Downgrade 4.2 to 4.0
On this page
The following page summarizes various considerations for downgrading to 4.0. For specific instructions for your deployment type, see:
Downgrade Path
Important
Before you upgrade or downgrade a replica set, ensure all replica set members are running. If you do not, the upgrade or downgrade will not complete until all members are started.
If you need to downgrade from 4.2, downgrade to the latest patch release of 4.0.
Tip
If you downgrade,
On Windows, downgrade to version 4.0.12 or later version. You cannot downgrade to a 4.0.11 or earlier version.
On Linux/macOS, if you are running change streams and want to seamlessly resume change streams, downgrade to 4.0.7 or later versions.
Considerations for Replica Sets and Sharded Clusters
Starting in MongoDB 4.2, change streams are
available regardless of the "majority" read concern
support; that is, read concern majority support can be either
enabled (default) or disabled
to use change streams.
In MongoDB 4.0 and earlier, change streams are
available only if "majority" read concern support is
enabled (default).
If you have disabled read concern "majority", change streams will be
disabled once you downgrade to 4.0-series.
Create Backup
Optional but Recommended. Create a backup of your database.
Prequisites
To downgrade from 4.2 to 4.0, you must remove incompatible features that are persisted and/or update incompatible configuration settings. These include:
Downgrade Feature Compatibility Version (fCV)
Before downgrading the binaries, you must downgrade the
featureCompatibilityVersion (fCV) to "4.0" and remove all persisted
fCV 4.2 features that are incompatible with 4.0, such as:
Indexes with a name that exceeds the Index Name Length limit.
Indexes with keys that exceeds the Index Key Limit.
Unique Indexes with new internal format.
Read-only view definitions and collection validation definition that include 4.2 operators.
For specific instructions to downgrade the fCV and remove these features, see:
zstd Compression
Using zstd for data compression, journal compression, or network messages requires additional considerations for downgrades.
For detailed instructions appropriate for your deployment type, see:
tls-Prefixed Configurations
Before downgrading the binaries, update tls-prefixed configuration
options for ssl-prefixed aliases.
For detailed instructions appropriate for your deployment type, see:
Remove Client Side Field Level Encryption Document Validation Keywords
Before downgrading binaries, remove any
automatic encryption rule keywords from collection
$jsonSchema validation objects.
For detailed instructions appropriate for your deployment type, see: