Postgresql C Extension
Tags: postgres, database
Published: 2023-07-30 21:54:17

## **Introduction**
PostgreSQL is a powerful and highly customizable open-source relational database management system (RDBMS) that supports a wide range of programming languages and interfaces. In addition to its native SQL language, PostgreSQL offers an extensive API that allows developers to write custom extensions and add new functionality to the database.

One of the most popular ways to extend PostgreSQL is by writing C language extensions. C is a powerful and efficient programming language that allows developers to write high-performance code that can be easily integrated with PostgreSQL. Writing a custom C extension for PostgreSQL can be a great way to add new functionality to the database, optimize performance, or integrate with other systems.


## **Steps**

**Step 1:** Set up the development environment
To set up the development environment, you will need to create a new directory for your extension and create a few files to get started.

1. Create a new directory for your extension:
**`$ mkdir myextension`**



2. Create a Makefile for your extension. This file will contain the build instructions for your extension.
**`MODULES = myextension
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)`**

3. Create a myextension.control file for your extension. This file contains metadata about your extension, such as its name, version, and dependencies.
**`# myextension extension
comment = 'My PostgreSQL extension'
default_version = '1.0'
module_pathname = '$libdir/myextension'`**


**Step 2:** Write the C code.

**`#include "postgres.h"`
`#include "fmgr.h"`
`PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(myfunction);
Datum
myfunction(PG_FUNCTION_ARGS)
{
    int arg = PG_GETARG_INT32(0);
    PG_RETURN_INT32(arg * 2);
}`**

This code defines a new function called myfunction that takes an integer argument and returns its double. The PG_MODULE_MAGIC macro is used to mark the module as a valid PostgreSQL extension.

**Step 3:** Compile the extension
Once you have written the C code for your extension, you can compile it into a shared library that can be loaded into PostgreSQL. To do this, simply run the make command in the directory where your extension is located:
**`$ make`**

This will compile your extension and create a shared library file called myextension.so.

**Step 4:** Install the extension
To install the extension in PostgreSQL, you will need to copy the shared library file to the PostgreSQL installation directory and create an entry for the extension in the pg_available_extensions system catalog.
**`$ echo "CREATE EXTENSION myextension;" | psql -U postgres -d mydatabase`**



**Step 5:** Use the extension
Once the extension is installed, you can use it in your SQL queries and functions like any other PostgreSQL extension. 
**`SELECT myfunction(42);`**
This will return the value 84.

## **Conclusion**
Creating a PostgreSQL C extension can be a powerful way to extend the functionality of the database and optimize performance. By following the steps outlined in this report, you can create your own custom C extension for PostgreSQL and integrate it with your database. Keep in mind that this is just a basic example, and there is much more that you can do with PostgreSQL C extensions. With a little creativity and programming skill, you can build powerful and customized extensions that can take your PostgreSQL database to the next level.