Hello everyone (and the NSA -- Kuppitz did it),
This is regarding this ticket:
https://issues.apache.org/jira/browse/TINKERPOP3-866
In group_step_2/ branch we have a new implementation of GroupStep. Here is an
example:
g.V.group.by('name').by(outE.weight).by(max()) // old way
g.V.group.by('name').by(outE.weight.max()) // new way
What is the difference, there is only two by()-modulators that can be passed to
group(): keyTraversal and valueTraversal. What happened to reduceTraversal?
Well, valueTraversal is that. If you want to reduce on your values, well, add a
reducing barrier step -- e.g. max, min, sum, count, fold, mean, etc. In the old
way, we would put all your values into a Collection<V> and then when the step
was complete, we would feed those into the reduceTraversal. Now -- we can
dynamically reduce on the fly. This will greatly improve speed and memory usage
as we don't have to create a big old Collection<V> and instead, can reduce as
new traversers are fed into valueTraversal.
So this is great and no would object. What sucks is that this is NOT backwards
compatible. What Stephen and I came up with (in the ticket) is to make:
https://github.com/apache/incubator-tinkerpop/blob/group_step_2/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.java#L637-L639
This new step groupV3d0() is a deprecated step that is what the "old way" was.
Note the naming convention that Stephen used for Kryo is now used here -- V3d0
(version 3<dot>0). Thus, for users moving forward, they will have to do a
"replace all" on their queries and rename "group()" to "groupV3d0()". Then
slowly, over time, convert their traversal to use the new group() step and its
respective semantics.
Note that in the past we have been able to do backwards compatibility via
having the new step (e.g. AddVertexStep) simulate the behavior of the old step
and have respective @Deprecates in there to say that particular GraphTraversal
methods will go away. However, in this situation, the best we can do is
groupV3d0().
Anywho. That is that. If people have any better ideas on how to solve this
backwards compatibility issue, I'm all (deaf) ears.
Thanks,
Marko.
http://markorodriguez.com
