I've been struggling with this problem for a while and I decided that
I should ask the list because someone here has surely solved this
before.  The trouble is that I haven't found an intelligent way to
update from one quarterly release to the next on a production server.
A mail delivery host that I administer is running Solaris 8 with
pkgsrc-2005Q1.  Obviously, I would like to update this to the latest
release.  What is a good way to do this with minimal downtime?

I know I could build binary packages on another Solaris 8 computer,
move those binary packages to the production server and then install
them.  This is possible but isn't my ideal for various reasons.

Another option I've tried, but hasn't been too successful so far, is
to set these variables in /etc/mk.conf.

LOCALBASE=/usr/pkg-alt
PKG_DBDIR=/var/db/pkg-alt

Then, in theory, I would be able to build an entirely new set of
packages from the latest quarterly.  I would change startup scripts
and PATHs to start binaries from /usr/pkg-alt/[s]bin.  Later I would
build a future quarterly under the default directories: /usr/pkg and
/var/db/pkg.  This idea appeals to me the most but I haven't had as
much luck building packages in this way as I would like.  Those two
lines are the only lines I have in my /etc/mk.conf when I'm building
the "alt" setup.  When building normally I have no /etc/mk.conf and
everything works great.  Is this idea reasonable?

What are some other ways to achieve my goal?  

Ryan