The wait type HADR_DBR_SUBSCRIBER is ranked #210 by Stedman Solutions and Database Health Monitor. Wait statistics, in the context of SQL Server, refer to the amount of time that a query spends waiting to access data in the database. When a client application requests data from the database, the request is placed in a queue and the client application must wait for its turn to access the data. The time that the query spends waiting is called a "wait" and is tracked by SQL Server. This information can be used to identify potential performance bottlenecks and optimize the performance of the database. Wait statistics are commonly used by database administrators to diagnose and troubleshoot performance issues in SQL Server.
In SQL Server, wait types provide crucial insights into the performance and health of your environment. One such wait type, HADR_DBR_SUBSCRIBER, is specific to Always On Availability Groups. It occurs when a secondary replica is waiting for the data it needs to apply transaction log records sent by the primary replica. In this blog post, well explain what the HADR_DBR_SUBSCRIBER wait type means, when it occurs, and how you can address it to maintain optimal performance. What Is the HADR_DBR_SUBSCRIBER Wait Type?The HADR_DBR_SUBSCRIBER wait type appears when a secondary replica is waiting for transaction log records to be sent from the primary replica. These logs are used by the secondary replica to stay synchronized with the primary database. During this wait, the secondary replica cannot apply changes until it receives the required log records. This wait type typically indicates that the secondary replica is ready to process logs but is being delayed by the log shipping process, network latency, or primary replica performance. When Does HADR_DBR_SUBSCRIBER Appear?This wait type is common in the following scenarios:
While some HADR_DBR_SUBSCRIBER waits are normal in Always On environments, frequent or prolonged waits may indicate performance issues that require attention. Why HADR_DBR_SUBSCRIBER Waits MatterExcessive or prolonged HADR_DBR_SUBSCRIBER waits can lead to increased latency between the primary and secondary replicas. This can delay failovers, reduce data availability, and negatively impact applications that rely on read-only access to the secondary replica. Common causes of these waits include:
How to Address HADR_DBR_SUBSCRIBER WaitsIf HADR_DBR_SUBSCRIBER waits are impacting performance, consider these strategies to address the issue:
Monitoring HADR_DBR_SUBSCRIBER WaitsTo monitor HADR_DBR_SUBSCRIBER waits, use SQL Servers ConclusionThe HADR_DBR_SUBSCRIBER wait type in SQL Server occurs when a secondary replica is waiting for transaction log records from the primary replica. While these waits are expected in Always On environments, excessive waits may indicate issues with network performance, resource availability, or workload optimization. By addressing these factors, you can reduce HADR_DBR_SUBSCRIBER waits and maintain efficient synchronization between replicas. If you need expert help with Always On Availability Groups, SQL Server performance tuning, or resolving wait types, Stedman Solutions offers managed services to help you achieve optimal performance and reliability in your SQL Server environment.
Applies toRelated WaitsHADR_AG_MUTEXHADR_AR_CRITICAL_SECTION_ENTRY HADR_AR_MANAGER_MUTEX HADR_AR_UNLOAD_COMPLETED HADR_ARCONTROLLER_NOTIFICATIONS_SUBSCRIBER_LIST HADR_BACKUP_BULK_LOCK HADR_BACKUP_QUEUE HADR_CLUSAPI_CALL HADR_COMPRESSED_CACHE_SYNC HADR_CONNECTIVITY_INFO HADR_DATABASE_FLOW_CONTROL HADR_DATABASE_VERSIONING_STATE HADR_DATABASE_WAIT_FOR_RESTART HADR_DATABASE_WAIT_FOR_TRANSITION_TO_VERSIONING HADR_DB_COMMAND HADR_DB_OP_COMPLETION_SYNC HADR_DB_OP_START_SYNC HADR_DBR_SUBSCRIBER_FILTER_LIST HADR_DBSEEDING HADR_DBSEEDING_LIST HADR_DBSTATECHANGE_SYNC HADR_FABRIC_CALLBACK HADR_FILESTREAM_BLOCK_FLUSH HADR_FILESTREAM_FILE_CLOSE HADR_FILESTREAM_FILE_REQUEST HADR_FILESTREAM_IOMGR HADR_FILESTREAM_MANAGER HADR_GROUP_COMMIT HADR_LOGCAPTURE_SYNC HADR_LOGCAPTURE_WAIT HADR_LOGPROGRESS_SYNC HADR_NOTIFICATION_DEQUEUE HADR_NOTIFICATION_WORKER_EXCLUSIVE_ACCESS HADR_NOTIFICATION_WORKER_STARTUP_SYNC HADR_NOTIFICATION_WORKER_TERMINATION_SYNC HADR_PARTNER_SYNC HADR_READ_ALL_NETWORKS HADR_RECOVERY_WAIT_FOR_CONNECTION HADR_RECOVERY_WAIT_FOR_UNDO HADR_REPLICAINFO_SYNC HADR_SYNC_COMMIT HADR_SYNCHRONIZING_THROTTLE HADR_TDS_LISTENER_SYNC HADR_TDS_LISTENER_SYNC_PROCESSING HADR_TIMER_TASK HADR_TRANSPORT_DBRLIST HADR_TRANSPORT_FLOW_CONTROL HADR_TRANSPORT_SESSION HADR_WORK_POOL HADR_WORK_QUEUE HADR_XRF_STACK_ACCESS See AlsoAll Wait Types |