Posts Tagged ‘branching and merging’

Branching and Merging, or How to Learn to Love Change

July 11th, 2011 by clucca

Branching and merging is one of those things in software development that tends to drive most developers right around the bend. It’s understandable why so many fear branching and merging – after all, so many things can go wrong once you veer off the baseline and wander into uncharted territory and try to get back. But instead of fearing the beast, here are two tips to help you drag it up out of the basement, smack it around, and show it who’s boss.

Just so we’re all on the same page, branching and merging is defined as the process of duplicating part of a software development project baseline so that some parallel development can take place, say, to fulfill a customer’s change request, then once completed it’s merged back into the baseline.

The fat can hit the fire in two places: first, determining when and why a branch should be started, and then when and how it’s merged back into the main development baseline. Done poorly, both of these actions can result in confusion, errors, and delays. No wonder branching and merging gives developers night-sweats.

Because branching and merging has the potential to be problematic, some developers unintentionally make it worse by either branching too often or merging too late. The result can be increased risk in errors and/or a decrease in productivity.

So what’s a developer to do?

Start by determining what should rightfully constitute a branch – does a branch get triggered by a change request? How about a specific integration effort? Perhaps it’s based on system architecture? These are just a few of the common branching strategies, so you need to decide which one provides you with an acceptable balance of risk versus productivity. Do you want to branch and merge early and often, reducing risk but also slowing productivity? Or are you willing to roll the dice that things go smoothly during development so you’ll hold off on merging to potentially increase productivity and value?

Where things can get really sticky is in the merging process.

So my second tip is to make sure you can fully track all your file changes, especially across code lines, or you run the risk of some seriously broken builds and test failures. At AccuRev we have a branching model that we call streams which provides some great code flexibility to make branching and merging as fast and efficient as possible. Stream branching easily accepts parent code while allowing you to then push code out to other streams. All file versions are stream-based, making merging easier because the entire file change history is available and automatically tracked. Pretty cool.

Here’s the big pay-off – because branching and merging is made a lot easier with streams, development teams can branch more often and more confidently, reducing risk without seriously impacting productivity. Perhaps best of all, it helps you avoid a potentially-disastrous end-of-release merge dump that could result in costly and time-consuming fixes and release delays.

So let’s recap: avoid a branching and merging nightmare by carefully considering the branching model that best suits your needs and your level of risk versus productivity. Make sure that your methodology provides maximum visibility into the process and enables you to fully track your file change history, enabling better decision-making and ensuring more effective merging that’s less prone to errors. The result? Better product,faster, and with less errors. How sweet is that?

From Merge Hell to Merge Master

March 23rd, 2011 by jsherwood

Are you frequently called on to perform the daunting task of ‘the merge’? Does tension mount and do groans grow louder when it’s time for a merge?  Are only a select few are willing to stand up and do the work?

Maybe these stages describe your merge process:

  1. Denial: It’s never going to work (in a timely manner).
  2. Anger: Why do I have to do the merge?
  3. Bargaining: I’ll work on maintenance and support if I don’t have to do the merge.
  4. Depression: How many compiler errors? Why won’t the jsp work with firefox?
  5. Acceptance: Not really, it’s compiling and (mostly) passing tests.

Before we try to get you through the 5 stages of merge, let’s a take a look at divergence, the cause of a complicated merge.

Converging Divergence

There are lots of reasons for divergence, and as many for merge product lines back together.

Maybe you’re delivering functionality to specific customers, creating customization and personalization of websites, internationalizing your product, even moving from Windows to Linux platforms. So what happens? These areas diverge, developers refactor code, and the product lines look very, very different over time. Sure, you try to propagate changes across the product lines, but each implementation is slightly different. Eventually you realize this is a maintenance nightmare, and some shared areas should be brought back in line (if not the whole product line moving to a single source).

Now comes the hard part. A select few of your developers have to start piecing the code back together. Determining what changes are acceptable, reviewing the functionality, and hopefully getting the appropriate test coverage to verify that the desired changes have been brought back into a single (or at least cleaner) product line. Here’s where tools really shine (or falter).

Now, I consider myself pretty experienced in the merge department. I’ve worked on a number of merges of different sizes, dealt with multiple languages (English/Italian), and even migrated to different platforms (Moving from Windows to Macintosh).  Sometimes, I found, tools were a complete hindrance- I remember back in the day, using PVCS or CVS was every man for himself. You just got it working, never mind worrying about who made what code decision, and hopefully extensive tests identified the problems. More modern tools, AccuRev in particular, give you another dimension with merge that I find to be an essential.

The Merge Master

AccuRev version tracking, and the changes it tracks (content, name, removal) really help in hunting down the straightforward changes that can result in truly subtle changes in product behavior. Simply knowing that files have been removed in one product, and merging those changes over with a click of a button can eliminate behavior that is hard to determine, especially when the developer doing the merge had a reasonable belief that the files may exist.

Even better, large or midsize merges, can be easily reviewed, grouped into areas of the code and dealt with in a manageable manner. I performed a merge that merged internationalization changes into a product at AccuRev. There were over 7000 files that were altered, added or removed that needed to be managed.

Simply grouping the files by directory structure quickly identified which were doc, help, client, java, etc. Then these areas could be dealt with by developers in the specific areas. Further, because AccuRev performs simple merges quickly, I was able to perform the initial merges in these areas without having a strong need to understand them, and leave the complex changes to those who specialized in particular areas. This further reduced the amount of effort (and pain) that other team members experienced.

