Aljoscha Krettek created FLINK-6353:
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Summary: Restoring using CheckpointedRestoring does not work from
1.2 to 1.2
Key: FLINK-6353
URL: https://issues.apache.org/jira/browse/FLINK-6353
Project: Flink
Issue Type: Bug
Components: DataStream API, State Backends, Checkpointing
Affects Versions: 1.2.0, 1.2.1
Reporter: Aljoscha Krettek
Assignee: Aljoscha Krettek
State that was checkpointed using {{Checkpointed}} (on a user function) cannot
be restored using {{CheckpointedRestoring}} when the savepoint was done on
Flink 1.2. The reason is an overzealous check in {{AbstractUdfStreamOperator}}
that only restores from "legacy" operator state using {{CheckpointedRestoring}}
when the stream is a {{Migration}} stream.
We can remove that check but still need to make sure to read away the byte that
indicates whether there is legacy state, which is written when we're restoring
from a Flink 1.1 savepoint.
Also, if we remove the check, the procedure for a user to migrate a user
function away from the {{Checkpointed}} interface is this:
# Perform savepoint with user function still implementing {{Checkpointed}},
shutdown job
# Change user function to implement {{CheckpointedRestoring}}
# Restore from previous savepoint, user function has to somehow move the state
that is restored using {{CheckpointedRestoring}} to another type of state, .e.g
operator state, using the {{OperatorStateStore}}.
# Perform another savepoint, shutdown job
# Remove {{CheckpointedRestoring}} interface from user function
# Restore from the second savepoint
# Done.
If the {{CheckpointedRestoring}} interface is not removed as prescribed in the
last steps then a future restore of a new savepoint will fail because Flink
will try to read legacy operator state that is not there anymore.
The above steps also apply to Flink 1.3, when a user want's to move away from
the {{Checkpointed}} interface.
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