PostgreSQL Server Programming Second Edition Table of Contents PostgreSQL Server Programming Second Edition Credits About the Authors About the Reviewers www.PacktPub.com Support files, eBooks, discount offers, and more Why subscribe? Free access for Packt account holders Preface What this book covers What you need for this book Who this book is for Conventions Reader feedback Customer support Downloading the example code Errata Piracy Questions 1. What Is a PostgreSQL Server? Why program in the server? Using PL/pgSQL for integrity checks About this book’s code examples Switching to the expanded display Moving beyond simple functions Data comparisons using operators Managing related data with triggers Auditing changes Data cleaning Custom sort orders Programming best practices KISS – keep it simple stupid DRY – don’t repeat yourself YAGNI – you ain’t gonna need it SOA – service-oriented architecture Type extensibility Caching Wrapping up – why program in the server? Performance Ease of maintenance Improved productivity Simple ways to tighten security Summary 2. Server Programming Environments Cost of acquisition Availability of developers Licensing Predictability Community Procedural languages Third-party tools Platform compatibility Application design Databases are considered harmful Encapsulation What does PostgreSQL offer? Data locality More basics Transactions General error reporting and error handling User-defined functions Other parameters More control Summary 3. Your First PL/pgSQL Function Why PL/pgSQL? The structure of a PL/pgSQL function Accessing function arguments Conditional expressions Loops with counters Statement termination Looping through query results PERFORM versus SELECT Looping Through Arrays Returning a record Acting on the function’s results Summary 4. Returning Structured Data Sets and arrays Returning sets Returning a set of integers Using a set returning function Functions based on views OUT parameters and records OUT parameters Returning records Using RETURNS TABLE Returning with no predefined structure Returning SETOF ANY Variadic argument lists A summary of the RETURN SETOF variants Returning cursors Iterating over cursors returned from another function Wrapping up of functions returning cursors Other ways to work with structured data Complex data types for the modern world – XML and JSON XML data type and returning data as XML from functions Returning data in the JSON format Summary 5. PL/pgSQL Trigger Functions Creating the trigger function Creating the trigger Working on a simple “Hey, I’m called” trigger The audit trigger Disallowing DELETE Disallowing TRUNCATE Modifying the NEW record The timestamping trigger The immutable fields trigger Controlling when a trigger is called Conditional triggers Triggers on specific field changes Visibility Most importantly – use triggers cautiously! Variables passed to the PL/pgSQL TRIGGER function Summary 6. PostgreSQL Event Triggers Use cases for creating event triggers Creating event triggers Creating an audit trail Preventing schema changes A roadmap of event triggers Summary 7. Debugging PL/pgSQL Manual debugging with RAISE NOTICE Throwing exceptions Logging to a file The advantages of RAISE NOTICE The disadvantages of RAISE NOTICE Visual debugging Installing the debugger Installing the debugger from the source Installing pgAdmin3 Using the debugger The advantages of the debugger The disadvantages of the debugger Summary 8. Using Unrestricted Languages Are untrusted languages inferior to trusted ones? Can you use untrusted languages for important functions? Will untrusted languages corrupt the database? Why untrusted? Why PL/Python? Quick introduction to PL/Python A minimal PL/Python function Data type conversions Writing simple functions in PL/Python A simple function Functions returning a record Table functions Running queries in the database Running simple queries Using prepared queries Caching prepared queries Writing trigger functions in PL/Python Exploring the inputs of a trigger A log trigger Constructing queries Handling exceptions Atomicity in Python Debugging PL/Python Using plpy.notice() to track the function’s progress Using assert Redirecting sys.stdout and sys.stderr Thinking out of the “SQL database server” box Generating thumbnails when saving images Sending an e-mail Listing directory contents Summary 9. Writing Advanced Functions in C The simplest C function – return (a + b) add_func.c Version 0 call