High Availability

What is Database Replication?

Database replication is the process of continuously copying data from one database server (the primary) to one or more other servers (replicas), so multiple co…

What is a Master-Slave Replication Topology?

A master-slave replication topology has exactly one server (the master) accepting all writes, while one or more slave servers continuously receive and apply a…

What is a Master-Master Replication Topology?

A master-master (multi-master) replication topology lets two or more servers each accept writes independently, and every master streams its changes to every ot…

Synchronous vs Asynchronous Replication: What is the Difference?

Synchronous replication waits for at least one replica to confirm it received a write before the primary reports the transaction as committed, while asynchrono…

What Causes Replication Lag and How Do You Reduce It?

Replication lag is the delay between a write committing on the primary and that same write becoming visible on a replica, and it is typically caused by network…

What is Quorum-Based Replication for Reads and Writes?

Quorum-based replication requires a write to be acknowledged by a minimum number of replicas (W) and a read to consult a minimum number of replicas (R) out of…

What are RPO and RTO in Database Disaster Recovery?

RPO (Recovery Point Objective) is the maximum acceptable amount of data loss measured in time, such as losing at most 15 minutes of writes, while RTO (Recovery…

Hot Backup vs Cold Backup: What is the Difference?

A hot backup is taken while the database stays online and serving reads and writes, using transaction-consistent snapshots or log coordination, whereas a cold…

What is Transaction Log Shipping and How is it Used?

Transaction log shipping is a high-availability technique where the write-ahead or transaction log records generated on a primary database are continuously cop…

Redis as a Cache vs a Primary Data Store: What Changes?

Using Redis as a cache means treating it as disposable, rebuildable-from-source data that the application never needs to survive as its only copy, whereas usin…

How Does Blue-Green Deployment Apply to Databases?

Blue-green deployment for databases means maintaining two full environments — the live blue database and an idle green database with the new schema and data fu…

What are Read Replica Routing Strategies?

Read replica routing strategies are the rules an application or proxy uses to decide which database server handles each query — sending writes to the primary a…

How Does Load Balancing Across Database Replicas Work?

Load balancing across database replicas is the practice of distributing read queries across multiple replica servers using a strategy such as round robin, leas…

What Strategies Exist for Upgrading a Production Database?

The main strategies for upgrading a production database are in-place upgrade (upgrade the existing server directly), blue-green upgrade (stand up a new version…

How Do Consistency Levels Work in Apache Cassandra?

A Cassandra consistency level (like ONE, QUORUM, or ALL) is a per-query setting that determines how many replica nodes must respond before a read or write is c…

What Are Database Failover Mechanisms and How Do They Work?

Database failover is the mechanism by which a standby or replica database automatically (or manually) takes over as the primary when the original primary becom…

Automatic Failover vs Manual Failover: What Is the Difference?

Automatic failover lets a monitoring system detect a primary database failure and promote a replica without any human decision, while manual failover requires…

What Is the Split-Brain Problem in Distributed Databases?

Split-brain occurs when a network partition or failed failover causes two nodes in a distributed database cluster to each believe they are the sole primary and…

How Do You Design a Robust Database Health Check?

A robust database health check goes beyond a simple TCP ping by verifying that the database can actually execute a real query within an acceptable time, checki…

What Is Chaos Engineering for Databases and Why Practice It?

Chaos engineering for databases is the practice of deliberately injecting controlled failures, like killing the primary, introducing replication lag, or partit…

DNS Load Balancing Explained

DNS load balancing spreads traffic across multiple servers by having the DNS server return different IP addresses for the same hostname to different clients or…

What is a Load Balancer in Networking?

A load balancer is a device or service that sits in front of a pool of backend servers and distributes incoming client requests across them using a chosen algo…

What is Link Aggregation?

Link aggregation combines multiple physical network links between two devices into a single logical link, increasing available bandwidth and providing redundan…

What is HSRP (Hot Standby Router Protocol)?

HSRP (Hot Standby Router Protocol) is a Cisco-proprietary first-hop redundancy protocol that lets two or more routers share a single virtual IP and virtual MAC…