by Brad Hart
In just about every situation in the last 8 years where I’ve gone into a prospect to talk about replacing ClearCase, I’ve been asked the question about ClearCase’s Dynamic Views and why AccuRev does not have a similar concept. It’s a fair question coming from those who are familiar with ClearCase and I’m posting this blog to help both give some background information on Dynamic Views and answer some of the common issues raised by former users of ClearCase before they made the switch to AccuRev. I used to work at Rational Software in both Support and in the Field and I spent a number of years as a ClearCase consultant before coming to AccuRev in 2001.
At the time Dynamic views were introduced, there was tremendous pain in the market using a local source copy model, especially in enterprise applications. Disk space was extremely expensive, and it was becoming increasingly infeasible to have large enough disks on each developer’s workstation. Networks were also much slower, and the time required to copy entire sets of source code to each developer’s workstation was unrealistic as applications grew in size and complexity. Dynamic views provided the appearance of each developer having a local copy of the source files, but without the time / disk space overhead associated with having real local copies. They also provided just-in-time access to files across a network connection which was transparent to the end user, similar to the way NFS works. Unlike NFS, which you only can access the latest version of files, the dynamic views allow the developer to reconfigure their view of the files to represent any given configuration past or present. Also, unlike a local copy model, reconfiguring what a developer sees does not require any file copying to reflect the changes. This saves time and money and the savings continue to scale the larger the development group gets.
Does it still hold water?
No. Both workstation and network hardware costs have dramatically dropped in recent years, and the performance has increased exponentially. It is very common and reasonable for developers to have near server-class systems on their desktops. In many cases, it is now a much better time savings to have developers work with local copies of their source files. In fact, Rational’s default usage model for developers is to do their development in a local copy source file model, contradicting the presence of Dynamic views. Dynamic views were a time and cost savings breakthrough when it was introduced, but given the changes in development environments in the current time, it is more often than not seen as a hindrance. There is also a much higher administrative burden associated with Dynamic views. Especially if you are working in a mixed environment (SAMBA, TAS, etc… need to be properly configured and maintained). Also, Dynamic views are notoriously unreliable and unusable over remote connections. Another major objection to Dynamic views from the developer perspective is that most developers don’t want “the rug pulled out from under them.” Your files are constantly changing in your view….how are you supposed to develop/build and test like that? Add in the fact that ClearCase does not have atomic transactions, and developers using Dynamic views will constantly have inconsistent sets of code to work on. Bottom line is that even Rational recommends developers use Snapshot views (like AccuRev workspaces) and only use the Dynamic views for integrations. Since AccuRev truly builds in parallel development, you don’t need an integration view/workspace. All your work can be done directly from one workspace.
Five things I’ve heard from developers on why they think dynamic views are important to an effective development environment:
WYSIWYG: The final test of your code changes before check-in is exactly the same thing as testing the release area code directly. No need to “check it out again in a different place just to make sure I checked in everything right.”
AccuRev allows your private work (keeps) and your check-ins (promote) to all occur from the same place (you don’t have to check out to a different place). AccuRev builds in best-practices like private-branching (workspace streams), atomic transactions, and copy-merge. You don’t get that out of the box with ClearCase. AccuRev’s built-in best practices absolutely improve the entire process. You absolutely must merge against the latest code before you promote your changes (for overlapped files). Plus, developers have total control of their workspace bringing in new changes as they are ready. That way if something is broken, they will know whether it is their code, or the latest code from the mainline. With Dynamic views, you will have to go find out for yourself and it is constantly changing. I have heard a lot of the “rug being pulled out from under me” analogies regarding dynamic views.
