I want to keep track of the number of times my single entry page is viewed. However, it seems that I have to disable page caching in order to do this. How much of a performance penalty will that be? Are there alternatives to counting the number of page views? I want to be able to display the page views, sort by page views, etc.
On an average site I would say that although there will be a performance impact it is highly unlikely to create any issues, or even be noticed.
When you scale up to bigger sites these things can be an issue but I think you need to be pulling a lot of traffic for that to become serious.
Of course, this is just my opinion and completely anecdotal. Faster is better but I do firmly believe that many folk worry about this unnecessarily. Often quite fast is fast enough.
Are you using ExpressionEngine to track page view? The way I generally desable all tracking in EE and rely on external services to provide me with the analytics I need. That way, I can be totally independent from caching.
To me EE is not the right tool for that. Any dedicated analytics service will be better at it.
Google Analytics is such a service at an entry level. While sufficient for most users, you might want to supplement it with other systems on bigger projects.