Databases Intermediate

What is Migration?

A version-controlled change to a database schema that can be applied and reversed systematically.

Database migrations track schema changes over time, similar to version control for code. Each migration defines an "up" (apply) and "down" (revert) operation, such as creating tables, adding columns, or modifying constraints.

Migrations ensure all environments (development, staging, production) have identical database schemas. They are run in sequence and tracked to prevent re-application. Tools include Flyway, Liquibase, Alembic, and framework-specific migration systems.

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Related Terms

A database command that shows how the query planner will execute a SQL query, revealing join methods, scan types, and estimated costs.

ORM (Object-Relational Mapping)

A technique that lets you interact with a database using object-oriented code instead of writing raw SQL queries.

Connection Pool

A cache of database connections that can be reused, avoiding the overhead of creating new connections for each request.

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.

Window Function

An SQL function that performs calculations across a set of rows related to the current row without collapsing the result set.

EXPLAIN ANALYZE

A PostgreSQL command that shows the execution plan of a query along with actual runtime statistics for performance tuning.

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