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Mastering PostgreSQL 15 - Fifth Edition

You're reading from  Mastering PostgreSQL 15 - Fifth Edition

Product type Book
Published in Jan 2023
Publisher Packt
ISBN-13 9781803248349
Pages 522 pages
Edition 5th Edition
Languages
Author (1):
Hans-Jürgen Schönig Hans-Jürgen Schönig
Profile icon Hans-Jürgen Schönig

Table of Contents (16) Chapters

Preface 1. Chapter 1: PostgreSQL 15 Overview 2. Chapter 2: Understanding Transactions and Locking 3. Chapter 3: Making Use of Indexes 4. Chapter 4: Handling Advanced SQL 5. Chapter 5: Log Files and System Statistics 6. Chapter 6: Optimizing Queries for Good Performance 7. Chapter 7: Writing Stored Procedures 8. Chapter 8: Managing PostgreSQL Security 9. Chapter 9: Handling Backup and Recovery 10. Chapter 10: Making Sense of Backups and Replication 11. Chapter 11: Deciding on Useful Extensions 12. Chapter 12: Troubleshooting PostgreSQL 13. Chapter 13: Migrating to PostgreSQL 14. Index 15. Other Books You May Enjoy

Understanding the transaction log

Every modern database system provides functionality to make sure that a system can survive a crash if something goes wrong or somebody pulls the plug. This is true for filesystems and database systems alike.

PostgreSQL also provides a means to ensure that a crash cannot harm the integrity of data or the data itself. It guarantees that if the power cuts out, the system will always be able to come back on again and do its job.

The means of providing this kind of security is achieved by the Write-Ahead Log (WAL), or xlog. The idea is to not write into a data file directly but instead to write to the log first. Why is this important? Imagine that we are writing some data, as follows:

INSERT INTO data ... VALUES ('12345678');

Let’s assume that this data was written directly to the data file. If the operation fails midway, the data file would be corrupted. It might contain half-written rows, columns without index pointers, missing...

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