public interface StateObject extends Serializable
State objects define how to
discard state and how to access the
size of the state.
State Objects are transported via RPC between JobManager and TaskManager and
serializable to support that.
Some State Objects are stored in the checkpoint/savepoint metadata. For long-term
compatibility, they are not stored via
Java Serialization, but
through custom serializers.
|Modifier and Type||Method and Description|
Discards the state referred to and solemnly owned by this handle, to free up resources in the persistent storage.
Returns the size of the state in bytes.
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
IOException). 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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