Why do some Performance measurements fail?
By Viktor Petersson
In some cases when Performance measuring using a given visitor profile, the measurement will fail and insights will not be provided. This can happen for a number of reasons, e.g. the structure of the web pages content, page hosting limitations, an inability to access the page from the profile, etc.
It's always best to try and re-check the given test first, although in some cases this itself won't be enough to resolve the issue. In these cases, we recommend that you edit the specific measurement to remove the failing visitor profile. An advantage of removing the profile is that Performance credits are fully refunded thereby freeing up credits to be used on other measurements.
Below you’ll find some of the most common reasons why a Performance measurement might fail to generate metrics and insights for a specific visitor profile.
The page is behind a login
Unfortunately, the performance module does not currently support checking pages behind a login authentication.
No access to the Page being checked
Sometimes when Performance tries to access a specific page using a certain visitor profile, the page will not be available for the simulated visitor. This prevents Siteimprove from generating any valuable data for the specific page measurement.
Examples of why this can occur are:
- Issues with the server infrastructure used to host the page
- Expired SSL-certificates
- User-agent used to check the page is blocked
Terms such as geo-blocking are explained in more detail in the article Performance: Terminology
Check that these issues are not preventing users from accessing the page, that the page has a valid SSL-certificate and that there is no geo-blocking in place for the specific region used in the visitor profile.
If you have any questions regarding this please contact the Siteimprove Technical Support team.
Timeout when generating specific metrics
Siteimprove Performance utilizes a scoring system based on Google Lighthouse in order to measure and determine the relative performance of a page for different visitor profiles. This means translating a range of specific metrics (First Contentful Paint, Time to Interactive, etc.) to an overall performance score and impact assessment. This is explored in greater detail in the article Understanding the Siteimprove Performance score?
This also means that in certain cases, the generation of specific metrics will take too long to be considered valid. A common example of this is Time to Interactive (TTI). For pages that are very heavy and slow, TTI attempts to measure the point in time where a page is optimally interactive. This essentially means being ready to receive user input without a noticeable delay, ensuring that the user has an acceptable interactive experience.
Some pages take too long (usually over 90 seconds) as there may be a lot of heavy scripting running on the page which delays this metric, thus preventing the measurement from generating a TTI. When this happens, the overall scoring system fails to generate a result, as there are metrics missing from the formula.
In these cases, it’s best to try and improve the page's performance using general recommendations initially. This should get you to the point where metrics are not timing out. Once this happens, Performance will once again be able to generate specific measurements and audits for the given page and visitor profiles.
Guidance on how to improve the performance can be found in the following articles: