sporadic batch update problem

[Jeff Drew <suppressed>]

Sporadically, the last few entries of a batch are not written.  I'm writing
to a mysql database using JDBC.   Here's a short version of my code.  Does
anyone have suggestions on possible causes or other diagnostics?

class DatabaseWriter{

int writeCount=0;

public DatabaseWriter(){

  PreparedStatement preparedStatement = connection.prepareStatement("insert
into       msgpersecond ( time , count , sendercompid , targetcompid )
values ( ? , ? , ? , ?  )");

  connection.setAutoCommit( false ); // turn off auto-Commit
}

public void process(Object input){

  preparedStatement.setFloat( 2 , event.msgPerSecond );
  preparedStatement.addBatch( );
  writeCount++:

  if (writeCount > 50) {
    updateCounts = preparedStatement.executeBatch( );
    connection.commit( );

    preparedStatement.clearBatch( );
    writeCount=0;
  }

}
}

process() gets called a lot.  The code usually works fine, but sometimes 3
to 20 or so records that definitely are added to the batch but don't get
written.

I'd greatly appreciate any suggestions.

Thanks