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Mastering PostgreSQL 13
Mastering PostgreSQL 13

Mastering PostgreSQL 13: Build, administer, and maintain database applications efficiently with PostgreSQL 13 , Fourth Edition

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Profile Icon Hans-Jürgen Schönig
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Full star icon Full star icon Full star icon Half star icon Empty star icon 3.6 (5 Ratings)
Paperback Nov 2020 476 pages 4th Edition
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Profile Icon Hans-Jürgen Schönig
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Full star icon Full star icon Full star icon Half star icon Empty star icon 3.6 (5 Ratings)
Paperback Nov 2020 476 pages 4th Edition
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Mastering PostgreSQL 13

Understanding Transactions and Locking

Now that we've covered an introduction to PostgreSQL 13, we want to focus our attention on the next important topic. Locking is a vital concept for any kind of database. It is not enough to understand just how it works to write proper or better applications—it is also essential from a performance point of view. Without handling locks properly, your applications might not only be slow; they might also behave in very unexpected ways. In my opinion, locking is the key to performance, and having a good overview of this will certainly help. Therefore, understanding locking and transactions is important for administrators and developers alike. In this chapter, you will learn about the following topics:

  • Working with PostgreSQL transactions
  • Understanding basic locking
  • Making use of FOR SHARE and FOR UPDATE
  • Understanding transaction isolation...

Working with PostgreSQL transactions

PostgreSQL provides you with highly advanced transaction machinery that offers countless features to developers and administrators alike. In this section, we will look at the basic concept of transactions.

The first important thing to know is that, in PostgreSQL, everything is a transaction. If you send a simple query to the server, it is already a transaction. Here is an example:

test=# SELECT now(), now();
now | now
-------------------------------+-------------------------------
2020-08-13 11:03:17.741316+02 | 2020-08-13 11:03:17.741316+02
(1 row)

In this case, the SELECT statement will be a separate transaction. If the same command is executed again, different timestamps will be returned.

Keep in mind that the now() function will return the transaction time. The SELECT statement will, therefore, always return two identical timestamps. If you want the real time, consider using clock_timestamp() instead of now...

Understanding basic locking

In this section, you will learn about basic locking mechanisms. The goal is to understand how locking works in general and how to get simple applications right.

To show you how things work, we will create a simple table. For demonstrative purposes, I will add one row to the table using a simple INSERT command:

test=# CREATE TABLE  t_test (id int);  
CREATE TABLE 
test=# INSERT INTO t_test VALUES (0); INSERT 0 1

The first important thing is that tables can be read concurrently. Many users reading the same data at the same time won't block each other. This allows PostgreSQL to handle thousands of users without any problems.

The question now is what happens if reads and writes occur at the same time? Here is an example. Let's assume that the table contains one row and its id = 0:

Transaction 1

Transaction 2

BEGIN;

BEGIN;

UPDATE t_test SET id = id + 1 RETURNING *;

User will see 1

SELECT * FROM t_test;

User will see 0

...

Making use of FOR SHARE and FOR UPDATE

Sometimes, data is selected from the database, then some processing happens in the application, and finally, some changes are made back on the database side. This is a classic example of SELECT FOR UPDATE.

Here is an example that shows the way SELECT is often executed in the wrong way:

BEGIN;
SELECT * FROM invoice WHERE processed = false; ** application magic will happen here ** UPDATE invoice SET processed = true ... COMMIT;

The problem here is that two people might select the same unprocessed data. Changes that are made to these processed rows will then be overwritten. In short, a race condition will occur.

To solve this problem, developers can make use of SELECT FOR UPDATE. Here's how it can be used. The following example will show a typical scenario:

BEGIN; 
SELECT * FROM invoice WHERE processed = false FOR UPDATE; 
** application magic  will  happen here  **  
UPDATE invoice SET processed = true ...  
COMMIT; 

SELECT FOR UPDATE...

Understanding transaction isolation levels

Up until now, you have seen how to handle locking, as well as some basic concurrency. In this section, you will learn about transaction isolation. To me, this is one of the most neglected topics in modern software development. Only a small fraction of software developers are actually aware of this issue, which in turn leads to mind-boggling bugs.

