Github user vrilleup commented on the pull request:
https://github.com/apache/spark/pull/964#issuecomment-47198628
multiply function is RowMatrix was using dense matrix - sparse vector
multiplication function, but in current breeze version there is no
implementation for this combination. So it was actually a dense matrix - dense
vector function invoked, which is very slow for sparse but large RowMatrix. I
changed it to use sparse vector - dense vector multiplication in breeze. This
larged improved the multiply function.
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