Book Image

PostgreSQL Server Programming

Book Image

PostgreSQL Server Programming

Overview of this book

Learn how to work with PostgreSQL as if you spent the last decade working on it. PostgreSQL is capable of providing you with all of the options that you have in your favourite development language and then extending that right on to the database server. With this knowledge in hand, you will be able to respond to the current demand for advanced PostgreSQL skills in a lucrative and booming market."PostgreSQL Server Programming" will show you that PostgreSQL is so much more than a database server. In fact, it could even be seen as an application development framework, with the added bonuses of transaction support, massive data storage, journaling, recovery and a host of other features that the PostgreSQL engine provides. This book will take you from learning the basic parts of a PostgreSQL function, then writing them in languages other than the built-in PL/PgSQL. You will see how to create libraries of useful code, group them into even more useful components, and distribute them to the community. You will see how to extract data from a multitude of foreign data sources, and then extend PostgreSQL to do it natively. And you can do all of this in a nifty debugging interface that will allow you to do it efficiently and with reliability.

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PostgreSQL Server Programming
Jun, 2013 | 264 pages
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Table of Contents (17 chapters)
PostgreSQL Server Programming
PostgreSQL Server Programming
Credits
Credits
About the Authors
About the Authors
About the Reviewer
About the Reviewer
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
What Is a PostgreSQL Server?
What Is a PostgreSQL Server?
Why program in the server?
About this book's code examples
Moving beyond simple functions
Managing related data with triggers
Auditing changes
Data cleaning
Custom sort orders
Programming best practices
On caching
Wrap up – why program in the server?
Summary
2
Server Programming Environment
Server Programming Environment
Cost of acquisition
Availability of developers
Licensing
Predictability
Community
Procedural languages
Summary
3
Your First PL/pgSQL Function
Your First PL/pgSQL Function
Why PL/pgSQL?
Structure of a PL/pgSQL function
Conditional expressions
Returning a record
Acting on function results
Summary
4
Returning Structured Data
Returning Structured Data
Sets and arrays
Returning sets
Using a set-returning function
Functions based on views
OUT parameters and records
Summary of RETURN SETOF variants
Returning cursors
Other ways to work with structured data
Summary
5
PL/pgSQL Trigger Functions
PL/pgSQL Trigger Functions
Creating the trigger function
Simple "Hey, I'm called" trigger
The audit trigger
Disallowing DELETE
Disallowing TRUNCATE
Modifying the NEW record
Immutable fields trigger
Controlling when a trigger is called
Visibility
Variables passed to the PL/pgSQL TRIGGER function
Summary
6
Debugging PL/pgSQL
Debugging PL/pgSQL
''Manual'' debugging with RAISE NOTICE
Visual debugging
Summary
7
Using Unrestricted Languages
Using Unrestricted Languages
Are untrusted languages inferior to trusted ones?
Will untrusted languages corrupt the database?
Why untrusted?
Quick introduction to PL/Python
Thinking out of the "SQL database server" box
Summary
8
Writing Advanced Functions in C
Writing Advanced Functions in C
Simplest C function – return (a + b)
Adding functionality to add(int, int)
Basic guidelines for writing C code
Error reporting from C functions
Running queries and calling PostgreSQL functions
Handling records as arguments or returned values
Fast capturing of database changes
Doing something at commit/rollback
Synchronizing between backends
Additional resources for C
Summary
9
Scaling Your Database with PL/Proxy
Scaling Your Database with PL/Proxy
Simple single-server chat
Dealing with success – splitting tables over multiple databases
Summary
10
Publishing Your Code as PostgreSQL Extensions
Publishing Your Code as PostgreSQL Extensions
When to create an extension
Unpackaged extensions
Extension versions
The .control file
Building an extension
Installing an extension
Publishing your extension
Installing an extension from PGXN
Summary
Index
Index

Error reporting from C functions

One thing which went unexplained in the previous sample was the error reporting part:

    if (ARR_NDIM(input_array) > 1)
        ereport(ERROR,
                (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                 errmsg("use only one-dimensional arrays!")));

All error reporting and other off-channel messaging in PostgreSQL is done using the ereport(<errorlevel>, rest) macro. The main purpose of which is to make error reporting look like a function call.

The only parameter which is processed directly by ereport() is the first argument error level, or perhaps more exactly severity level or log level. All the other parameters are actually function calls which independently generate and store additional error information in the system to be written to logs and/or be sent to client. Being placed in the argument list of the ereport() makes sure that these other functions are called before the actual error is reported. This is important because in the...

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