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 <[email protected]> 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 > http://bickson.blogspot.com/2011/02/mahout-svd-matrix-factorization.html > 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 > https://issues.apache.org/jira/browse/MAHOUT-376 in hope that I can figure > out why it is so slow.
