Considering that the causes of slowness can be numerous and simultaneous, it's better to proceed by elimination.
First of all, make sure it's the website that's slow and not the device used to visit it. It often happens, especially with mobile devices (due to the wireless connection), that the download speed is reduced due to poor reception, increasing page loading time. Also, ensure the device isn't too old and slow in processing data.
Next, check the browser being used; it can affect the speed at which a website is displayed. For example, if too many additional plug-ins or antivirus software are installed, they might be checking everything you view. If this is the case, it's better to reinstall the browser to rule out this issue.
Undoubtedly, other client-side reasons can make a website seem slow, but in this article, I'd like to focus on the ones related to the server side.
One of the most common reasons for slowness is that the website has pages that are too heavy or have incorrectly set content. By heavy content, I mean large images, videos, animations, graphics effects, etc. Also, pay attention to the number of such elements on the page. Unlike textual content, which is rarely too heavy, these elements can slow things down. It's also important to know how and in what order they are loaded when the page is called. If they're too large, it's better to have them load deferred only after the page fully loads or enable a caching system so the server isn't overwhelmed during subsequent visits.
Also, be mindful of invisible content, such as external files called within the page's code, such as CSS and JavaScript files, which can themselves call other files. You'll only notice their presence by analyzing the page's source code.
There may also be errors in the programming code that call other content or functions in a non-optimized or incorrect way, like database queries or functions built with faulty logic. This type of issue is more complex to discover than those mentioned earlier. Fortunately, it usually only severely affects sites with many visitors and databases populated with many entries. Activating logs to measure database query activity can help identify where to optimize.
From the server side, it's also crucial to know the performance, configuration, and geolocation of the machine hosting your website. Of course, higher server performance is always better, but it can be pointless without proper configuration. Monitoring the site's statistics and adapting the machine's configuration over time is also essential. For example, if a website goes from 100 visitors a day to 50,000, something needs to be adjusted, such as my.cnf file (for managing database interactions) or the caching system.
As for geolocation, remember that purchasing hosting in China because it's cheaper and more powerful doesn't make sense if most of your visitors are in Europe due to the data transfer times.
As you can see, solving this type of problem can be complex, and sometimes, you'll need help. The areas involved in these cases span multiple branches of IT, making it challenging to find experts who are deeply knowledgeable in all the fields required to solve this issue.
