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From "Stephen Yuan Jiang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-16507) Procedure v2 - Force DDL operation to always roll forward
Date Thu, 01 Sep 2016 16:00:22 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15455853#comment-15455853

Stephen Yuan Jiang commented on HBASE-16507:

I +1 in the RB.  Since this patch contains some improvement in the rollback and it is critical
for the proc-V2-based AM implementation.  I 'd like to see this patch to be done to unblock
the AM work.

However, I'd like to have additional JIRA to have DDL rollback to be re-implemented in the
future (preferably before 3.0 release - not have to be 2.0, could be 2.x)
A general comments (some from our private conversation):  

I know from technical point of view, the DDL rollback code is tricky. However, I think we
do need to provide a robust way for users to rollback hanging or transient failed DDL operation.
 We can have this patch committed and later implement a better version of DDL rollback. 

More comments:
- Direction should be trying to support robust rollback to all DDLs, instead of remove it.
DDL rollback is part of database technology forever.  I don't see any major database technology
not support rollback.  Technical difficulty apart, we should move to a direction that makes
rollback more robust; instead of disallow it - why split region has to be completed, even
with all the errors, why not allow it to rollback quick so users can start to access the region;
if a create table meets tons of issues, instead of hanging there forever or manual cleanup,
isn't "kill it and let the inconsistent state to be cleaned automatically" a logic choice?

- We have already had DDL rollbacks in HBASE, cannot just reduce functionality (a good functionality)
due to complication of procedure implementation.  

> Procedure v2 - Force DDL operation to always roll forward
> ---------------------------------------------------------
>                 Key: HBASE-16507
>                 URL: https://issues.apache.org/jira/browse/HBASE-16507
>             Project: HBase
>          Issue Type: Sub-task
>          Components: master, proc-v2
>    Affects Versions: 2.0.0
>            Reporter: Matteo Bertozzi
>            Assignee: Matteo Bertozzi
>            Priority: Minor
>             Fix For: 2.0.0
>         Attachments: HBASE-16507-v0.patch, HBASE-16507-v1.patch
> Having rollback for DDLs was a bad idea. 
> and it turns out to be an unexpected behavior for the user. 
> DDLs only have transient errors (e.g. zk, hdfs, meta down)
> if we abort/rollback on a transient failure the user will get a failure,
> and it is not clear why the user needs to retry the command when the system can do that.

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