tor/doc/spec/proposals/104-short-descriptors.txt

                      Long and Short Router Descriptors


  Some of the costliest fields in the current directory protocol are ones
  that no client actually uses.  In particular, the "read-history" and
  "write-history" fields are used only by the authorities for monitoring the
  status of the network.  If we took them out, the size of a compressed list
  of all the routers would fall by about 60%.  (No other disposable field
  would save more than 2%.)

  One possible solution here is that routers should generate and upload a
  short-form and long-form descriptor.  Only the short-form descriptor should
  ever be used by anybody for routing.  The long-form descriptor should be
  used only for analytics and other tools.  (If we allowed people to route with
  long descriptors, we'd have to ensure that they stayed in sync with the
  short ones somehow.)  We can ensure that the short descriptors are used by
  only recommending those in the network statuses.

  Another possible solution would be to drop these fields from descriptors,
  and have them uploaded as a part of a separate "bandwidth report" to the
  authorities.  This could help prevent the mistake of using long descriptors
  in the place of short ones.

  Thoughts? -NM

Migration:

  For long/short descriptors:
     * In 0.1.2.x:
       * Authorities should accept both, now, and silently drop short
         descriptors.
       * Routers should upload both once authorities accept them.
       * There should be a "long descriptor" url and the current "normal" URL.
         Authorities should serve long descriptors from both URLs.
     * Once tools that want long descriptors support fetching them from the
       "long descriptor" URL:
       * Have authorities remember short descriptors, and serve them from the
         'normal' URL.