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https://issues.apache.org/jira/browse/HDDS-16954?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated HDDS-16954:
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Labels: pull-request-available (was: )
> SnapshotChainManager iterator throws NoSuchElementException when a snapshot
> is purged during iteration
> ------------------------------------------------------------------------------------------------------
>
> Key: HDDS-16954
> URL: https://issues.apache.org/jira/browse/HDDS-16954
> Project: Apache Ozone
> Issue Type: Bug
> Components: Ozone Manager
> Reporter: Siyao Meng
> Assignee: Siyao Meng
> Priority: Major
> Labels: pull-request-available
>
> {{SnapshotChainManager#iterator(boolean)}} is not safe against a concurrent
> snapshot purge. {{hasNext()}} and {{next()}} read {{currentSnapshotId}} and
> then call {{hasPreviousGlobalSnapshot}} / {{previousGlobalSnapshot}} (or the
> next variants), which throw {{NoSuchElementException}} if the snapshot was
> removed from the chain in between. The iterator does not hold the chain lock
> across iterations, so callers such as {{DirectoryDeletingService#getTasks}},
> {{KeyDeletingService#getTasks}}, {{SnapshotDeletingService}} and
> {{SnapshotDefragService}} can hit this when a snapshot purge runs
> concurrently.
> {code}
> ERROR om.SnapshotChainManager
> (SnapshotChainManager.java:hasPreviousGlobalSnapshot(516)) - No snapshot
> found in snapshot chain for provided snapshotId: b0ef2d42-...
> {code}
> HDDS-16949 stops a {{getTasks()}} failure from cancelling the background
> service schedule, but each affected service still loses a whole cycle (the
> AOS task and every snapshot task) when the race hits.
> h3. Fix
> Make the iterator race safe, for example by taking a consistent snapshot of
> the chain order under the chain lock when the iterator is created, or by
> ending the walk gracefully when the current snapshot has been removed. Add a
> unit test that purges a snapshot while iterating.
> - Found in
> https://github.com/apache/ozone/actions/runs/38252733251/job/114829762795
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