Book Image

Mastering PostgreSQL 15 - Fifth Edition

By : Hans-Jürgen Schönig
Book Image

Mastering PostgreSQL 15 - Fifth Edition

By: Hans-Jürgen Schönig

Overview of this book

Starting with an introduction to the newly released features of PostgreSQL 15, this updated fifth edition will help you get to grips with PostgreSQL administration and how to build dynamic database solutions for enterprise apps, including designing both physical and technical aspects of the system. You'll explore advanced PostgreSQL features, such as logical replication, database clusters, advanced indexing, and user management to manage and maintain your database. You'll then work with the PostgreSQL optimizer, configure PostgreSQL for high speed, and move from Oracle to PostgreSQL. Among the other skills that the book will help you build, you’ll cover transactions, handling recursions, working with JSON and JSONB data, and setting up a Patroni cluster. It will show you how to improve performance with query optimization. You'll also focus on managing network security and work with backups and replication while exploring useful PostgreSQL extensions that optimize the performance of large databases. By the end of this PostgreSQL book, you’ll be able to use your database to its utmost capacity by implementing advanced administrative tasks with ease.
Table of Contents (16 chapters)

Understanding noteworthy error scenarios

After going through the basic guidelines to hunt down the most common issues that you will face in your database, the upcoming sections will discuss some of the most common error scenarios that occur in the PostgreSQL world.

Facing clog corruption

PostgreSQL has a thing called the commit log (now called pg_xact; it was formally known as pg_clog). This tracks the state of every transaction on the system and helps PostgreSQL determine whether a row can be seen. In general, a transaction can be in four states:

#define TRANSACTION_STATUS_IN_PROGRESS    0x00
#define TRANSACTION_STATUS_COMMITTED      0x01
#define TRANSACTION_STATUS_ABORTED        0x02
#define TRANSACTION_STATUS_SUB_COMMITTED  0x03

The clog has a separate directory in the PostgreSQL database instance (pg_xact).

In the past, people have reported something called clog corruption...