Скачать или смотреть Understanding the Correct Way to Install PostgreSQL Extensions with Custom Libraries

A detailed guide on installing PostgreSQL extensions with custom libraries, including troubleshooting tips and best practices for linking shared libraries.
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Getting Started: The Importance of Custom Libraries in PostgreSQL Extensions

When working with PostgreSQL, you may find a need to extend its capabilities with custom libraries. For instance, a developer creating a foreign data wrapper (FDW) might require a custom library that provides specific data handling functions. However, integrating these libraries properly can prove to be challenging, especially when dealing with undefined symbols and library linking issues.

This guide dives into the correct method for installing PostgreSQL extensions that rely on custom libraries, highlighting common pitfalls and providing a step-by-step guide to ensure a seamless experience.

The Problem at a Glance

A developer attempting to create a foreign data wrapper (FDW) for PostgreSQL faced an issue where, despite compiling and installing their extension without errors, they encountered undefined symbols when using their custom library. The specific error indicated that the PostgreSQL environment could not locate a function from their custom library.

The Solution: Step-by-Step Guide

To successfully compile and install a PostgreSQL extension that uses a custom library, follow these structured steps:

Step 1: Compile Your Custom Library

You must first compile your custom library as a shared library to make its functions accessible to PostgreSQL. Here’s how you can do it:

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Step 2: Include the Shared Library in Your Extension's Makefile

Next, you need to modify your PostgreSQL extension's Makefile to include your shared library and its dependencies. Here’s an example of how your Makefile might look:

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Step 3: Setting Up the Environment Variable for Library Paths

You need to inform PostgreSQL about the location of your custom libraries by setting the LD_LIBRARY_PATH. This can be done by adding a line to the environment configuration file of PostgreSQL:

Editing the Environment File

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Once you've made these changes, remember to restart PostgreSQL.

Step 4: Compile and Install the Extension

After setting up the Makefile and the environment variable, you can compile and install your extension by running:

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Step 5: Handling Dependencies for Shared Libraries

You might find that your custom library itself depends on other shared libraries. Ensure that any such dependencies are also included in your Makefile's SHLIB_LINK variable. For example:

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If you are using another library, such as libwarp.so, for your custom library, ensure you have that listed as well.

Troubleshooting Tips

If you continue to see errors concerning undefined symbols, check the following:

Ensure your shared libraries are properly compiled and endings are naming conventions are followed.

Confirm that the environment variable LD_LIBRARY_PATH includes the directories of all the dependent shared libraries.

Run ldd on your compiled shared object to see which libraries it is linking against and if it finds all the necessary symbols.

Conclusion

Integrating custom libraries into PostgreSQL extensions can be straightforward if you follow the right steps. By compiling your libraries correctly, modifying your extension’s Makefile, and ensuring proper environment setup, you can avoid common pitfalls like undefined symbols and ensure your extension functions as intended.

This guide should empower you to implement your extensions smoothly and effectively. As you venture into building more complex functionalities, keep these best practices in mind to ease your Post