I have a collection "nene_msg" where has many data and is online with high qps (2k qps). And I run: 
db.nene_msg.renameCollection("nene_msg_2021_09_27"),  
then after some minutes,   query from "nene_msg" online is very slow, from 1~3 milliseconds to hundreds of  milliseconds.
 
I use mongoTemplate to query online, and add index with background mode, such as:

//代码占位符
@CompoundIndex(name = "current_room_status_sender_dest_createTime",
 def = "{'" + ActionEventMO.Fields.currentRoomId + "': 1, '" + ActionEventMO.Fields.actionStatus + "': 1, '"
 + ActionEventMO.Fields.senderId + "': 1, '" + ActionEventMO.Fields.destId + "': 1, '" + ActionEventMO.Fields.createTime + "': 1}",
 background = true),

Could you please help me to find the reason?
Thanks a million.
 
The statistics of the document "nene_msg" is as follows:
DOCUMENTS
6.4m
TOTAL SIZE
18.2GB
AVG. SIZE
3.0KB