A client of mine has a blog with high traffic. Yesterday we had some problems with that in our server, so I asked him to enable WP Super Cache. After he did so, I still noticed that I had about 10-15 MySQL connections in sleep status. This is really weird, because that usually happens when you use mysql_pconnect which WordPress doesn't do. I even did an extensive search in all his blog code (including plugins) and didn't find any call to mysql_pconnect (or any other way to connect to MySQL which could create a persistent connection).
My question is: if the blog is using WP Super Cache to cache all of his pages, why is WordPress opening so many database connections? I could understand a couple of connections if the content being served is not cached, but the number of them remained very high for a long time. Is there any way (some configuration error maybe) that database connections could still be established despite of WP Super Cache being enabled? Is it possible that WP Super Cache doesn't prevent the connection even when the page is cached?