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SDC, Part 12: Parallel Development with Merge Rules

Lee has started to talk about merging in his last blog, as he showed how to apply a hotfix to the current development version. I’ll take on his topic to talk about one of PureCM’s most powerful features: automated merging with ‘Merge Rules’.

Where does merging happen?

PureCM is a client/server based solution, so the all project data is stored in a safe repository. As a developer, you work in a so called ‘workspace’, a local copy of any project held in the repository. This solutions has the benefit of supporting both concurrent and offline development.

The following diagram shows you that there are basically two cases when you might merge:

  1. When updating your workspace based on a version or feature to get your colleagues’ changes.
  2. Directly between branches on the server. Examples for the latter are merging between different versions or development stages of a project, e.g. from development to test.


Updating a workspace is always ‘on demand’ to let the developer decide when to get the changes. Merging on the server can be performed by a user with the necessary permissions, or automatically using merge rules. 

It’s worth noting here that PureCM always merges tasks, i.e. a submitted changeset and not individual file changes. This makes merging extremely transparent, as you’re able to track that you just merged ‘bugfix a’ or ‘feature b’.

Why you want to automate merging with ‘merge rules’

Merge rules are a very powerful feature that allows you two things:

  1. Automatically track changes submitted to one branch (source) that are not present in another (destination). For example, the owner of a development version gets notified about new bug fixes made to a maintenance version
  2. Automatically merge changes submitted to one branch (source) that are not present in a second (destination).

This means that a development manager can basically work with two levels of automation. Level 1 highlights pending merges and lets him preview and confirm (or exclude) the merges. Level 2 merges changes straight away and only notifies in case of a merge conflict that has to be resolved.

This results in reduced overhead when managing parallel development and avoids human error and regression bugs. Merge rules are created automatically in the following cases:

  1. Automatic tracking is enabled from parent to child versions, e.g. from ‘Version 1’ to ‘Version 2’ as seen in the last blog
  2. Automatic merging is enabled into features to keep the feature branch automatically up to date and minimise overhead

A development manager can get an overview of all existing merge rules in the ‘Merging’ view. Here, all merge rules between active versions and features are listed. To keep the view tidy and avoid unplanned merging, merge rules are automatically removed as soon as the version or feature is completed.


Customising merge rules

The Merging view is also the place where development managers can change merge rules as needs dictate. They can change existing merge rules from automated tracking to automated merging and vice versa, or create new merge rules from the menu of the ‘Merge Rule’ folder:

The one condition to respect when creating new merge rules is that the source and destination branch must be part of the same branching hierarchy. In other words, they must have a common ancestor, which is typically the case within a project.

Performing one-off merges

Merge rules are the perfect solution if two branches have a longer lived relationship. However, sometimes you just want to merge a single change without the need to create a merge rule. This is very simple in PureCM and can be done by selecting a completed task and select ‘Merge Change To’.

This will bring up a dialogue where you can select the destination. That’s it. 

Merge tracking

Thanks to its stream-based branching, PureCM can track the merge history of any task throughout the full project hierarchy. Simply access the task properties and select the history tab to see to which versions and features it has been applied to.

We’ve actually finalised another nice feature for our next release in July that allows users to list all releases a task is present. If you’ve ever wondered whether a bugfix has gone into this or that release, this new feature will be an invaluable time saver!


This blog has covered how development managers can take advantage of PureCM Professional’s merging capabilities to automate parallel development.

  • Merge rules either track or merge changes automatically
  • Existing merge rules can be customised and new merge rules created
  • Notifications are automatically made to the owner of the destination version
  • Merge rules are automatically removed once a version or feature is completed

Stay with us and learn how you can reschedule tasks and features as part of an agile planning process – even if coding has already started!

PureCM 2009-1 Preview

Before we talk features

The first blog in the new year, so first of all my best wishes for 2009! Let me use this fresh start to give you a summarised outlook on PureCM 2009-1, our next major release coming with some rather big changes. So now you might expect a huge list with all the main features, but allow me to make a small detour before getting there...

How you would like to look at your data

If you look at your file system, your data is organised in folders and files. Typically, the highest level folder separates your projects. This is also the approach used by most source control tools such as VSS, SVN or Perforce to structure data in their database. You make changes to a copy of your files or folders, and they get sent back to the database and stored as a new revision.

PureCM uses an additional high level object that includes the files and folders of a project: streams. Streams have two major advantages. First, they remember the relationship between each other, making merging (and merge tracking!) much more transparent. Second, they allow for so called “cheap” snapshots, i.e. branching without making file copies. This allows you to setup your configuration for parallel development, increasing productivity.

Depending on the complexity of your shop, you can create as many (or little) streams as you wish to separate projects, teams, development from maintenance etc... All projects –organised in streams – are stored in the PureCM repository database to keep it safe. You can find some examples later in this blog [anchor].

As a development manager, you need to have all information about your projects at hand. You want to know which changes have gone into a project, which bugfixes need to be merged, or where you are including a specific version of a shared library. So the first big change in PureCM 2009-1 is its repository-centric GUI. To structure the large amount of information present in a repository, the new task-specific views filter the information you need to speed up navigation.

