How to Fix MongoDB Error Code - 138 - RemoteOplogStale

MongoDB is a popular open-source NoSQL database that offers high performance, scalability, and flexibility. However, like any software, it can encounter errors that need to be resolved. One such error is MongoDB Error Code - 138 - RemoteOplogStale. In this article, we will explore what this error means and how to fix it.

Understanding MongoDB Error Code - 138 - RemoteOplogStale

When working with MongoDB's replication feature, you might come across Error Code - 138 - RemoteOplogStale. This error occurs when a secondary replica set member falls too far behind the primary member, resulting in a stale remote oplog. The oplog is a capped collection that records all the operations performed on the primary member, allowing secondary members to replicate those operations.

When a secondary member falls behind the primary member by more than the configured oplog window size, it becomes stale. This can happen due to various reasons, such as network issues, high load on the secondary member, or long-running operations on the primary member.

Resolving MongoDB Error Code - 138 - RemoteOplogStale

To fix the RemoteOplogStale error, you can follow these steps:

Step 1: Identify the Stale Member

The first step is to identify the secondary member that is experiencing the RemoteOplogStale error. You can use the following command in the MongoDB shell:

rs.printReplicationInfo()

This command will display information about the replication status of each member in the replica set. Look for the member with a large replication lag or a significant difference in the optime values.

Step 2: Check Network Connectivity

Ensure that there are no network connectivity issues between the primary and secondary members. Check for any firewall rules, network congestion, or DNS resolution problems that might be affecting the replication process.

Step 3: Increase Oplog Size

If the secondary member consistently falls behind the primary member, you might need to increase the oplog size. The oplog size determines how much data can be stored in the oplog collection. By default, the oplog size is set to 5% of the available disk space on the primary member.

To increase the oplog size, you need to restart the primary member with a larger oplog size. Follow these steps:

1. Stop the MongoDB service on the primary member.
2. Start the MongoDB service with the --oplogSize parameter, specifying the desired oplog size. For example:

mongod --oplogSize 10240

This command sets the oplog size to 10 GB. Adjust the value according to your requirements.

Step 4: Catch Up the Stale Member

If the secondary member is only slightly behind the primary member, it might be able to catch up by itself. However, if the lag is significant, you can manually resync the member. Follow these steps:

1. Stop the MongoDB service on the stale secondary member.
2. Delete the contents of the data directory on the stale secondary member.
3. Start the MongoDB service on the stale secondary member.
4. Add the member back to the replica set using the rs.add() command.

After adding the member back to the replica set, it will perform an initial sync with the primary member and catch up with the latest operations.

Summary

MongoDB Error Code - 138 - RemoteOplogStale occurs when a secondary replica set member falls too far behind the primary member, resulting in a stale remote oplog. To fix this error, you need to identify the stale member, check network connectivity, increase the oplog size if necessary, and manually resync the member if the lag is significant.

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