How the single-leader and multi-leader configurations happen in a multi datacenter deployment?

Let's dissect

Single-Leader Configuration (Multi-Datacenter Deployment)

1. Performance:

   • Every write must go over the internet to the leader's datacenter, adding significant latency.

   • May defeat the purpose of having multiple datacenters.

2. Tolerance of Datacenter Outages:

   • If the leader datacenter fails, a follower in another datacenter can be promoted as the new leader (failover process).

3. Tolerance of Network Problems:

   • Very sensitive to inter-datacenter network issues since writes depend on synchronous communication with the leader datacenter.

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Multi-Leader Configuration (Multi-Datacenter Deployment)

1. Performance:

   • Writes are processed in the local datacenter, hiding inter-datacenter network delays from users.

   • Better perceived performance due to asynchronous replication between datacenters.

2. Tolerance of Datacenter Outages:

   • Each datacenter can operate independently even during an outage, with replication catching up when the failed datacenter recovers.

3. Tolerance of Network Problems:

   • More resilient to inter-datacenter network interruptions as writes can still be processed locally.

4. Challenges:

   • Write Conflicts: Concurrent modifications of the same data in different datacenters require conflict resolution.

   • Subtle Issues: Autoincrement keys, triggers, and integrity constraints may behave unpredictably due to retrofitting of multi-leader replication in many databases.

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Key Takeaways

• Single-Leader Configurations are simpler but can suffer from latency and failover delays in multi-datacenter setups.

• Multi-Leader Configurations offer better performance and fault tolerance but introduce complexities like write conflicts and configuration pitfalls.

• Multi-leader replication is often considered risky and should be avoided unless absolutely necessary.

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