Is this a dos attack?

Hello 

Can you please take a look at this access log?
 
 
They request some pages that doesn't exist on my site at the same time with my own IP (54.36.158.33) and the site get database error.

What's the problem?
How can I prevent it?

Thanks

which log file is that nginx/apache? if you are using nginx then try to check nginx log file in /var/log/nginx/