Скачать или смотреть Troubleshooting Postgres Reindex: Why Your CONCURRENTLY Command Might Be Hanging

Discover the reasons behind the hanging `reindex index concurrently` command in Postgres and learn how to resolve this issue effectively.
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Troubleshooting Postgres Reindex: Why Your CONCURRENTLY Command Might Be Hanging

If you've been working with Postgres, especially with version 13, you might have encountered the frustrating issue of the reindex index concurrently command not finishing. This can be an incredibly puzzling problem, particularly when everything appears to be functioning correctly on the surface. In this guide, we’ll break down this issue and provide you with a thorough understanding of the underlying problem and its solution.

The Problem at Hand

You might have successfully executed a simple reindex command without any hiccups:

[[See Video to Reveal this Text or Code Snippet]]

This command often completes rapidly, even for small indexes. However, when you attempt to run the concurrent variant:

[[See Video to Reveal this Text or Code Snippet]]

You are met with a nightmare scenario where the process hangs for days on end! Despite checking for locks on the server, nothing seems out of the ordinary.

This begs the question: What could be causing this prolonged delay?

Uncovering the Root Cause

After investigating the issue, it turns out that the culprit was a myriad of open connections that were marked as "Idle in Transaction." Each of these connections was creating a blockage, preventing the reindexing process from starting.

Here are the key indicators:

Running the command SELECT * FROM pg_stat_progress_create_index; revealed that it was stuck in a phase waiting for the old snapshot to become available.

Despite no database locks, the active transactions were halting operations.

The Solution: Restarting the Postgres Server

The fix for this annoying problem is relatively straightforward. The persistent hanging was due to these idle transactions consuming resources. By restarting the Postgres server, you effectively:

Terminate all open connections: A fresh start means that all the idle transactions and hanging processes are cleared out.

Free Resources: The resources are reallocated, allowing the reindex index concurrently command to execute without the previous restrictions.

Steps to Implement the Solution:

Restart your Postgres Server:

Before doing this, ensure that you communicate with your team and schedule a maintenance window to minimize disruption.

Use the appropriate command to safely restart your server, considering your specific setup (service management tool, etc.).

Monitor Connections:

After restarting, utilize monitoring queries such as SELECT * FROM pg_stat_activity; to ensure that idle transactions are no longer a concern.

Attempt Reindexing Again:

Execute the command once more:

[[See Video to Reveal this Text or Code Snippet]]

This time, you should see it finish promptly.

Conclusion

Managing an efficient Postgres environment requires diligent monitoring of connections and transactions, especially during operations like reindexing. The issue of a hanging reindex index concurrently command can usually be traced back to idle transactions, which are easily cleared by restarting the server.

By being proactive, you can avoid these headaches in the future and ensure your database operations run smoothly. Have you experienced similar issues with Postgres? Feel free to share your experiences and solutions in the comments below!