Problem with installation

[elgaita99]

Hello !

We're trying to install mongo_fdw in in 18.4 (Ubuntu 18.4-1.pgdg24.04+1) .
The autogen.sh did it work ok , but :

postgres=# create extension mongo_fdw; ERROR: could not load library "/usr/lib/postgresql/18/lib/mongo_fdw.so": /usr/lib/postgresql/18/lib/mongo_fdw.so: undefined symbol: bson_array_as_legacy_extended_json CONTEXT: SQL statement "CREATE FUNCTION mongo_fdw_handler() RETURNS fdw_handler AS '$libdir/mongo_fdw' LANGUAGE C STRICT" extension script file "mongo_fdw--1.1.sql", near line 9 postgres=# \q

We started from zero and did the Manual installation , but with the same results

What could be happening?

[vaibhavdalvi93]

Hi @elgaita99,

Thank you for reporting this issue.

The undefined symbol: bson_array_as_legacy_extended_json error typically indicates a library mismatch or linking issue during compilation—meaning the build process might be picking up an older or incorrect version of libbson that lacks this specific function.

To help us investigate this further, could you please provide the following details?

1. Build Outputs

• The full console output of your autogen.sh script execution.
• The output of your make and make install commands.

2. Environment Details

• Are you compiling using the latest source code from the master branch?
• Could you please confirm you are compiling this specifically against PostgreSQL 18?

Did you ensure that the LD_LIBRARY_PATH environment variable includes the path to your mongo-c installation directory (where libmongoc-1.0.so and libbson-1.0.so reside)?

For example, if your installation directory is /home/mongo-c and the libraries were built under lib64, you need to export it like this before starting PostgreSQL or running the build:

export LD_LIBRARY_PATH=/home/mongo-c/lib64:$LD_LIBRARY_PATH

Sharing the exact step-by-step commands you used from scratch will greatly help us pinpoint where the linking is failing.

[elgaita99]

Hello aibhavdalvi93,

Thx u for the quick response .

I've clean it up and installed it again (more than 5 attempts ) using the manual installation. It ended ok but still got the same Error when CREATE EXTENSION.

I'm attaching my step-by-step guide , and the log output of the whole operation .

When I recently tried it on PG14 , it worked as expected .

mongo_fdw step by step .sh

Log terminal mongo_fdw.log

Thx u for your help

[vaibhavdalvi93]

Hi @elgaita99,

Thank you for providing the detailed step-by-step guide and the terminal log.

Looking at your locate output, the core issue is that your LD_LIBRARY_PATH is currently pointing to a path (/usr/local/lib/) where the system isn't finding the correct or updated libbson libraries.

Your actual libraries are located in standard system directories:

/usr/lib/libbson-1.0.so.0
/usr/lib/x86_64-linux-gnu/libbson-1.0.so.0

To resolve the undefined symbol error, please try the following steps:

1. Update your LD_LIBRARY_PATH
   Set the environment variable to point to the correct library locations. You can export either of these paths (ensuring there are no spaces after the = sign):

export LD_LIBRARY_PATH=/usr/lib:$LD_LIBRARY_PATH

or

export LD_LIBRARY_PATH=/usr/lib/x86_64-linux-gnu:$LD_LIBRARY_PATH

2. Verify the environment before running Postgres/psql
   Environment variables like LD_LIBRARY_PATH only persist in the specific terminal session where they are exported. Please make sure you are exporting this on the same terminal session where your PostgreSQL server is launched or where you are executing psql to create the extension.

Before running the CREATE EXTENSION command, please verify it by running:

echo $LD_LIBRARY_PATH

3. Missing Build Step
   I also noticed that the output for the actual installation step seems to be missing from your Log terminal mongo_fdw.log file:

cmake --build . --target install

Please double-check that this command completes successfully without any compilation or permission warnings.

Let me know if updating the library path clears the error!

4. Alternative: Using autogen.sh with custom paths
   Is there a specific reason you switched to a manual installation instead of using script autogen.sh?

If you avoided autogen.sh because the default installation directories require root (sudo) permissions, you can actually use the script to install the libraries into a custom, non-root location. You just need to export MONGOC_INSTALL_DIR and JSONC_INSTALL_DIR before running it:

export MONGOC_INSTALL_DIR=/home/youruser/custom_mongo_c
export JSONC_INSTALL_DIR=/home/youruser/custom_json_c
./autogen.sh

Using autogen.sh with these flags handles the internal paths cleanly and might save you from the linking issues you are experiencing with the manual setup.

Let me know if updating the library path clears the error, or if you try rebuilding with the custom autogen.sh paths!

[elgaita99]

Hello vaibhavdalvi93

1. I've wiped out everything and started from zero, now using autogen.sh executed as root . It hangs in a compilation step forever, I've cut it out after 14min . Log attached

autogen.log.txt
htop.pdf

2.Starting from the last point of autogen.sh , doing the manual installation of mongo-c , json-c and mongo_fdw . Attached execution-log ( same Error )

manual_mongo_fdw_2.txt

You talked about a missing
cmake --build . --target install

From the instructions

• To finish the mongo-c driver installation : cmake --build . --target install
• To finish the json-c installation : make install
• Mongo_fdw installation:make USE_PGXS=1 install

After which step should be executed this cmake --build . --target install?

Thx for your help !

[vaibhavdalvi93]

Hello,

Thank you for the detailed logs — they make the issue very clear. There are two problems in your setup:

Problem 1: cmake --build . --target install was never run for mongo-c-driver
You ran cmake --build . (which only compiles) but never ran the install step. This step is what copies the headers and libraries to a known prefix that mongo_fdw can then link against. You need to add this step right after cmake --build . inside the mongo-c-driver directory.

Problem 2: MONGOC_INSTALL_DIR was never set
In your log you can see:

export PKG_CONFIG_PATH=.../mongo-c-driver/src/libmongoc/src:.../$MONGOC_INSTALL_DIR/lib/pkgconfig

Because MONGOC_INSTALL_DIR was not exported before this line, it expanded to an empty string, so PKG_CONFIG_PATH pointed nowhere for the installed libraries. This is why make USE_PGXS=1 compiled against /include/libmongoc-1.0 (an empty/wrong path) and produced the undefined symbol: bson_array_as_legacy_extended_json error at load time.

To summarise the answer to your original question: cmake --build . --target install must be run inside the mongo-c-driver directory, right after cmake --build ., and it requires MONGOC_INSTALL_DIR to be set first so CMake knows where to install the files.

Please find the attached terminal log and steps.
I was able to successfully create the extension using manual installation as the root user.

detail_terminal_output_log.txt
steps.txt

[vaibhavdalvi93]

Hi @elgaita99,

I wanted to follow up and check if you had a chance to try updating the LD_LIBRARY_PATH to point to your system paths (/usr/lib or /usr/lib/x86_64-linux-gnu), or if you were able to test the custom installation directories using autogen.sh.

Please let us know if you were able to successfully run CREATE EXTENSION or if you are still encountering any linking issues. We'll be happy to help you troubleshoot further!