We have three node production replica set. We received critical flush alert when we were adding images to product catalog, what increased from ~150k MB to ~330KMB the product catalog collection.
The primary flush took 5ms at about that time where the secondary and tertiary took +500ms.
Currently, we have Mongo flush critical alert set to 400ms.

We would like to know why it takes much more time between Primary/master and slaves.
Should we increase current threshold for that alert?

Any information and help is appreciated.
Thank you,
Aggie Filarska