[jira] [Closed] (SPARK-2465) Use long as user / item ID for ALS

["Sean Owen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-2465?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sean Owen closed SPARK-2465.
----------------------------

    Resolution: Won't Fix

Will possibly revisit this in the long term, or look at creating a parallel LongALS / LongRating API.

> Use long as user / item ID for ALS
> ----------------------------------
>
>                 Key: SPARK-2465
>                 URL: https://issues.apache.org/jira/browse/SPARK-2465
>             Project: Spark
>          Issue Type: Improvement
>          Components: MLlib
>    Affects Versions: 1.0.1
>            Reporter: Sean Owen
>            Priority: Minor
>         Attachments: ALS using MEMORY_AND_DISK.png, ALS using MEMORY_AND_DISK_SER.png, Screen Shot 2014-07-13 at 8.49.40 PM.png
>
>
> I'd like to float this for consideration: use longs instead of ints for user and product IDs in the ALS implementation.
> The main reason for is that identifiers are not generally numeric at all, and will be hashed to an integer. (This is a separate issue.) Hashing to 32 bits means collisions are likely after hundreds of thousands of users and items, which is not unrealistic. Hashing to 64 bits pushes this back to billions.
> It would also mean numeric IDs that happen to be larger than the largest int can be used directly as identifiers.
> On the downside of course: 8 bytes instead of 4 bytes of memory used per Rating.
> Thoughts? I will post a PR so as to show what the change would be.



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