Extremely Slow ALS Recommender in 0.8, but faster in 0.9.

Hi mahout. Im finding that in 0.8, my ALS recommender goes extremely slow,
but it goes very fast in 0.9 .

- At the time the jobs slows down, there is virtually no disk io.
- The CPU cycles fluctuate up and down during this time, but they arent at
100% the whole time.
- Mapper percentages increatse by about 2% every hour. So its essentially
a hanging job (i.e. the input data set is super small, and the exact same
command finishes in about 2 minutes when using mahout 0.9).

To look into it,

- I saw that, between these two releases, there is a improvement thats been
made:
https://issues.apache.org/jira/browse/MAHOUT-1264, But there is no
associated patch.

- Doing a quick git diff, its clear that the VectorSumCombiner seems to
have been removed (probably so that mahout could a utility class vector
combiner).

Im wondering : Has anyone ever seen the 0.8 ALS Recommender job progress
*very* slowly, so slowly, that its essentially hanging? Like i said, this
bug appears gone in 0.9.

Any thoughts would be appreciated.

thanks!