Downgrade 3.6 Standalone to 3.4

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Downgrade Path

Create Backup
Prerequisites
Procedure

This version of the documentation is archived and no longer supported. View the current documentation to learn how to upgrade your version of MongoDB.

Before you attempt any downgrade, familiarize yourself with the content of 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 feature compatibility version and remove any 3.6 features incompatible with 3.4 versions as outlined below. These steps are necessary only if featureCompatibilityVersion 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".
```
db.adminCommand({setFeatureCompatibilityVersion: "3.4"})
```
The setFeatureCompatibilityVersion command performs writes to an internal system collection and is idempotent. If for any reason the command does not complete successfully, retry the command on the mongod instance.

2. Remove Backwards Incompatible Persisted Features

Remove all persisted features that are incompatible with 3.4. For example, if you have defined any any view definitions, document validators, and partial index filters 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 latest release in the 3.4 series. If using a package manager, add a new repository for the 3.4 binaries, then perform the actual downgrade process.

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 existing binary with the downloaded mongod binary and restart.

Perform a clean shut down of the mongod process.
Note
If you do not perform a clean shut down, errors may result that prevent the mongod process from starting.
Forcibly terminating the mongod process may cause inaccurate results for db.collection.count() and db.stats() as well as lengthen startup time the next time that the mongod process is restarted.
This applies whether you attempt to terminate the mongod process from the command line via kill or similar, or whether you use your platform's initialization system to issue a stop command, like sudo systemctl stop mongod or sudo service mongod stop.
Replace the 3.6 binary with the 3.4 binary.
Start the 3.4 mongod process.

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