How to Fix Sitecore JSS Middleware Performance

This guide addresses a specific issue where users of Sitecore JSS on Vercel experience 504: MIDDLEWARE_INVOCATION_TIMEOUT or 500: JavaScript heap out of memory errors when requests contain a large number of URL query parameters.

Teams deploying Next.js applications with Sitecore JSS on Vercel may observe a pattern of request failures, specifically in the Edge Middleware.

• Error Codes: Function invocations fail with a 504: MIDDLEWARE_INVOCATION_TIMEOUT status code or a 500 error referencing JavaScript heap out of memory.
• Trigger: The errors are consistently triggered by accessing URLs that contain a large quantity of query string parameters. This is most common with URLs from marketing and ad campaigns, which often include numerous UTM parameters and tracking identifiers (e.g., utm_source, utm_campaign, gclid, gbraid).

• Behavior:
• Requests to the site's root domain or pages without query parameters succeed.
• Requests with a small number of query parameters (e.g., 1-5) may also succeed.
• As the number of parameters increases, the request either slows down dramatically or fails, crossing a threshold that triggers the timeout or memory limit.
• Impact: This issue can significantly impact the effectiveness of paid marketing campaigns, as users clicking on sponsored links are unable to access the site, leading to a drop in tracked traffic and potential revenue loss.

Through investigation of multiple occurrences, this issue has been traced back to a specific performance problem within the Sitecore JSS for Next.js library.

• Affected Version: The performance degradation is a known issue in Sitecore JSS version 22.2.0.
• Technical Explanation: The logic within the @sitecore-jss/sitecore-jss-nextjs/middleware package in version 22.2.0 is inefficient at processing and handling a large volume of URLSearchParams. This inefficiency leads to prolonged execution times and/or high memory consumption, eventually exceeding the platform's limits and causing the invocation to terminate. This is a code-level performance issue within the dependency, not a limitation of the Vercel platform.

To confirm if your project is affected by this specific issue, follow these steps:

1. Check Sitecore JSS Version: Inspect your project's package.json file and look for the version of @sitecore-jss/sitecore-jss-nextjs. If the version is 22.2.0 or newer, but less than 22.6.0, you are likely affected.
2. Reproduce with Test Parameters: Isolate the issue from specific campaign parameters by testing a URL with an increasing number of generic parameters.
3. Test a working URL (few parameters): https://[your-domain]/?p1=1&p2=2&p3=3&p4=4&p5=5
4. Test a failing URL (many parameters): https://[your-domain]/?p1=1&p2=2&p3=3&p4=4&p5=5&p6=6&p7=7&p8=8 If the first URL loads and the second one times out, it strongly indicates that the quantity of parameters is the trigger.
5. Review Function Logs: Examine the logs for your Vercel project. Look for function invocations corresponding to the failing requests. You will see error messages confirming the timeout or out-of-memory error originating from your Edge Middleware.

The definitive solution is to upgrade the Sitecore JSS dependency in your project.

• Action: Upgrade @sitecore-jss/sitecore-jss-nextjs to version 22.6.0 or newer.
• Reason: Sitecore has officially addressed and resolved this performance issue in later releases of the library. Upgrading will replace the inefficient middleware logic with a more performant version that can handle a large number of query parameters without timing out.

For detailed instructions on upgrading, consult the official Sitecore JSS documentation or contact Sitecore Support to ensure a smooth update process tailored to your specific implementation.

If an immediate upgrade is not possible, you can mitigate the impact by reducing the number of query parameters used in your marketing campaigns. However, this is not a long-term solution and may limit your tracking capabilities. The recommended path is to upgrade the dependency.