Updating node locks outgoing relation deletion for APOC but not for normal queries

[saadali5997]

Guidelines

I already posted the question on forums but didn't get any clear response so writing here. I want to understand the behaviour/limitation behind it and if there's some documentation anywhere which explains this behaviour, that would be really nice.

Expected Behavior (Mandatory)

Updating a node should not lock deletion of its edges.
This works (without APOC) and deletes all draft_entities

MATCH (d: Dataset { id: "D1" })
SET d.updatedAt = datetime()
WITH d
OPTIONAL MATCH (d)-[r:ENTITY]->(draft_entities)
DETACH DELETE draft_entities

So the following query should delete all draft_entities along with their relationships

MATCH (d: Dataset { id: "D1" })
SET d.updatedAt = datetime()
WITH d
CALL apoc.periodic.iterate(
    '   WITH $d as d
        OPTIONAL MATCH (d)-[r:ENTITY]->(draft_entities)
        RETURN draft_entities
    ',
    '  
        DETACH DELETE draft_entities // Or we can also just do DELETE r for testing 
    ',
    { batchSize: 100, parallel: false, params: { d: d } }
) YIELD batches AS draft_batches, total AS draft_total
RETURN draft_total

Actual Behavior (Mandatory)

The following query gets stuck and never finishes because we can not delete the edges when a node is edited:

MATCH (d: Dataset { id: "D1" })
SET d.updatedAt = datetime()
WITH d
CALL apoc.periodic.iterate(
    '   WITH $d as d
        OPTIONAL MATCH (d)-[r:ENTITY]->(draft_entities)
        RETURN draft_entities
    ',
    '  
        DETACH DELETE draft_entities // Or we can also just do DELETE r for testing 
    ',
    { batchSize: 100, parallel: false, params: { d: d } }
) YIELD batches AS draft_batches, total AS draft_total
RETURN draft_total

Even if I do the following behaviour is still the same

CALL apoc.cypher.doIt(
  'MATCH (d:Dataset {id: $id})
   SET d.mutationLock__lockedBy = "3a631518-1726-5bde-a537-e9cb1068e2c1", 
       d.mutationLock__expiresAt = $newDatetime, 
       d.updatedAt = datetime()
   RETURN d',
  { id: $id, newDatetime: $newDatetime }
) YIELD value
MATCH (d: Dataset { id: "D1" })
SET d.updatedAt = datetime()
WITH d
CALL apoc.periodic.iterate(
    '   WITH $d as d
        OPTIONAL MATCH (d)-[r:ENTITY]->(draft_entities)
        RETURN draft_entities
    ',
    '  
        DETACH DELETE draft_entities // Or we can also just do DELETE r for testing 
    ',
    { batchSize: 100, parallel: false, params: { d: d } }
) YIELD batches AS draft_batches, total AS draft_total
RETURN draft_total

How to Reproduce the Problem

By running the queries above it can be reproduced.

Simple Dataset (where it's possibile)

CREATE (d:Dataset {id: "D1", name: "Dataset A"})
CREATE (cd1:CompanyDepartment {id: "CD1", name: "Department 1"})
CREATE (cd2:CompanyDepartment {id: "CD2", name: "Department 2"})
CREATE (cd3:CompanyDepartment {id: "CD3", name: "Department 3"})
CREATE (d)-[:ENTITY]->(cd1)
CREATE (d)-[:ENTITY]->(cd2)
CREATE (d)-[:ENTITY]->(cd3)
RETURN d, cd1, cd2, cd3

Screenshots (where it's possibile)

Specifications (Mandatory)

Neo4j 5.23, using through browser.

Currently used versions

Versions

• OS: Browser UI
• Neo4j: 5.23.0
• Neo4j-Apoc: 5.23.0

[loveleif]

Thanks for your report @saadali5997. The issue is that apoc.periodic.iterate runs in inner transactions. When you do SET d.updatedAt = datetime() in the outer transaction that node is locked and the inner transactions will not be able to write to the node. You can rewrite your query to run in a single transaction. Or perform the SET d.updatedAt = datetime() operation separately (since apoc.periodic.iterate commits multiple transactions there is no atomicity anyway so the effect will be the same).