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PostgreSQL Replication, Second Edition

PostgreSQL Replication, Second Edition

By : Hans-Jürgen Schönig
4.5 (4)
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PostgreSQL Replication, Second Edition

PostgreSQL Replication, Second Edition

4.5 (4)
By: Hans-Jürgen Schönig

Overview of this book

This book is ideal for PostgreSQL administrators who want to set up and understand replication. By the end of the book, you will be able to make your databases more robust and secure by getting to grips with PostgreSQL replication.
Table of Contents (17 chapters)
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Preface
Preface
What this book covers
What you need for this book
Who this book is for
Conventions
Reader feedback
Customer support
Free Chapter
1
1. Understanding the Concepts of Replication
1. Understanding the Concepts of Replication
The CAP theorem and physical limitations of replication
Different types of replication
Using sharding and data distribution
Summary
2
2. Understanding the PostgreSQL Transaction Log
2. Understanding the PostgreSQL Transaction Log
How PostgreSQL writes data
The XLOG and replication
Understanding consistency and data loss
Tuning checkpoints and the XLOG
Experiencing the XLOG in action
Making use of replication slots
Summary
3
3. Understanding Point-in-time Recovery
3. Understanding Point-in-time Recovery
Understanding the purpose of PITR
Archiving the transaction log
Taking base backups
Replaying the transaction log
Summary
4
4. Setting Up Asynchronous Replication
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4. Setting Up Asynchronous Replication
Setting up streaming replication
Configuring a cascaded replication
Turning slaves into masters
Mixing streaming-based and file-based recovery
Making streaming-only replication more robust
Efficient cleanup and the end of recovery
Conflict management
Dealing with timelines
Delayed replicas
Summary
5
5. Setting Up Synchronous Replication
5. Setting Up Synchronous Replication
Synchronous replication setup
Understanding the practical implications and performance
Redundancy and stopping replication
Summary
6
6. Monitoring Your Setup
6. Monitoring Your Setup
Checking your archive
Checking pg_stat_replication
Checking for operating system processes
Checking for replication slots
Dealing with monitoring tools
Summary
7
7. Understanding Linux High Availability
7. Understanding Linux High Availability
Understanding the purpose of High Availability
Measuring availability
Durability and availability
Detecting failures
The split-brain syndrome
Understanding Linux-HA
Setting up a simple HA cluster
Common maintenance tasks
Summary
8
8. Working with PgBouncer
8. Working with PgBouncer
Understanding the fundamental PgBouncer concepts
Installing PgBouncer
Configuring your first PgBouncer setup
Improving performance
Maintaining PgBouncer
Summary
9
9. Working with pgpool
9. Working with pgpool
Installing pgpool
Understanding the features of pgpool
Understanding the pgpool architecture
Setting up replication and load balancing
Checking the replication
Running pgpool with streaming replication
Dealing with failovers and High Availability
Summary
10
10. Configuring Slony
10. Configuring Slony
Installing Slony
Understanding how Slony works
Replicating your first database
Deploying DDLs
Adding tables to replication and managing problems
Performing failovers
Summary
11
11. Using SkyTools
11. Using SkyTools
Installing SkyTools
Dissecting SkyTools
Managing pgq queues
Using Londiste to replicate data
A word about walmgr
Summary
12
12. Working with Postgres-XC
12. Working with Postgres-XC
Understanding the Postgres-XC architecture
Installing Postgres-XC
Configuring a simple cluster
Optimizing for performance
Creating tables and issuing queries
Adding nodes
Handling failovers and dropping nodes
Summary
13
13. Scaling with PL/Proxy
13. Scaling with PL/Proxy
Understanding the basic concepts
Setting up PL/Proxy
Extending and handling clusters in a clever way
Summary
14
14. Scaling with BDR
14. Scaling with BDR
Understanding BDR replication concepts
Installing BDR
Setting up a simple cluster
Understanding sets
Controlling replication
Summary
15
15. Working with Walbouncer
15. Working with Walbouncer
The concepts of walbouncer
Installing walbouncer
Using additional configuration options
Adjusting filtering rules
Summary
16
Index
Index

Conflict management

In PostgreSQL, the streaming replication data flows in one direction only. The XLOG is provided by the master to a handful of slaves, which consume the transaction log and provide you with a nice copy of the data. You might wonder how this could ever lead to conflicts. Well, there can be conflicts.

Consider the following scenario: as you know, data is replicated with a very small delay. So, the XLOG ends up at the slave after it has been made on the master. This tiny delay can cause the scenario shown in the following diagram:

Let's assume that a slave starts to read a table. It is a long read operation. In the meantime, the master receives a request to actually drop the table. This is a bit of a problem, because the slave will still need this data to perform its SELECT statement. On the other hand, all the requests coming from the master have to be obeyed under any circumstances. This is a classic conflict.

Tip

In the event of a conflict, PostgreSQL will issue the Terminating...

End of Chapter 4
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