Document count showing zero despite documents existing in secondary

I have a MongoDB replica set with 6 members. 3 members (including the primary) are using MongoDB 3.4 and remaining 3 are MongoDB 3.6 which i have added as part of upgrading.

For 2 collections documents have been replicated to new secondary (version 3.6) but when I query document count is zero . Remaining collections are replicated to secondary without any issues.

I’m not sure why document count displays zero for these two collections.


This issue sounds unusual, but I wouldn’t recommend running mixed major releases for an extended period of time beyond validating your upgrade.

It has been some time since you posted this question - were you able to find a solution? If you are still running mixed versions, what specific version(s) of MongoDB 3.4 are you using?

One possibility is that the collection metadata (count & size stats) is somehow incorrect. Usually this happens after an unexpected shutdown, but you could try to run validate on affected collections to see if this corrects your issue.