How to diagnose and fix the HV014 fdw_too_many_handles error code in Postgres.

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The HV014 error code in PostgreSQL is related to Foreign Data Wrappers (FDWs) and indicates “fdw_too_many_handles.” This error occurs when the FDW tries to open more file descriptors or handles than the operating system allows. This can happen when dealing with a large number of foreign tables or executing many concurrent operations involving foreign data.

To diagnose and fix the HV014 error, you can follow these steps:

  1. Check System Limits:
    The number of file descriptors available to a process is typically controlled by system limits. You can check the current limits with the ulimit -n command on Unix-like systems. If the number is low, you might encounter the HV014 error.
  2. Increase File Descriptor Limits:
    If the limit is too low, you can increase it. For a temporary change (lasting until the next reboot), use the ulimit -n new_limit command, where new_limit is the number of file descriptors you want to allow. For a permanent change, you might need to edit system configuration files like /etc/security/limits.conf on Linux systems.
  3. Close Unnecessary Connections:
    Review your application and close any unnecessary connections to the foreign server. Ensure that your application properly releases handles after they are no longer needed.
  4. Optimize FDW Usage:
    If you have a large number of foreign tables, consider whether they all need to be accessed concurrently. You could redesign your application to access foreign data in batches or sequences, reducing the number of simultaneous connections.
  5. Review FDW Configuration:
    Check if the FDW you are using has any configuration parameters that control resource usage or connection pooling. Adjusting these parameters may help to avoid exceeding the handle limit.
  6. Upgrade or Patch the FDW:
    There might be updates or patches available for the FDW that address handle management issues. Ensure you are using the latest version of the FDW.
  7. Consult the FDW Documentation and Community:
    Review the FDW’s documentation for any recommendations regarding handle limits and resource management. If the problem persists, consider reaching out to the PostgreSQL community or professional support channels for assistance.

Here’s an example of how you might increase the file descriptor limit on a Unix-like system:

# Check the current limit
ulimit -n

# Increase the limit to 4096
ulimit -n 4096

And an example of how to make a permanent change by editing /etc/security/limits.conf:

# Add these lines to the file, replacing 'username' with the actual user running PostgreSQL
username soft nofile 4096
username hard nofile 10240

Remember to replace username with the actual user that runs the PostgreSQL process. After making changes to system limits, you will need to restart the PostgreSQL service for the new limits to take effect.

When working with system resources, it’s crucial to make changes carefully and monitor the system for any unintended side effects. Always test changes in a non-production environment before applying them to your live systems.

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