[[_clustering_db_lock]]
=== Serialized Cluster Startup

{{book.project.name}} cluster nodes are allowed to boot concurrenty.
When {{book.project.name}} server instance boots up it may do some database migration, importing, or first time initializations.
A DB lock is used to prevent start actions from conflicting ith one another when cluster nodes boot up concurrently.

By default, the maximum timeout for this lock is 900 seconds.  If a node is waiting on this lock for more than the timeout
it will fail to boot.  This lock is checked every 2 seconds by default.
Typically you won't need to increase/decrease the default value, but just in case it's possible to configure it in `keycloak-server.json`:

[source,json]
----
"dblock": {
    "jpa": {
        "lockWaitTimeout": 900,
        "lockRecheckTime": 2
    }
}
----

{% if book.community %}
If you are using Mongo DB replace `jpa` with `mongo`.
{% endif %}