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https://issues.apache.org/jira/browse/HDFS-13688?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16554874#comment-16554874
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Chen Liang commented on HDFS-13688:
-----------------------------------
Had an offline discussion with [~shv], updated v003 patch. Some notes/updates
here:
1. decided to break the msync implementation into two parts: client side and
server side. This JIRA is specifically addressing only the client side by
introducing msync API to {{ClientProtocol}}. The server side is completely
missing. This is also the reason why I did not include unit test in v003 patch.
As no meaningful test can actually be done as for now, will follow up with
tests in next part. Please let me know if tests here are still preferred.
2. msync should not take {{syncTxid}} as a parameter, because it is already
being passed around via {{AlignmentContext}}. Removing syncTxid significantly
simplified client, as compared to v002 patch.
3. In addition to having a explicit msync API call, msync should also by
default be implicitly done for every single call to Observer in order to
maintain consistency. Using deferred response can still achieve this, but it
would mean using deferred response for every single read API call. Which is not
ideal. An alternative way would be leveraging callQueue so that if server
hasn't caught up with client id, the call stays in the queue. The next JIRA
will be implementing this approach.
> Introduce msync API call
> ------------------------
>
> Key: HDFS-13688
> URL: https://issues.apache.org/jira/browse/HDFS-13688
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Chen Liang
> Assignee: Chen Liang
> Priority: Major
> Attachments: HDFS-13688-HDFS-12943.001.patch,
> HDFS-13688-HDFS-12943.002.patch, HDFS-13688-HDFS-12943.002.patch,
> HDFS-13688-HDFS-12943.003.patch, HDFS-13688-HDFS-12943.WIP.002.patch,
> HDFS-13688-HDFS-12943.WIP.patch
>
>
> As mentioned in the design doc in HDFS-12943, to ensure consistent read, we
> need to introduce an RPC call {{msync}}. Specifically, client can issue a
> msync call to Observer node along with a transactionID. The msync will only
> return when the Observer's transactionID has caught up to the given ID. This
> JIRA is to add this API.
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