Author: Peter Whyte

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_WORK_QUEUE is recorded by Availability Group background worker threads while they sit waiting for new work to appear in the AG work queue. AGs keep a pool of ready workers for replication tasks; a worker…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_WORK_POOL is recorded when a thread waits for access to the Availability Group work queue object, the concurrency control around AG background workers getting into position to wait for work. It sits one step before…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_TIMER_TASK is recorded around the Availability Group timer machinery: threads waiting for access to the list of AG timers, plus the deliberate waits between runs of periodic AG tasks. A task that runs every ten…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_SEEDING_LIMIT_BACKUPS is recorded during Availability Group automatic seeding operations, and its observed behaviour is long waits, thousands of seconds in reported cases, lasting for the duration of some seeding runs. The name suggests throttling around…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_NOTIFICATION_DEQUEUE is recorded by the background task that processes Windows Server Failover Clustering notifications while it waits for the next notification to arrive. Availability Groups need to hear about cluster events (node changes, resource moves,…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_LOGPROGRESS_SYNC is recorded when a thread waits for exclusive access to the structure holding the latest log-harden LSN on an Availability Group primary with a synchronous replica. That structure is the release gate for synchronous…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_LOGCAPTURE_WAIT is recorded by the Availability Group log capture thread on the primary while it waits for log records to become available to ship to secondaries. If the capture thread has already sent everything up…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability Two small Availability Group internals share this page: 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,…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability HADR_GROUP_COMMIT is recorded when transaction commit processing on an Availability Group primary waits briefly so that multiple commit records can be packed into a single log block. Group commit is an optimisation: fewer, fuller log…