[jira] [Updated] (CASSANDRA-5546) Gc_grace should start at the creation of the column, not when it expires

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-5546?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jonathan Ellis updated CASSANDRA-5546:
--------------------------------------

    Fix Version/s:     (was: 2.0 beta 1)
                   2.1
    
> Gc_grace should start at the creation of the column, not when it expires
> ------------------------------------------------------------------------
>
>                 Key: CASSANDRA-5546
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5546
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Sylvain Lebresne
>             Fix For: 2.1
>
>
> Currently, gc_grace determines "the minimum time we keep a column that has been marked for deletion", where "marked for deletion" is creation time for a DeletedColumn or the expiration time for an ExpiringColumn.
> However, in the case of expiring columns, if you want to optimize deletions while making sure you don't resurrect overwritten data, you only care about keeping expired columns gc_grace seconds *since their creation time*, not *since their expiration time*. It would thus be better to have gc_grace be "the minimum time we keep a column since it's creation" (which would change nothing for tombstones, but for TTL would basically ensure we remove the expiration time from the time we keep the column once expired).
> To sum it up, this would have the following advantages:
> # This will make fine tuning of gc_grace a little less of a black art.
> # This will be more efficient for CF mixing deletes and expiring columns (we'll remove tombstones for the expiring one sooner).
> # This means gc_grace will be more reliable for things like CASSANDRA-5314.
> Doing this is pretty simple. The one concern is backward compatilibity: it means people that have fine tuned gc_grace to a very low value because they knew it was ok due to their systematic use of ttls might have to update it back to a bigger, more reasonable value before updates.

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