Eventual Consistency

What is CAP Theorem?

CAP theorem states that a distributed data store can only guarantee two of three properties at once — Consistency, Availability, and Partition tolerance — duri…

Wide-Column Store vs Relational Database: What is the Difference?

A wide-column store lets each row hold millions of dynamically named, sparse columns grouped by family and distributed by row key across many nodes, while a re…

What is the Saga Pattern in Microservices?

The Saga pattern manages a business transaction that spans multiple microservices by breaking it into a sequence of local transactions, where each step publish…

What is Eventual Consistency in Databases?

Eventual consistency is a consistency model where, after writes stop arriving, all replicas of a piece of data are guaranteed to converge to the same value eve…

Strong Consistency vs Eventual Consistency: What is the Difference?

Strong consistency guarantees that any read immediately after a write returns that write's value everywhere, while eventual consistency allows reads to briefly…

What is Tunable Consistency and the N/R/W Quorum Model in NoSQL?

Tunable consistency lets a distributed NoSQL store trade consistency for availability and latency per-request, using three configurable numbers: N (replicas ho…

What is a Global Secondary Index (GSI) in DynamoDB?

A Global Secondary Index (GSI) in DynamoDB is an alternate partition-and-sort-key view of a table that lets you query items efficiently by attributes other tha…

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 is the CQRS Pattern and When Should You Use It?

CQRS (Command Query Responsibility Segregation) splits the logic and often the data models used for writing data (commands) from the logic and models used for…

SQL vs NoSQL for Scale: Which Should You Choose?

SQL databases scale best when data is relational and consistency matters, typically via vertical scaling or read replicas, while NoSQL databases are built to s…

What is Eventual Consistency?

Eventual consistency is a consistency model in which, if no new updates are made to a piece of data, all replicas will converge to the same value over time, th…

How Would You Design a Distributed Counter (e.g. Like Counts)?

A distributed counter tracks a fast-changing count (like a like button) across many concurrent writers by sharding the counter into multiple sub-counters that…

ACID vs BASE: What’s the Difference and When Does Each Apply?

ACID (Atomicity, Consistency, Isolation, Durability) describes transactions that are all-or-nothing, always valid, isolated from each other, and permanently sa…

Strong Consistency vs Eventual Consistency: How Do You Choose?

Strong consistency guarantees that every read returns the most recently written value across all replicas, typically by requiring writes and reads to coordinat…

What is the Saga Pattern?

The saga pattern breaks a distributed transaction into a sequence of local transactions, each owned by a different service, where every step has a correspondin…

What is CQRS (Command Query Responsibility Segregation)?

CQRS is an architectural pattern that splits a system into two separate models — one for writes (commands) and one for reads (queries) — instead of using a sin…

What is a Gossip Protocol and How Does It Work?

A gossip protocol is a decentralized way for nodes in a distributed system to spread information by periodically exchanging state with a few randomly chosen pe…

What are Vector Clocks and Why Are They Used?

A vector clock is a data structure — one counter per node — that a distributed system attaches to events so it can determine whether one event causally happene…

Why and How Do You Denormalize Data at Scale?

Denormalization means deliberately duplicating data across records or tables to avoid expensive joins at read time, trading storage space and write complexity…

What is Database Federation and When Do You Use It?

Database federation splits a single monolithic database into multiple smaller databases organized by function or domain (such as one database per service or bu…

What Are Read Replicas and How Do They Scale Reads?

A read replica is a copy of a primary database that continuously receives updates via replication and serves read-only queries, letting an application scale re…

What is Multi-Master Replication?

Multi-master replication is a topology where two or more nodes can each independently accept writes and replicate them to one another, unlike single-leader rep…

What is the Database-per-Service Pattern?

The database-per-service pattern means each microservice owns and exclusively accesses its own private database, so no other service can read or write its data…

What Is Event-Driven Architecture in DevOps Systems?

Event-driven architecture is a design style where services communicate by emitting and reacting to events — immutable facts describing something that already h…