[jira] [Updated] (HDDS-11721) Container export may fail for Schema v2 container while it is being scanned

["Attila Doroszlai (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDDS-11721?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Attila Doroszlai updated HDDS-11721:
------------------------------------
    Status: Open  (was: Patch Available)

> Container export may fail for Schema v2 container while it is being scanned
> ---------------------------------------------------------------------------
>
>                 Key: HDDS-11721
>                 URL: https://issues.apache.org/jira/browse/HDDS-11721
>             Project: Apache Ozone
>          Issue Type: Sub-task
>          Components: Ozone Datanode
>            Reporter: Ethan Rose
>            Assignee: Rishabh Patel
>            Priority: Major
>              Labels: pull-request-available
>
> For container schema versions older than v3, there is a DB handle cache that uses reference counting to handle cache eviction. The container scanner is holding a reference to the DB as it is scanning the blocks while the container is being exported. The scanner operates without a lock which is expected since it is a slow, read-only background process. However, the export code makes an assumption that every caller who has allocated a schema v2 DB reference has done so under a container lock, and it will block until the other thread has released the lock, meaning that once it tries to free the DB, it knows there are no other references. In this case the scanner has a reference but no lock, so export obtains the write lock and attempts to evict the DB from the cache, but it fails due to the scanner's reference.
> This is incorrect because export should be a read-only operation. It is a copy, not a move, so it should not be evicting from the cache. We should remove the cache eviction step, and probably convert the write lock it takes to at least a read lock.



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