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From "Aleksey Yeschenko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4565) TTL columns with older then gcgrace do not need to flush
Date Wed, 12 Sep 2012 04:30:07 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13453697#comment-13453697
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Aleksey Yeschenko commented on CASSANDRA-4565:
----------------------------------------------

bq. Not sure how this will work if a total column with a shorter total shadows a title column
with a longer ttl. Then lost update might be an issue.

Or a column with tll shadowing a regular column with no ttl at all. This ttl change will be
lost.
I'm certain that nothing can be done about it. Turning them into tombstones is an option though.

[~jbellis] there is a solution for 4542, but only because we know that if a row is in the
memtable it can't exist in any of the sstables. I can implement that at least.
                
> 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: Aleksey Yeschenko
>             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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