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From Aram Mkrtchyan <aram.mkrtchyan...@gmail.com>
Subject Re: Apache Spark ALS recommendations approach
Date Wed, 18 Mar 2015 12:04:05 GMT
Thanks much for your reply.

By saying on the fly, you mean caching the trained model, and querying it
for each user joined with 30M products when needed?

Our question is more about the general approach, what if we have 7M DAU?
How the companies deal with that using Spark?


On Wed, Mar 18, 2015 at 3:39 PM, Sean Owen <sowen@cloudera.com> wrote:

> Not just the join, but this means you're trying to compute 600
> trillion dot products. It will never finish fast. Basically: don't do
> this :) You don't in general compute all recommendations for all
> users, but recompute for a small subset of users that were or are
> likely to be active soon. (Or compute on the fly.) Is anything like
> that an option?
>
> On Wed, Mar 18, 2015 at 7:13 AM, Aram Mkrtchyan
> <aram.mkrtchyan.87@gmail.com> wrote:
> > Trying to build recommendation system using Spark MLLib's ALS.
> >
> > Currently, we're trying to pre-build recommendations for all users on
> daily
> > basis. We're using simple implicit feedbacks and ALS.
> >
> > The problem is, we have 20M users and 30M products, and to call the main
> > predict() method, we need to have the cartesian join for users and
> products,
> > which is too huge, and it may take days to generate only the join. Is
> there
> > a way to avoid cartesian join to make the process faster?
> >
> > Currently we have 8 nodes with 64Gb of RAM, I think it should be enough
> for
> > the data.
> >
> > val users: RDD[Int] = ???           // RDD with 20M userIds
> > val products: RDD[Int] = ???        // RDD with 30M productIds
> > val ratings : RDD[Rating] = ???     // RDD with all user->product
> feedbacks
> >
> > val model = new ALS().setRank(10).setIterations(10)
> >   .setLambda(0.0001).setImplicitPrefs(true)
> >   .setAlpha(40).run(ratings)
> >
> > val usersProducts = users.cartesian(products)
> > val recommendations = model.predict(usersProducts)
>

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