Databases Advanced

What is 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.

Write-Ahead Logging is fundamental to database reliability. Before any data modification is written to the actual data files, it is first recorded in a sequential log. If the database crashes, it can replay the WAL to recover committed transactions and undo incomplete ones. PostgreSQL uses WAL extensively — it powers crash recovery, point-in-time recovery (PITR), streaming replication, and logical replication. WAL settings like wal_level, max_wal_size, and checkpoint_timeout directly impact performance and recovery capabilities.

Learn More About This Topic

SQL for Absolute Beginners

Related reading

Redis Fundamentals

Related reading

MongoDB Fundamentals: Building Scalable NoSQL Applications with Document Databases

Related reading

Related Terms

Full-Text Search

A technique for searching natural language text in databases using word stemming, ranking, and relevance scoring.

Time-Series Database

A database optimized for storing and querying timestamped data points like metrics, sensor readings, and event logs.

CTE (Common Table Expression)

A temporary named result set defined within a SQL statement using the WITH clause, improving query readability and enabling recursion.

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

Query Optimization

The process of improving database query performance through indexing, query rewriting, and schema design techniques.

A database object that automatically executes a specified function when certain events (INSERT, UPDATE, DELETE) occur on a table.

View All Databases Terms →