Delete a connected graph with Cypher

Question

I want to delete a connected graph related to a particular node in a Neo4j database using Cypher. The use case is to delete a "start" node and all the nodes where a path to the start node exists. To limit the transaction the query has to be iterative and must not disconnect the connected graph.

Until now I am using this query:

OPTIONAL MATCH (start {indexed_prop: $PARAM})--(toDelete)
OPTIONAL MATCH  (toDelete)--(toBind)
WHERE NOT(id(start ) = id(toBind)) AND NOT((start)--(toBind))
WITH start, collect(toBind) AS TO_BIND, toDelete limit 10000
DETACH DELETE toDelete
WITH start, TO_BIND
UNWIND TO_BIND AS b
CREATE (start)-[:HasToDelete]->(b)

And call it until deleted node is equal to 0.

Is there a better query for this ?

I take it you tried a variable length path to all connected nodes and DETACH DELETE of every connected node? Does that blow up your heap? — InverseFalcon
Yes, but the problem is that the query doesn't work on a large graph, calling the query multiple times may break the connected graph. — cde

InverseFalcon InverseFalcon · Accepted Answer · 2016-12-07T09:06:00

You could try a mark and delete approach, which is similar to how you would detach and delete the entire connnected graph with a variable match, but instead of DETACH DELETE you can apply a :TO_DELETE label.

Something like this (making up a label to use for the start node, as otherwise it has to comb the entire db looking for a node with the indexed param):

MATCH (start:StartNodeLabel {indexed_prop: $PARAM})-[*]-(toDelete)
SET toDelete:TO_DELETE

If that blows up your heap, you can run it multiple times, with the added predicate WHERE NOT toDelete:TO_DELETE before the SET, and using a combination of LIMIT and/or a limit on the depth of the variable-length relationship.

When you're sure you've labeled every connected node, then it's just a matter of deleting every node in the TO_DELETE label, and you can run that iteratively, or use APOC procedure apoc.periodic.commit() to handle that in batches.

Delete a connected graph with Cypher

1 Answers