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 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 Java Serialization
,
but through custom serializers.
Modifier and Type | Method and Description |
---|---|
void |
discardState()
Discards the state referred to and solemnly owned by this handle, to free up resources in
the persistent storage.
|
long |
getStateSize()
Returns the size of the state in bytes.
|
void discardState() throws Exception
Exception
long getStateSize()
0
.
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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