When your website is hitting one or more of its hosting account resource limits, it can result in 'Resource Limit Reached' errors or slow down the website. What error will appear depends on the resource limit the account is hitting.
The error 508 appears when entry processes hit the limit. If this limit is reached, mod_hostinglimits will not be able to place Apache process into LVE and will return error code 508. This way a very heavy site start returning 508 errors without affecting other users on the server.
However, if the site is limited by CPU or IO - the site will start responding slower.
If the site is limited by memory or number of processes limits - the user will see 500 or 503 errors that server cannot execute the script.
Everything you do on your website, from uploading files, installing plugins to having visitors, uses server resources. Most common causes of the resource over usage are:
• Increased legitimate website traffic: your website may suddenly receive a high amount of visitors and the error will be shown until the number of the visitors is reduced or the resource limits are increased.
• Backend scripts or cron jobs: scripts running in the background, including automatic backups and demanding cron jobs can create significant load, which in addition to normal traffic can affect the website performance and cause the overusage.
• Web crawlers or search engines indexing your website too often.
• Badly written scripts: scripts and plugins that are outdated or incorrectly coded can malfunction and cause loops. Even a few concurrent requests to such scripts can push the website over its resource limits.
• DDOS: Denial of service attack overloads the server, making it unavailable for normal use.