Distributed Latent Dirichlet Allocation

Note

See Distributed Computing for an introduction to distributed computing in gensim.

Setting up the cluster

See the tutorial on Distributed Latent Semantic Analysis; setting up a cluster for LDA is completely analogous, except you want to run lda_worker and lda_dispatcher scripts instead of lsi_worker and lsi_dispatcher.

Running LDA

Run LDA like you normally would, but turn on the distributed=True constructor parameter

>>> # extract 100 LDA topics, using default parameters
>>> lda = LdaModel(corpus=mm, id2word=id2word, num_topics=100, distributed=True)
using distributed version with 4 workers
running online LDA training, 100 topics, 1 passes over the supplied corpus of 3199665 documets, updating model once every 40000 documents
..

In serial mode (no distribution), creating this online LDA model of Wikipedia takes 10h56m on my laptop (OS X, C2D 2.53GHz, 4GB RAM with libVec). In distributed mode with four workers (Linux, Xeons of 2Ghz, 4GB RAM with ATLAS), the wallclock time taken drops to 3h20m.

To run standard batch LDA (no online updates of mini-batches) instead, you would similarly call

>>> lda = LdaModel(corpus=mm, id2word=id2token, num_topics=100, update_every=0, passes=20, distributed=True)
using distributed version with 4 workers
running batch LDA training, 100 topics, 20 passes over the supplied corpus of 3199665 documets, updating model once every 3199665 documents
initializing workers
iteration 0, dispatching documents up to #10000/3199665
iteration 0, dispatching documents up to #20000/3199665
...

and then, some two days later:

iteration 19, dispatching documents up to #3190000/3199665
iteration 19, dispatching documents up to #3199665/3199665
reached the end of input; now waiting for all remaining jobs to finish

>>> lda.print_topics(20)
topic #0: 0.007*disease + 0.006*medical + 0.005*treatment + 0.005*cells + 0.005*cell + 0.005*cancer + 0.005*health + 0.005*blood + 0.004*patients + 0.004*drug
topic #1: 0.024*king + 0.013*ii + 0.013*prince + 0.013*emperor + 0.008*duke + 0.008*empire + 0.007*son + 0.007*china + 0.007*dynasty + 0.007*iii
topic #2: 0.031*film + 0.017*films + 0.005*movie + 0.005*directed + 0.004*man + 0.004*episode + 0.003*character + 0.003*cast + 0.003*father + 0.003*mother
topic #3: 0.022*user + 0.012*edit + 0.009*wikipedia + 0.007*block + 0.007*my + 0.007*here + 0.007*edits + 0.007*blocked + 0.006*revert + 0.006*me
topic #4: 0.045*air + 0.026*aircraft + 0.021*force + 0.018*airport + 0.011*squadron + 0.010*flight + 0.010*military + 0.008*wing + 0.007*aviation + 0.007*f
topic #5: 0.025*sun + 0.022*star + 0.018*moon + 0.015*light + 0.013*stars + 0.012*planet + 0.011*camera + 0.010*mm + 0.009*earth + 0.008*lens
topic #6: 0.037*radio + 0.026*station + 0.022*fm + 0.014*news + 0.014*stations + 0.014*channel + 0.013*am + 0.013*racing + 0.011*tv + 0.010*broadcasting
topic #7: 0.122*image + 0.099*jpg + 0.046*file + 0.038*uploaded + 0.024*png + 0.014*contribs + 0.013*notify + 0.013*logs + 0.013*picture + 0.013*flag
topic #8: 0.036*russian + 0.030*soviet + 0.028*polish + 0.024*poland + 0.022*russia + 0.013*union + 0.012*czech + 0.011*republic + 0.011*moscow + 0.010*finland
topic #9: 0.031*language + 0.014*word + 0.013*languages + 0.009*term + 0.009*words + 0.008*example + 0.007*names + 0.007*meaning + 0.006*latin + 0.006*form
topic #10: 0.029*w + 0.029*toronto + 0.023*l + 0.020*hockey + 0.019*nhl + 0.014*ontario + 0.012*calgary + 0.011*edmonton + 0.011*hamilton + 0.010*season
topic #11: 0.110*wikipedia + 0.110*articles + 0.030*library + 0.029*wikiproject + 0.028*project + 0.019*data + 0.016*archives + 0.012*needing + 0.009*reference + 0.009*statements
topic #12: 0.032*http + 0.030*your + 0.022*request + 0.017*sources + 0.016*archived + 0.016*modify + 0.015*changes + 0.015*creation + 0.014*www + 0.013*try
topic #13: 0.011*your + 0.010*my + 0.009*we + 0.008*don + 0.008*get + 0.008*know + 0.007*me + 0.006*think + 0.006*question + 0.005*find
topic #14: 0.073*r + 0.066*japanese + 0.062*japan + 0.018*tokyo + 0.008*prefecture + 0.005*osaka + 0.004*j + 0.004*sf + 0.003*kyoto + 0.003*manga
topic #15: 0.045*da + 0.045*fr + 0.027*kategori + 0.026*pl + 0.024*nl + 0.021*pt + 0.017*en + 0.015*categoria + 0.014*es + 0.012*kategorie
topic #16: 0.010*death + 0.005*died + 0.005*father + 0.004*said + 0.004*himself + 0.004*took + 0.004*son + 0.004*killed + 0.003*murder + 0.003*wife
topic #17: 0.027*book + 0.021*published + 0.020*books + 0.014*isbn + 0.010*author + 0.010*magazine + 0.009*press + 0.009*novel + 0.009*writers + 0.008*story
topic #18: 0.027*football + 0.024*players + 0.023*cup + 0.019*club + 0.017*fc + 0.017*footballers + 0.017*league + 0.011*season + 0.007*teams + 0.007*goals
topic #19: 0.032*band + 0.024*album + 0.014*albums + 0.013*guitar + 0.013*rock + 0.011*records + 0.011*vocals + 0.009*live + 0.008*bass + 0.008*track

If you used the distributed LDA implementation in gensim, please let me know (my email is at the bottom of this page). I would like to hear about your application and the possible (inevitable?) issues that you encountered, to improve gensim in the future.