So I haven't played around with streaming k means at all, but given
that no one responded to your message a couple of days ago, I'll say
what I can.
1. Can you not sample out some % of the stream for training?
2. Can you run multiple streams at the same time with different values
for k and compare their performance?
3. foreachRDD is fine in general, can't speak to the specifics.
4. If you haven't done any transformations yet on a direct stream,
foreachRDD will give you a KafkaRDD. Checking if a KafkaRDD is empty
is very cheap, it's done on the driver only because the beginning and
ending offsets are known. So you should be able to skip empty
batches.
On Sat, Nov 19, 2016 at 10:46 AM, debasishg <ghosh.debas...@gmail.com> wrote:
> Hello -
>
> I am trying to implement an outlier detection application on streaming data.
> I am a newbie to Spark and hence would like some advice on the confusions
> that I have ..
>
> I am thinking of using StreamingKMeans - is this a good choice ? I have one
> stream of data and I need an online algorithm. But here are some questions
> that immediately come to my mind ..
>
> 1. I cannot do separate training, cross validation etc. Is this a good idea
> to do training and prediction online ?
>
> 2. The data will be read from the stream coming from Kafka in microbatches
> of (say) 3 seconds. I get a DStream on which I train and get the clusters.
> How can I decide on the number of clusters ? Using StreamingKMeans is there
> any way I can iterate on microbatches with different values of k to find the
> optimal one ?
>
> 3. Even if I fix k, after training on every microbatch I get a DStream. How
> can I compute things like clustering score on the DStream ?
> StreamingKMeansModel has a computeCost function but it takes an RDD. I can
> use dstream.foreachRDD { // process RDD for the micro batch here } - is this
> the idiomatic way ?
>
> 4. If I use dstream.foreachRDD { .. } and use functions like new
> StandardScaler().fit(rdd) to do feature normalization, then it works when I
> have data in the stream. But when the microbatch is empty (say I don't have
> data for some time), the fit method throws exception as it gets an empty
> collection. Things start working ok when data starts coming back to the
> stream. But is this the way to go ?
>
> any suggestion will be welcome ..
>
> regards.
>
>
>
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