Fix msgs consumed before seek appear in output after seek (#11419)

Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>

internal/util/rocksmq/client/rocksmq/client_impl.go

@@ -82,8 +82,6 @@ func (c *client) Subscribe(options ConsumerOptions) (Consumer, error) {
 				return nil, err
 			}
 		}
-		c.wg.Add(1)
-		go c.consume(consumer)
 		return consumer, nil
 	}
 	consumer, err := newConsumer(c, options)
@@ -113,8 +111,6 @@ func (c *client) Subscribe(options ConsumerOptions) (Consumer, error) {
 
 	// Take messages from RocksDB and put it into consumer.Chan(),
 	// trigger by consumer.MsgMutex which trigger by producer
-	c.wg.Add(1)
-	go c.consume(consumer)
 	c.consumerOptions = append(c.consumerOptions, options)
 
 	return consumer, nil

internal/util/rocksmq/client/rocksmq/consumer_impl.go

@@ -12,6 +12,8 @@
 package rocksmq
 
 import (
+	"sync"
+
 	"github.com/milvus-io/milvus/internal/log"
 	"go.uber.org/zap"
 )
@@ -22,6 +24,8 @@ type consumer struct {
 	consumerName string
 	options      ConsumerOptions
 
+	startOnce sync.Once
+
 	msgMutex  chan struct{}
 	messageCh chan ConsumerMessage
 }
@@ -95,6 +99,10 @@ func (c *consumer) MsgMutex() chan struct{} {
 }
 
 func (c *consumer) Chan() <-chan ConsumerMessage {
+	c.startOnce.Do(func() {
+		c.client.wg.Add(1)
+		go c.client.consume(c)
+	})
 	return c.messageCh
 }