[jira] [Commented] (HDFS-13608) [Edit Tail Fast Path Pt 2] Add ability for JournalNode to serve edits via RPC

["Chen Liang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-13608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16504065#comment-16504065 ] 

Chen Liang commented on HDFS-13608:
-----------------------------------

Thanks [~xkrogen] for the patch, looks good to me overall, a couple minor comments:

 1. Looks like {{maxTxns}}, unlike nameservice ID, is always set and got picked up, and since Journal#getJournalEdits always takes maxTxns, I wonder if it makes sense to make this {{required}}. If it should be optional, probably we should check {{hasMaxTxns}} in getJournaledEdits for better readability and so that the value does't rely on protobuf setting a default value.
 2. {{getJournaledEdits}} requires cache not null, which requires {{DFS_HA_TAILEDITS_INPROGRESS_KEY}} to be set. I feel that this information should be present somehow, e.g. in the javadoc of {{getJournaledEdits}}, or even rename this method to indicate the dependency on tail edits be enabled.
3. Having another random thought: Since this is under the context of SbN read, I wonder will we have multiple observers calling into {{getJournaledEdits}} of same node at the same time? If so, do we need any additional protection?

> [Edit Tail Fast Path Pt 2] Add ability for JournalNode to serve edits via RPC
> -----------------------------------------------------------------------------
>
>                 Key: HDFS-13608
>                 URL: https://issues.apache.org/jira/browse/HDFS-13608
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Erik Krogen
>            Assignee: Erik Krogen
>            Priority: Major
>         Attachments: HDFS-13608-HDFS-12943.000.patch, HDFS-13608-HDFS-12943.001.patch
>
>
> See HDFS-13150 for full design.
> This JIRA is to make the JournalNode-side changes necessary to support serving edits via RPC. This includes interacting with the cache added in HDFS-13607.



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