Optimize Cypher query on multiple unique labels

Question

In Neo4j, is it faster to run a query against all nodes (AllNodesScan) and then filter on their labels with a WHERE clause, or to run multiple queries with a NodeByLabelScan?

To illustrate, I want all nodes that are labeled with one of the labels in label_list:

label_list = ['label_1', 'label_2', ...]

Which would be faster in an application (this is pseudo-code):

for label in label_list:
    run.query("MATCH (n:{label}) return n")

or

run.query("MATCH (n) WHERE (n:label_1 or n:label_2 or ...)")

EDIT:

Actually, I just realized that the best option might be to run multiple NodeByLabelScan in a single query, with something looking like this:

MATCH (a:label_1)
MATCH (b:label_2)
...
UNWIND [a, b ..] as foo
RETURN foo

Could someone speak to it?

cybersam cybersam · Accepted Answer · 2020-04-17T20:29:19

Yes, it would be better to run multiple NodeByLabelScans in a single query.

For example:

OPTIONAL MATCH (a:label_1)
WITH COLLECT(a) AS list
OPTIONAL MATCH (b:label_2)
WITH list + COLLECT(b) AS list
OPTIONAL MATCH (c:label_3)
WITH list + COLLECT(c) AS list
UNWIND list AS n
RETURN DISTINCT n

Notes on the query:

It uses OPTIONAL MATCH so that the query can proceed even if a wanted label is not found in the DB.
It uses multiple aggregation steps to avoid cartesian products (also see this).
And it uses UNWIND so that it can useDISTINCT to return distinct nodes (since a node can have multiple labels).

Optimize Cypher query on multiple unique labels

1 Answers