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Just random notes at this point:
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- Razor is a package management system replacing rpm and yum. Razor
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implements management of packages installed on the system,
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dependency solving, and upgrading in a small compact code base with
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minimal dependencies.
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- Key points: one file format for package sets, specified and
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implemented by razor; no point in splitting dep-solver and package
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manager, there is too much implementation overlap. By hand coding
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the on-disk format we have a solid foundation on which to
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implementing fast dependency solving, error recovery etc. No
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complex dependencies in package management stack. In other words,
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package management is *simple*, no need to overdesign it.
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- Use one simple file format as the core of the system. The razor
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package set data structure represents a set of packages and is used
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for the current installed set, the sets available from upstream
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sources, and the set currently being install during a transaction.
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Tiered systems such as rpm+yum, deb+apt etc end up duplicating and
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reimplementing common operations on packages. Other systems
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typically pull in external database libraries to manage the package
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meta data and in some cases each layer in the stack uses a
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different database dependency to represent essentially the same
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data.
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- Using external database libraries may seem a good idea up front,
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but monotone vs git is a good example of how you need to control
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the data structure and the on-disk format to really get excellent
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performance. The razor package set data structure is fairly
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simple; it's an read-only, mmap()'able on-disk data structure. The
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package set has a sorted index of the packages in the set, a sorted
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index of all dependencies and a sorted, compact directory of all
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files in all the packages. Operations such as merging package
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sets, satisfying requires from one set against another can all be
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implemented in linear time. Razor implements the package set
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representation down to the bytes on the disk and can optimize the
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representation and access methods to make the necessary operations
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fast and reliable.
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- The set of installed packages on a system is represented by just
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one package set file. As we install a set of new packages, we
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prepare the new package set a temporary file and once the install
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has succeeded, we copy the package set file to the real filename.
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If there is a system crash, razor will notice the temporary file on
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boot and resume the update.
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- We want to keep the numer of dependencies down in a system critical
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component such as the package manager. Between rpm and yum we're
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pulling in berkeley db, sqlite, expat, python.
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- During update of several packages rpm+yum leaves the system in an
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inconsistent state for long periods of time. Power failure in this
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window causes critical system corruption. We want to minimize the
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window.
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