Executing a large batch delete is very slow

I noticed that batch deletes are quire slow. In the profiler I found that almost all of the time is spent in org.apache.hadoop.hbase.regionserver.wal.FSHLog.blockOnSync().

Looking at TransactionProcessor.preDelete it is obvious why:

The batch delete is translated into single puts that are added to the region one by one, so each time the WAL is flushed.