MongoDB replica set Member states

In MongoDB each member of a replica set has a state so in this blog we can see about replica set member states & its explanation.

MongoDB replica set has three types of states.

• Core states.
• Other states.
• Error states.

Core states :

In Core states has three members and all are eligible to vote in election.

• PRIMARY.
• SECONDARY.
• ARBITER.

PRIMARY –

• PRIMARY is the only member that can accept write operations.
• A replica set has at most one primary at a time.

SECONDARY –

• SECONDARY state replicate the primary’s data set & can be configured to accept read operations.
• It may be elected to the PRIMARY state if the primary becomes unavailable.

ARBITER –

• ARBITER state do not replicate data or accept write operations.
• Replica sets should only have a member in the ARBITER state and exist solely participate in elections.

Other states :

In Other states has four members and all are eligible to vote in election expect STARTUP.

• STARTUP.
• STARTUP2.
• RECOVERING.
• ROLLBACK.

STARTUP –

• Each member of a replica set start up in STARTUP state.
• They are not yet a recognized member of any replica state.

STARTUP2 –

• It has joined the set and is running an initial sync.

RECOVERING –

• Either it perform startup self-checks or transition from completing a rollback or resync.
• Data is not available for reads.

ROLLBACK –

• The member is actively performing a rollback.

Error states :

In Error states has three members & all are not eligible to vote in election.

• UNKNOWN.
• DOWN.
• REMOVED.

UNKNOWN –

• Members that have never communicated status information to the replica set.

DOWN –

• Members that lose their connection to the replica set & it’s an unreachable mode.

REMOVED –

• Members that are removed from the replica set.

I hope this blog will help you find out MongoDB replica set member states.

Thank you !!