CODEWITHSUNDEEP
neo4jcypher
laila
laila

Reputation: 1059

COUNT and DISTINCT queries in CYPHER causing javaheap memory error

The cypher query:

MATCH (n1:ANIMAL)-[r:COHABITS]-(n2:ANIMAL)
RETURN distinct[id(n1),id(n2)] as tups, count(distinct[id(n1),id(n2)]) AS count
LIMIT 5

Never finishes, i.e. the query keeps running until neo4j encounters a javaheap memory failure. However when I execute:

MATCH (n1:ANIMAL)-[r:COHABITS]-(n2:ANIMAL)
RETURN n1,r,n2
LIMIT 5

I get a fast response.

Is there a reason/workaround for this?

Upvotes: 0

Views: 468

Answers (1)

Stefan Armbruster
Stefan Armbruster

Reputation: 39915

For distinct Cypher needs to build up the result set in memory to check if a new result is already present in the set. Without distinct, it just streams the results and only has very little need for heap space.

Depending on the number of :COHABITS relationships you need to increase your heap space settings in neo4j-wrapper.conf

Upvotes: 1

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