[jira] [Commented] (CASSANDRA-13643) converting expired ttl cells to tombstones causing unnecessary digest mismatches

["Blake Eggleston (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-13643?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16065637#comment-16065637 ] 

Blake Eggleston commented on CASSANDRA-13643:
---------------------------------------------

unit test run here: https://circleci.com/gh/bdeggleston/cassandra/55

> converting expired ttl cells to tombstones causing unnecessary digest mismatches
> --------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-13643
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13643
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Blake Eggleston
>            Assignee: Blake Eggleston
>            Priority: Minor
>
> In [{{AbstractCell#purge}}|https://github.com/apache/cassandra/blob/26e025804c6777a0d124dbc257747cba85b18f37/src/java/org/apache/cassandra/db/rows/AbstractCell.java#L77]  , we convert expired ttl'd cells to tombstones, and set the the local deletion time to the cell's expiration time, less the ttl time. Depending on the timing of the purge, this can cause purge to generate tombstones that are otherwise purgeable. If compaction for a row with ttls isn't at the same state between replicas, this will then cause digest mismatches between logically identical rows, leading to unnecessary repair streaming and read repairs.



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