Here is an example of what can happen:

Transaction 1

Transaction 2

BEGIN;

SELECT sum(balance) FROM t_account;

User will see 300

BEGIN;

INSERT INTO t_account (balance) VALUES (100);

COMMIT;

SELECT sum(balance) FROM t_account;

User will see 400

COMMIT;

Most users would actually expect the first transaction to always return 300, regardless of the second transaction. However, this isn't true. By default, PostgreSQL runs in the READ COMMITTED transaction isolation mode. This means that every statement inside a transaction will get a new snapshot of...

Observing deadlocks and similar issues

Deadlocks are an important issue and can happen in every database. Basically, a deadlock will happen if two transactions have to wait on each other.

In this section, you will see how this can happen. Let's suppose we have a table containing two rows:

CREATE TABLE t_deadlock (id int);
INSERT INTO t_deadlock VALUES (1), (2);

The following example shows what can happen:

Transaction 1

Transaction 2

BEGIN;

BEGIN;

UPDATE t_deadlock

SET id = id * 10

WHERE id = 1;

UPDATE t_deadlock

SET id = id * 10

WHERE id = 2;

UPDATE t_deadlock

SET id = id * 10

WHERE id = 2;

Waiting on transaction 2

UPDATE t_deadlock

SET id = id * 10

WHERE id = 1;

Waiting on transaction 2

Waiting on transaction 1

Deadlock will be resolved after 1 second

(deadlock_timeout)

COMMIT;

ROLLBACK;

As soon as the deadlock is detected, the following error message will show up:

psql: ERROR: deadlock detected
DETAIL: Process 91521 waits for ShareLock...

Utilizing advisory locks

PostgreSQL has highly efficient and sophisticated transaction machinery that is capable of handling locks in a really fine-grained and efficient way. A few years ago, people came up with the idea of using this code to synchronize applications with each other. Thus, advisory locks were born.

When using advisory locks, it is important to mention that they won't go away on COMMIT as normal locks do. Therefore, it is really important to make sure that unlocking is done properly and in a totally reliable way.

If you decide to use an advisory lock, what you really lock is a number. So, this isn't about rows or data; it is really just a number. Here's how it works:

Session 1

Session 2

BEGIN;

SELECT pg_advisory_lock(15);

SELECT pg_advisory_lock(15);

It has to wait

COMMIT;

It still has to wait

SELECT pg_advisory_unlock(15);

It is still waiting

Lock is taken

The first transaction will lock 15. The second transaction...

Optimizing storage and managing cleanup

Transactions are an integral part of the PostgreSQL system. However, transactions come with a small price tag attached. As we've already shown in this chapter, sometimes, concurrent users will be presented with different data. Not everybody will get the same data returned by a query. In addition to this, DELETE and UPDATE are not allowed to actually overwrite data since ROLLBACK would not work. If you happen to be in the middle of a large DELETE operation, you cannot be sure whether you will be able to COMMIT or not. In addition to this, data is still visible while you perform the DELETE operation, and sometimes data is even visible once your modification has long since finished.

Consequently, this means that cleanup has to happen asynchronously. A transaction cannot clean up its own mess and any COMMIT/ROLLBACK might be too early to take care of dead rows.

The solution to this problem is VACUUM. The following code block provides you with a...

Summary

In this chapter, you learned about transactions, locking and its logical implications, and the general architecture the PostgreSQL transaction machinery can have for storage, concurrency, and administration. You saw how rows are locked and some of the features that are available in PostgreSQL.

In Chapter 3, Making Use of Indexes, you will learn about one of the most important topics in database work: indexing. You will also learn about the PostgreSQL query optimizer, as well as various types of indexes and their behavior.

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Key benefits

  • Master advanced PostgreSQL 13 concepts with the help of real-world datasets and examples
  • Leverage PostgreSQL’s indexing features to fine-tune the performance of your queries
  • Extend PostgreSQL's functionalities to suit your organization's needs with minimal effort

Description

Thanks to its reliability, robustness, and high performance, PostgreSQL has become one of the most advanced open source databases on the market. This updated fourth edition will help you understand PostgreSQL administration and how to build dynamic database solutions for enterprise apps with the latest release of PostgreSQL, including designing both physical and technical aspects of the system architecture with ease. Starting with an introduction to the new features in PostgreSQL 13, this book will guide you in building efficient and fault-tolerant PostgreSQL apps. You’ll explore advanced PostgreSQL features, such as logical replication, database clusters, performance tuning, advanced indexing, monitoring, 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. The book also covers transactions, locking, and indexes, and shows you how to improve performance with query optimization. You’ll also focus on how to manage 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 get the most out of your database by executing advanced administrative tasks.

Who is this book for?

This database administration book is for PostgreSQL developers and database administrators and professionals who want to implement advanced functionalities and master complex administrative tasks with PostgreSQL 13. Prior experience in PostgreSQL and familiarity with the basics of database administration will assist with understanding key concepts covered in the book.

What you will learn

  • Get well versed with advanced SQL functions in PostgreSQL 13
  • Get to grips with administrative tasks such as log file management and monitoring
  • Work with stored procedures and manage backup and recovery
  • Employ replication and failover techniques to reduce data loss
  • Perform database migration from Oracle to PostgreSQL with ease
  • Replicate PostgreSQL database systems to create backups and scale your database
  • Manage and improve server security to protect your data
  • Troubleshoot your PostgreSQL instance to find solutions to common and not-so-common problems

Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Nov 13, 2020
Length: 476 pages
Edition : 4th
Language : English
ISBN-13 : 9781800567498
Vendor :
PostgreSQL Global Development Group
Category :
Languages :
Concepts :
Tools :

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Product Details

Publication date : Nov 13, 2020
Length: 476 pages
Edition : 4th
Language : English
ISBN-13 : 9781800567498
Vendor :
PostgreSQL Global Development Group
Category :
Languages :
Concepts :
Tools :

