# Each httpd runs in its own fork and memory space so we cannot
# share the cache info across httpd's (even if we could, it wouldn't
# work for multiple web server machines).  So each httpd keeps a
# cache for itself.  A problem arises when one httpd process modifies
# a node that another process has in its cache.  How does that other
# httpd process know that what it has in its cache is stale?