conventions Makefile CREATE FUNCTION add(int, int) add_func.sql.in Summary for writing a C function Adding functionality to add(int, int) Smart handling of NULL arguments Working with any number of arguments Basic guidelines for writing C code Memory allocation Use palloc() and pfree() Zero-fill the structures Include files Public symbol names Error reporting from C functions “Error” states that are not errors When are messages sent to the client? Running queries and calling PostgreSQL functions A sample C function using SPI Visibility of data changes More info on SPI_* functions Handling records as arguments or returned values Returning a single tuple of a complex type Extracting fields from an argument tuple Constructing a return tuple Interlude – what is Datum? Returning a set of records Fast capturing of database changes Doing something at commit/rollback Synchronizing between backends Writing functions in C++ Additional resources for C Summary 10. Scaling Your Database with PL/Proxy Creating a simple single-server chat Dealing with success – splitting tables over multiple databases What expansion plans work and when? Moving to a bigger server Master-slave replication – moving reads to slave Multimaster replication Data partitioning across multiple servers Splitting the data PL/Proxy – the partitioning language Installing PL/Proxy The PL/Proxy language syntax CONNECT, CLUSTER, and RUN ON SELECT and TARGET SPLIT – distributing array elements over several partitions The distribution of data Configuring the PL/Proxy cluster using functions Configuring the PL/Proxy cluster using SQL/MED Moving data from the single to the partitioned database Connection Pooling Summary 11. PL/Perl – Perl Procedural Language When to use PL/Perl Installing PL/Perl A simple PL/Perl function Passing and returning non-scalar types Writing PL/Perl triggers Untrusted Perl Summary 12. PL/Tcl – Tcl Procedural Language Installing PL/Tcl A simple PL/Tcl function Null checking with Strict functions The parameter format Passing and returning arrays Passing composite-type arguments Accessing databases Writing PL/Tcl triggers Untrusted Tcl Summary 13. Publishing Your Code as PostgreSQL Extensions When to create an extension Unpackaged extensions Extension versions The .control file Building an extension Installing an extension Viewing extensions Publishing your extension Introduction to PostgreSQL Extension Network Signing up to publish your extension Creating an extension project the easy way Providing the metadata about the extension Writing your extension code Creating the package Submitting the package to PGXN Installing an extension from PGXN Summary 14. PostgreSQL as an Extensible RDBMS What can’t be extended? Creating a new operator Overloading an operator Optimizing operators COMMUTATOR NEGATOR Creating index access methods Creating user-defined aggregates Using foreign data wrappers Summary Index PostgreSQL Server Programming Second Edition PostgreSQL Server Programming Second Edition Copyright © 2015 Packt Publishing All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews. Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the authors, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book. Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information. First published: June 2013 Second edition: February 2015 Production reference: 1210215 Published by Packt Publishing Ltd. Livery Place 35 Livery Street Birmingham B3 2PB, UK. ISBN 978-1-78398-058-1 www.packtpub.com Credits Authors Usama Dar Hannu Krosing Jim Mlodgenski Kirk Roybal Reviewers Stephen Frost Rick van Hattem Vibhor Kumar Jeff Lawson Mariano Reingart Julien Tachoires Commissioning Editor Usha Iyer Acquisition Editors Antony Lowe Meeta Rajani Sam Wood Content Development Editor Adrian Raposo Technical Editors Mrunmayee Patil Chinmay Puranik Copy Editors Dipti Kapadia Aarti Saldanha Project Coordinator Kinjal Bari Proofreaders Maria Gould Linda Morris Indexer Monica Ajmera Mehta Production Coordinator Nitesh Thakur Cover Work Nitesh Thakur About the Authors Usama Dar is a seasoned software developer and architect. During his 14 years’ career, he has worked extensively with PostgreSQL and other database technologies. He worked on PostgreSQL internals extensively while he was working for EnterpriseDB. Currently, he lives in Munich where he works for Huawei’s European Research Center. He designs the next generation of high-performance database systems