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What is an Oplog in MongoDB?
The oplog (operations log) is a special capped collection that keeps a rolling record of all operations that modify the data stored in your databases.
Where is Oplog size in MongoDB?
To view the current size of the oplog, switch to the local database and run db. collection. stats() against the oplog.rs collection. stats() displays the oplog size as maxSize .
Is MongoDB transactional?
MongoDB doesn’t support transactions, but saving one document is atomic. So, it is better to design you database schema in such a way, that all the data needed to be saved atomically will be placed in one document.
How is the OpLog created in MongoDB?
MongoDB Oplog happens to be a special collection that keeps a record of all the operations that modify the data stored in the database. The Oplog in MongoDB can be created after starting a Replica Set member. The process is carried out for the first time with a default size.
Can a replica set be written to in MongoDB?
Starting in MongoDB 4.4.2, it is no longer possible to perform manual write operations to the oplog on a cluster running as a replica set. Performing write operations to the oplog when running as a standalone instance should only be done with guidance from MongoDB Support.
Is there a minimum retention period for MongoDB?
By default MongoDB does not set a minimum oplog retention period and automatically truncates the oplog starting with the oldest entries to maintain the configured maximum oplog size. To configure the minimum oplog retention period when starting the mongod, either: Add the storage.oplogMinRetentionHours setting to the mongod configuration file.
What’s the change in MongoDB version 4.0?
Changed in version 4.0: Starting in MongoDB 4.0, unlike other capped collections, the oplog can grow past its configured size limit to avoid deleting the majority commit point. New in version 4.4: MongoDB 4.4 supports specifying a minimum oplog retention period in hours, where MongoDB only removes an oplog entry if: