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.
Table of Contents (17 chapters)
PostgreSQL Server Programming
Credits
About the Authors
About the Reviewer
www.PacktPub.com
Preface
Index

Synchronizing between backends


All the preceding functions are designed to run in a single process/backend as if the other PostgreSQL processes did not exist.

But what if you want to log something to a single file from multiple backends?

Seems easy—just open the file and write what you want. Unfortunately, it is not that easy if you want to do it from multiple parallel processes and you do not overwrite or mix up the data with what other processes write.

To have more control over the writing order between backends, you need to have some kind of inter-process synchronization, and the easiest way to do this in PostgreSQL is to use shared memory and light-weight locks (LWLocks).

To allocate its own shared memory segment your .so file needs to be pre-loaded, that is, it should be one of the pre-load libraries given in postgresql.conf variable shared_preload_libraries.

In the _PG_init() function of your module, you ask for the address of a name shared memory segment. If you are the first one asking...