My DB get stuck some time about 6-10 second and repeat again inifinitely.

My DB design model:

• DBName:
  + chatlogextension1
• Collection names are mongo objectIds represent user ids - 200.000 collections per DB:
  5d21f0b2383cb27bfc908f3b
  5d21f0c2383cb27bfc908f72
  5d21f0dd383cb27bfc908fce
  5d21f0e9383cb27bfc909001
  5d21f10d383cb27bfc9090b1
  5d21f114383cb27bfc9090e1
  5d21f12d383cb27bfc909143
  ...

And i have about 5 chat DBs: chatlogextension1, chatlogextension2,...chatlogextension5.
When i query to these chat DBs, chat DB get stuck about per one minutes and repeat.

• While other DB is not effected.
• This is my OS Resources:
  + CPU: everage 15%
  + RAM: everage 72% (92/128 GB)
  + Max open files: 1000000 (ulimit -n)

May MongoDB handle about 800.000 collections or wiretiger  can handle 800.000 files?