UCS_SESSION_REGISTRATION is recorded when a thread waits for access to the list of Service Broker sessions so it can add or remove one. The Unified Communications Stack (UCS) underlies Broker’s connection handling, and session registration passes through this small lock.
Broker connection lifecycle bookkeeping, in a word.
Is It a Problem?
No; it has not been a contention point, and even Broker-heavy environments see only traces, since session registration happens at connection establishment and teardown rather than per message.
Broker connection problems worth investigating show up as transmission queue errors and endpoint connectivity failures in the error log, several layers above this registration lock.
Common Causes
- Service Broker network sessions being established or torn down.
What To Do
- Filter it out of wait analysis.
- Route Broker connectivity questions through
sys.transmission_queuestatus text and endpoint configuration.
How To See It
Rank waits with Get-WaitStatistics; expect near-zero everywhere.
Part of the SQL Server Wait Types Library.
Related deep dive: SOS_SCHEDULER_YIELD Wait Type.
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