setFeatureCompatibilityVersion

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Definition

setFeatureCompatibilityVersion

New in version 3.4.

Changed in version 3.6.

Enables or disables the features that persist data incompatible with earlier versions of MongoDB. You can only issue the setFeatureCompatibilityVersion against the admin database.

The command takes the following form:

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db.adminCommand( { setFeatureCompatibilityVersion: <version> } )

The values for the version are:

Version Description

Version	Description
`"3.6"`	Available on MongoDB 3.6 Deployments Enables the 3.6 features that persist data incompatible with MongoDB 3.4. Enabling these backwards-incompatible features can complicate the downgrade process since you must remove any persisted backwards-incompatible features before you downgrade. It is recommended that after upgrading, you allow your deployment to run without enabling these features for a burn-in period to ensure the likelihood of downgrade is minimal. When you are confident that the likelihood of downgrade is minimal, enable these features.
`"3.4"`	Available on MongoDB 3.4 and MongoDB 3.6 Deployments If set on MongoDB 3.4 deployments, Enables the 3.4 features that persist data incompatible with MongoDB 3.2. Enabling these backwards-incompatible features can complicate the downgrade process. For details, see Remove 3.4 Incompatible Features. It is recommended that after upgrading, you allow your deployment to run without enabling these features for a burn-in period to ensure the likelihood of downgrade is minimal. When you are confident that the likelihood of downgrade is minimal, enable these features. If set on MongoDB 3.6 deployments, Disables the 3.6 features that persist data incompatible with MongoDB 3.4.
`"3.2"`	Available on MongoDB 3.4 Deployments Disables the 3.4 features that persist data incompatible with MongoDB 3.2.

"3.6"

Available on MongoDB 3.6 Deployments

Enables the 3.6 features that persist data incompatible with MongoDB 3.4.

Enabling these backwards-incompatible features can complicate the downgrade process since you must remove any persisted backwards-incompatible features before you downgrade.

It is recommended that after upgrading, you allow your deployment to run without enabling these features for a burn-in period to ensure the likelihood of downgrade is minimal. When you are confident that the likelihood of downgrade is minimal, enable these features.

"3.4"

Available on MongoDB 3.4 and MongoDB 3.6 Deployments

If set on MongoDB 3.4 deployments,

Enables the 3.4 features that persist data incompatible with MongoDB 3.2.

Enabling these backwards-incompatible features can complicate the downgrade process. For details, see Remove 3.4 Incompatible Features.

It is recommended that after upgrading, you allow your deployment to run without enabling these features for a burn-in period to ensure the likelihood of downgrade is minimal. When you are confident that the likelihood of downgrade is minimal, enable these features.
If set on MongoDB 3.6 deployments,

Disables the 3.6 features that persist data incompatible with MongoDB 3.4.

"3.2"

Available on MongoDB 3.4 Deployments

Disables the 3.4 features that persist data incompatible with MongoDB 3.2.

Note

For a standalone, run the command on the standalone mongod instance.
For a replica set, run the command on the primary. A majority of the data-bearing members must be available.
For a sharded cluster, run the command on a mongos instance.

Behavior

Conflicts with Background Operations

Certain background operations, such as index builds, may prevent execution of setFeatureCompatibilityVersion. Use currentOp to identify any ongoing operations.

Default Values

Deployments	`featureCompatibilityVersion`
For new 3.6 deployments	`"3.6"`
For deployments upgraded from 3.4	`"3.4"` until you `setFeatureCompatibilityVersion` to `"3.6"`.
For new 3.4 deployments	`"3.4"`
For deployments upgraded from 3.2	`"3.2"` until you `setFeatureCompatibilityVersion` to `"3.4"`.

Idempotency

This command must perform writes to an internal system collection. If for any reason the command does not complete successfully, you can safely retry the command as the operation is idempotent.

Access Control

To run setFeatureCompatibilityVersion if your deployment enforces access control, you must have a role that grants the following privilege:

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{
  resource: { db: "$setFeatureCompatibilityVersion", collection: "version" },
  actions: [ "update" ]
}

The clusterAdmin and clusterManager roles grant privileges to run setFeatureCompatibilityVersion. [1]

The clusterAdmin also grants privileges to view featureCompatibilityVersion.

Alternatively, you can create a custom role with just the privileges to run setFeatureCompatibilityVersion and getParameter to view featureCompatibilityVersion:

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db.getSiblingDB("admin").createRole({
   role: "fcvRole",
   privileges: [
      { resource: { db: "$setFeatureCompatibilityVersion", collection: "version" }, actions: [ "update" ] },
      { resource: { cluster: true }, actions: [ "getParameter" ] }
   ],
   roles: [ ]
})

Examples

View FeatureCompatibilityVersion

To view the featureCompatibilityVersion for a mongod instance, run the following command on a mongod instance:

Note

The operation is undefined on the mongos instances. For a sharded cluster that has access control enabled, to run the command against a member of the shard replica set, you must connect to the member as a shard local user.

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db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )

In the results document, the value of the featureCompatibilityVersion can have one of the following forms.

For MongoDB 3.4 mongod instances:

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"featureCompatibilityVersion" : <version>

For MongoDB 3.6+ mongod instances:

If the deployment has the default featureCompatibilityVersion, or if the setFeatureCompatibilityVersion command has run successfully against the deployment, the featureCompatibilityVersion has the form:
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```
"featureCompatibilityVersion" : {
   "version" : <version>
}
```
If the mongod is in a partially upgraded or downgraded state, the featureCompatibilityVersion has the following form:
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```
"featureCompatibilityVersion" : {
   "version" : <version> ,
   "targetVersion" : <target version>
}
```
For instance, if a sharded cluster has a shard replica set that is read only when you run setFeatureCompatibilityVersion command against the mongos, the command will fail, and the featureCompatibilityVersion of the config servers will include the targetVersion field.

Or if a replica set becomes read only while setFeatureCompatibilityVersion is running, the command will fail, and the featureCompatibilityVersion of the replica set will include the targetVersion field as well.