NEW: Task-specific GUI views

As a developer, getting your own sandbox to work on a task in isolation is one of the main views you need, so this is what you get with PureCM 2009-1: the project files and folders, as well as your current changes and all submitted changes to the stream your current workspace is based on. You can thus organise your own changes into changesets, and track the submitted changes from your colleagues you need to integrate.

Note the navigation bar just below the menu bar, which gives you quick access to all the task-specific views. Say you are required to switch to an urgent bugfix and would like to get an overview of your workspaces in this repository, just click on “Workspaces” and select or create the appropriate one.

Likewise, go to the “Streams” view to browse the server, branch your project, and create a release or a stable baseline. You can find out more details about the advantages of the task-specific views in this blog.

Once you have finished a task and would like to move your workspace to the next project or baseline, another new feature in 2009-1 helps you to do this easily: Workspace Rebasing. This feature automatically populates your workspace with the content of any stream you select. No need to delete the existing workspace and create a new one anymore.

NEW: Merge paths for parallel development

Talking of streams actually brings us back to the above discussion about the project structure of a PureCM repository. According to the complexity of your projects, your repository might resemble one of the following (stylised) examples:

In example A, the streams remain typically the same and changes get merged (or promoted) from development to QA to Production. Example B shows a mainline development example with release snapshots, while example C extends the former to a multi-product setup with shared libraries.

You can immediately see that you can use stream folders to organise your streams (or codelines). In this way, you can define permissions on the folder level that get inherited by the streams. This would allow you to define release streams as read only or editable, i.e. used as labels or maintenance branches. In other words, any stream will evolve in isolation or stay static after creation, depending on the stream (folder) policy.

With the new 2009-1 release, you will be able to define Merge Paths between any two streams to track and merge changes in real time. Say you know that you want to keep track of differences between “Feature A” and “Mainline”. Create a Merge Path and you will be able to see at any time, which changes are present in one stream but not in the other, just as in the screenshot below.

This information is also visible in the "Streams" view to highlight pending merges in your stream hierarchy. After merging, the changes get moved to the “Merged changesets” node to track them. Note that all that happens directly on the server, without the need to create a workspace for merging (but you could of course choose to do so as an option).

Using merge paths, you will even be able to define automatic merges! This basically means that any change submitted to the base stream gets instantly merged into the destination stream. In case of conflicts, PureCM automatically moves the change to “Pending Changesets” to allow you to resolve the conflict manually. Of course, one can still choose to make a one-off merge directly on the changeset without defining a merge path.

Feature summary

The essence of the PureCM 2009-1 release is its focus on making work with multiple projects easier. It will not just be easier to work with parallel configurations using Merge Paths and Workspace Rebasing, but also to get the relevant information with the new task-specific views. But before I forget: PureCM obviously gives you more than just that, including advantages like:-

  • Eclipse and Visual Studio integration
  • Proxy Server for distributed teams
  • CruiseControl.NET and FinalBuilder integration
  • Shared libraries between projects (called “Components” in PureCM)
  • Integrated issue management
  • .NET/Java APIs

We will shortly publish the PureCM 2009-1 beta2, which I will certainly announce in this blog. I look forward to getting your feedback once you have been able to play around with it!


Better Merging - Part 1

One of the great strengths of PureCM has always been it's support for parallel development. PureCM's merge functionality allows you to keep track of your changesets and which streams they have been submitted against while making it easy for you to merge these changes into other streams as desired. Now we are looking at making merging even more powerful and simple, but let's first take a look at how merging works today.

Merging Today

The original merge process required you to own a workspace for the stream you are merging into. This gives you a number of benefits such as the ability to easily test each change before submitting it to the server. This is shown as (B) in the lower half of the picture below.

However this process can be time consuming and is hard for manager who may not always have a workspace for each stream. This led to a solution that allows users to quickly merge changes between similar streams, which we called “quick merge”. This allows you to merge changes directly on the server removing the need for a workspace in these situations (A in the picture above).

So far, quick merge will only merge changes where there is no possibility of a conflict. This works well for merging last minute fixes into a release stream or early on in the development cycle when not much has changed in the new development stream but we felt there was a need to improve on this restriction.

Moving Forward

The next stage in this evolution is to allow you to resolve conflicts as part of quick merge without the need for a workspace. This will simply launch the familiar PureCM resolve tool when quick merge finds a conflict.

Combining this new functionality with automated test and build processes (such as PureCM's Cruise Control plug-in) provides a fast and simple way to keep your streams up to date while giving you the security that any errors are picked up immediately so you can assign someone to look at it.

This new advancement to quick merge opens up a realm of possible future features for the tool to help speed up your development process through merging. One example of this is the creation of automatic merge paths to control the flow of your changes through your development streams. Plenty of reasons to look forward to the 2009-1 release – and keep your eyes open for future blogs for information about where we go from here!