Typically when you run a lot of traffic you want to have heavy-duty apps and support behind it, such as WebSphere or WebLogic, Oracle, etc. Although Linux is Linux, certain distros are officially blessed by performance vendors such as IBM - meaning that they have taken care to configure and test their products according to the peculiar ways in which those distros may store things whose proper home and/or format isn't universally acknowledged. I think probably in the US, RedHat is best supported for such use. SuSe is also blessed, it's more popular in Europe. There are other regional specialities as well, so look around where you live and check the requirements for the products you intend to use.
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