How does AlwaysOn synchronization work in asynchronous mode?
If all secondary replicas are in an asynchronous availability mode, the success of this step is good enough to send an acknowledge message of a successful commit back to the application when the I/O to the local transaction log is successfully executed. The log blocks in the log pool are read by a thread called log capture.
How does AlwaysOn work in SQL Server 2012?
Independent on the Availability Mode being synchronous or asynchronous, AlwaysOn will add network load to the involved systems and infrastructure. As AlwaysOn works, the moment the transaction log buffer in the primary replica is flushed and persisted the same content needs to be moved to the replicas.
What does it mean to be in synchronous commit Availability mode?
Synchronous-Commit Availability Mode. Under synchronous-commit availability mode (synchronous-commit mode), after being joined to an availability group, a secondary database catches up to the corresponding primary database and enters the SYNCHRONIZED state.
How does the secondary replica work in AlwaysOn?
Primary replica is generating transaction log blocks. The secondary replica establishes a valid connection to the primary replica using the configured mirroring endpoints. The secondary initiates a request to the primary, asking for the log blocks to be shipped.
What happens in asynchronous commit Availability mode?
If the current primary is configured for asynchronous commit availability mode, it will commit transactions asynchronously for all secondary replicas regardless of their individual availability mode settings. For more information, see Asynchronous-Commit Availability Mode, later in this topic.
What happens to a secondary database in asynchronous commit?
Under asynchronous-commit mode, the secondary replica never becomes synchronized with the primary replica. Though a given secondary database might catch up to the corresponding primary database, any secondary database could lag behind at any point.
When to use asynchronous-commit mode in SQL Server?
Asynchronous-commit mode is a disaster-recovery solution that works well when the availability replicas are distributed over considerable distances. If every secondary replica is running under asynchronous-commit mode, the primary replica does not wait for any of the secondary replicas to harden the log.