[Bug]: Mixcoord recover too slow if there's too much database

[chyezh]

Is there an existing issue for this?

• [X] I have searched the existing issues

Environment

- Milvus version: master
- Deployment mode(standalone or cluster): cluster
- MQ type(rocksmq, pulsar or kafka):    
- SDK version(e.g. pymilvus v2.0.0rc2):
- OS(Ubuntu or CentOS): 
- CPU/Memory: 
- GPU: 
- Others:

Current Behavior

• mixcoord can only recover 700 partitions in 30s.

Expected Behavior

mixcoord should recover as fast as possible.

Steps To Reproduce

No response

Milvus Log

No response

Anything else?

No response

[yanliang567]

/assign @chyezh /unassign