8000 daily viewers should not be an issue for a 2GB droplet but this will depend on your site(s) configuration and resource use. What messages are you seeing in the MySQL log file in /var/log/? The log should provide more detail about what is occurring and will give us a starting point to resolve it.

Sorry. Can you give me detailed instructions? Because I am not a professional user.

Thanks

Look at your memory consumption (free -h) and CPU loading (command top, check the value of loading average, if it’s more than ~2 your CPU is highly loaded). Also, make sure you have enough disk space (df -h).

As a way to improve overall performance you can use Varnish cache as a reverse proxy for all of your website, but this would help only with anonymous traffic.