Neo4J: Expand node with children childrens (Performance)

Question

I thought this would be very easy, because i have a typical graph use case: Expand a node.

This is easy if there are no additional requirements:

MATCH (s:Entity)-[]-(dest) WHERE s._id = 'xxx'
RETURN dest

Problem Nr.1: sometimes there are many children so i want to limit the return count!

MATCH (s:Entity)-[]-(dest) WHERE s._id = 'xxx'
RETURN dest
LIMIT 100

Additional requirement: Return all children ids of the children childrens!

MATCH (s:Entity)-[]-(dest) WHERE s._id = 'xxx'
WITH collect(dest) as childrenSource
LIMIT 100
MATCH (childrenSource)-[]-(childDestination)
RETURN childrenSource as expandNode, collect(childDestination) as childrenIds
LIMIT 100

Problem 2: The limits are in the wrong place, because collect already did the collection before the limit.

Possible solution:

MATCH (s:Entity)-[]-(dest) WHERE s._id = 'xxx'
WITH collect(dest)[..100] as childrenSource
LIMIT 100
MATCH (childrenSource)-[]-(childDestination)
RETURN childrenSource as expandNode, collect(childDestination)[..100] as childrenIds

But i dont thinks this is a performant solution. Because it takes quite a lot of time

Exact Problem description: If i have 1 node with 1000 children and each child has another 1000 children i want to execute a query which returns 100 children with 100 child ids

-------------------------------------------------
| node 1   | child id 1_1,....   child id 1_100 |
| node 2   | child id 2_1,....   child id 2_100 |
| ...      | ...                                |
| node 100 | child id 100_1,.. child id 100_100 |
-------------------------------------------------

Other solution: i do a simple expand for the node. and than i call an expand on each child node. But doing 101 queries instead of 1 query sounds not too performant either.

InverseFalcon InverseFalcon · Accepted Answer · 2017-02-23T18:37:21

EDIT

As usual, APOC Procedures to the rescue. Using apoc.cypher.run(), you can use LIMIT within a subquery, which lazy-load the expansion up to your limit.

MATCH (s:Entity)-[]-(dest) WHERE s._id = 'xxx'
WITH dest
LIMIT 100
CALL apoc.cypher.run('
 MATCH (dest)-[]-(childDestination)
 RETURN childDestination LIMIT 100
 ', {dest:dest}) YIELD value
RETURN dest as expandNode, COLLECT(value.childDestination) as childrenIds

Neo4J: Expand node with children childrens (Performance)

2 Answers