Databases Advanced

What is Deadlock?

A situation where two or more transactions permanently block each other by each holding locks that the other needs.

A deadlock occurs when Transaction A locks Row 1 and waits for Row 2, while Transaction B locks Row 2 and waits for Row 1. Neither can proceed. Databases detect deadlocks and abort one transaction to break the cycle.

Prevention strategies include consistent lock ordering (always lock resources in the same order), keeping transactions short, using appropriate isolation levels, and using SELECT FOR UPDATE SKIP LOCKED for queue patterns.

Related Terms

ETL (Extract, Transform, Load)

A data pipeline process that extracts data from sources, transforms it into a suitable format, and loads it into a destination system.

The process of copying and maintaining database data across multiple servers for redundancy, failover, and read scaling.

A set of four properties (Atomicity, Consistency, Isolation, Durability) that guarantee reliable database transactions.

A query that transforms rows into columns, creating a pivot table view of aggregated data.

The structure definition of a database including tables, columns, data types, relationships, indexes, and constraints.

Database Constraint

Rules enforced by the database to maintain data integrity, including NOT NULL, UNIQUE, CHECK, PRIMARY KEY, and FOREIGN KEY.

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