Table of Contents (3.3.22)

# Data migration

## Preparing for data migration

Before starting a migration, there are a few important things to do first:

1. Take a complete backup.

2. Take some time to purge obsolete branches.

A complete backup gives you a safety net in case anything goes wrong.

Purging obsolete branches reduces the amount of data that needs to be migrated. See `Finding obsolete branches`_ later for some tips on doing this.

## Introducing the upgrade-related commands

There are 3 important commands to be aware of when migrating data.

- check - check a repository, branch or tree for data integrity errors

- reconcile - fix data integrity errors

- upgrade - migrate data to a different format.

reconcile is rarely needed but it’s good practice to run check before and after running upgrade.

For detailed help on these commands, see the Breezy User Reference.

## Communicating with your community

To enable a smooth transition to the new format, you should:

1. Make one person responsible for migrating the trunk.

2. Test the migration of trunk works successfully.

3. Schedule a time for the trunk migration and notify your community in advance.

This advance warning should be long enough for users to have time to upgrade Breezy and any required plugins before the migration date.

For larger projects, allow some time for the migration itself. You should have a good idea of how long the migration will take after doing the test migration. It may make sense to do the migration on a weekend or a Friday, giving yourself some breathing space if things go wrong.

After the trunk is migrated, you’ll need to notify your community accordingly, giving them instructions as to how to migrate their local branches. Sample instructions are provided later in this document.

## Migrating a standalone branch

The steps are:

1. Run brz check.

2. If there are errors, try using brz reconcile to fix them. If that fails, file a bug so we can help you resolve the issue and get your trunk clean. If it works, take a backup copy of your now clean trunk.

2. Run brz upgrade –format where format is 2a or later.

3. Run brz check to confirm the final result is good.

## Migrating branches in a shared repository

Upgrade things in the following order:

1. Upgrade the shared repository.

2. Upgrade the branches.

3. Upgrade any lightweight checkouts.

As in the standalone branch case, be sure to run check before and after the upgrade to check for any existing or introduced issues.

## Migrating branches on Launchpad

You have two options for upgrading your Launchpad branches. You can either upgrade them remotely or you can upgrade them locally and push the migrated branch to Launchpad. We recommend the latter. Upgrading remotely currently requires a fast, rock solid network connection to the Launchpad servers, and any interruption in that connection can leave you with a partially upgraded branch. The instructions below are the safest and often fastest way to upgrade your Launchpad branches.

To allow isolation between public and private branches, Launchpad uses stacked branches rather than shared repositories as the core technology for efficient branch storage. The process for migrating to a new format for projects using Launchpad code hosting is therefore different to migrating a personal or in-house project.

In Launchpad, a project can define a development series and associate a branch with that series. The branch then becomes the focus of development and gets special treatment and a shortcut URL. By default, if anybody branches your project’s focus of development and pushes changes back to Launchpad, their branch will be stacked on your development focus branch. Also, branches can be associated with other Launchpad artifacts such as bugs and merge proposals. All of these things mean that upgrading your focus of development branch is trickier.

Here are the steps to follow:

1. The nominated person grabs a copy of trunk and does the migration locally.

2. On Launchpad, unset the current trunk from being the development focus. (This must be done or the following step won’t work as expected.)

   1. Go to your project’s home page on Launchpad

   2. Look for “XXX is the current focus of development”

   3. Click on the edit (pencil) icon

   4. Click on “Change details” in the portlet on the right

   5. Scroll down to where it says “Branch: (Optional)”

   6. Blank out this input field and click “Change”

3. Push the migrated trunk to Launchpad. See below if you want your new migrated development focus branch to have the same name as your old pre-migration development focus branch.

4. Set it as the development focus. Follow the instructions above but at step 5, enter the name of the newly migrated branch you just pushed.

5. Ask users subscribed to the old trunk to subscribe to the new one.

In summary, these steps mean that the old trunk is still available and existing branches stacked on it will continue to be so. However, the development focus has switched to the migrated trunk and any new branches pushed to Launchpad for your project will now stack on it.

You are now ready to tell your community that the new trunk is available and to give them instructions on migrating any local branches they have.

If you want your new migrated development focus branch to have the same name as your old pre-migration branch, you need to do a few extra things before you establish the new development focus.

1. Rename your old pre-migration branch; use something like foo-obsolete-do-not-use. You will really not want to delete this because there will be artifacts (bugs, merge proposals, etc.) associated with it.

2. Rename the new migrated branch to the pre-migration branch’s old name.

3. Re-establish the development focus branch using the new migrated branch’s new name (i.e. the old pre-migration branch’s original name).

## Migrating local branches after a central trunk has migrated

To migrate a standalone branch:

1. Grab the latest branch from the central location into a new directory.

2. Pull or merge any changes you’ve made in your existing branch into the new branch.

To migrate branches in a shared repository:

1. Create a fresh shared repository in the new format (2a or later).

2. Grab the latest branch from the central location into a new directory inside the shared repository.

3. Decide which of your local branches you want to migrate. (If you haven’t already, now’s a good time for `Finding obsolete branches`_ and purging them, after backing up first of course.)

4. To migrate each local branch of interest, there are 2 options:

> - init an empty branch in the new repository and pull the revisions from the branch in the old repository across.

> - In the new repository, branch from trunk to the new branch name then merge your changes from the matching branch in the old repository.

The first method will give you a branch which is identical (in terms of revision history) to the old branch, but it’s parent branch will be set to the old branch, not your new trunk. If you use this method, you’ll probably update the `parent_location` configuration variable in the `branch.conf` file with:

    brz config parent_location=XXX

`XXX` being the URL to your new trunk.

In contrast, the second approach sets up the parent branch correctly. However, it isn’t ideal if you’re not ready to include all the latest revisions from trunk into that branch yet.