Method startHeartbeat

session.go:381–395

startHeartbeat starts heartbeat for read-write transaction. If no reads or DMLs happen within 10 seconds, the rw-transaction is considered idle at Cloud Spanner server. This "SELECT 1" query prevents the transaction from being considered idle. cf. https://godoc.org/cloud.google.com/go/spanner#hdr-I

()

// at least one user-initialized SQL query has been executed on the transaction.
// Background: https://github.com/cloudspannerecosystem/spanner-cli/issues/100
func (s *Session) startHeartbeat() {
	interval := time.NewTicker(5 * time.Second)
	defer interval.Stop()

	for {
		select {
		case <-interval.C:
			s.tcMutex.Lock()
			if s.tc != nil && s.tc.rwTxn != nil && s.tc.sendHeartbeat {
				heartbeat(s.tc.rwTxn, s.currentPriority())
			}
			s.tcMutex.Unlock()
		}
	}
}

func heartbeat(txn *spanner.ReadWriteStmtBasedTransaction, priority pb.RequestOptions_Priority) error {
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)