For WFLY-259 when a slave connects to the DC to pull down missing data, it does this by either getting a lock for the DC, or by joining the permit of the existing DC lock if the request to update a slave's server-config was executed as part of a composite obtaining a lock on the DC.

The way it works at present there is a thread per slave which is blocked until the transaction completes. The DC threads are a finite resource, so a large number of slaves trying to pull down dats will cause deadlock