@Marvin We have an issue with duplicate key values, causing our DB to fill up very quickly and eventually crash. This is the error message we see in our postgreSQL logs. 2025-02-24 123639.619 CET [2640] ERROR: duplicate key value violates unique constraint "uq_task_run_state__task_run_id_timestamp_desc" 2025-02-24 123639.619 CET [2640] DETAIL: Key (task_run_id, "timestamp")=(1bd02673-558c-4fdd-89fa-0cfe317f641e, 2025-02-24 081825.87801+01) already exists.

It seems you're encountering a problem with duplicate key values in your PostgreSQL database, specifically related to the unique constraint

"uq_task_run_state__task_run_id_timestamp_desc"

. This indicates that there is an attempt to insert or update a record in the

task_run_state

table that has the same

(task_run_id, timestamp)

combination as an existing record. Here are some steps you can take to troubleshoot and resolve this issue: 1. Identify the Source of Duplicates: - Review the process or application logic that inserts or updates records in the

task_run_state

table. Ensure that the logic correctly handles the uniqueness of

(task_run_id, timestamp)

. 2. Check for Transaction Handling: - Make sure that transactions are being handled correctly. If there are concurrent transactions trying to insert or update the same record, it might lead to such conflicts. 3. Examine Prefect Flow Logic: - If you're using Prefect to manage workflows, ensure that the logic for task runs is designed to prevent duplicate entries. This might involve checking how task run states are updated and ensuring idempotency. 4. Database Maintenance: - Clean up any existing duplicate records if they exist. This can be done by identifying and removing duplicates, but be cautious to retain the correct records. 5. Logging and Monitoring: - Implement logging and monitoring to catch these issues early. This can help in identifying patterns or specific operations that lead to the error. 6. Consult Prefect Documentation: - Since this issue involves task runs, reviewing the Prefect documentation related to task and flow run management might provide insights into preventing duplicate entries. If you can provide more specifics about how your system is set up or if you're using Prefect in a particular way, I can assist further.

@Marvin It seems it happens and a task run gets stuck in pending, happened on several different work pools, even though they only have one worker running for each work-queue

The issue you're experiencing with tasks getting stuck in a pending state and causing duplicate key errors in PostgreSQL is a known problem, particularly with Prefect's handling of task state timestamps. Here's a summary of the findings and potential solutions: 1. Duplicate Timestamps: The problem arises when multiple task states (e.g., PENDING, RUNNING, COMPLETED) are recorded with the same timestamp. This violates the unique constraint on the

(task_run_id, timestamp)

combination in the

task_run_state

table. 2. Known Issue: This has been documented in GitHub issues, where tasks sometimes have identical timestamps due to the resolution limits of timestamp generation, especially on Windows systems. This can cause the UI to break and tasks to remain in a pending state. 3. Workaround: A temporary workaround that has been suggested is altering the index to include the

state

field, which allows the UI to remain functional. However, tasks with identical timestamps for all states will not appear correctly in the UI. 4. Resolution: Prefect has addressed this issue in newer versions by adjusting the timestamp logic to ensure uniqueness. If you're not already using the latest version, consider upgrading to a version where this fix has been implemented. 5. Concurrency Management: Ensure that your work pools and queues are correctly configured to handle concurrency limits, as this can also impact task state transitions. For further details and potential fixes, you can refer to the following resources: - GitHub Issue on Duplicate Timestamps - Prefect Documentation on Work Pools - Prefect Documentation on Transactions If you're using Prefect 3.x, consider reviewing and updating your Prefect setup to incorporate these fixes and workarounds.

@Marvin if i upgrade my prefect version on the server to the newest 3.2.7, will the scripts that use prefect version 3.1.12 have any issues?

Upgrading your server to Prefect version 3.2.7 while running scripts on version 3.1.12 could introduce some compatibility challenges, but these can be managed with some considerations: 1. Client/Server Compatibility: Prefect 3.2.7 introduces a warning about potential client/server incompatibilities, suggesting that there could be issues if the server and client versions differ significantly. It's essential to ensure that both the server and client are within compatible version ranges to avoid unexpected behavior. 2. API Changes: Prefect 3.x has some notable changes from 2.x, such as the replacement of agents with workers and the introduction of work pools. Ensure that your scripts do not rely on deprecated features or APIs that have been removed or altered in 3.2.7. 3. Pydantic Version: Prefect 3.x uses Pydantic 2, which might affect how configurations and data models are handled. If your scripts depend on data models or configurations, verify that they are compatible with Pydantic 2. 4. Task and Flow Management: Ensure that your task and flow management logic aligns with the latest Prefect 3.x practices. For instance, the handling of futures and task state management might have subtle differences. 5. Database and Infrastructure: With enhancements in database tuning settings for PostgreSQL and infrastructure management, verify that your database configurations and infrastructure setups are compatible with the latest version. For a smooth transition, it would be advisable to: - Test your scripts in a development environment using the latest server version. - Review the release notes for specific changes and enhancements. - Consult the Prefect documentation for any updated practices or migration guides. By addressing these considerations, you can minimize potential disruptions when upgrading your Prefect server.

If anyone else sees this, the issue was indeed fixed by upgrading our prefect server to 3.1.15 from 3.1.2. We did not have to upgrade the virtual env of the many different scripts that we schedule through prefect.