Before making the domain move the other day, I made a mistake by deleting something I shouldn’t have from the database. It was the comment_karma field located within the wp_comments table. A long time ago, I remember installing a plugin called Comment Karma which enabled visitors to rate a comment up or down thus promoting the best user rated comments to the top.
I thought that by installing this plugin a long time ago, that it had created this entry in my database. Thinking another plugin left its stuff behind in my database, I removed it only to find out that removing it broke my commenting system to the point where the incrementer broke. To make matters worst, I didn’t do a database backup since I thought I was removing something plugin related. However, thanks to Michael Torbert, he helped me put the comment_karma field back in its location and once I did that, everything worked again.
So, when I dived into the WordPress-Dev IRC channel to see what this field is used for, someone said it was not used by anything in core and Michael told me he couldn’t find anywhere that field was being used. But, if it was not being used in core, why would it cause the commenting system to break when it’s removed?
The overall lesson here, don’t do ANYTHING to your database unless you backup first. Complacency is your enemy.