I have had a big problem with my wordpress setup since long time on this blog. It is that the comment replying and approving process was very slow and sometimes it made the web server to give timeout errors for all people trying to access the site including me when I was replying to the readers comments, I had to press the submit button twice on wordpress comments admin panel to reply to the comments, and even after I have approved the comments, some leaves unapproved when i refresh the page. For a long period I thought the problem might be the nginx+memcached setup I was using, and sometimes I have even made my mind to switch away from these complex configurations and run a fine tuned LAMP stack to eliminate this kind of problems. And sometimes I have even thought to offload the comments system to disqus because then I don’t have to face this serious trouble when replying and approving comments, but I like the traditional in built comments system and I wanted to keep that
I’m not a programmer and I if you face these kind of problems you also don’t need to be one to possibly fix it
WordPress is community built software and its very unlikely that it will have a severe bugs like I faced for such a long time, if something is wrong for a long time period and doesn’t fix with WordPress upgrades, you are just doing it wrong,
Check your plugins
These kind of problems are caused by the badly coded plugins ( If you run complex server configuration like me you cant actually blame those at first hand for not working with your site ) .
Solution
WordPress’s rule of thumb to evaluate these problems is disabling your plugins one by one and see what happens. And you will be amazed how a small plugin can cause so much problems to you. Of course you can try by disabling plugins one by one by checking but the easiest method is just deactivate all the plugins and see whats up, if the problem is gone, the problem definitely lies on plugins, and now go to “Recently active” plugins list and activate one by one and find the problematic plugin. Its just simple as that 
In case if you interested about the plugin which caused all my comment section problems, its the “Subscribe to comments” plugin, I have checked the support section of that plugin and no one seemed to have the problems which I had, So it simply reflects the fact that you cant always blame the developer if you doesn’t run it on stuff it intended to.