Neptune's implementation of .order().by() incorrectly filters out objects

[Daniel C. Weber]

Hello,

In Tinkerpop version 3.5, the handling of empty traversals in the by-modulators of order steps has been changed to not fail the entire query but to assume some notion of null for the value that is compared.

This works well in Gremlin Server 3.5.x: Ordering some vertices on a non-existent property will neither fail nor filter out any of those vertices, but instead produce some ordering of the vertices.

Neptune, however, in Engine release 1.2.0.0 (and at least 1.1.0.0) will also not fail but filter out the vertices. But order() must not act as a filter-step.

This is easy to reproduce:

- g.addV().addV()

- g.V().count() -> 2

- g.V().order().by('key').count() -> 0

This is also the case with both values for "Neptune#useDFE".

Can anybody confirm this behaviour?

Thanks a lot

Daniel

[Stephen Mallette]

Neptune is behaving with 3.6.x logic in this case (despite there not being specific 3.6.x support just yet):

https://tinkerpop.apache.org/docs/current/upgrade/#_consistent_by_behavior

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[Daniel C. Weber]

This is unfortunate since Neptune advertises 3.5.2 as compatibility level. I'm not questioning the design decisions and I am usually able to work around these things, but I think having an OrderGlobalStep behave like a filter step is going to cause trouble for a lot of people.

Do you have an ETA for 3.6 on Neptune?

Thanks a lot

[Phil Crosland]

is it possible to add a parameter to order() to allow inclusion of all items?

[Stephen Mallette]

> Do you have an ETA for 3.6 on Neptune?

I dont really - I can just say it's under development.

> is it possible to add a parameter to order() to allow inclusion of all items?

it depends on whether or not the graph supports ProductiveByStrategy. adding that in should produce nulls: 

https://tinkerpop.apache.org/docs/current/upgrade/#_productivebystrategy

Neptune doesn't support that which is part of the reason why it is exhibiting the 3.6.x behavior. You could also always just be explicit about it in your Gremlin:

g.V().order().by(coalesce(values('lang'),constant(null)))

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