Udi Dahan   Udi Dahan – The Software Simplist
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One wrong DLL = 3 months gone

Saturday, June 24th, 2006.

A couple of days ago, one of the programmers on a project I’m consulting on came in to ask me a question. With a puzzled look on his face, Alex asked me “Udi, in your design you have these two tiny interfaces, IEntity and IMapEntity, that together wouldn’t justify belonging in their own DLL, and you gave each of them their very own DLL! Why?!” Right then and there I decided to hold a project-wide standup. I got everyone into the room, from project manager, to tester, to programmer, and spun the following scenario.

“Patrick”, I said to the project manager, “you know how we have our iterations set up so that each iteration we work on an entire feature, end to end, and keep the number of features down?” Patrick nodded.

“And Daniel”, I said to our test lead, “you know how you report defects on a feature by feature basis, correlated with the version of the system being tested?” Daniel, too, nodded.

“And Beth”, I said to our SCM/integrator, “you know how each check-in gets the relevant project’s version number to increase, gets built, unit tests run, and, if everything’s OK, the DLL gets put out?” Beth was quick to jump in, “and don’t forget that the version number is taken from the DLL and applied as a label to the corresponding source files.”

“So, what’s the point of all this ceremony?” I asked, turning to the entire group. I got some blank stares. “Why are we doing things like this, and not differently?” Alex spoke up. “This all has to do with the DLL thing I asked you before, doesn’t it?”

I won’t draw this story out too much, so let’s just cut to the chase.

When a tester logs a defect, that defect is tied to a feature and a system wide version number. From that version number, we can find all the specific version numbers of the DLLs that comprise that system wide version number. We can also see which DLLs have changed from the previous iteration. From there, we can find the tree of DLLs which are somehow dependent on those few that have changed. Only a few change because we keep our iterations small. From the specific version of a DLL, we can go into our source control repository and, from the label, find the exact source which comprised that DLL. Those are the source files that a programmer has to sift through in order to locate the origin of the defect.

Obviously, if there is less source to go through, the programmer will, on average, find the origin of the defect faster. And, as we all know, it usually takes longer to find the bug than to actually fix it.

So, by splitting up different classes and interfaces into different DLLs, we can manage dependencies in the system so that less source needs to be examined. For instance, in the case of the interfaces mentioned above, IMapEntity depends on IEntity. However, there are multiple classes that depend on IEntity (like views and presenters/controllers) which don’t really care above IMapEntity. The opposite isn’t true, though. The renderer and layer classes are dependent both on IEntity and IMapEntity. If these two interfaces were in the same DLL, and for a new feature we needed to add the “AlphaBlend” property to IMapEntity, when a bug would be found in that iteration, all the view and presenter classes would have to be examined as well. This is because the version number of the IEntity/IMapEntity DLL would have increased, and all the dependent DLLs could have been adversely affected by that change. Had these two interfaces been separated into different DLLs, this alpha blend change would have left an entire tree of DLLs uninvolved. This means less source for a programmer to look through, which means less time to get the feature working.

While I’m not sure the statement “1 wrong DLL = 3 months gone” is necessarily true, I can’t say it isn’t either. All these tiny little things add up to either huge productivity gains, or losses. Especially when you consider larger, more complex projects. A good design, by itself, can’t save you from the failure conditions described above. You need all the practices in place, working in harmony, and people paying attention to make the project succeed.

That’s if the politics don’t nail you first 🙂

  
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  1. Chris Sterling Says:

    I entirely agree and use many of the same practices when developing a product for our customers. Our entire Professional Services division runs their projects using Scrum and many of the Agile development best practices such as TDD, continuous integration, collective code ownership, most use pair programming, and others.

    What we have found to be one of the biggest time savers, and therefore money savers for our customers, is the use of an agreed upon versioning system for our projects. This is a cross-cutting concern which involves our SCM, project dashboards, project structures, requirements tracking, and issue tracker. It comes down to having the right infrastructure in place to make getting work done much easier.

