[CASSANDRA-4917] Optimize tombstone creation for ExpiringColumns

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 2.0 beta 1
• Assignee: Christian Spriegel
• Reporter: Christian Spriegel

Authors

Christian Spriegel

Reviewers

Sylvain Lebresne

• Created: 06/Nov/12 00:15
• Updated: 16/Apr/19 09:32
• Resolved: 24/Mar/13 05:58

Description

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:

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
}

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

Issue Links

• is related to: CASSANDRA-4905 Repair should exclude gcable tombstones from merkle-tree computation
• is related to: CASSANDRA-2698 Instrument repair to be able to assess it's efficiency (precision)
• is related to: CASSANDRA-5398 Remove localTimestamp from merkle-tree calculation (for tombstones)