[jira] [Comment Edited] (CASSANDRA-18824) Cleanup behaviour during node decommission caused missing replica

["Szymon Miezal (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-18824?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17762314#comment-17762314 ] 

Szymon Miezal edited comment on CASSANDRA-18824 at 9/6/23 8:58 AM:
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[~samt] thank you it indeed looks like a duplicate, wouldn't it be worth to backport it to 3.11 line as well (that's the one I have managed to replicate the problem for with a test)?


was (Author: JIRAUSER302037):
[~samt] thank you it indeed looks like a duplicate, wouldn't it be worth to backport it to 3.11 line as well?

> 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: Local/SSTable
>            Reporter: Szymon Miezal
>            Assignee: Szymon Miezal
>            Priority: Normal
>
> 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.



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