Add rocksmq comments (#8362)

Signed-off-by: fishpenguin <kun.yu@zilliz.com>

internal/util/rocksmq/server/rocksmq/rocksmq.go

@@ -11,21 +11,26 @@
 
 package rocksmq
 
+// ProducerMessage that will be write to rocksdb
 type ProducerMessage struct {
 	Payload []byte
 }
 
+// Rocksmq consumer
 type Consumer struct {
 	Topic     string
 	GroupName string
 	MsgMutex  chan struct{}
 }
 
+// ConsumerMessage that consumed from rocksdb
 type ConsumerMessage struct {
 	MsgID   UniqueID
 	Payload []byte
 }
 
+// Rocksmq is an interface thatmay be implemented by the application
+// to do message queue operations based ion rocksdb
 type RocksMQ interface {
 	CreateTopic(topicName string) error
 	DestroyTopic(topicName string) error

internal/util/rocksmq/server/rocksmq/rocksmq_retention.go

@@ -27,10 +27,16 @@ import (
 	"go.uber.org/zap"
 )
 
+// RocksmqRetentionTimeInMinutes is the time of retention
 var RocksmqRetentionTimeInMinutes int64
+
+// RocksmqRetentionSizeInMB is the size of retention
 var RocksmqRetentionSizeInMB int64
+
+// TickerTimeInMinutes is the time of expired check
 var TickerTimeInMinutes int64 = 1
 
+// Const value that used to convert unit
 const (
 	MB     = 2 << 20
 	MINUTE = 60
@@ -477,6 +483,7 @@ func (ri *retentionInfo) expiredCleanUp(topic string) error {
 	return DeleteMessages(ri.db, topic, startID, endID)
 }
 
+// Delte messages in rocksdb by range of [startID, endID)
 func DeleteMessages(db *gorocksdb.DB, topic string, startID, endID UniqueID) error {
 	// Delete msg by range of startID and endID
 	startKey, err := combKey(topic, startID)