Category
consistency
9 articles across 8 sub-topics
The Dual Write Problem in NoSQL: MongoDB, DynamoDB, and Cassandra
TLDR: NoSQL databases trade cross-entity atomicity for scale — and every database draws that atomicity boundary in a different place. MongoDB's boundary is the document (pre-4.0) or the replica set (4.0+ multi-doc transactions). DynamoDB's boundary i...
The Dual Write Problem: Why Two Writes Always Fail Eventually — and How to Fix It
TLDR: Any service that writes to a database and publishes a message in the same logical operation has a dual write problem. try/catch retries don't fix it — they turn failures into duplicates. The Transactional Outbox pattern co-writes business data ...
Data Anomalies in Distributed Systems: Split Brain, Clock Skew, Stale Reads, and More
TLDR: Distributed systems produce anomalies not because the code is buggy — but because physics makes it impossible to be perfectly consistent, available, and partition-tolerant simultaneously. Split brain, stale reads, clock skew, causality violatio...
Isolation Levels in Databases: Read Committed, Repeatable Read, Snapshot, and Serializable Explained
TLDR: Isolation levels control which concurrency anomalies a transaction can see. Read Committed (PostgreSQL and Oracle's default) prevents dirty reads but still silently allows non-repeatable reads, write skew, and lost updates. Repeatable Read adds...
Database Anomalies: How SQL and NoSQL Handle Dirty Reads, Phantom Reads, and Write Skew
TLDR: Database anomalies are the predictable side-effects of concurrent transactions — dirty reads, phantom reads, write skew, and lost updates. SQL databases use MVCC and isolation levels to prevent them; PostgreSQL's Serializable Snapshot Isolation...
Azure Cosmos DB Consistency Levels Explained: Strong, Bounded Staleness, Session, Consistent Prefix, and Eventual
TLDR: Cosmos DB offers five consistency levels — Strong, Bounded Staleness, Session, Consistent Prefix, Eventual — each with precise, non-obvious internal mechanics. Session does not mean HTTP session; it means a client-side token that tracks what yo...
Understanding Consistency Patterns: An In-Depth Analysis
TLDR TLDR: Consistency is about whether all nodes in a distributed system show the same data at the same time. Strong consistency gives correctness but costs latency. Eventual consistency gives speed but requires tolerance for briefly stale reads. C...
BASE Theorem Explained: How it Stands Against ACID
TLDR TLDR: ACID (Atomicity, Consistency, Isolation, Durability) is the gold standard for banking. BASE (Basically Available, Soft state, Eventual consistency) is the standard for social media. BASE intentionally sacrifices instant accuracy in exchan...