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From Dmitriy Lyubimov <>
Subject Re: SSVD too slow to handle large matrix?
Date Fri, 14 Sep 2012 21:19:09 GMT
Q job is actually the fastest and map-only.I'd say you drop all the
optional parameters (including p) and use mahout 0.7.

Actually reducing split size is unlikely to help. Default split should be fine.

i'd say running -k 10 on any sized input should result in Q mapper
task running in at most couple of minutes.

using -k200 -p100 is fairly ambitious (mapper task running time will
scale a little worse then proportional to k+p).

if you use -q1 you will likely to have more problems with ABt job and
that may require some memory tuning...

otherwise check the usual things -- memory, cluster capacity (do you
actually have capacity running 100 mappers? Do they have at least 1G
of RAM on -Xmx without scratching the swap? Are you seeing GC
thrashing? etc.)

That said your problem doesn't seem too big (judging from 100 mappers
with a regular split size, that should be ok). with -k 100 and default
p you should expect single q task to run about 20-25 minutes,
depending on your hardware. It is cpu-bound (or rather, mostly
fpu-bound, assuming you tackled memory issues etc.)

On Fri, Sep 14, 2012 at 1:24 PM, lei tang <> wrote:
> Hi,
> I am using mahout's  SSVD (stochastic SVD) to factorize a huge sparse
> matrix (around 30M x 1M).    I used a modified script of
> to store the input matrix with <key, value> pairs being integer, and
> vectorwritable (in particular, SequentialAccessSparseVector). Should I
> change to RandomAccessSparseVector?
> I managed to run mahout SSVD with the following specification.
> mahout ssvd -Dmapred.max.split.size=1000000 -i mf/tr_full.seq -o
> mf/out_full -k 200 -p 100 -r 100000 -U true -V true -t 20 --tempDir mf/tmp
> I specified the max split in order to have more mappers.  However, the
> first Qjob seems not moving. After 1 hour, it is still 12% with 100
> mappers.  Is this expected?  Should I change any parameter?
> Any suggestion is highly appreciated.
> - Lei
> P.S.  I'm also reading the docs from
>  in hope that I can figure
> out why it is so slow.

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