If your server's load is unusually high. You may want to check your raw access logs.
You may find suspicious IPs that seems to brute force / overwhelm / attack your site.
If you find it, just block those IPs and you will save / reduce your server's load greatly.

In your .htaccess file, you can add the following codes somewhere (changing the IPs to suit your needs. Each command on one line each):

order allow,deny
deny from 1.2.3.4
deny from 2.3.4.
allow from all

You can deny access based upon IP address or an IP block. The above blocks access to the site from 1.2.3.4, and from any sub domain under the IP block 2.3.4. (2.3.4.1, 2.3.4.2, 2.3.4.3, etc.) I have yet to find a useful application of this, maybe if there is a site scraping your content you can block them, who knows.

You can also set an option for deny from all, which would of course deny everyone. You can also allow or deny by domain name rather than IP address (allow from .xhanch.com works for www.xhanch.com or xxx.xhanch.com, and so on)