[erlang-questions] How to do this in Erlang -- any suggestions ?

Banibrata Dutta <>
Sun Jun 12 17:38:20 CEST 2011


gr8 questions, and they certainly need clarification.
cc'ing the group s.t. others could contribute too.

On Sun, Jun 12, 2011 at 8:48 PM, Mihai Balea <> wrote:

>
> On Jun 12, 2011, at 10:51 AM, Banibrata Dutta wrote:
>
> Prematurely sent.
>
> On Sun, Jun 12, 2011 at 7:59 PM, Banibrata Dutta <
> > wrote:
>
>>
>> What would be a good way to correlate asynchronous events, spot patterns
>> over a sliding window (s.a. of no. of events elapsed or time elapsed), with
>> millions of events occurring simultaneously, using Erlang ?
>>
>> The set of possible events is known, and any unknown event is just flagged
>> as 'unknown' (so all unknowns are similar). The set of possible event
>> patterns can be enumerated, but is possibly quite a large set of patterns.
>>
>
> Was wondering as to what could be the approach taken to implement such a
> thing in pure Erlang. My initial thoughts were along the line of maintaining
> FSMs per event source, but with so many events and so many possible/valid
> patterns, the thing seems kind of unwieldy. Also, I'd like a non-programmer
> to be able to define new events and valid event patterns.
>
> I believe 'Complex Event Processing' is quite likely to be the standard
> approach for such things, as I've found from some posts, and solutions exist
> in Java world for same, but both as an academic exercise (for the fun of
> learning) and for a potentially simpler + better solution, would like to try
> doing this is Erlang.
>
>
> I think you need to define your problem better.
>

Sure, let me try.


> What exactly do you mean by "millions of events occurring simultaneously"?
>

Okay, so I can say something like 500 events/second handled for correlation
would be a more realistic number.


> At exactly the same time?
>

Yes... some of the events might be from same source, but spaced by as little
as 50ms, but mostly from different sources. There could be some heirarchical
relationship between sources. Very typical case of network management
scenario. E.g. a fault port on a switch, could probably cause hundreds of
destination unreachable events, application response timeouts, heartbeat
losses etc..


> Millions of events per second? Minute? Is that peak rate, average rate or
> minimum rate?
>

Okay, I got over-enthusiastic :-) . Say 100 events/second typical, 500
events/second peak, no real minimum.

What exactly is a pattern?
>

Node-A failed, Power in room-X where Node-A is kept failed, Nodes B,C,D
which are served thru Node-A became unreachable, due to which Services L & M
became unavailable, and due to which another dependent service N started
giving inconsistent answers. So this is a pattern. However in this case,
there's a possibility that Power-failure had nothing to do with Noda-A's
failure, as backup power was available.

Another pattern is, Power in room X failed, then Noda A failed, leading to
failure of only Node D, because somehow Nodes B & C were dynamically
configured to reroute. This is another pattern.

What do you mean by "quite a large set of patterns"? Hundreds, thousands,
> millions?
>

Several hundreds is a distinct possibility, and thousands are not
impossible, but millions -- probably not.


> How long is that sliding window?
>

>From few minutes (for certain type of events), to few days (for another type
of events).


> Can patterns encompass events coming from multiple sources or just one
> source?
>

Yes, indeed. However in this case, there needs to a "relationship" between
the event sources, that is pre-defined. E.g. some sense of "topology"
exists. However it is likely that only 2% of the event sources are
interrelated.


> Are patterns concerned only with event ordering and occurrence or there are
> timing issues involved as well?
>

Ordering, Timing, or any kind of causal relationship.
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