Detecting cycles in neo4j property graph using cypher

Question

What is the best way to detect for cycles in a graph of a considerable size using cypher.

I have a graph which has about 250000 nodes and about 270000 relationship and I would like to detect cycles in sub graph of about 10k nodes and involving 100k relationships. The cypher I have written is like

start 
      n = node:node_auto_index(some lucene query that returns about 10k nodes)
match
    p =  n-[:r1|r2|r3*]->n
return p

However this is not turning out to be very efficient.

Can somebody suggest a better way to do this.

score 0 · Answer 1 · answered Aug 16 '16 at 23:22

1) Count un-flagged nodes
2) Flag nodes with no outgoing relations (leaves)
3) Flag nodes with no incoming relations (roots)
4) If any nodes were flagged in 2 or 3 return to step 1

5) If un-flagged nodes remain you have at least 1 cycle

the cycle(s) will be in the set of un-flagged nodes
looking at nodes with fewest [in|out] edges may help
if there are still too many to identify cycle

score 0 · Answer 2 · answered Sep 03 '18 at 06:24

The query you are using at the moment will return all paths for each node. Changing it to

start 
      n = node:node_auto_index(some lucene query that returns about 10k nodes)
where (n)-[*]->(n)
return distinct p, n

will let Neo4j stop once it finds a path for a given node. It will probably still be slow, but definitely less so.

Detecting cycles in neo4j property graph using cypher

2 Answers2