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 > > > > > > > > > >
