I faced an issue when using the upsert operation to insert some rows into the table，
sometimes，it successfully insert some rows into table ,somes it Insert failed ，but the Kudu API upsert does not throw any exception and does not insert/update any data. The probability of failure is about 3 percent。
I set AUTO_FLUSH_BACKGROUND mode and call KuduSession.getPendingErrors to catch exception 。
The environment is:
3 masters 8 tservers.