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https://issues.apache.org/jira/browse/CASSANDRA-18824?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17762976#comment-17762976
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Szymon Miezal commented on CASSANDRA-18824:
-------------------------------------------
I was thinking that we might end up with a similar situation - conflict of
cleanup and streaming which results in pending ranges. Namely when a cleanup
process has been already started and passed the safeguard on let's say a node A
and then concurrently the node B starts decommission process. Initially I
thought it might be valuable to break the cleanup (which might take time for
sizeable data) in the process by throwing the exception inside the method that
processes a single SSTable:
https://github.com/apache/cassandra/blob/65ee0d082caac70de704852deed52b9dd52120e6/src/java/org/apache/cassandra/db/compaction/CompactionManager.java#L907
but then I realized that the list of SSTables to process is generated before
touching the first SSTable:
https://github.com/apache/cassandra/blob/65ee0d082caac70de704852deed52b9dd52120e6/src/java/org/apache/cassandra/db/compaction/CompactionManager.java#L299.
It means that all new SSTables that are generated due to streaming after the
cleanup started are not going to be touched by cleanup and breaking the cleanup
in the process would not have much value.
> Backport CASSANDRA-16418: Cleanup behaviour during node decommission caused
> missing replica
> -------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-18824
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18824
> Project: Cassandra
> Issue Type: Bug
> Components: Consistency/Bootstrap and Decommission
> Reporter: Szymon Miezal
> Assignee: Szymon Miezal
> Priority: Normal
> Fix For: 3.0.x, 3.11.x
>
>
> Node decommission triggers data transfer to other nodes. While this transfer
> is in progress,
> receiving nodes temporarily hold token ranges in a pending state. However,
> the cleanup process currently doesn't consider these pending ranges when
> calculating token ownership.
> As a consequence, data that is already stored in sstables gets inadvertently
> cleaned up.
> STR:
> * Create two node cluster
> * Create keyspace with RF=1
> * Insert sample data (assert data is available when querying both nodes)
> * Start decommission process of node 1
> * Start running cleanup in a loop on node 2 until decommission on node 1
> finishes
> * Verify of all rows are in the cluster - it will fail as the previous step
> removed some of the rows
> It seems that the cleanup process does not take into account the pending
> ranges, it uses only the local ranges -
> [https://github.com/apache/cassandra/blob/caad2f24f95b494d05c6b5d86a8d25fbee58d7c2/src/java/org/apache/cassandra/db/compaction/CompactionManager.java#L466].
> There are two solutions to the problem.
> One would be to change the cleanup process in a way that it start taking
> pending ranges into account. Even thought it might sound tempting at first it
> will require involving changes and a lot of testing effort.
> Alternatively we could interrupt/prevent the cleanup process from running
> when any pending range on a node is detected. That sounds like a reasonable
> alternative to the problem and something that is relatively easy to implement.
> The bug has been already fixed in 4.x with CASSANDRA-16418, the goal of this
> ticket is to backport it to 3.x.
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