[jira] [Commented] (HDDS-12247) WaitForApply on data writes for ratis keys

["Ivan Andika (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDDS-12247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17985231#comment-17985231 ] 

Ivan Andika commented on HDDS-12247:
------------------------------------

The current purpose is to ensure that when the PutBlock returns to the client, the chunks are written persistently (applied) in the disk in all 2 / 3 datanodes. Currently, we use ALL_COMMITTED and MAJORITY_COMMITTED when, which means that the only guarantee is that the chunks are only written on the DN leader since the followers might have committed the logs (i.e. promise to apply the commits and write the chunks sometimes in the future), but haven't applied it. Additionally, due to the Raft group remove mechanism, those committed logs might not be applied in some cases (e.g. disk is full, pipeline is closed, etc). Therefore, we can sometimes see that only 1 or 2 replicas of the chunks / blocks are created (e.g. Container 1 has blockCommitSequenceId 10 in DN leader, but blockCommitSequenceId 8 in other DNs). If the DN leader (with the most up-to-date data) is down, client that tries to read the chunk written after blockCommitSequenceId 8 will throw UNKNOWN_BCSID or BCSID_MISMATCH). 

However, this will increase the write latency considerably, so might not be desirable.

> WaitForApply on data writes for ratis keys
> ------------------------------------------
>
>                 Key: HDDS-12247
>                 URL: https://issues.apache.org/jira/browse/HDDS-12247
>             Project: Apache Ozone
>          Issue Type: Sub-task
>          Components: Ozone Datanode
>            Reporter: Swaminathan Balachandran
>            Priority: Major
>
> In order to ensure the data is completely written to at least majority of the nodes/all the nodes, a waitForApply where the ratis leader can optionally wait for the followers to apply the transaction and just not commit the transaction to raft log. This would mean that the applyIndex would have to be shared in the raft protocol



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