Janusgraph 0.5.3 potential memory leak


JG 0.5.3(same on 0.5.2), cannot be reproduced on JG 0.3.2
Backend: scyllaDB
Indexing backend: ElasticSearch

Steps to reproduce: 
1) Create a node with a composite index for the field "X"
2) Create another kind (Y) of node and fill with a lot of data (several millions nodes)
3) Create edges between node X and all the nodes Y with the label L
4) Execute the following query in gremlin: g.V().has("X","value").out("Y").valueMap(true)
5) Query should time out after some time

The main idea - only scylla/cassandra is involved in the query

Expected result: Janusgraph operates normally

Observed result: Janusgraph starts consuming all the allocated memory and one of the CPU cores is loaded 100%, another execution will load another core and so on until there are no available. CPU load and CPU consumption happens even if there is no any further interaction with the system. In the end JG becomes unresponsive.

Flame chart looks like this

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