Slow row deletion performance in comparison to insertion

[Jeff Whiting]

I'm struggling to understand why my deletes are taking longer than my inserts.  My understanding is 
that a delete is just an insertion of a tombstone.  And I'm deleting the entire row.

I do a simple loop (pseudo code) and insert the 100 byte rows:
for (int i=0; i < 50000; i++)
{
    puts.append(new Put(rowkey[i], oneHundredBytes[i]));

    if (puts.size() % 1000 == 0)
    {
        Benchmark.start();
        table.batch(puts);
        Benchmark.stop();
    }
}


The above takes about 8282ms total.

However the delete takes more than twice as long:

Iterator it = table.getScannerScan(rowkey[0], rowkey[50000-1]).iterator();
while(it.hasNext())
{
    r = it.next();
    deletes.append(new Delete(r.getRow()));
    if (deletes.size() % 1000 == 0)
    {
        Benchmark.start();
        table.batch(deletes);
        Benchmark.stop();
    }
}

The above takes 17369ms total.

I'm only benchmarking the deletion time and not the scan time. Additionally if I batch the deletes 
into one big one at the end (rather than while I'm scanning) it takes about the same amount of time. 
I am deleting the entire row so I wouldn't think it would be doing a read before the delete 
(http://mail-archives.apache.org/mod_mbox/hbase-user/201206.mbox/%3CE83D30E8F408F94A96F992785FC29D82063395D6@s2k3mntaexc1.mentacapital.local%3E).

Any thoughts on why it is slower and how I can speed it up?

Thanks,
~Jeff

--
Jeff Whiting
Qualtrics Senior Software Engineer
je...@qualtrics.com