still changing; flapping? ...) >>> write out the current "aggregate" value anyways. > > > -- > : Lars Ellenberg > : LINBIT | Your Way to High Availability > : DRBD/HA support and consulting http://www.linbit.com > > DRBD® and LINBIT® are registered trademarks of LINBIT, Austria. > _______________________________________________ > Linux-HA mailing list > Linux-HA@lists.linux-ha.org > http://lists.linux-ha.org/mailman/listinfo/linux-ha > See also: http://linux-ha.org/ReportingProblems
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