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From "David P Grove" <gro...@us.ibm.com>
Subject Re: Invoker activation queueing proposal
Date Thu, 05 Oct 2017 21:49:11 GMT
I can see the value in delaying the binding of activations to invokers when
the system is loaded (can't execute "immediately" on its target invoker).

Perhaps in ignorance, I am a little worried about the scalability of a
single backlog topic.  With a few hundred invokers, it seems like we'd be
exposed to frequent and expensive partition rebalancing operations as
invokers crash/restart.  Maybe if we have N = K*M invokers, we can get away
with M backlog topics each being read by K invokers.   We could still get
imbalance across the different backlog topics, but it might be good enough.

I think we'd also need to do some thinking of how to ensure that work put
in a backlog topic doesn't languish there for a really long time.  Once we
start having work in the backlog, do we need to stop putting work in
immediately topics?  If we do, that could hurt overall performance.  If we
don't, how will the backlog topic ever get drained if most invokers are
kept busy servicing their immediately topics?

--dave



From:	Tyson Norris <tnorris@adobe.com.INVALID>
To:	"dev@openwhisk.apache.org" <dev@openwhisk.apache.org>
Date:	10/04/2017 07:45 PM
Subject:	Invoker activation queueing proposal



Hi -

I’ve been discussing a bit with a few about optimizing the queueing that
goes on ahead of invokers so that things behave more simply and
predictable.



In short: Instead of scheduling activations to an invoker on receipt, do
the following:

- execute the activation "immediately" if capacity is available

- provide a single overflow topic for activations that cannot execute
“immediately"

- schedule from the overflow topic when capacity is available



(BTW “Immediately” means: still queued via existing invoker topics, but
ONLY gets queued there in the case that the invoker is not fully loaded,
and therefore should execute it “very soon")



Later: it would also be good to provide more container state data from
invoker to controller, to get better scheduling options - e.g. if some
invokers can handle running more containers than other invokers, that info
can be used to avoid over/under-loading the invokers (currently we assume
each invoker can handle 16 activations, I think)



I put a wiki page proposal here:
https://urldefense.proofpoint.com/v2/url?u=https-3A__cwiki.apache.org_confluence_display_OPENWHISK_Invoker-2BActivation-2BQueueing-2BChange&d=DwIGaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=Fe4FicGBU_20P2yihxV-apaNSFb6BSj6AlkptSF2gMk&m=UE8OIR_GnMltmRZyIuLVHMlzyQvNku-H7kLk67u45IM&s=LD75-npfzA7qzUGNgYbFBy4qKatnkdO5I2vKYSGUBg8&e=




WDYT?



Thanks

Tyson



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