    Now, most of the projects I work with are Java based but they have similar issues as described above. We use Maven 2 to build, test, deploy, and view project dashboard across these projects. We found this to be so helpful that we even created plugins (or Mojos as they put it) for our .NET projects. Reports for FxCop, NDepend, NUnit, and others all get placed into the Maven 2 dashboard. It can even build our solutions.

    The consistency allows our developers to help across project lines without dealing with as much getting up to speed homework. It doesn’t eliminate it, but we are working on that. 😉


  2. John Wood Says:

    Udi,
    While there may be benefits specific to your project, in my experience more DLLs simply equates to more headaches.

    >> From that version number, we can find all the specific version numbers of the DLLs that comprise that system wide version number. <<

    But why. From a version number you can go to source control and see what changed between labels. What does this have to do with DLLs? The only source they have to look through will be a diff report between those two version labels.

    I think there are very few reasons to separate /components/ into their own DLLs, let alone individual interfaces. In my mind DLLs are a necessary evil – necessary only when sharing classes or interfaces between modules.

    Surely you’ve heard the phrase ‘DLL hell?’ – it’s not limited to COM at all. It’s limited to anything that is deployed piecemeal. The more granular your deployment, the more room there is for errors caused by mismatched DLLs, or a botched compilation that linked against the wrong DLLs. In my experience it causes FAR more headaches than it’s worth. I’m 100% a proponent of deploying applications as an atomic entity. Even patches go out as the entire thing, just to ensure that somebody doesn’t apply a patch in the wrong order and mess everything up. You say it reduces the source code – but I don’t see it. A DLL means an extra project file, extra references list, extra using statements, the list goes on. And this isn’t to mention the performance hits of all those assembly resolutions. In my experience you can increase the size of the project by an order of magnitude by being DLL happy.


  3. Paul Louth Says:

    Your methods of defect hunting are crazy. Do you really check all code/DLLs that have changed? I think most experienced developers would instinctively know where to look and would then do a diff on the source file(s) in question. Checking DLL version numbers to see what’s changed seems insane to me, and increasing the DLL count just means more headaches.

    Also if you were on my project and randomly downed-tools to grandstand in front of the whole team then I’d fire you. There’s no room for prima donna programmers of development teams in my opinion.

    And your grandstanding adds-up too does it not?

    One Prima Donna Coder = 3 Months Gone


  4. Mehran Nikoo Says:

    Components (assemblies in .NET terms) are units of deployment. This should ideally be the main deciding factor for the number of components in the application. For example if you want to be able to install only part of the application (i.e. the core framework) without optional components, you need to break it down to multiple components.

    Same applies if you want to minimise the number of files that need to be re-deployed in a patch release. But be careful. If your application has too many components, it is very likely that a bug fix needs many components to be re-deployed. Look at Windows service packs for instance; they include hundreds of updated files, which is defeating the purpose of minimising the number of re-deployed files and could end up in versioning conflicts too.

    In terms of development, in the same way that having one large project (and therefore one assembly) can prove to be very slow, having too many projects with project references will have the same effect as the referenced projects need to be recompiled and the references in parent projects need to be updated, and this process can be repeated many times, based on the depth of project reference tree.

    As you mentioned, it is up to the solution architect to decide which way to do based on project environment and complexity.


  5. Udi Dahan - The Software Simplist Says:

    First of all, thanks for all the comments. Take my suggestions in the context of large, complex projects with numerous developers and teams, and even companies working on the same project. The kinds of project where the average success rate doesn’t even make double digits.

    John,

    1. Not all source is necessarily in a single repository.
    2. By having more granular deployment, and smaller iterations, a smaller percentage of your deployment footprint changes each time. That means higher stability.

    Paul,

    I shall consider myself fired. But, for those clients who haven’t fired me yet…

    I’m not worried about the cases where programmers quickly home in on a bug, fix it, and move on. I’m worried about the bugs that don’t show up on the programmers machine, or sometimes do, and sometimes don’t. I’m worried about bugs that we thought we fixed 2 iterations ago, but have suddenly come back. These are the kinds of things that eat up project time, and don’t behave deterministically.

