For ALS if you want real time recs (and usually this is order 10s to a few 100s ms response), then Spark is not the way to go - a serving layer like Oryx, or prediction.io is what you want.

(At graphflow we've built our own).

You hold the factor matrices in memory and do the dot product in real time (with optional caching). Again, even for huge models (10s of millions users/items) this can be handled on a single, powerful instance. The issue at this scale is winnowing down the search space using LSH or similar approach to get to real time speeds.

For word2vec it's pretty much the same thing as what you have is very similar to one of the ALS factor matrices.

One problem is you can't access the wors2vec vectors as they are private val. I think this should be changed actually, so that just the word vectors could be saved and used in a serving layer.


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On Fri, Nov 7, 2014 at 7:37 PM, Evan R. Sparks <evan.sparks@gmail.com> wrote:

There are a few examples where this is the case. Let's take ALS, where the result is a MatrixFactorizationModel, which is assumed to be big - the model consists of two matrices, one (users x k) and one (k x products). These are represented as RDDs.

You can save these RDDs out to disk by doing something like

model.userFeatures.saveAsObjectFile(...) and model.productFeatures.saveAsObjectFile(...) 

to save out to HDFS or Tachyon or S3.

Then, when you want to reload you'd have to instantiate them into a class of MatrixFactorizationModel. That class is package private to MLlib right now, so you'd need to copy the logic over to a new class, but that's the basic idea.

That said - using spark to serve these recommendations on a point-by-point basis might not be optimal. There's some work going on in the AMPLab to address this issue.

On Fri, Nov 7, 2014 at 7:44 AM, Duy Huynh <duy.huynh.uiv@gmail.com> wrote:
you're right, serialization works.

what is your suggestion on saving a "distributed" model?  so part of the model is in one cluster, and some other parts of the model are in other clusters.  during runtime, these sub-models run independently in their own clusters (load, train, save).  and at some point during run time these sub-models merge into the master model, which also loads, trains, and saves at the master level.

much appreciated.



On Fri, Nov 7, 2014 at 2:53 AM, Evan R. Sparks <evan.sparks@gmail.com> wrote:
There's some work going on to support PMML - https://issues.apache.org/jira/browse/SPARK-1406 - but it's not yet been merged into master.

What are you used to doing in other environments? In R I'm used to running save(), same with matlab. In python either pickling things or dumping to json seems pretty common. (even the scikit-learn docs recommend pickling - http://scikit-learn.org/stable/modules/model_persistence.html). These all seem basically equivalent java serialization to me..

Would some helper functions (in, say, mllib.util.modelpersistence or something) make sense to add?

On Thu, Nov 6, 2014 at 11:36 PM, Duy Huynh <duy.huynh.uiv@gmail.com> wrote:
that works.  is there a better way in spark?  this seems like the most common feature for any machine learning work - to be able to save your model after training it and load it later.

On Fri, Nov 7, 2014 at 2:30 AM, Evan R. Sparks <evan.sparks@gmail.com> wrote:
Plain old java serialization is one straightforward approach if you're in java/scala.

On Thu, Nov 6, 2014 at 11:26 PM, ll <duy.huynh.uiv@gmail.com> wrote:
what is the best way to save an mllib model that you just trained and reload
it in the future?  specifically, i'm using the mllib word2vec model...
thanks.



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