code: protected void bufferInsertRow(String table, Object[][] row) throws IOException {
  		StringBuffer sql = (StringBuffer)insertBuffers.get(table);
  		if (sql != null) {
  			if (traits.supportsMultiRowInsert() && (sql.length() < blockSize)) {
  				sql.append(',');
  				appendInsertValues(sql, row);
  				return;
  			} else {
  				flushInsertBuffer(table);
  			}
  		}
  		sql = new StringBuffer(blockSize);
  		synchronized (sql) { //only for StringBuffer
  			appendInsertStatement(sql, table, row);
  			insertBuffers.put(table, sql);
  		}
  	}
docs: default 512k inserts