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From "Edward Capriolo (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4565) TTL columns with older then gcgrace do not need to flush
Date Tue, 28 Aug 2012 17:26:07 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13443295#comment-13443295
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Edward Capriolo commented on CASSANDRA-4565:
--------------------------------------------

 I noticed this because the method I added had loggers that I never saw in the output.  What
I saw happening was ExpiringColumns past TTL never made it into the flush. After some tracing
I came to the conclusion that maybeResetDeletionTimes takes into account ttl time, and converts
them to DeletedColumns which do not get flushed. 

Also if you take the unit test I added, it passes without modification to the code base so
unless my test is not doing what I think it seems like cassandra is already handling this.


If you are finding this not to be the case we can re-open and I will take a look. 
                
> TTL columns with older then gcgrace do not need to flush
> --------------------------------------------------------
>
>                 Key: CASSANDRA-4565
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4565
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Edward Capriolo
>            Assignee: Edward Capriolo
>             Fix For: 1.3
>
>         Attachments: cassandra-4565.patch.1.txt
>
>
> With memcache many people are willing to sacrifice durability for performance. Cassandra
has a TimeToLive feature that can be used in caching scenarios with low values for gc_grace_seconds.
However from a code dive it seems that cassandra will always write TTL to disk, even those
that are beyond gc_grace_seconds. If a use case very large memtables,small ttl, and small
gc_grace it is possible that flushing these columns to disk can be skipped entirely in some
scenarios. 

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