Hi Fabian, It should be trivial to implement inDegrees and outDegrees using the new algorithms. We are now doing this for the translate methods in FLINK-3771. The algorithms implement additional customization but the Graph methods are kept simple. ScatterGatherIteration could be simplified as well by using VertexPairDegree. These changes to the Graph API should be considered in the context of FLINK-3277.
I am not familiar with the use of getDegrees which simply sums inDegrees and outDegrees but would remain unchanged. Performance was discussed in the Jira as follows. "Each of the "join" methods is implemented as a coGroup as is each of the degree methods, so the trade-off is a coGroup vs a reduce to calculate each degree, and a coGroup vs a hash-join for each annotated degree. As you note the user is required to compose multiple methods and must be aware of implementation details such as using inDegrees or outDegrees instead of getDegrees on an undirected graph. Performance impacts include the use of coGroup, immutable types, and that the degree functions materialize the vertex set." Greg On Mon, Apr 25, 2016 at 8:46 AM, Fabian Hueske <fhue...@gmail.com> wrote: > Hi Greg and Vasia, > > thanks for starting this discussion. > I think it is a good idea to update the Gelly roadmap. As Vasia said, many > items on the list have been implemented and other have been more or less > dropped. > Also new persons who want to improve Gelly have joint the community while > others have become idle. > So from my point of view it makes perfect sense to gather the input of the > community and update the Gelly roadmap. > > Regarding the specific changes of FLINK-3772, I am usually always in favor > of performance improvements. > How much would the suggested functionality for degree computation overlaps > with the current methods? > Could the current methods be replaced by the more efficient implementations > or would there be two methods which look very similar and behave almost the > same? > > Best, Fabian > > > > 2016-04-22 11:00 GMT+02:00 Vasiliki Kalavri <vasilikikala...@gmail.com>: > > > Hi all, > > > > I asked Greg to start a discussion here about FLINK-3771 and FLINK-3772, > to > > make sure we're all on the same page about future Gelly development. > > > > About a year ago we created the Gelly roadmap [1]. Many of these items > have > > been implemented and others were researched and either developed > externally > > or dropped. Graph translators and degree annotations were not in the > > roadmap, but I personally think that they are both helpful features and > I'm > > in favor of adding them to Gelly. > > > > That said, I find this a perfect timing for revisiting and updating our > > Gelly development plans. We should update the roadmap so that it reflects > > current state and future plans. This way, the community can have a clear > > picture of what we are working on and what are upcoming features. This is > > also very important for new contributors. They can always refer to the > > roadmap to see what the community is interested in and we can avoid > having > > people spending their time on obsolete or dropped features. We should > also > > go through existing JIRAs and clean them up. Several are assigned to > people > > who have been inactive or might need help. > > > > In the following days I will go through the roadmap and then start a new > > thread where we can discuss features and agree on future plans. In the > > meantime, it would be great if you give us your view on FLINK-3771 and > > FLINK-3772. > > > > Cheers, > > -Vasia. > > > > [1]: https://cwiki.apache.org/confluence/display/FLINK/Flink+Gelly > > > > On 21 April 2016 at 18:52, Greg Hogan <c...@greghogan.com> wrote: > > > > > Vasia and I are looking for additional feedback on FLINK-3772. This > > ticket > > > [0] and PR [1] provides a set of graph algorithms which compute and > store > > > the degree for vertices and edges. > > > > > > Degree annotation is a basic component of many algorithms. For example, > > > PageRank requires the vertex out-degree to evenly divide the vertex > score > > > among neighbors. The triangle enumeration algorithm in Gelly requires > > both > > > source and target degree for each edge as an optimization. The Jaccard > > and > > > Adamic-Adar similarities require the target degree for each edge. > > > > > > As discussed in the ticket, Graph has methods for outDegrees, > inDegrees, > > > and getDegrees. These are simple but difficult or impossible to use > > > efficiently. > > > > > > Stepping back, I believe algorithms should be composable and reused > where > > > possible, not only to improve Flink but also to support users. > > Implementing > > > algorithms as classes rather than Graph methods enables customization > and > > > optimization such as used here. > > > > > > One such optimization is CachingGraphAlgorithm which implicitly reuses > > > DataSets. There is overlap between algorithms. From this ticket, > > annotating > > > edges with source and target degree on an undirected graph can reuse > > vertex > > > degree. Local clustering coefficient requires a triangle listing and > > global > > > clustering coefficient requires a triangle count, there is no need to > > > generate the list three times. > > > > > > Further optimizations include the use of mutable types, reusing sort > > order, > > > avoidance of coGroup, configurable parallelism, and not unnecessarily > > > materializing DataSets. I see all this as the expectation for inclusion > > in > > > Flink. > > > > > > Greg > > > > > > [0] https://issues.apache.org/jira/browse/FLINK-3772 > > > [1] https://github.com/apache/flink/pull/1901/files > > > > > >
