Hi Avery, Thanks for the response. I reached out to the graph user mailing list because I am quite interested in helping develop / execute standardized scalability testing for Giraph, so I'm glad to see that there is interest!
Here's some follow up to some of the points you raised / questions you asked: Currently, the biggest limitation faced by GoldenOrb is the capacity issue; it can't handle more than roughly 100,000 vertices per node. This low maximum vertices per node limitation, coupled with instability issues, obviously hampered the ability to conduct ideal scalability testing, but even with graphs totaling 100,000 to 250,000 vertices a clear power law slope can be found before hitting an inevitable communication bottleneck. This can be seen by noting that the log-log slopes of the 20k, 50k, and 100k graphs (for SSSP) remain fairly constant, and negative, as the number of nodes in the cluster grows, unlike the slopes for 5k, 2k, and 1k graphs which demonstrate a framework overhead bottleneck, corresponding to the point where the slope changes from negative to roughly 0 or positive (which appears to happen at around 1k vertices per node). On to the second issue you brought up… Graph problems can be notoriously difficult to implement scalability testing for precisely for the reasons you brought up. A few things were done to allow an apples-to-apples comparison with the Pregel results. First, the single source shortest path algorithm used for testing comes directly from the Pregel paper. Second, just as in the Pregel tests, binary tree graphs were used to ensure that each vertex had the same fixed, low order, outdegree. Last, the tests were repeated using non-binary tree graphs (generated by a python script) with a non-constant, but low order, average outdegree per vertex (average 10 edges per vertex, then again with graphs averaging 90 edges per vertex), the results of which were seen to be quite close to the binary tree graph data. As mentioned in passing, the scalability test results allow for a direct comparison with the Pregel results, but should also allow for a meaningful comparison to your scalability results for Giraph precisely because the edges per vertex have been fixed. While this is not ideal (I would prefer a standardized set of tests which everybody runs in standardized configurations), the proposition that the results can be meaningfully compared is backed up by two points; First, the log-log slope of the data you presented is right in line with the value reported by Pregel for their SSSP tests, both of which are realistic values (and show very good parallelization!), meaning that both algorithms display similar properties for configurations in the regime not dominated by a framework overhead bottleneck. And second, the GoldenOrb SSSP results being compared are also from configurations which have reached a steady power law slope over the range of nodes considered, for runs using the same algorithm as the Pregel results. These two points, I feel, justify the comparisons made (though, again, it would be better to have a standardized set of configurations for testing to facilitate comparing results, even between algorithms). Since all three sets of scalability tests yield fairly linear complexity plots (execution time vs. number of vertices in the graph, slide 29 of your talk), it also makes sense to compare weak scaling results, a proposition supported by the consistency of the observed GoldenOrb weak scaling results for SSSP across multiple test configurations. As for the results found in your October 2011 talk, they are impressive and clearly demonstrate an ability to effectively scale to large graph problems (shown by the weak scaling slope of ~ 0.01) and to maximize the benefit of throwing additional computational resources at a known problem (shown by the strong scaling slope of ~ -0.93), so I'm interested to see the results of the improvements that have been made. I'm a big proponent of routine scalability testing using a fixed set of configurations as part of the software testing process, as the comparable results help to quantify "improvement" as the software is developed further and can often help to identify unintended side effects of changes / find optimal configurations for various regimes of problems, and would like to see Giraph succeed, so let me know if there's any open issues which I might be able to dig into (I'm on the dev mailing list as well, though haven't posted there). Thanks, Jon On Dec 11, 2011, at 1:02 PM, Avery Ching wrote: > Hi Jon, > > -golden...