[jira] [Commented] (HBASE-14790) Implement a new DFSOutputStream for logging WAL only

["Duo Zhang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-14790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15111963#comment-15111963 ] 

Duo Zhang commented on HBASE-14790:
-----------------------------------

https://github.com/Apache9/hbase/blob/HBASE-14790/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AsyncFSHLog.java

Could pass a simple {{TestLogRolling}} now.

Next I will try to make it more robust and use it to run some large test.

Thanks.

> Implement a new DFSOutputStream for logging WAL only
> ----------------------------------------------------
>
>                 Key: HBASE-14790
>                 URL: https://issues.apache.org/jira/browse/HBASE-14790
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Duo Zhang
>
> The original {{DFSOutputStream}} is very powerful and aims to serve all purposes. But in fact, we do not need most of the features if we only want to log WAL. For example, we do not need pipeline recovery since we could just close the old logger and open a new one. And also, we do not need to write multiple blocks since we could also open a new logger if the old file is too large.
> And the most important thing is that, it is hard to handle all the corner cases to avoid data loss or data inconsistency(such as HBASE-14004) when using original DFSOutputStream due to its complicated logic. And the complicated logic also force us to use some magical tricks to increase performance. For example, we need to use multiple threads to call {{hflush}} when logging, and now we use 5 threads. But why 5 not 10 or 100?
> So here, I propose we should implement our own {{DFSOutputStream}} when logging WAL. For correctness, and also for performance.



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