Downgrade a MongoDB from 3.6 to 3.4 when featureCompatibilityVersion is 3.6

In order to downgrade from featureCompatibilityVersion=3.6 to featureCompatibilityVersion=3.4, you must perform the following steps manually:

1. Backup your database before beginning the downgrade procedure.
2. Follow the Prerequisites for your type of deployment to downgrade the featureCompatibilityVersion and remove any backward incompatible, persisted features:
3. • Downgrade 3.6 Standalone to 3.4
   • Downgrade 3.6 Replica Set to 3.4
   • Downgrade 3.6 Sharded Cluster to 3.4

Preventing future downgrade issues

If you are upgrading a MongoDB deployment from 3.4 to 3.6, we recommend you continue to use featureCompatibilityVersion=3.4 until the likelihood of downgrading is minimal. You can then enable the backwards incompatible features by setting featureCompatibilityVersion=3.6 .