Downgrade 3.6 Standalone to 3.4

Before you attempt any downgrade, familiarize yourself with the contentof this document.

Downgrade Path

Once upgraded to 3.6, if you need to downgrade, we recommend downgrading to the latest patch release of 3.4.

Create Backup

Optional but Recommended. Create a backup of your database.

Prerequisites

Before downgrading the binaries, you must downgrade the featurecompatibility version and remove any 3.6 featuresincompatible with 3.4versions as outlined below. These steps are necessary only iffeatureCompatibilityVersion has ever been set to "3.6".

1. Downgrade Feature Compatibility Version

  • Connect a mongo shell to the mongod instance.

  • Downgrade the featureCompatibilityVersion to "3.4".

  1. db.adminCommand({setFeatureCompatibilityVersion: "3.4"})

The setFeatureCompatibilityVersion command performs writesto an internal system collection and is idempotent. If for any reasonthe command does not complete successfully, retry the command on themongod instance.

2. Remove Backwards Incompatible Persisted Features

Remove all persisted features that are incompatible with 3.4. For example, if you have definedany any view definitions, document validators, and partial indexfilters that use 3.6 query features such as $jsonSchema or$expr, you must remove them.

Procedure

Download the latest 3.4 binaries.

Using either a package manager or a manual download, get the latestrelease in the 3.4 series. If using a package manager, add a newrepository for the 3.4 binaries, then perform the actual downgradeprocess.

Once upgraded to 3.6, if you need to downgrade, we recommend downgrading to the latest patch release of 3.4.

Restart with the latest 3.4 mongod instance.

Shut down your mongod instance. Replace the existingbinary with the downloaded mongod binary and restart.

Note

If you do not perform a clean shut down, errors may result thatprevent the mongod process from starting.

Forcibly terminating the mongod process may causeinaccurate results for db.collection.count() anddb.stats() as well as lengthen startup time the next timethat the mongod process is restarted.

Invoking sudo service mongod stop does not guarantee aclean shutdown. This service script forceably stops themongod process if it takes longer than fiveminutes to shut down.

  • Replace the 3.6 binary with the 3.4 binary.

  • Start the 3.4 mongod process.