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https://issues.apache.org/jira/browse/HBASE-16507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15455992#comment-15455992
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Matteo Bertozzi commented on HBASE-16507:
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The all point of the proc-v2 work is to remove conflict situation via a single
writer/coordinator.
In this ddl case the rollback is not really removed for technical difficulties.
Aside from the fact that some implementation like enable/disable/modify are
wrong and end up causing possible corruptions. The point here is that DDLs are
operations that will always be able to complete. There may be transient failure
along the way (e.g zk/hdfa/meta hiccups) but as soon those are resolved and the
master is fully operational again the operation will be able to complete.
At the moment we rollback on transient failures which will result in users
being confused about why the operation failed and a simple retry will succeed.
Ending up in support calls and request about why the system can't handle it
since it was just a transient failure.
The RS puts behaves with a roll forward approach like we have in this patch.
Once the operation is written to the wal we know that the operation will
complete (at some point) no matter how many transient failure we will get.
Rollback as in traditional database are triggered by situation where the
operation is stuck due to conflicts and it will never be able to complete. In
this case our DDLs will always be able to complete.
The only case that rollback can be applied to DDLs here is when the user
request an abort of the operation. But DDLs are too short in duration to have
the user be able to abort them when started. Note that in the patch attached
the user is able to rollback the DDLs operation up to the first prepare step.
Which is the most likely case where you want to abort. E.g. Your operation is
stuck behind another operation that is making slow progress and you decide to
abort it.
long operation like assignment, snapshot/backups will have rollback support.
because they are long and because for "technical difficulties" may end up stuck
in conflicts.
> 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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