public interface StateObject extends Serializable
State Objects are transported via RPC between JobManager and
TaskManager and must be
serializable to support that.
Some State Objects are stored in the checkpoint/savepoint metadata. For long-term
compatibility, they are not stored via
but through custom serializers.
void discardState() throws Exception
The values produced by this method are only used for informational purposes and for metrics/monitoring. If this method returns wrong values, the checkpoints and recovery will still behave correctly. However, efficiency may be impacted (wrong space pre-allocation) and functionality that depends on metrics (like monitoring) will be impacted.
Note for implementors: This method should not perform any I/O operations
while obtaining the state size (hence it does not declare throwing an
Instead, the state size should be stored in the state object, or should be computable from
the state stored in this object.
The reason is that this method is called frequently by several parts of the checkpointing
and issuing I/O requests from this method accumulates a heavy I/O load on the storage
system at higher scale.
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