Hello,

We are currently reviewing the upgrade from mongo 3.0.9 to 3.2.8 in a test environment.

Our current configuration has 3x 3.0.9 nodes and 3x 3.2.8 nodes, with half of the nodes hidden at any time.

Whilst running our own application testing script against we have noticed a significant increase in the amount of data and writes to the journal disks on both the master and slaves when running 3.2.8 in comparison to 3.0.9.

We are trying to understand the changes between the versions as it may impact the performance of our applications.

Replication Process: -

Build a mongo cluster comprising of 3.2.8 nodes and 3.0.9 nodes. ( /var/lib/mongo and /var/lib/mongo/journal as dedicate separate disks)
Run a large amount of inserts (50,000 fewer may highlight the issue) whilst monitoring the dedicated journal disk.
You should see results similar the attached dataset.

Results: -
mongomaster.txt - Mongo Master running Mongo 3.0.9
mongoslave.txt - Mongo Slave running Mongo 3.28
*.png - Graph showing data gathered every minuet.

Kind regards,
Luke