Fix the problem that adaptive update interval doesn't recovers back a…

…nd there's too much logs about setting the config (tikv#1502) (tikv#1504)

 

Signed-off-by: MyonKeminta <MyonKeminta@users.noreply.github.com>

oracle/oracles/pd.go

@@ -459,6 +459,8 @@ func (o *pdOracle) updateTS(ctx context.Context) {
 	ticker := time.NewTicker(currentInterval)
 	defer ticker.Stop()
 
+	// Note that as `doUpdate` updates last tick time while `nextUpdateInterval` may perform calculation depending on the
+	// last tick time, `doUpdate` should be called after finishing calculating the next interval.
 	doUpdate := func(now time.Time) {
 		// Update the timestamp for each txnScope
 		o.lastTSMap.Range(func(key, _ interface{}) bool {
@@ -478,9 +480,12 @@ func (o *pdOracle) updateTS(ctx context.Context) {
 	for {
 		select {
 		case now := <-ticker.C:
+			// nextUpdateInterval has calculation that depends on the time of the last tick. Calculate next interval
+			// before `doUpdate` as `doUpdate` is responsible for updating the time of the last tick.
+			newInterval := o.nextUpdateInterval(now, 0)
+
 			doUpdate(now)
 
-			newInterval := o.nextUpdateInterval(now, 0)
 			if newInterval != currentInterval {
 				currentInterval = newInterval
 				ticker.Reset(currentInterval)