Continue-As-New is a mechanism by which the latest relevant state is passed to a new Workflow Execution, with a fresh Event History.
As a precautionary measure, the Temporal Platform limits Event History to 50,000 Events, and will warn you every 10,000 Events. To prevent a Workflow Execution Event History from exceeding this limit and failing, use Continue-As-New to start a new Workflow Execution with a fresh Event History.
All values passed to a Workflow Execution through parameters or returned through a result value are recorded into the Event History. A Temporal Cluster stores the full Event History of a Workflow Execution for the duration of a Namespace's retention period. A Workflow Execution that periodically executes a large number of Activities has the potential of hitting the size limit.
A very large Event History can adversely affect the performance of a Workflow Execution. For example, in the case of a Workflow Worker failure, the full Event History must be pulled from the Temporal Cluster and given to another Worker via a Workflow Task. If the Event history is very large, it may take some time to load it.
The Continue-As-New feature enables developers to complete the current Workflow Execution and start a new one atomically.
The new Workflow Execution has the same Workflow Id, but a different Run Id, and has its own Event History.
In the case of Temporal Cron Jobs, Continue-As-New is actually used internally for the same effect.