Configure a Secondary’s Sync Target¶
Secondaries capture data from the primary member to maintain an up to date copy of the sets’ data. However, by default secondaries may automatically change their sync targets to secondary members based on changes in the ping time between members and the state of other members’ replication. See Replica Set Data Synchronization and Manage Chained Replication for more information.
For some deployments, implementing a custom replication sync topology may be more effective than the default sync target selection logic. MongoDB provides the ability to specify a host to use as a sync target.
To temporarily override the default sync target selection logic, you may manually configure a secondary member’s sync target to temporarily pull oplog entries. The following provide access to this functionality:
Only modify the default sync logic as needed, and always exercise
rs.syncFrom(), will not affect an in-progress initial sync
operation. To affect the sync target for the initial sync, run
rs.syncFrom(), operation before initial sync.
The member to sync from must be a valid source for data in the set. To sync from a member, the member must:
- Have data. It cannot be an arbiter, in startup or recovering mode, and must be able to answer data queries.
- Be accessible.
- Be a member of the same set in the replica set configuration.
- Build indexes with the
- A different member of the set, to prevent syncing from itself.
If you attempt to replicate from a member that is more than 10 seconds
behind the current member,
mongod will log a warning but will
still replicate from the lagging member.