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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

Window Function
An SQL function that performs calculations across a set of rows related to the current row without collapsing the result set.
Normalization
The process of organizing database tables to reduce data redundancy and improve data integrity.
View
A virtual table defined by a SQL query that provides a simplified or restricted view of data from one or more tables.
Database Sharding
A horizontal scaling strategy that distributes data across multiple database servers based on a partition key.
Write-Ahead Log (WAL)
A technique where changes are first written to a log before being applied to the database, ensuring crash recovery and data integrity.
Migration
A version-controlled change to a database schema that can be applied and reversed systematically.
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