(6th bug found in 3.2.1 this week and counting)

After upgrading our cluster to pv1 - we noticed that chunk migrations were extremely slow. 20 documents per second. We have 10TB of data and can't afford this speeds. Especially when the cluster can only move a single chunk at time (scalable architecture).

Cancelling _secondaryThrottle fixed it, so we figured out it has something to do with replication.

We reverted to pv0 and it was fixed.

To prove that it was the case, we even changed the pv in the middle of a single chunk migration - the first half (pv1) was super slow, the second was fast as always (pv0).

We're guessing it has something to do with the way you implemented majority writes in pv1, which is inefficient.

This is one of many issues with pv1, and 3.2.1 in general.

Mongodb seems unusable as a database in its current form.