nosql-expert

# NoSQL Expert Patterns (Cassandra & DynamoDB) ## Overview This skill provides professional mental models and design patterns for **distributed wide-column and key-value stores** (specifically Apache Cassandra and Amazon DynamoDB). Unlike SQL (where you model data entities), or document stores (like MongoDB), these distributed systems require you to **model your queries first**. ## When to Use - **Designing for Scale**: Moving beyond simple single-node databases to distributed clusters. - **Technology Selection**: Evaluating or using **Cassandra**, **ScyllaDB**, or **DynamoDB**. - **Performance Tuning**: Troubleshooting "hot partitions" or high latency in existing NoSQL systems. - **Microservices**: Implementing "database-per-service" patterns where highly optimized reads are required. ## The Mental Shift: SQL vs. Distributed NoSQL | Feature | SQL (Relational) | Distributed NoSQL (Cassandra/DynamoDB) | | :--- | :--- | :--- | | **Data modeling** | Model Entities + Relationships | Model **Queries** (Access Patterns) | | **Joins** | CPU-intensive, at read time | **Pre-computed** (Denormalized) at write time | | **Storage cost** | Expensive (minimize duplication) | Cheap (duplicate data for read speed) | | **Consistency** | ACID (Strong) | **BASE (Eventual)** / Tunable | | **Scalability** | Vertical (Bigger machine) | **Horizontal** (More nodes/shards) | > **The Golden Rule:** In SQL, you design the data model to answer *any* query. In NoSQL, you design the data model to ...