Distributed Database

What is Database Sharding?

Database sharding is a horizontal partitioning technique that splits a large dataset across multiple independent database servers (shards), where each shard ho…

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 the Document Database Model?

A document database stores each record as a self-contained, semi-structured document, typically JSON or BSON, where related fields and nested data live togethe…

What is a Column-Family Database Model?

A column-family database groups related columns into named families and stores each row's data physically by column family rather than by row, so queries touch…

What Are the Basics of Cassandra Data Modeling?

Cassandra data modeling means designing tables around the exact queries your application will run, since Cassandra has no joins and limited ad-hoc filtering, s…

How Do You Choose a Sharding Key?

A good sharding key is a column with high cardinality and an even, predictable value distribution that matches your query patterns, so writes and reads spread…

What is Range-Based Sharding?

Range-based sharding assigns rows to shards based on contiguous ranges of the shard key's value, so each shard owns a specific, ordered slice such as user IDs…

What is Hash-Based Sharding?

Hash-based sharding applies a hash function to the shard key and uses the result (typically modulo the shard count) to assign each row to a shard, which spread…

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 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 are Raft and Paxos? Consensus Algorithms Explained

Raft and Paxos are consensus algorithms that let a group of distributed nodes agree on a single value or an ordered sequence of operations even when some nodes…

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 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…

How Does MongoDB Sharding Architecture Work?

MongoDB sharding distributes a collection’s documents across multiple shards (each a replica set) using a shard key, coordinated by lightweight mongos routers…

What is Adaptive Query Execution?

Adaptive query execution is the ability of a query engine to change its execution plan mid-run based on actual runtime statistics observed during execution, ra…

How Does Parallel Query Execution Work in a Database?

Parallel query execution splits a single query’s work — such as a table scan, sort, or join — across multiple CPU cores or worker processes that run concurrent…

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…