Developer Document Catalog (3.3.22)

# Development repository formats

## Using development repository formats

### Motivation

We believe that we can continue to gain substantial performance benefits by altering the repository storage in bzr. The more feedback we can get on the changes during the development process the better.

To make it possible to get more feedback we are going to expose the current development formats to the users of our development trunk ‘bzr.dev’. The technical details of the individual formats are at the end of this document.

### Format names

The current development format will be called ‘development’. Each time the development format changes, the prior development format will be renamed to e.g. ‘development0’, ‘development1’ etc.

When a release of bzr is done, all the older numbered development formats will be removed from ‘bzr.dev’, so we will not be carrying the code for them around indefinately.

### Support for upgrade and migration

The preservation and renaming policy makes it quite safe for users to test out development formats (though we cannot guarantee bugs of course - it is development code):

> - users of a given development format can always get back onto regular formats by switching to the next bzr released version which is guaranteed to be able to upgrade from that development format.

> - users that routinely use bzr.dev should upgrade to the most recent development version available before pulling in bzr.dev changes around release time, as that is when old format cleanups will occur.

We cannot guarantee backwards compatibility though, because some of the planned work may be ‘upgrade only’. Please see `bzr help formats` for the text of the ‘development’ format which will indicate its compatibility with other formats if you need to interoperate with users or services that do not have bzr.dev.

### Before converting to a development format

Run a `bzr check` with the version of bzr that you will be using. `bzr check` gets updated as we find new things that are inconsistent with existing repositories. While only a small number of repositories are likely to have any given error, it is best to check just in case.

If `bzr check` reports a problem, run this command:

    bzr reconcile

Note that reconcile can take many hours, particularly if you are reconciling one of the ‘knit’ or ‘dirstate’ format repositories. If you have such a repository, consider upgrading it to ‘pack-0.92’ first, which will perform reconcile significantly faster.

### Creating a new development format branch

If you’re starting a project from scratch, it’s easy to make it a `development` one. Here’s how:

    cd my-stuff
    bzr init --development
    bzr add
    bzr commit -m "initial import"

In other words, use the normal sequence of commands but add the `--development` option to the `init` command.

### Creating a new development format repository

If you’re starting a project from scratch and wish to use a shared repository for branches, you can make it a `development` repository like this:

    cd my-repo
    bzr init-shared-repo --development .
    cd my-stuff
    bzr init
    bzr add
    bzr commit -m "initial import"

In other words, use the normal sequence of commands but add the `--development` option to the `init-shared-repo` command.

### Upgrading an existing branch or repository to development

If you have an existing branch and wish to migrate it to a `development` format, use the `upgrade` command like this:

    bzr upgrade --development path-to-my-branch

If you are using a shared repository, run:

    bzr upgrade --development ROOT_OF_REPOSITORY

to upgrade the history database. Note that this will not alter the branch format of each branch, so you will need to also upgrade each branch individually if you are upgrading from an old (e.g. < 0.17) bzr. More modern bzr’s will already have the branch format at our latest branch format which adds support for tags.

### Starting a new development format branch from one in an older format

This can be done in one of several ways:

1. Create a new branch and pull into it

2. Create a standalone branch and upgrade its format

3. Create a knitpack shared repository and branch into it

Here are the commands for using the `pull` approach:

    bzr init --development my-new-branch
    cd my-new-branch
    bzr pull my-source-branch

Here are the commands for using the `upgrade` approach:

    bzr branch my-source-branch my-new-branch
    cd my-new-branch
    bzr upgrade --development .

Here are the commands for the shared repository approach:

    cd my-repo
    bzr init-shared-repo --development .
    bzr branch my-source-branch my-new-branch
    cd my-new-branch

As a reminder, any of the above approaches can fail if the source branch has inconsistent data within it and hasn’t been reconciled yet. Please be sure to check that before reporting problems.

### Develoment formats for bzr-svn users

If you are using `bzr-svn` or are testing the prototype subtree support, you can still use and assist in testing the development formats. The commands to use are identical to the ones given above except that the name of the format to use is `development-subtree`.

WARNING: Note that bzr only supports one-way conversion to the subtree format `development-subtree`. Once you are using `development-subtree` you cannot pull or merge back into a regular format such as `pack-0.92`, `development` etc.

The `development-subtree` format is required for the bzr-svn plug-in but should otherwise not be used until the subtree feature is complete within bzr.

### Reporting problems

If you need any help or encounter any problems, please contact the developers via the usual ways, i.e. chat to us on IRC or send a message to our mailing list. See https://www.breezy-vcs.org/pages/support.html for contact details.

## Technical notes

### When to create a new development format

Whenever a code change will result in incorrect behaviour with existing `development` repositories. Changes in push/pull/init/commit/merge have all been known to do this in the past.

### How to create a new development format

1. Register two new formats with the next available sequence number. e.g. `development1` and `development1-subtree`. (You can see the current development format for an example. These should:

   - Use your new development repository/branch/tree classes

   - Have really bare bones help - something like ‘changes X to be Y see …developers/development-repo.html’

   - Be hidden and experimental.

2. Change the repository class (or branch or tree) in the `development` and `development-subtree` formats to point to the new class you are creating.

3. Add a new development format (and tests!). Repository formats are in `breezy.repofmt`. You probably want to reproduce the current development format from `breezy.repofmt.pack_repo` with just new disk format strings, `_get_matching_bzrdir` and help.

4. Register your development format with the various registries. At the moment you need to update:

   > 1. `breezy/bzrdir.py` to register the WT/Branch/Repository collection.

   > 2. `breezy/workingtree.py`, `breezy/branch.py`, `breezy/repository.py`, each one maintains a direct list of their respective formats.

   > 3. For repositories, you also need to update the InterKnit1and2 class. This is responsible for converting between rich-root and non-rich-root repositories.

   > 4. For repositories based on KnitPackRepository, you need to update `breezy/tests/test_pack_repository.py` to add the class to the tested permutations.

5. Alter any other things that do class based tests. The easiest way to find these is a grep for Development in breezy - and please refactor as you find these to reduce the relevance this step has, as it should not need to exist.

6. Now subclass/create from scratch/whatever the live object code you need to change to introduce your new format. Keep in mind that eventually it will become the default format, so please don’t keep subclassing the last releases code, rather consider making the last releases code a subclass of your new code (if there is a lot in common) so that we can eventually remove that format once it becomes ancient (or relegate it to a plugin).

7. Once you have made the changes that required a new disk format, you should submit the resulting branch to be merged. Other changes - to take advantage of whatever new feature you have added - should be sent in separately, because the disk level changes are a contention point between multiple developers.

## Format Details

### development

Not currently available, as our development formats are all rich root or subtrees now.

### development-rich-root

Currently an alias for Development6Subtree

### development-subtree

Currently an alias for Development6Subtree

### Development6RichRoot[Subtree]

These formats use the new groupcompress delta compress and a CHK(Content Hash Key) based inventory store which is much faster at incremental operations than the prior XML based store. Note Converting from a non-rich-root to a rich-root format is a one-way upgrade, and you cannot merge back afterwards: using this format for everyday use is likely to cause all developers of a project to upgrade to a rich-root format themselves. This is fine, as bzr is moving to make rich-root formats the default and to get all users to upgrade, but we have not finalised the migration process, and until we do do not recomment that casual users upgrade. Users of bzr-svn are already using rich-root formats and can test with this with impunity.