CODEWITHSUNDEEP
neo4jquery-optimizationcyphergraph-databases
SamWiicks
SamWiicks

Reputation: 95

Neo4j out of memory Error

I have modeled my neo4j database according to this answer by Nicole White in this link

and I also successfully tested the cypher query

MATCH (a:Stop {name:'A'}), (d:Stop {name:'D'})
MATCH route = allShortestPaths((a)-[:STOPS_AT*]-(d)),
stops = (a)-[:NEXT*]->(d)
RETURN EXTRACT(x IN NODES(route) | CASE WHEN x:Stop THEN 'Stop ' + x.name
                                    WHEN x:Bus THEN 'Bus ' + x.id
                               ELSE '' END) AS itinerary,
   REDUCE(d = 0, x IN RELATIONSHIPS(stops) | d + x.distance) AS distance

against a small test graph with 10 nodes.

But my original graph which contains about 2k nodes and 6k relationships causes trouble with the query. The query simply stops and I get an error:

java.lang.OutOfMemoryError: Java heap space

Can you help me to optimize my query or any other solution?

Thank you

Upvotes: 0

Views: 720

Answers (1)

Stefan Armbruster
Stefan Armbruster

Reputation: 39926

try to introduce a WITH to limit the calculation of :NEXT paths to only those pairs of a, d that are known to be a shortestpath. It's also a good practice to supply an upper limit for variable path length matches - im using 100 here as an example:

MATCH route = allShortestPaths(
   (a:Stop {name:'A'})-[:STOPS_AT*100]-(d:Stop {name:'D'})
)
WITH route, a, d
MATCH stops = (a)-[:NEXT*100]->(d)
RETURN EXTRACT(x IN NODES(route) | CASE WHEN x:Stop THEN 'Stop ' + x.name
                                WHEN x:Bus THEN 'Bus ' + x.id
                           ELSE '' END) AS itinerary,
REDUCE(d = 0, x IN RELATIONSHIPS(stops) | d + x.distance) AS distance

Upvotes: 1

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