Change the Size of the Oplog

New in version 3.6.

This procedure changes the size of the oplog on each member of a replica set using the replSetResizeOplog command, starting with the secondary members before proceeding to the primary.


You can only run replSetResizeOplog on replica set member’s running with the Wired Tiger storage engine.

Perform these steps on each secondary replica set member first. Once you have changed the oplog size for all secondary members, perform these steps on the primary.

A. Connect to the replica set member

Connect to the replica set member using the mongo shell:

mongo --host <hostname>:<port>


If the replica set enforces authentication, you must authenticate as a user with privileges to modify the local database, such as the clusterManager or clusterAdmin role.

B. (Optional) Verify the current size of the oplog

To view the current size of the oplog, switch to the local database and run db.collection.stats() against the collection. stats() displays the oplog size as maxSize.

use local

The maxSize field displays the collection size in bytes.

C. Change the oplog size of the replica set member

To change the size, run the replSetResizeOplog passing the desired size in megabytes as the size parameter. The specified size must be greater than 990, or 990 megabytes.

The following operation changes the oplog size of the replica set member to 16 gigabytes, or 16000 megabytes.

db.adminCommand({replSetResizeOplog: 1, size: 16000})