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From "Christian Spriegel (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-4917) Optimize tombstone creation for ExpiringColumns
Date Tue, 06 Nov 2012 00:16:13 GMT
Christian Spriegel created CASSANDRA-4917:
---------------------------------------------

             Summary: Optimize tombstone creation for ExpiringColumns
                 Key: CASSANDRA-4917
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4917
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Christian Spriegel



The goal of this ticket is to reduce the amount of tombstones created from ExpiringColumns.

Currently tombstones will always stay a full gc_grace time, which is not neccessary for ExpiringColumns.
We only need to ensure that ExpiringColumn and tombstone together live as long as gc_grace.
If the ExpiringColumn's TTL>=gc_grace then we can create an already gcable tombstone and
drop that instantly.

My initial proposal was to use the ExpiringColumns creation-timestamp as deletiontime for
the tombstone, but Sylvain pointed out that we should not mix local and client timestamps.
So I changed it to this:
{code}
public static Column create(ByteBuffer name, ByteBuffer value, long timestamp, int timeToLive,
int localExpirationTime, int expireBefore, IColumnSerializer.Flag flag)
{
    if (localExpirationTime >= expireBefore || flag == IColumnSerializer.Flag.PRESERVE_SIZE)
        return new ExpiringColumn(name, value, timestamp, timeToLive, localExpirationTime);
    // the column is now expired, we can safely return a simple tombstone
    return new DeletedColumn(name, *localExpirationTime-timeToLive*, timestamp);
    // return new DeletedColumn(name, localExpirationTime, timestamp); // old code
}
{code}


This was discussed on the mailinglist: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/repair-compaction-and-tombstone-rows-td7583481.html

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