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From "Blake Eggleston (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12888) Incremental repairs broken for MVs and CDC
Date Wed, 17 May 2017 00:40:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16013313#comment-16013313
] 

Blake Eggleston commented on CASSANDRA-12888:
---------------------------------------------

+1 on the design doc, or at least a comment thoroughly explaining the approach, since this
seems to be a bit different from what was discussed above. Paulo, you're correct about #9143,
we're going to need to preserve the pendingRepair value as well.

At a high level though, I think the patch, and some of the solutions discussed, are approaching
the problem from the wrong direction. Having to bend and repurpose storage system components
like this to make streaming and repair work properly, to me, indicates there’s a problem
in the MV implementation. Specifically, we shouldn't have to rewrite data that was just streamed.
I think it would be better to focus on fixing those problems, instead of adding complexity
to the storage layer to work around them. The contents of Mutations and UnfilteredRowIterators
are pretty similar, decoupling the MV code from the write path should make it possible to
apply the MV logic to sstable data without having to run it through the entire write path.

> Incremental repairs broken for MVs and CDC
> ------------------------------------------
>
>                 Key: CASSANDRA-12888
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12888
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Streaming and Messaging
>            Reporter: Stefan Podkowinski
>            Assignee: Benjamin Roth
>             Fix For: 3.0.x, 3.11.x
>
>
> SSTables streamed during the repair process will first be written locally and afterwards
either simply added to the pool of existing sstables or, in case of existing MVs or active
CDC, replayed on mutation basis:
> As described in {{StreamReceiveTask.OnCompletionRunnable}}:
> {quote}
> We have a special path for views and for CDC.
> For views, since the view requires cleaning up any pre-existing state, we must put all
partitions through the same write path as normal mutations. This also ensures any 2is are
also updated.
> For CDC-enabled tables, we want to ensure that the mutations are run through the CommitLog
so they can be archived by the CDC process on discard.
> {quote}
> Using the regular write path turns out to be an issue for incremental repairs, as we
loose the {{repaired_at}} state in the process. Eventually the streamed rows will end up in
the unrepaired set, in contrast to the rows on the sender site moved to the repaired set.
The next repair run will stream the same data back again, causing rows to bounce on and on
between nodes on each repair.
> See linked dtest on steps to reproduce. An example for reproducing this manually using
ccm can be found [here|https://gist.github.com/spodkowinski/2d8e0408516609c7ae701f2bf1e515e8]



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