Databases Intermediate

What is Transaction?

A sequence of database operations that are treated as a single unit — either all succeed or all are rolled back.

Transactions ensure data consistency through ACID properties: Atomicity (all or nothing), Consistency (valid state transitions), Isolation (concurrent transactions don't interfere), and Durability (committed data persists).

Commands include BEGIN/START TRANSACTION, COMMIT (save changes), and ROLLBACK (undo changes). Isolation levels (READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE) balance consistency and performance.

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Connection String

A formatted string containing all parameters needed to establish a connection to a database server.

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.

A centralized repository optimized for analytical queries that integrates data from multiple operational sources.

Stored Procedure

A precompiled collection of SQL statements stored in the database that can be executed as a single unit.

A category of databases that store data in non-tabular formats, optimized for specific data models and access patterns.

A PostgreSQL maintenance operation that reclaims storage from dead tuples and updates statistics for the query planner.

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