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Description

This error indicates that the MongoDB replica set is not configured to support `readConcern: "majority"`. It typically occurs when a client attempts to use this read concern, but the underlying replica set configuration or storage engine prevents it, impacting data consistency guarantees.

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Error Message

Read Concern Majority Not Enabled

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Known Causes

4 known causes

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Read Concern Majority Disabled

The replica set configuration (`replSetGetConfig`) has `readConcernMajority` explicitly set to `false`.

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Incompatible Storage Engine

The replica set members are using a storage engine (e.g., MMAPv1) that does not support `readConcern: "majority"`.

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Old Feature Compatibility Version

The replica set's `featureCompatibilityVersion` is set to an older MongoDB version that predates `readConcern: "majority"` support.

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Unhealthy Replica Set State

The replica set is not fully initialized, lacks a primary, or has an insufficient number of healthy members to form a majority.

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Solutions

3 solutions available

1. Enable Majority Read Concern for Existing Replica Set medium

Modify the replica set configuration to enable majority read concern.

1

Connect to your MongoDB replica set using the mongo shell or mongosh.

mongosh mongodb://your_replica_set_host:27017

2

Access the admin database.

use admin

3

Initiate a configuration update to enable majority read concern. This requires updating the `settings.readConcern.default` parameter. You might need to fetch the current configuration first to avoid overwriting other settings.

var cfg = rs.conf();
cfg.settings.readConcern.default = "majority";
rs.reconfig(cfg);

4

Verify the configuration change by checking the replica set status.

rs.status()

2. Configure Majority Read Concern During New Replica Set Initialization medium

Set majority read concern when creating a new replica set.

1

When starting your MongoDB instances for a new replica set, use the `--replSet` option and configure the `settings.readConcern.default` parameter in the `mongod.conf` file.

# Example mongod.conf snippet
replication:
  replSetName: myReplicaSetName
settings:
  readConcern:
    default: "majority"

2

Start the mongod processes with the specified configuration file.

mongod --config /path/to/your/mongod.conf

3

Connect to one of the mongod instances and initialize the replica set.

mongosh mongodb://your_primary_host:27017

4

Initialize the replica set. The configuration defined in the `mongod.conf` will be applied.

rs.initiate()

3. Temporarily Use a Less Strict Read Concern easy

For non-critical reads, switch to a read concern that doesn't require majority confirmation.

1

When executing read operations, specify a read concern other than 'majority'. Common alternatives include 'local' or 'available'. This is done at the application level or within the mongo shell.

db.collection.find().readConcern("local")

2

For application code, check your MongoDB driver's documentation for how to set read concerns per operation or per client session.

// Example in Node.js driver
const client = new MongoClient(uri, { readConcern: { level: 'local' } });

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Related Errors

5 related errors

MongoDB Error 148: Majority Read Concern Disabled