diff --git a/syncer/heartbeat.go b/syncer/heartbeat.go
index 36f6715497..0e59f3ffb6 100644
--- a/syncer/heartbeat.go
+++ b/syncer/heartbeat.go
@@ -18,6 +18,7 @@ import (
 	"database/sql"
 	"fmt"
 	"reflect"
+	"strings"
 	"sync"
 	"time"
 
@@ -33,7 +34,7 @@ import (
 // GRANT SELECT,UPDATE,INSERT,CREATE ON `your_database`.`heartbeat` to 'your_replicate_user'@'your_replicate_host';
 
 const (
-	// when we not need to support MySQL <=5.5, we can replace with `2006-01-02 15:04:05.000000`
+	// still use "2006-01-02 15:04:05" rather than `2006-01-02 15:04:05.000000` to support parse old `2006-01-02 15:04:05`.
 	timeFormat = "2006-01-02 15:04:05"
 )
 
@@ -96,8 +97,8 @@ func GetHeartbeat(cfg *HeartbeatConfig) (*Heartbeat, error) {
 		heartbeat = &Heartbeat{
 			lock:     make(chan struct{}, 1), // with buffer 1, no recursion supported
 			cfg:      cfg,
-			schema:   filter.DMHeartbeatSchema,
-			table:    filter.DMHeartbeatTable,
+			schema:   strings.ToUpper(filter.DMHeartbeatSchema),
+			table:    strings.ToUpper(filter.DMHeartbeatTable),
 			slavesTs: make(map[string]float64),
 			logger:   log.With(zap.String("component", "heartbeat")),
 		}
@@ -181,7 +182,7 @@ func (h *Heartbeat) RemoveTask(name string) error {
 
 // TryUpdateTaskTs tries to update task's ts
 func (h *Heartbeat) TryUpdateTaskTs(taskName, schema, table string, data [][]interface{}) {
-	if schema != h.schema || table != h.table {
+	if strings.ToUpper(schema) != h.schema || strings.ToUpper(table) != h.table {
 		h.logger.Debug("don't need to handle non-heartbeat table", zap.String("schema", schema), zap.String("table", table))
 		return // not heartbeat table
 	}
@@ -292,8 +293,7 @@ func (h *Heartbeat) createTable() error {
 
 // updateTS use `REPLACE` statement to insert or update ts
 func (h *Heartbeat) updateTS() error {
-	// when we not need to support MySQL <=5.5, we can replace with `UTC_TIMESTAMP(6)`
-	query := fmt.Sprintf("REPLACE INTO `%s`.`%s` (`ts`, `server_id`) VALUES(UTC_TIMESTAMP(), ?)", h.schema, h.table)
+	query := fmt.Sprintf("REPLACE INTO `%s`.`%s` (`ts`, `server_id`) VALUES(UTC_TIMESTAMP(6), ?)", h.schema, h.table)
 	_, err := h.master.Exec(query, h.cfg.serverID)
 	h.logger.Debug("update ts", zap.String("sql", query), zap.Uint32("server ID", h.cfg.serverID))
 	return terror.WithScope(terror.DBErrorAdapt(err, terror.ErrDBDriverError), terror.ScopeUpstream)
@@ -308,6 +308,9 @@ func (h *Heartbeat) calculateLag(ctx context.Context) error {
 	select {
 	case h.lock <- struct{}{}:
 		for taskName, ts := range h.slavesTs {
+			if ts == 0 {
+				continue // do not update metrics if no valid slave TS exists.
+			}
 			lag := masterTS - ts
 			reportLagFunc(taskName, lag)
 		}
diff --git a/tests/README.md b/tests/README.md
index b3bdfbdd06..03778146f7 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -91,6 +91,6 @@ Several convenient commands are provided:
 * `check_port_alive <PORT>` - Wrapper to check a port is alive, at most 20 times.
 * `check_port <HOST> <PORT>` - Checks a host:port is alive.
 * `wait_process_exit <process_name>` - Wait for one or more processes to exit by given process name.
-* `check_metric <PORT> <METRIC_NAME> <RETRY_COUNT> <VALUE PATTERN LIST>...` - check metric value from prometheus.
+* `check_metric <PORT> <METRIC_NAME> <RETRY_COUNT> <LOWER BOUND> <UPPER BOUND>` - check metric value from prometheus.
 * `truncate_trace_events <PORT>` - truncate trace server events records.
 
diff --git a/tests/_utils/check_metric b/tests/_utils/check_metric
index f41f5e6dee..279ac2c1c7 100755
--- a/tests/_utils/check_metric
+++ b/tests/_utils/check_metric
@@ -9,17 +9,19 @@ set -eu
 port=$1
 metric_name=$2
 retry_count=$3
+lower=$4
+upper=$5
 
 shift 3
 
 counter=0
 while [ $counter -lt $retry_count ]; do
     metric=$(curl -s http://127.0.0.1:$port/metrics | grep $metric_name | awk '{print $2}')
-    for pattern in "$@"; do
-        if [ "$metric" == "${pattern}" ]; then
-            exit 0
-        fi
-    done
+    cmp1=$(awk 'BEGIN{ print "'$lower'"<"'$metric'" }')
+    cmp2=$(awk 'BEGIN{ print "'$metric'"<"'$upper'" }')
+    if [ $cmp1 -eq 1 ] && [ $cmp2 -eq 1 ]; then
+        exit 0
+    fi
     ((counter+=1))
     echo "wait for valid metric for $counter-th time"
     sleep 1
diff --git a/tests/all_mode/run.sh b/tests/all_mode/run.sh
index aa434d3ba6..f7d1a2cc6b 100755
--- a/tests/all_mode/run.sh
+++ b/tests/all_mode/run.sh
@@ -101,8 +101,8 @@ function run() {
     # use sync_diff_inspector to check data now!
     check_sync_diff $WORK_DIR $cur/conf/diff_config.toml
 
-    check_metric $WORKER1_PORT 'dm_syncer_replication_lag{task="test"}' 3 0 1
-    check_metric $WORKER2_PORT 'dm_syncer_replication_lag{task="test"}' 3 0 1
+    check_metric $WORKER1_PORT 'dm_syncer_replication_lag{task="test"}' 3 0 2
+    check_metric $WORKER2_PORT 'dm_syncer_replication_lag{task="test"}' 3 0 2
 
     export GO_FAILPOINTS=''
 }