What is the recommended way to paginate the results from a query?
Specifically:
Is range() step pushed to the cassandra tables or in-memory calculation is performed by Graph module?
Other tinkerpop graph db vendors discourage use of range and recommend to use app-level predicates instead.
the answer is that it depends on the query. (I am assuming you are using DSE Graph 6.8)
In simple queries, where the range step is applied in the first step (before traversing), the upper limit of the range is pushed down, but not the lower.
In queries where the range step is applied after traversing, the limit is not pushed down.
Here are some examples for range query profiles on vertices (it's similar for edges):
gremlin> g.V().hasLabel("person").range(3,4).profile()
==>Traversal Metrics
Step Count Traversers Time (ms) % Dur
=============================================================================================================
__.V().hasLabel("person").limit(4L) 4 4 5.282 92.07
CQL statements ordered by overall duration 3.840
\_1=SELECT * FROM friends.person LIMIT 4 / Duration: 3 ms / Count: 1 / Index type: Table: person
HasStep([~label.eq(person)]) 4 4 0.310 5.41
RangeGlobalStep(3,4) 1 1 0.029 0.52
ReferenceElementStep 1 1 0.114 1.99
>TOTAL - - 5.737 -
gremlin> g.V().hasLabel("person").out("knows").hasLabel("person").range(1,2).profile()
==>Traversal Metrics
Step Count Traversers Time (ms) % Dur
=============================================================================================================
__.V().hasLabel("person") 5 5 3.423 29.30
CQL statements ordered by overall duration 1.548
\_1=SELECT * FROM friends.person / Duration: 1 ms / Count: 1 / Index type: Table: person
HasStep([~label.eq(person)]) 5 5 0.073 0.63
__.out().hasLabel("person").hasLabel("knows") 2 2 7.756 66.40
CQL statements ordered by overall duration 21.167
\_1=SELECT * FROM friends.person__knows__person WHERE out_person_id = ? / Duration: 20 ms / Count: 5 / In
dex type: Table: person__knows__person
\_2=SELECT * FROM friends.person WHERE person_id = ? / Duration: 1 ms / Count: 2 / Index type: Table: per
son
HasStep([~label.eq(person)]) 2 2 0.315 2.70
RangeGlobalStep(1,2) 1 1 0.042 0.36
ReferenceElementStep 1 1 0.071 0.61
>TOTAL - - 11.682 -
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