Ted, like i commented in the issue, 100m dense data elements means ~800M to load a vector. If (suppose) i have 1G in a mapper (which is not terribly common, not in our case, we only run jobs with -500M), then require 80% of RAM for prebuffering (i.e. just being able to get access to the data) and leave 20% for algorithm? Setting aside other considerations, doesn't this strike you as being off-balance in requirements ? it does to me and unfortunately in my practical application with the hardware constraints i got i won't be able to afford that luxury. So it is a problem for my task for the moment, believe it or not. At this moment even 100Mb for prebuffering the data is prohibitively costly in my app.
-d On Mon, Dec 13, 2010 at 11:12 AM, Ted Dunning <[email protected]> wrote: > I really don't see this as a big deal even with crazy big vectors. > > Looking at web scale, for instance, the most linked wikipedia article only > has 10 million in-links or so. On the web, the most massive web site is > unlikely to have >100 million in-links. Both of these fit in very modest > amounts of memory. > > Where's the rub? > > On Mon, Dec 13, 2010 at 11:05 AM, Dmitriy Lyubimov <[email protected] > >wrote: > > > Jake, > > No i was trying exactly what you were proposing some time ago on the > list. > > I > > am trying to make long vectors not to occupy a lot of memory. > > > > E.g. a 1m-long dense vector would require 8Mb just to load it. And i am > > saying, hey, there's a lot of sequential techniques that can provide a > > hander that would inspect vector element-by-element without having to > > preallocate 8Mb. > > > > for 1 million-long vectors it doesn't scary too much but starts being so > > for > > default hadoop memory settings at the area of 50-100Mb (or 5-10 million > > non-zero elements). Stochastic SVD will survive that, but it means less > > memory for blocking, and the more blocks you have, the more CPU it > requires > > (although CPU demand is only linear to the number of blocks and only in > > signficantly smaller part of computation, so that only insigificant part > of > > total CPU flops depends on # of blocks, but there is part that does, > still. > > ) > > > > Like i said, it also would address the case when rows don't fit in the > > memory (hence no memory bound for n of A) but the most immediate benefit > is > > to speed/ scalability/memory req of SSVD in most practical LSI cases. > > > > -Dmitriy > > > > On Mon, Dec 13, 2010 at 10:24 AM, Jake Mannix <[email protected]> > > wrote: > > > > > Hey Dmitriy, > > > > > > I've also been playing around with a VectorWritable format which is > > backed > > > by a > > > SequenceFile, but I've been focussed on the case where it's essentially > > the > > > entire > > > matrix, and the rows don't fit into memory. This seems different than > > your > > > current > > > use case, however - you just want (relatively) small vectors to load > > > faster, > > > right? > > > > > > -jake > > > > > > On Mon, Dec 13, 2010 at 10:18 AM, Ted Dunning <[email protected]> > > > wrote: > > > > > > > Interesting idea. > > > > > > > > Would this introduce a new vector type that only allows iterating > > through > > > > the elements once? > > > > > > > > On Mon, Dec 13, 2010 at 9:49 AM, Dmitriy Lyubimov <[email protected] > > > > > > wrote: > > > > > > > > > Hi all, > > > > > > > > > > I would like to submit a patch to VectorWritable that allows for > > > > streaming > > > > > access to vector elements without having to prebuffer all of them > > > first. > > > > > (current code allows for the latter only). > > > > > > > > > > That patch would allow to strike down one of the memory usage > issues > > in > > > > > current Stochastic SVD implementation and effectively open memory > > bound > > > > for > > > > > n of the SVD work. (The value i see is not to open up the the bound > > > > though > > > > > but just be more efficient in memory use, thus essentially speeding > u > > p > > > > the > > > > > computation. ) > > > > > > > > > > If it's ok, i would like to create a JIRA issue and provide a patch > > for > > > > it. > > > > > > > > > > Another issue is to provide an SSVD patch that depends on that > patch > > > for > > > > > VectorWritable. > > > > > > > > > > Thank you. > > > > > -Dmitriy > > > > > > > > > > > > > > >