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Table of Contents

14 Chapters
PostgreSQL 13 Overview Chevron down icon Chevron up icon
Understanding Transactions and Locking Chevron down icon Chevron up icon
Making Use of Indexes Chevron down icon Chevron up icon
Handling Advanced SQL Chevron down icon Chevron up icon
Log Files and System Statistics Chevron down icon Chevron up icon
Optimizing Queries for Good Performance Chevron down icon Chevron up icon
Writing Stored Procedures Chevron down icon Chevron up icon
Managing PostgreSQL Security Chevron down icon Chevron up icon
Handling Backup and Recovery Chevron down icon Chevron up icon
Making Sense of Backups and Replication Chevron down icon Chevron up icon
Deciding on Useful Extensions Chevron down icon Chevron up icon
Troubleshooting PostgreSQL Chevron down icon Chevron up icon
Migrating to PostgreSQL Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Half star icon Empty star icon 3.6
(5 Ratings)
5 star 40%
4 star 20%
3 star 0%
2 star 40%
1 star 0%
C. C Chin Dec 29, 2023
Full star icon Full star icon Full star icon Full star icon Full star icon 5
IRS uses that version
Amazon Verified review Amazon
Tim Smith Mar 29, 2022
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I genuinely don't know why some of the other reviews have had poor experiences with this book. It was perfect for what I needed, which was exposure to all parts of PostgreSQL. It methodically takes you through the ins and outs. It is well written and explains things clearly.
Amazon Verified review Amazon
KS Mar 26, 2021
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
This book des not include any introductory contents including 'What is Postgresql', 'Installing PostgreSQL', 'Getting started', and so on.This is a book for PostgreSQL DBA and application developer with these introductory and intermediate level experience and knowledge.This book does not contain any advanced information about general SQL usage. Instead, this book is full of information about unique feature of PostgreSQL, not only for the latest version but also for all the recent versions, covering many important TIPS for DBA work, database design and application development.First chapter covers major new features with version 13. Readers may need to learn basics of underlyning techniques such as B-Tree, WAL and VACUUM, which is available from many sources online.Important topics in the book include:1) Locking and use of SELECT FOR SHARE/UPDATE,2) Vacuum3) Index management and query plan4) Clustering5) Adding new index6) GiST and GIN index basics7) Full text search8) File configuration and log9) Database monitoring and inspection10) PostgreSQL configuration11) Inheritance and partitioning12) Parallel query13) Stored procedure using various languages including PL/PgSQL, PL/Python, C-language using SPI,14) Security, various authentication and permission setups,15) Backup and recovery16) Physical and logical replication17) Migration to PostgreSQLThese topics cover most of the important PostgreSQL-specific behavior and functionality needed for advanced usage.These topics are a very good introduction for deeper dive. Codes used in this book are provided online and are simple enough to run by readers. It must be a great help to learn.One more topic I'd like to see is JSON and JSONB. PostgreSQL has native JSON features with excellent performance, beating NoSQLs. Many readers may want to learn this more.
Amazon Verified review Amazon
Andrew Jan 23, 2021
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
I bought this book in the expectation that it would give me a much deeper understanding of PostgreSQL beyond what documentation would give me - as the name suggested it would. But it really didn't live up to expectations - it is a weird mixture of trivial observations that anyone who has worked with PostgreSQL a bit, and recitations of selected obscure areas of PostgreSQL that someone could easily look up if they needed it without really giving any insight into how they are useful.Particularly grating was how blatantly the author advertises his own business and other book - often to the detriment of the quality of the book (and especially to the credibility of it, when they are advising which third-party tools to use and they have a dog in the race which they are pushing in the book). Often the strategy of the author seems to be to keep the reader in the dark about how to solve problems and hint that they could engage the author's company (e.g. "Even if it is broken, our PostgreSQL support company might need it to track down the reason for the crash." - with nothing about how to do it yourself).Particularly disappointing was the quality of the replication chapter - replication is an area I particularly wanted to understand deeper, since it is one of the hardest parts of getting HA and PostgreSQL right. The author opens the chapter with an admission that it is "only a short introduction" to replication and pushing people to another of his books - but this candour is of course only after someone has already purchased the book.The book doesn't mention many other parts of the ecosystem at all - pgbackrest, Patroni, barman, etc... that someone who has mastered PostgreSQL would know.Overall, if I knew what I know now, I wouldn't have purchased it, and wouldn't recommend it.
Amazon Verified review Amazon
Johnson J. Dec 21, 2020
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
The book describes concepts associated to relational databases and sets them into context of PostgreSQL (version 13). Unfortunately, the author is not able to draw a red line and focus on key aspects. In many areas the book remains superficial and it is better to read the online documentation of PostgreSQL instead. Additionally, the book does not seem to be completely updated to version 13 of PostgreSQL. I cannot recommend it and would not buy it again.Here is an example of what I mean with missing a red line and omitting key aspects. In section 7 (Writing Stored Procedures), the reader would expect a sound introduction followed by details in procedures (maybe routines in general) and procedural programming as supported by PostgreSQL. The section begins with page 292 (position 5511 in kindle). A description of procedural syntax, however, is not introduced before page 321 (position 5967 in kindle). From there to the end of the section (which is on page 342 or position 6275 in kindle), the reader is served mostly simplistic and no interesting procedures and functions. For the whole sections, the author is not capable to illustrate the difference between function and procedures (neither in the description nor in terms of subsections). The beginning of the section is promising but the author starts to mix other concepts and topics instead of explaining what would be relevant here. For example the topic of how to handle quotes turns into a discussion about SQL injection – while this is an important topic of its own, again neither handling quotes nor SQL injection is covered in a sense that you could have a real take away. In that specific example the auther introduces the quote_literal function calls it important (to prevent the SQL injection) but does not provide or explain by example how to use it in a procedure. This is a pattern you will find throughout the book.Good about the book is, that most code examples are executable (that is why I rate it with two instead of one star). However, the layout is not fully consistent and system responses are sometimes a bit creepy in layout (at least with the kindle version). Referencing code could be done better as well. While I believe that the author possesses profound knowledge about PostgreSQL, he is just not a good author and should not write books – sorry!
Amazon Verified review Amazon
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