I'm not sure if its relevant for this ticket, but I have another use-case for combiners in an OLTP use-case. In Unipop (to which I'll hopefully have documentation very soon and be able to share with you guys) we have GroupStep optimizations. But since we can have results for the same step coming from different back-ends, we need some way to combine them to one result. If we had a simple way to combine the results, that would be great. If not, we'll just implement something by ourselves...
On Mon, 8 Feb 2016 at 17:29 Marko A. Rodriguez (JIRA) <j...@apache.org> wrote: > Marko A. Rodriguez created TINKERPOP-1136: > --------------------------------------------- > > Summary: GroupStep OLAP does not combine, only reduces. > Key: TINKERPOP-1136 > URL: https://issues.apache.org/jira/browse/TINKERPOP-1136 > Project: TinkerPop > Issue Type: Improvement > Components: process > Affects Versions: 3.1.1-incubating > Reporter: Marko A. Rodriguez > Fix For: 3.2.0-incubating > > > Right now, {{GroupStep}} does not support a combiner. Unfortunately, this > is a necessary consequence of not knowing the semantics of the reduction > :|. This is analogous to why Spark has {{reduceByKey}} vs. {{groupByKey}}. > HOWEVER, if a {{Barrier}} is used for reduction in the {{reduceTraversal}} > and that {{Barrier}} is a {{ReducingBarrierStep}}, then a combiner can be > used. I suspect that 99% of the time, the {{Barrier}} is a > {{ReducingBarrierStep}}. Once TINKERPOP-1131 is merged, it should be > possible to make {{GroupStep}} more intelligent by doing an analysis of its > {{Barrier}}-step. > > > > -- > This message was sent by Atlassian JIRA > (v6.3.4#6332) >
