Debugging PostgreSQL Crash Loop in OpenShift

April 20, 2024

3 min read

Introduction

This article describes how to fix a common PostgreSQL issue in OpenShift when the database enters a crash loop with a “tuple concurrently updated” error. This problem typically occurs due to an unclean shutdown of the PostgreSQL server, leaving the database in an inconsistent state.

Understanding the Error

When starting a PostgreSQL pod in OpenShift, you might encounter the following error:

pg_ctl: another server might be running; trying to start server anyway
waiting for server to start....LOG:  redirecting log output to logging
collector process
HINT:  Future log output will appear in directory "pg_log".
..... done
server started
=> sourcing /usr/share/container-scripts/postgresql/start/set_passwords.sh ...
ERROR:  tuple concurrently updated

This error indicates that PostgreSQL has detected an issue with its internal data consistency. The “tuple concurrently updated” message suggests that a database tuple (row) was modified by multiple processes simultaneously, leaving the database in an inconsistent state.

Step-by-Step Solution

Follow these steps to resolve the issue:

  1. Find the problematic PostgreSQL pod

    First, locate the PostgreSQL pod that is stuck in the crash loop.

  2. Start a debug session

    Use the OpenShift command-line tool to start a debug session with the pod:

    oc debug pod/<postgres-pod-name>

  3. Scale down the deployment

    In another terminal, scale the associated PostgreSQL deployment to zero pods:

    oc scale deployment/<postgres-deployment-name> --replicas=0

  4. Run the PostgreSQL startup script

    From the debug session terminal, run the PostgreSQL startup script:

    run-postgresql

    This creates necessary configuration files that will allow you to manage the PostgreSQL server. You should see the same error output described above.

  5. Stop PostgreSQL cleanly

    Stop the PostgreSQL server with the following command:

    pg_ctl stop -D /var/lib/pgsql/data/userdata

    Expected output:

    waiting for server to shut down.... done
server stopped

  6. Start PostgreSQL manually

    Start the PostgreSQL server manually to check if it initializes correctly:

    pg_ctl start -D /var/lib/pgsql/data/userdata

    Expected output:

    server starting
LOG:  redirecting log output to logging collector process
HINT:  Future log output will appear in directory "pg_log".

    The server should remain running without errors.

  7. Stop PostgreSQL cleanly again

    Ensure a clean shutdown by stopping PostgreSQL:

    pg_ctl stop -D /var/lib/pgsql/data/userdata

    Expected output:

    waiting for server to shut down.... done
server stopped

  8. Exit the debug session

    Type exit to leave the debug session.

  9. Scale up the deployment

    Finally, scale the PostgreSQL deployment back up:

    oc scale deployment/<postgres-deployment-name> --replicas=1

    The PostgreSQL pod should now start normally without crashing.

Why This Works

This procedure works because it:

  1. Allows PostgreSQL to perform a clean shutdown, ensuring all data is properly written

  2. Clears any potentially corrupted transaction logs

  3. Creates the necessary configuration files needed for proper operation

  4. Eliminates race conditions that might occur during the container’s normal startup process

If you encounter this issue frequently with a particular PostgreSQL deployment, consider investigating:

  • Storage performance issues

  • Abrupt pod terminations

  • Resource constraints causing timeouts during shutdown

  • Improper backup procedures