Two small Availability Group internals share this page:
HADR_ARCONTROLLER_NOTIFICATIONS_SUBSCRIBER_LIST: a thread waiting for exclusive access to the list of availability replica event subscribers, taken when replica events (state changes, configuration changes) are published to their internal listeners.HADR_FILESTREAM_IOMGR: a thread waiting on the reader-writer lock protecting the FILESTREAM AG I/O manager during its startup or shutdown.
Both are single-purpose locks around infrequent events.
Are They a Problem?
No; neither has been a contention point. The subscriber-list lock is touched when replica events fire, which is occasional by nature; the FILESTREAM I/O manager lock is touched at its start and stop, rarer still. Their totals stay negligible on any AG estate.
They are documented so lookups land somewhere: seeing either name means AG event plumbing or FILESTREAM transport lifecycle did something, and that is the whole story.
What To Do
- Filter both with the AG background set.
- AG health continues to live in the replica-state DMVs and the actionable waits (
HADR_SYNC_COMMIT, flow control, redo).
How To See It
Rank waits with Get-WaitStatistics; expect traces around AG state changes only.
Part of the SQL Server Wait Types Library.
Related deep dive: HADR_SYNC_COMMIT Wait Type.
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