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https://issues.apache.org/jira/browse/ZOOKEEPER-3306?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andor Molnar resolved ZOOKEEPER-3306.
-------------------------------------
Resolution: Fixed
Fix Version/s: 3.6.0
Issue resolved by pull request 848
[https://github.com/apache/zookeeper/pull/848]
> Node may not accessible due the the inconsistent ACL reference map after SNAP
> sync
> -----------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3306
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3306
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.5.4, 3.6.0, 3.4.13
> Reporter: Fangmin Lv
> Assignee: Fangmin Lv
> Priority: Critical
> Labels: pull-request-available
> Fix For: 3.6.0
>
> Time Spent: 1h
> Remaining Estimate: 0h
>
> This is a new bug we found on production.
> ZooKeeper uses ACL reference id and count to save the space in snapshot.
> During fuzzy snapshot sync, the reference count may not be updated correctly
> in case like the znode is already exist.
> When ACL reference count reaches 0, it will be deleted from the system, but
> actually there might be other nodes still using it. And when visiting a node
> with the deleted ACL id, it will be rejected because it doesn't exist anymore.
> Here is the detailed flow for one of the scenario here:
> # Server A starts to have snap sync with leader
> # After serializing the ACL map to Server A, there is a txn T1 to create a
> node N1 with new ACL_1 which was not exist in ACL map
> # On leader, after this txn, the ACL map will be ID1 -> (ACL_1, COUNT: 1),
> and data tree N1 -> ID1
> # On server A, it will be empty ACL map, and N1 -> ID1 in fuzzy snapshot
> # When replaying the txn T1, it will skip at the beginning since the node is
> already exist, which leaves an empty ACL map, and N1 is referencing to a
> non-exist ACL ID1
> # Node N1 will be not accessible because the ACL not exist, and if it became
> leader later then all the write requests will be rejected as well with
> marshalling error.
> We're still working on the fix, suggestions are welcome.
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