Upgrades
========

Bazaar has a strong commitment to inter-version compatibility both on disk and
over the network.  Newer clients should be able to interact with older
versions on the server (although perhaps not at optimal speed) and older
clients should also be able to communicate with newer versions of Bazaar on
the server.  Divergences from this rule are considered bugs and are fixed in
later versions.

That said, Bazaar is constantly improving and the most recent versions are the
most featureful and have better performance.  In particular, the Bazaar
versions 2.0 and later have significant advantages over earlier versions,
including a more compact disk format, faster network operations and overall
performance improvements.  With the 2.0 release, Bazaar has moved to a
stable/development release model where the 2.x series is maintained with
bugfixes releases for six months, while simultaneously the 2.(x+1) series is
being developed with monthly beta releases that are suitable for everyday use.
Bazaar development has a stable trunk with an extensive test suite, so there
is no reason to fear using the development series for everyday use, it simply
changes more often than the stable series.  Many users do run the development
version of Bazaar and update it regularly, including most of the Bazaar
developers themselves.


Software upgrades
-----------------

Upgrading the Bazaar software is as simple as re-installing the Python package
using either the latest binary package for Windows or Mac OS X, the binary
package provided by your GNU/Linux distribution, or installing from the source
release.  See http://wiki.bazaar.canonical.com/Downloads for the latest
releases for all supported platforms.

Bazaar's later versions support all of the earlier disk formats (back to the
very first one), so there is no need to upgrade the branches on the disk when
upgrading the software.  To make use of particular new features that might
need updated versions on both the server and developer's machines, it does not
matter if the clients or the servers are upgraded first.


Disk format upgrades
--------------------

In its evolution, Bazaar has used a sequence of disk formats for improved
storage efficiency and speed.  With the new disk format released in version
2.0, there is a commitment to keep that disk format until version 3.0 is
released, which has not even been planned yet.  (Bazaar 2.0 was released
almost two years after Bazaar 1.0.)  As a result, disk format upgrades should
be extremely infrequent.

If there are existing branches in an older format that you would like to
upgrade to the latest format, you can see the `2.0 Upgrade Guide
<../upgrade-guide/index.html>`_ for more information.  From the system
administration perspective, it is important to coordinate the timing of
various upgrades in the process.  First, the central branches on the server
should be upgraded.  Next, any local mirrors that developers have should be
upgraded.  Finally, developers' local branches should be upgraded.  These
upgrades will require an appropriate version of the software whenever they are
performed.  (It is possible to upgrade branches remotely over the network, but
it may be much slower.)


Plugin upgrades
---------------

When Bazaar does update its version, plugins that use the Bazaar API may need
to be upgraded to reflect changes in that API.  Some plugins have strict
version dependencies on the version of the Bazaar API that they will accept.
If this is the case, then you should ensure that the plugins you depend on
have been updated *before* you upgrade your Bazaar version to avoid a
situation where your plugins won't work with the installed version of Bazaar.
If this does happen, then the solution is simply to reinstall the previous
version of Bazaar that *did* work with the plugins.  For installations that
depend on a large number of plugins, this sort of version upgrade should be
tested in a safe sandbox to ensure that the entire collection of Bazaar and
its plugins can all work together.
