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Yun Tang commented on FLINK-24852: ---------------------------------- I think the suggestion to use the "previous+1" checkpoint id should be oaky for changelog case to avoid unexpected deletion. I think cleaning folders with different job id is very risky. We ever create another standalone tool outside the Flink itself, which would analysis the {{_metadata}} and delete files not in the {{_metadata}} and older than the timestamp created by the last successful checkpoint. It might not be wise for a community to offer such a tool as different DFS might not obey the rule that still-in-use files having larger timestamp than last complete checkpoint due to unexpected reason. Moreover, we could also face the case that a larger checkpoint-id {{_metadata}} with older timestamp (maybe caused by the fixed job id with different runs), which would make the cleaning logic very complex and easy to delete files by mistake. > Cleanup of Orphaned Incremental State Artifacts > ----------------------------------------------- > > Key: FLINK-24852 > URL: https://issues.apache.org/jira/browse/FLINK-24852 > Project: Flink > Issue Type: Improvement > Components: Runtime / State Backends > Affects Versions: 1.14.0 > Reporter: Stephan Ewen > Priority: Major > > Shared State Artifacts (state files in the "shared" folder in the DFS / > ObjectStore) can become orphaned in various situations: > * When a TaskManager fails right after it created a state file but before the > checkpoint was ack-ed to the JobManager, that state file will be orphaned. > * When the JobManager fails all state newly added for the currently pending > checkpoint will be orphaned. > These state artifacts are currently impossible to be cleaned up manually, > because it isn't easily possible to understand whether they are still being > used (referenced by any checkpoint). > We should introduce a "garbage collector" that identifies and deletes such > orphaned state artifacts. > h2. Idea for a cleanup mechanism > A periodic cleanup thread would periodically execute a cleanup procedure that > searches for and deletes the orphaned artifacts. > To identify those artifacts, the cleanup procedure needs the following inputs: > * The oldest retained checkpoint ID > * A snapshot of the shared state registry > * A way to identify for each state artifact from which checkpoint it was > created. > The cleanup procedure would > * enumerate all state artifacts (for example files in the "shared" directory) > * For each one check whether it was created earlier than the oldest retained > checkpoint. If not, that artifact would be skipped, because it might come > from a later pending checkpoint, or later canceled checkpoint. > * Finally, the procedure checks if the state artifact is known by the shared > state registry. If yes, the artifact is kept, if not, it is orphaned and will > be deleted. > Because the cleanup procedure is specific to the checkpoint storage, it > should probably be instantiated from the checkpoint storage. > To make it possible to identify the checkpoint for which a state artifact was > created, we can put that checkpoint ID into the state file name, for example > format the state name as {{"<checkpointID>_<UUID>"}}. -- This message was sent by Atlassian Jira (v8.20.1#820001)