[[_clustering_db_lock]]
=== Serialized Cluster Startup

Note that {{book.project.name}} supports concurrent startup by more cluster nodes at the same.
When {{book.project.name}} boots up it may do some database migration, importing, or first time initializations.  The server
makes use of a DB lock which prevents these startup actions from running and conflicting with eachother when nodes are
booted concurrently.

By default, the maximum timeout for lock is 900 seconds, so in case that second node is not able to acquire the lock within 900 seconds, it fails to start.
The lock checking is done 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
    }
}
----
or similarly if you're using Mongo (just by replace `jpa` with `mongo`)