As I understand from the documentation, it should be possible to resume a Flink job from a checkpoint just as from a savepoint by specifing the checkpoint path in the "Savepoint path" input box of the web UI (e.g. /path/to/my/checkpoint/chk-1, where "chk-1" contains the "_metadata" file).
I've been trying this out but the I get the following exception:
2020-09-04 10:35:11
java.lang.Exception: Exception while creating StreamOperatorStateContext.
at org.apache.flink.streaming.api.operators.StreamTaskStateInitializerImpl.streamOperatorStateContext(StreamTaskStateInitializerImpl.java:191)
at org.apache.flink.streaming.api.operators.AbstractStreamOperator.initializeState(AbstractStreamOperator.java:255)
at org.apache.flink.streaming.runtime.tasks.StreamTask.initializeStateAndOpen(StreamTask.java:1006)
at org.apache.flink.streaming.runtime.tasks.StreamTask.lambda$beforeInvoke$0(StreamTask.java:454)
at org.apache.flink.streaming.runtime.tasks.StreamTaskActionExecutor$SynchronizedStreamTaskActionExecutor.runThrowing(StreamTaskActionExecutor.java:94)
at org.apache.flink.streaming.runtime.tasks.StreamTask.beforeInvoke(StreamTask.java:449)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:461)
at org.apache.flink.runtime.taskmanager.Task.doRun(Task.java:707)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:532)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.flink.util.FlinkException: Could not restore keyed state backend for LegacyKeyedProcessOperator_632e4c67d1f4899514828b9c5059a9bb_(1/1) from any of the 1 provided restore options.
at org.apache.flink.streaming.api.operators.BackendRestorerProcedure.createAndRestore(BackendRestorerProcedure.java:135)
at org.apache.flink.streaming.api.operators.StreamTaskStateInitializerImpl.keyedStatedBackend(StreamTaskStateInitializerImpl.java:304)
at org.apache.flink.streaming.api.operators.StreamTaskStateInitializerImpl.streamOperatorStateContext(StreamTaskStateInitializerImpl.java:131)
... 9 more
Caused by: org.apache.flink.runtime.state.BackendBuildingException: Caught unexpected exception.
at org.apache.flink.contrib.streaming.state.RocksDBKeyedStateBackendBuilder.build(RocksDBKeyedStateBackendBuilder.java:336)
at org.apache.flink.contrib.streaming.state.RocksDBStateBackend.createKeyedStateBackend(RocksDBStateBackend.java:548)
at org.apache.flink.streaming.api.operators.StreamTaskStateInitializerImpl.lambda$keyedStatedBackend$1(StreamTaskStateInitializerImpl.java:288)
at org.apache.flink.streaming.api.operators.BackendRestorerProcedure.attemptCreateAndRestore(BackendRestorerProcedure.java:142)
at org.apache.flink.streaming.api.operators.BackendRestorerProcedure.createAndRestore(BackendRestorerProcedure.java:121)
... 11 more
Caused by: java.nio.file.NoSuchFileException: /tmp/flink-io-ee95b361-a616-4531-b402-7a21189e8ce5/job_c71cd62de3a34d90924748924e78b3f8_op_LegacyKeyedProcessOperator_632e4c67d1f4899514828b9c5059a9bb__1_1__uuid_ae7dd096-f52f-4eab-a2a3-acbfe2bc4573/336ed2fe-30a4-44b5-a419-9e485cd456a4/CURRENT
at sun.nio.fs.UnixException.translateToIOException(UnixException.java:86)
at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:102)
at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:107)
at sun.nio.fs.UnixCopyFile.copy(UnixCopyFile.java:526)
at sun.nio.fs.UnixFileSystemProvider.copy(UnixFileSystemProvider.java:253)
at java.nio.file.Files.copy(Files.java:1274)
at org.apache.flink.contrib.streaming.state.restore.RocksDBIncrementalRestoreOperation.restoreInstanceDirectoryFromPath(RocksDBIncrementalRestoreOperation.java:483)
at org.apache.flink.contrib.streaming.state.restore.RocksDBIncrementalRestoreOperation.restoreFromLocalState(RocksDBIncrementalRestoreOperation.java:218)
at org.apache.flink.contrib.streaming.state.restore.RocksDBIncrementalRestoreOperation.restoreFromRemoteState(RocksDBIncrementalRestoreOperation.java:194)
at org.apache.flink.contrib.streaming.state.restore.RocksDBIncrementalRestoreOperation.restoreWithoutRescaling(RocksDBIncrementalRestoreOperation.java:168)
at org.apache.flink.contrib.streaming.state.restore.RocksDBIncrementalRestoreOperation.restore(RocksDBIncrementalRestoreOperation.java:154)
at org.apache.flink.contrib.streaming.state.RocksDBKeyedStateBackendBuilder.build(RocksDBKeyedStateBackendBuilder.java:279)
... 15 more
Anyone has an idea of what's causing this?
UPDATE: After some tests, I noticed that this behavior depends on the state backend used. In this case I'm using RocksDBStateBackend with incremental checkpointing enabled. When I switched to FsStateBackend, the error disappeared.
Come to think of it, that would make sense since, from what I understand, checkpoints taken with incremental checkpointing enabled only record the changes compared to the previous completed checkpoint instead of the full job state, so it would not be possible to restore the job from this kind of checkpoint.
If that's correct, I think it would be useful to add a notice on the documentation (https://ci.apache.org/projects/flink/flink-docs-stable/ops/state/checkpoints.html#resuming-from-a-retained-checkpoint)
