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Replication Concepts

These documents describe and provide examples of replica set operation, configuration, and behavior. For an overview of replication, see Replication Introduction. For documentation of the administration of replica sets, see Replica Set Tutorials. The Replication Reference documents commands and operations specific to replica sets.

Replica Set Members

Introduces the components of replica sets.

Replica Set Primary
The primary is the only member of a replica set that accepts write operations.
Replica Set Secondary Members
Secondary members replicate the primary’s data set and accept read operations. If the set has no primary, a secondary can become primary.
Priority 0 Replica Set Members
Priority 0 members are secondaries that cannot become the primary.
Hidden Replica Set Members
Hidden members are secondaries that are invisible to applications. These members support dedicated workloads, such as reporting or backup.
Replica Set Arbiter
An arbiter does not maintain a copy of the data set but participate in elections.
Replica Set Deployment Architectures
Introduces architectural considerations related to replica sets deployment planning.
Replica Set High Availability

Presents the details of the automatic failover and recovery process with replica sets.

Replica Set Elections
Elections occur when the primary becomes unavailable and the replica set members autonomously select a new primary.
Read Preference
Applications specify read preference to control how drivers direct read operations to members of the replica set.
Replication Processes
Mechanics of the replication process and related topics.
Master Slave Replication
Master-slave replication provided redundancy in early versions of MongoDB. Replica sets replace master-slave for most use cases.