The following excerpt from [this post](http://2bits.com/articles/drupal-core-caching-and-contributed-content-caching-modules.html) led me to this question:

> 
> **Cache contention**
> 
> 
> On a large site, if you are using
> MyISAM, contention occurs in the
> database tables when the cache is
> forced to clear after a node or a
> comment is added. With tens of
> thousands of filter text snippets
> needing to be deleted, the table will
> be locked for a long period, and any
> accesses to it will be queued pending
> the purge of the data in it. The same
> is true for the page cache as well.
> 
> 
> This often causes a "site hang" for a
> minute or two. During that time new
> requests keep piling up, and if you do
> not have the MaxClients parameter in
> Apache setup correctly, the system can
> go into thrashing because of excessive
> swapping.
> 
> 
>