Why is my website showing 'Timeout Expired' errors with 20,000-60,000 daily users, and how can I fix it?

Web Application "Timeout Expired" Error Troubleshooting Guide

When a download website faces a large number of users (20,000-60,000 daily), a "server unavailable" error occurs, and a more specific "connection timeout" error may occur. This error is usually caused by query execution taking longer than allowed or by the server becoming unresponsive.

Cause of "timeout expired" error

The "timeout expired" error can come from three reasons:

1. Deadlock: Occurs when two or more processes wait for each other to release resources, causing both to block indefinitely.
2. Incorrect database statistics: A suboptimal query plan due to outdated statistics may result in inefficient query execution.
3. Complex or unoptimized queries: Queries involving multiple connections or complex logic may consume too much time, resulting in timeouts.

Troubleshooting and Solutions

To resolve this error, the key is to identify the problematic query that is causing the timeout. Referring to the stack trace and code (especially Global.asax) should provide clues as to the specific query regarding the problem.

Verification Deadlock

Use SQL Server Management Studio’s Activity Monitor to monitor running processes and identify any blocked processes. Examining the process details will show the most recently executed queries.

Reset database statistics

Execute the following command to clear the statistics:

• exec sp_updatestats
• dbcc freeproccache

Note: This operation may temporarily affect performance, so it is recommended to perform it when the server load is low.

Prevent query plan reuse

Force SQL Server to generate optimal query plans by enabling the following setting:

"SET FORCEPLAN ON"

Query Optimization

If the previous steps didn't resolve the issue, you may need to adjust the query itself. This includes optimizing the structure and logic of the query to make it more efficient. The exact query can be raised as a separate question for further assistance.

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