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https://issues.apache.org/jira/browse/HBASE-19543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16443604#comment-16443604
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Duo Zhang commented on HBASE-19543:
-----------------------------------

After abstracting the ReplicationQueueStorage interface, the assumption is that 
the upper layer should not know anything about the details of the storage, for 
example, we are going to implement a new table based ReplicationQueueStorage, 
then there will be no znode. Then it is not necessary to create the 
'/hbase/replication/rs' znode, it will be created automatically when we want to 
store a wal file into a queue.

Is this behavior break something?

> Abstract a replication storage interface to extract the zk specific code
> ------------------------------------------------------------------------
>
>                 Key: HBASE-19543
>                 URL: https://issues.apache.org/jira/browse/HBASE-19543
>             Project: HBase
>          Issue Type: Sub-task
>          Components: proc-v2, Replication
>            Reporter: Duo Zhang
>            Assignee: Duo Zhang
>            Priority: Major
>             Fix For: 3.0.0, 2.1.0
>
>         Attachments: HBASE-19543-HBASE-19397-v1.patch, 
> HBASE-19543-HBASE-19397-v2.patch, HBASE-19543-HBASE-19397-v3.patch, 
> HBASE-19543-HBASE-19397.patch, HBASE-19543-HBASE-19397.patch
>
>
> For now, we will do sanity checks at the same time when updating replication 
> peer. But this is not a safe way for procedure based replication peer 
> modification.
> For the old zk watcher way, the only thing is updating the data on zk, so if 
> the data is updated and then we crashes, there is no problem.
> For the new procedure way, we need to trigger refresh by ourselves after 
> updating zk. If we crashes after the updating and before we record the state 
> change of the procedure, we may fail with IllegalArgumentException when we 
> execute the procedure next time since the data on zk has already been updated.
> So the current way is to do sanity checks in PRE_PEER_MODIFICATION state, and 
> in UPDATE_STORAGE state we will not do sanity checks any more, just 
> update(overwrite) the peer storage.



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