Query to kill transactions that take longer than X seconds and doesn’t contain certain keywords

In Neo4j we currently have the configuration property referred to as execution guard:

dbms.transaction.timeout=30s

that can be set automatically to kill transactions that take more than “x” seconds (x is equal to what is assigned to dbms.transaction.timeout, in this case 30s). However this is at global level and can’t be controlled for specific User or Query type.

So in order to implement this, a small script can be written and scheduled to run and kill the queries that take more than 30 seconds. This script can be triggered via cypher-shell. The query to kill the transaction that are not part of LOAD CSV and taking more than 30 seconds can be written as:

call dbms.listQueries() yield query, elapsedTimeMillis, queryId, username
where  NOT query contains toLower(“LOAD")
and elapsedTimeMillis >30000
with query, collect(queryId) as q
call dbms.killQueries(q) yield queryId
return query, queryId

The query to kill the transaction where the user executing the query is not “neo4j” and taking more than 30 seconds:

call dbms.listQueries() yield query, elapsedTimeMillis, queryId, username
where  NOT username contains toLower("neo4j")
and elapsedTimeMillis >30000
with query, collect(queryId) as q
call dbms.killQueries(q) yield queryId
return query, queryId

You can modify the above query based on either certain parameters for queries or for certain users that should not be killed.

Note: This applies to Neo4j 3.1 and newer only!

So far, so good. If we execute the above query once, it will check once for those long running queries. No repetition what so ever, so far. In order to automate this, we can use apoc:

CALL apoc.periodic.repeat("kill long-running queries", "
    call dbms.listQueries() yield query, elapsedTimeMillis, queryId, username
    where NOT username contains toLower("neo4j")
    and elapsedTimeMillis >30000
    with query, collect(queryId) as q
    call dbms.killQueries(q) yield queryId
    return query, queryId
", 10)

In that case, the query to check for the long running queries would be executed every ten seconds on the instance and database, where we have executed the apoc command. Adjust the timing parameters to your needs.

In case you want to manually cancel the job, you can use:

CALL apoc.periodic.cancel("kill long-running queries")

Note, that those jobs added via apoc.periodic.repeat do not survive restarts of the database. So if we want to install that permanently, we can use apoc’s initializer (https://neo4j.com/labs/apoc/4.1/operational/init-script/):

Add the following line to your conf/apoc.conf file (see also https://neo4j.com/labs/apoc/4.1/config/):

apoc.initializer.cypher.1=CALL apoc.periodic.repeat("kill long-running queries", "CALL dbms.listQueries() yield query, elapsedTimeMillis, queryId, username WHERE username contains toLower('neo4j') AND elapsedTimeMillis > 10000 WITH query, collect(queryId) as q CALL dbms.killQueries(q) yield queryId return query, queryId", 10)

Note that this is on instance level and applies to all databases.

You might want to use a dedicated cypher file on disk to store the query, so that you don’t have complex queries in the config file. Here is an example for doing so: https://neo4j.com/labs/apoc/4.1/operational/init-script/ ”’

  • Last Modified: 2020-10-15 08:05:54 UTC by Rohan Kharwar.
  • Relevant for Neo4j Versions: 3.1, 3.2.
  • Relevant keywords timeout,cancel,query,cypher.