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How to know if MongoDB replica set is recovering?
Login to RECOVERING instance. If you find the difference between oplog last event time and now. That means this particular instance is not PRIMARY and SECONDARY and not an active member of the replica set. 1. Login to RECOVERING instance 2. Delete data from existing db which will be /data/db 3. Restart this RECOVERING instance
When does a replica set replace a primary?
Whenever the replica set replaces a primary in an election, the old primary may contain documents that did not replicate to the secondary members. In this case, the old primary member reverts those writes. During rollback, the member will have ROLLBACK state. Members in the ROLLBACK state are eligible to vote in elections.
What happens when a secondary joins a replica set?
SECONDARY state does not guarantee anything about the staleness of the data with respect to the primary. Due to overload, a secondary may fall far enough behind the other members of the replica set such that it may need to resync with the rest of the set. When this happens, the member enters the RECOVERING state and requires manual intervention.
What are the member states of a replica set?
Replica Set Member States ¶ Number Name State Description 0 STARTUP Not yet an active member of any set. All 1 PRIMARY The member in state primary is the only 2 SECONDARY A member in state secondary is replicati 3 RECOVERING Members either perform startup self-chec
How are primary, secondary and arbiters on MongoDB?
I build a replication set with one primary, one secondary and one arbiter on MongoDB 3.0.2. The primary and arbiter are on the same host and the secondary is on another host. With the growing of write overload, the secondary can’t follow the primary and step into the state of recovering.
How does the secondary stack work in MongoDB?
When the data of that point in time is synced over, the secondary connects to the oplog and applies the changes that were made between said point in time and now according to the oplog entries. This works well as long as the oplog holds all operations between the mentioned point in time.
Is there a bug or a bug in MongoDB?
The problem is a known one and not a bug, but a result of the inner workings of MongoDB and several fail-safe assumptions made by the development team. Hence, there are several ways to deal with the situation.
When to sync MongoDB to empty DATA directory?
Schedule the synchronization during a time of low usage or during a maintenance window. MongoDB provides two options for performing an initial sync: Restart the mongod with an empty data directory and let MongoDB’s normal initial syncing feature restore the data. This is the more simple option but may take longer to replace the data.
Can a MongoDB backup be used to copy data?
If copying data files, ensure that your copy includes the content of the local database. You cannot use a mongodump backup for the data files: only a snapshot backup. For approaches to capturing a consistent snapshot of a running mongod instance, see the MongoDB Backup Methods documentation.
How to automatically sync a member of a replica set?
Restart the mongod with an empty data directory and let MongoDB’s normal initial syncing feature restore the data. This is the more simple option but may take longer to replace the data. See Automatically Sync a Member. Restart the machine with a copy of a recent data directory from another member in the replica set.