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https://issues.apache.org/jira/browse/HDDS-8420?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17955370#comment-17955370
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Ivan Andika commented on HDDS-8420:
-----------------------------------

[~peterxcli] Thanks for checking this out. IMO it should be ok to close this 
since follower might still use SnapshotCache for other reasons, but I think we 
can ask people who know more about Snapshot feature  [~smeng][~hemantk] 
[~swamirishi]

> [Snapshot] Optionally purge SnapshotCache on OM (ex)leader when it 
> transitions to a follower
> --------------------------------------------------------------------------------------------
>
>                 Key: HDDS-8420
>                 URL: https://issues.apache.org/jira/browse/HDDS-8420
>             Project: Apache Ozone
>          Issue Type: Sub-task
>            Reporter: Siyao Meng
>            Assignee: Chu Cheng Li
>            Priority: Minor
>
> SnapshotCache can be cleaned up when OM leader transitions to a follower. But 
> not by simply calling {{snapshotCache.invalidateAll()}}.
> Cache entries with zero refCount can be safely invalidated. However, it could 
> happen that some instances are still in-use by:
> 1. running SnapshotDiff jobs that is not finished during leader to follower 
> transition -- those jobs need to be cancelled/aborted
> 2. any unfinished client read or write requests against snapshots issued 
> before the leader OM to follower OM transition
> 3. new Ratis requests reading or writing to snapshot DB, including 
> {{OMSnapshotMoveDeletedKeysRequest}}



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