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From "Tyler Hobbs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8498) Replaying commit log records that are older than gc_grace is dangerous
Date Thu, 26 May 2016 21:34:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15302972#comment-15302972
] 

Tyler Hobbs commented on CASSANDRA-8498:
----------------------------------------

bq.  I'd prefer to log an error and skip the records involved but otherwise start up normally.

This would cause problems for tables with low (or 0) {{gc_grace_seconds}}, which is common
for tables where everything is TTL'ed.

It seems like this problem is equivalent to "should we allow a node to start that's been down
for more than {{gc_grace_seconds}}".  We advise operators not to do this (in order to avoid
zombie data), but there are cases where it makes sense, like the TTL case above, or if deletes
are never performed on a cluster.  I'm sure there are operators out there who are not aware
of these guidelines, so it might make sense to make them more explicit by requiring a {{-D}}
flag to start when commit log segments are older than gc_grace.  If the flag is not used,
we fail to start and print a message about the guidelines and mention the flag.

> Replaying commit log records that are older than gc_grace is dangerous
> ----------------------------------------------------------------------
>
>                 Key: CASSANDRA-8498
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8498
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benedict
>
> If we replay commit log records that are older than gc_grace we could introduce data
corruption to the cluster. We should either (1) fail and suggest a repair, or (2) log an exception.
I prefer (1).



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