In this 7000+ file example, only about 400 files actually required more specialized investigation. And of the 400, only about 50 had truly complex changes where both sides of the merge made what looked like contrary decisions. Here is another place where AccuRev shines. By looking at the changes made at different points in each of the product lines, and working with change packages that described what the developers where trying to accomplish, I was able to make intelligent decisions about how the code should integrate, instead of just picking ‘he who changed it last’.

The two product lines in this case had diverged for about 9 months, and had about 10 developers making changes in each product line. Even with the amount of changes that occurred over this time period, it only took a single developer about 2 weeks time to bring the two product lines together. It took only a couple of days to complete the initial code process, walking through the changes and picking (via the AccuRev GUI) which of the changes to take, and editing inline where it was obvious.

During the first week, we were able to finish digging around developer changes via the AccuRev version browser in order to help resolve initial compilation failures. This work brought the product to the point where it was compiling on multiple platforms (which is usually even a problem with nightly builds). After another week of going through the validation and user tests, the merge was stable enough to be considered the baseline for the next release. Of course development had already occurred during the two weeks that the merge process took, but with the version tracking AccuRev performs with merges, it became almost trivial to bring in the new changes- within 1 day they were validated and ready to be the new baseline.

Sounds like acceptance to me.

Agile and SCM: Helping You Get to “Done”

January 24th, 2011 by clucca

You spent the last 2 weeks working on 10 user stories for you sprint. Your team has completed 8 of the 10 user stories, and now it’s time to show a working demo for your sprint review. Sounds like a typical scenario right?

Here’s the problem, the 2 remaining user stories have partial work associated with them. That code is in your source control system, and in order to correctly demo or ship what was accomplished in your sprint, you’re going to have to do some work to create a “done” product. You will have to subtractively merge those changes, or put them on another branch, then re-test the application, redeploy.. check the changes again etc. There is still a lot of work to finished in getting this sprint to “done.”

One way to get around this is to associate user stories with code changes in your SCM tool.  AccuRev already creates a link between your user stories and code in the form of change packages. Creating that link between the user stories and your code is the first step. But using a powerful story-driven process out of this linkage is the key to “getting to done” in an Agile environment.

Your user story will move through different stages as you move through your process. One user story may have these states:

chart Agile and SCM: Helping You Get to DoneDEV- Currently in progress with dev team, or “coding”
QA- Coding finished, ready for QA to test
UAT- QA finished ready for user acceptance testing
PROD- Tested by QA and users, ready to ship

However, while  user stories move through this process, the code doesn’t follow. Traditional SCM systems are designed around single branches and a long and lengthy merge processes. Fast paced Agile environments expose those limitations as development teams struggle to ship code to customers at the end of iterations.

During that iteration, testers may want to test completed user stories, but need a stable configuration to do so. If you’re using a traditional waterfall branching and merging based SCM tool, you may end up with some user stories ready for QA, and some still in the DEV stage, creating a poor testing environment and broken builds. As a result, developers often delay committing code so changes can be implemented, tested, and passed to QA before they integrate.

During your retrospective of the previous iteration, you may decide that parts of your process need modification. For example, you may decide to add a code review process right before testing. Your SCM system has to be flexible to enable this new step without time consuming tasks, like re-writing scripts.

SCM and an Agile Process

The trick is to have an SCM system that can help you manage and enforce an Agile process. Code should be able to follow the same process user stories follow. If a user story is in QA, all of the code needed to test that issue should reside in a QA configuration. The same goes for DEV, UAT, PROD, or any other process that is part of your environment.

A stream structure is an easy way to  process change – streams can be added to adjust your process. In a few clicks, you can add a code review between a DEV, and QA step.

Agile and SCM: Avoiding Agile Merge Hell

As you start to scale Agile, code and user stories have to be merged more often. Sometimes changes my flow from one organization to another. This means that you will need to take code from one team, merge, integrate and test those changes with everyone. Each team needs to be able to work on their own schedule, this means that if multiple teams want to work on different sized iterations they can. In addition they can deliver changes as they need to on a regular basis, independent of the the other teams.

The problem here is that to do this in a traditional SCM system, you would have to merge these code changes daily for them to be of any use. You also still need to keep visibility into what stories are shared between teams, because delivering changes from user stories that are not completed in a sprint would be disastrous.

Typically, the type of configuration people use for this is a single baseline or “trunk” methodology, where all changes from each team are delivered to trunk and pulled from trunk as their iterations are completed.

Working within an Agile context, your teams will have to deal with these branching and merging issues. But there are other problems that can happen when you use this methodology:

  1. Delivering 2 weeks worth of changes only causes isolation among teams.
  2. It’s too hard to pick out each user story as it completes from our codebase.
  3. Figuring out the dependencies of those user stories is complex.
  4. Being able to identify what changes came from each branch is impossible.

This “baseline pollution” is not scale-able. You can get around this by using a development hierarchy, and manage the relationship of dependencies between branches. This could also include process steps such as integration, quality assurance, and code reviews.  A separate code configuration can be used for each step and user stories could simply be drag and dropped between each team, state or branch instead of a merge.

Doing this will increase code stability. As a completed user story is pushed from one stage to the next, the particular change, as well as the system as a whole, reaches a higher level of maturity. While many traditional SCM tools do not easily support or surface a development hierarchy, AccuRev supports the creation of a hierarchy, gives visibility into the changes at each stage, and enables straightforward merging between stages.