I installed an existing Magento installation on a clean CentOS server.
This installation was running fast, with no problems and without any caching module.
Now, suddenly over the weekend, the speed dropped down from 2s/page to 5s/page.
Where do i have to look for a reason?
Update: I cleared the Magento cache folder, and now it's running fast again.
How to avoid this in the future?
Best Answer
If you are running Magento 1.8+ I highly recommend you enabled REDIS cache (See KB article here)
Here is some great information on speeding up Magento, implement the features that apply: http://www.magentocommerce.com/boards/viewthread/36225/
Finally look into optimizing your database using mysqltuner.pl and tuning-primer.sh Google these and run against your database, follow the recommendations.
You should also configure your store to periodically clean the visitor logs:
Personal note: I too experienced the same performance drop, implementing a lot of the above helped significantly. You need to keep monitoring your sites performance and adjust settings as necessary.
Good luck!