Gremlin (with Python + Neptune) Out of Memory Error with .toList()[0], .next() Fixes It. But Why?

Question

This is not really a question, but more of a discussions on how internally this would cause an out of memory error.

I have the following construct and last night, it resulted in out of memory error.

path_v is a single well defined V. I am expecting it is returning a single V.
All values in valueMap() I wanted were single cardinality string values.

I know that it is obvious that toList() will not be efficient if I am only interested in one value, however, this only should return a single record set, so even though it isn't efficient, it should not blow up the memory.

vm = g.V(path_v).valueMap("kind", "tag", "uuid").toList()[0]
The change to the following seems to fix this. Obviously this will be asking for a single value from a cursor type interaction

vm = g.V(path_v).valueMap("kind", "tag", "uuid").next()
Very intriguing...

Gremlin (with Python + Neptune) Out of Memory Error with .toList()[0], .next() Fixes It. But Why?

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