I was working on a site tonight and the site was shutdown by the host for a massive 18% cpu spike, this site has been recently upgraded (last several weeks) to 2.3 version. Seems the support staff said this:
Here is a summary of your CPU and memory usage on your account over the past 24 hours:
CPU: 2.47 %
MEM: 0.71 %
We believe the processes shown below are responsible for this level of resource usage, please keep in mind if you run a dynamic site off WordPress or another script it might just show index.php which is the primary file that runs the entire site:
artanv articleanvil.com 2.47 0.71 1.8
Top Process %CPU 18.0 /usr/bin/php /home/artanv/public_html/index.php
Top Process %CPU 14.0 /usr/bin/php /home/artanv/public_html/admin/index.php
Top Process %CPU 11.0 /usr/bin/php /home/artanv/public_html/index.php
While I was doing some general edits, adding banner blocks etc, I did nothing that should have caused such a spike. The site has been intact since like 2005, and has 75k articles active with 123k more to go, and 50k users.
The resource usage has been steady at 3.4 gigs xfer and a few hundred hits a day without problem.
Further info from support:
Also we have found your mysql queries are causing major problem for the server. And queries are consuming too much cpu time.
595 rows in set (0.00 sec)
We have found too many logs in slow quereies for your database:
User@Host: artanv_articlems[artanv_articlems] @ localhost 
# Query_time: 5 Lock_time: 0 Rows_sent: 1 Rows_examined: 2838
SELECT COUNT(*) AS found_rows FROM ams_articles WHERE article_state = 1 AND MATCH (article_title, article_text, article_keywords) AGAINST('I Still Remember You: The Future of Social Networking') LIMIT 300;
# Time: 100419 8:30:16
I am hoping to get this site back up and running, but am waiting for support to release / restore the files (they deleted them it seems as I cannot access them, trust me I am pissed but thats a seperate issue).
I know there was an issue with a sql injection attacks vulnerability in the past? have these been corrected?
The only change I could have made that might impact things was the "allowed tags" for posts, I removed the "ALL" and put in the tags for i,u,a, etc, but not sure if it needed commas seperating the tags, or if it needed closed tags ex: <i> </i>. so not sure if that screwed anything up
More from support:
Thank you for your attention to this, and I apologize for these issues. I re-enabled your account to see the usage, and the server's load immediately started to spike. It had started spawning many processes for your site's index.php, and I've attached a file that shows a snippet of these processes. Your account was also generating many long mysql queries that were causing tmp table writes, which cause performance issues as well. I've added this to the attached file also.
If you believe that this could be due to coding related issues with your site, then I'll be happy to create a backup for you to download so that you may investigate in a local environment.
Iwill try to check the attached files and post more.
Please I need help so bad.