diff --git a/pkg/streaming/walimpls/impls/pulsar/backlog_clear_helper.go b/pkg/streaming/walimpls/impls/pulsar/backlog_clear_helper.go
index d4d0933e8b..4024d19482 100644
--- a/pkg/streaming/walimpls/impls/pulsar/backlog_clear_helper.go
+++ b/pkg/streaming/walimpls/impls/pulsar/backlog_clear_helper.go
@@ -114,7 +114,8 @@ func (h *backlogClearHelper) getConsumer() (pulsar.Consumer, error) {
 		Topic:                    h.channelName.Name,
 		SubscriptionName:         backlogClearHelperName,
 		Type:                     pulsar.Shared, // use shared subscription to avoid the subscription is rejected because of consumer exists.
-		MaxPendingChunkedMessage: 0,
+		MaxPendingChunkedMessage: 1,             // We cannot set it to 0, because the 0 means 100.
+		ReceiverQueueSize:        1,             // We cannot set it to 0, because the 0 means 1000.
 		StartMessageIDInclusive:  true,
 	})
 	if err != nil {
diff --git a/pkg/streaming/walimpls/impls/pulsar/wal.go b/pkg/streaming/walimpls/impls/pulsar/wal.go
index c49563ffe0..f7cc404c3a 100644
--- a/pkg/streaming/walimpls/impls/pulsar/wal.go
+++ b/pkg/streaming/walimpls/impls/pulsar/wal.go
@@ -146,7 +146,8 @@ func (w *walImpl) Truncate(ctx context.Context, id message.MessageID) error {
 		Topic:                    w.Channel().Name,
 		SubscriptionName:         truncateCursorSubscriptionName,
 		Type:                     pulsar.Exclusive,
-		MaxPendingChunkedMessage: 0,
+		MaxPendingChunkedMessage: 1, // We cannot set it to 0, because the 0 means 100.
+		ReceiverQueueSize:        1, // We cannot set it to 0, because the 0 means 1000.
 		StartMessageIDInclusive:  true,
 	})
 	if err != nil {