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 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 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 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 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 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 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 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 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 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 ... PostgreSQL Server Programming Second Edition Table of Contents PostgreSQL Server Programming Second Edition Credits About the Authors About the Reviewers... 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... 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