@googlegroups.com (so as to not clog up their mailing list > uninvited) > > First of all, thank you for sharing this comparison. I would like to note a > few things. The results I posted in October 2011 were actually a bit old > (done in June 2011) and do not have several improvements that reduce memory > usage significantly (i.e. GIRAPH-12 and GIRAPH-91). The number of vertices > loadable per worker is highly dependent on the number of edges per worker, > the amount of available heap memory, number of messages, the balancing of the > graph across the workers, etc. In recent tests at Facebook, I have been able > to load over 10 million vertices / worker easily with 20 edges / vertex. I > know that you wrote that the maximum per worker was at least 1.6 million > vertices for Giraph, I just wanted to let folks know that it's in fact much > higher. We'll work on continuing to improve that in the future as today's > graph problems are in the billions of vertices or rather hundreds of billions > =). > > Also, with respect to scalability, if I'm interpreting these results > correctly, does it mean that GoldenOrb is currently unable to load more than > 250k vertices / cluster as observed by former Ravel developers? if so, given > the small tests and overhead per superstep, I wouldn't expect the scalability > to be much improved by more workers. Also, the max value and shortest paths > algorithms are highly data dependent to how many messages are passed around > per superstep and perhaps not a fair scaling comparison with Giraph's > scalability designed page rank benchmark test (equal messages per superstep > distributed evenly across vertices). Would be nice to see an > apples-to-apples comparison if someone has the time...=) > > Thanks, > > Avery > > On 12/10/11 3:16 PM, Jon Allen wrote: >> Since GoldenOrb was released this past summer, a number of people have asked >> questions regarding scalability and performance testing, as well as a >> comparison of these results with those of Giraph ( >> http://incubator.apache.org/giraph/ ), so I went forward with running tests >> to help answer some of these questions. >> >> A full report of the scalability testing results, along with methodology >> details, relevant information regarding testing and analysis, links to data >> points for Pregel and Giraph, scalability testing references, and background >> mathematics, can be found here: >> >> http://wwwrel.ph.utexas.edu/Members/jon/golden_orb/ >> >> Since this data will also be of interest to the Giraph community (for >> methodology, background references, and analysis reasons), I am cross >> posting to the Giraph user mailing list. >> >> A synopsis of the scalability results for GoldenOrb, and comparison data >> points for Giraph and Google's Pregel framework are provided below. >> >> The setup and execution of GoldenOrb scalability tests were conducted by >> three former Ravel (http://www.raveldata.com ) developers, including myself, >> with extensive knowledge of the GoldenOrb code base and optimal system >> configurations, ensuring the most optimal settings were used for scalability >> testing. >> >> >> RESULTS SUMMARY: >> >> >> MAX CAPACITY: >> >> Pregel (at least): 166,666,667 vertices per node. >> >> Giraph (at least): 1,666,667 vertices per worker. >> >> GoldenOrb: ~ 100,000 vertices per node, 33,333 vertices per worker. >> >> >> STRONG SCALING (SSSP): >> Note: Optimal parallelization corresponds to the minimum value -1.0. >> Deviation from the minimum possible value of -1.0 corresponds to non-optimal >> parallelization. >> >> Pregel: -0.924 (1 billion total vertices) >> >> Giraph: -0.934 (250 Million total vertices) >> >> GoldenOrb: -0.031 Average, -0.631 Best (100000 total vertices), 0.020 Worst >> (1000 total vertices) >> >> >> WEAK SCALING (SSSP): >> Note: Optimal weak scalability corresponds to the value 0.0. Deviation from >> the optimal value of 0.0, corresponds to non-optimal usage of computational >> resources as managed by the framework. >> >> Pregel: No Data Available >> >> Giraph: 0.01 (1,666,667 vertices per worker) >> >> GoldenOrb: 0.37 Average, 0.23 Best (500 vertices per node), 0.48 Worst >> (12500 vertices per node) >> >> >> >> I hope this answers some of the many questions which have been posted >> regarding scalability and performance. Be sure to check out the full >> scalability testing report at >> http://wwwrel.ph.utexas.edu/Members/jon/golden_orb/ Please let me know if >> you have any questions. >> >> Thanks, >> Jon >
