README

Just random notes at this point:

 - Razor is a package management system replacing rpm and yum.  Razor
   implements management of packages installed on the system,
   dependency solving, and upgrading in a small compact code base with
   minimal dependencies.

 - Key points: one file format for package sets, specified and
   implemented by razor; no point in splitting dep-solver and package
   manager, there is too much implementation overlap.  By hand coding
   the on-disk format we have a solid foundation on which to
   implementing fast dependency solving, error recovery etc.  No
   complex dependencies in package management stack.  In other words,
   package management is *simple*, no need to overdesign it.

 - Use one simple file format as the core of the system.  The razor
   package set data structure represents a set of packages and is used
   for the current installed set, the sets available from upstream
   sources, and the set currently being install during a transaction.
   Tiered systems such as rpm+yum, deb+apt etc end up duplicating and
   reimplementing common operations on packages.  Other systems
   typically pull in external database libraries to manage the package
   meta data and in some cases each layer in the stack uses a
   different database dependency to represent essentially the same
   data.

 - Using external database libraries may seem a good idea up front,
   but monotone vs git is a good example of how you need to control
   the data structure and the on-disk format to really get excellent
   performance.  The razor package set data structure is fairly
   simple; it's an read-only, mmap()'able on-disk data structure.  The
   package set has a sorted index of the packages in the set, a sorted
   index of all dependencies and a sorted, compact directory of all
   files in all the packages.  Operations such as merging package
   sets, satisfying requires from one set against another can all be
   implemented in linear time.  Razor implements the package set
   representation down to the bytes on the disk and can optimize the
   representation and access methods to make the necessary operations
   fast and reliable.

 - The set of installed packages on a system is represented by just
   one package set file.  As we install a set of new packages, we
   prepare the new package set a temporary file and once the install
   has succeeded, we copy the package set file to the real filename.
   If there is a system crash, razor will notice the temporary file on
   boot and resume the update.  

 - We want to keep the number of dependencies down in a system critical
   component such as the package manager.  Between rpm and yum we're
   pulling in berkeley db, sqlite, expat, python.

 - During update of several packages rpm+yum leaves the system in an
   inconsistent state for long periods of time.  Power failure in this
   window causes critical system corruption.  We want to minimize the
   window.