    Mehran,

    By following my “first principle of design”, I usually avoid the problems you describe. See:
    http://udidahan.weblogs.us/archives/035032.html
    http://udidahan.weblogs.us/archives/035222.html


  6. John Wood Says:

    >> Not all source is necessarily in a single repository. > By having more granular deployment, and smaller iterations, a smaller percentage of your deployment footprint changes each time. That means higher stability. <<

    I disagree. That means lower stability because you cannot be sure what it is they’re running without looking at the version number of each and every DLL. The more unknowns there are, the less stable the system is. When you release everything from source control it is controlled – if you have a good build system it can dump out what has changed since the last build was performed (including the files) so you can be absolutely sure what it is they’re getting. I mean, if you don’t know what your build produces then what hope is there?

    Like I said, it greatly depends on your setup and the nature of your development – but I can say that for at least 5 larger projects I’ve worked on, they were each in DLL hell until we made the decision to move towards holistic deployment.


  7. John Wood Says:

    A bit that somehow got missed…

    >> Not all source is necessarily in a single repository. <<

    Well that’s probably your biggest problem. I would make a point of converging the source depots even if it means having a process that pulls stuff from other SCCSs nightly.


  8. Udi Dahan - The Software Simplist Says:

    Would you take responsibility for the build process for another company’s deliverables? I wouldn’t. Each company has their own process, and you just can’t change that. The integration I perform needs to be done at the level of modules (or CSCIs as they’re called in my industry), where each CSCI can be made up of numerous assemblies, config files, databases, etc.


  9. John Wood Says:

    But Udi, from what you were saying it sounded like this was *your* decision – after all, you were the one who took the team into a room to justify yourself. From what you were describing it sounded like you already had taken responsibility for the build process, given this has a direct effect on the granularity of deployment. You say “the integration I perform” – yet what you were describing was a decision on whether to create DLLs for each and every interface. That’s not integration, that’s development and that’s taking a direct role in deciding how the developed components are deployed. Or did I miss something?
    It’s not worth me harping on because without being directly involved in the project it’s impossible for me to construct any informed opinions. But from what I’ve understood from the little I have read, I just don’t see the justification.


  10. Udi Dahan - The Software Simplist Says:

    John,

    As the architect for the whole system, I am responsible for making sure that when we connect all the pieces together, and they don’t work, we’ll be able to quickly find out why.

    The fact that some of these pieces are developed at other companies doesn’t change that. Also, beyond affecting what interfaces those pieces expose/implement, I can’t dictate how those companies develop/build their pieces. I want to receive from those companies binary artifacts whose behavior I can verify (with unit tests, for instance).

    Although I wish that I could positively affect those other companies’ build processes, its more important for me to focus on the team, or teams, in my company.

    As to the issue of whether an interface being an element of development or integration – I think that its both, if done right.

    Consider the case where 2 or more companies depend on a common package, like the one containing IEntity. Its really important for me to know that all the binaries provided by all companies were developed and tested against the same version of that shared package, otherwise there’s a good chance that things will break in unexpected ways (depending on the backwards and forwards compatibility characteristics of that package).

    Of course, such a process may not scale down so well.


  
   


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Rhys Campbell Rhys Campbell, Owner at Artemis West
“For many years I have been following the works of Udi. His explanation of often complex design and architectural concepts are so cleanly broken down that even the most junior of architects can begin to understand these concepts. These concepts however tend to typify the "real world" problems we face daily so even the most experienced software expert will find himself in an "Aha!" moment when following Udi teachings.
It was a pleasure to finally meet Udi in Seattle Alt.Net OpenSpaces 2008, where I was pleasantly surprised at how down-to-earth and approachable he was. His depth and breadth of software knowledge also became apparent when discussion with his peers quickly dove deep in to the problems we current face. If given the opportunity to work with or recommend Udi I would quickly take that chance. When I think .Net Architecture, I think Udi.”

Sverre Hundeide Sverre Hundeide, Senior Consultant at Objectware
“Udi had been hired to present the third LEAP master class in Oslo. He is an well known international expert on enterprise software architecture and design, and is the author of the open source messaging framework nServiceBus. The entire class was based on discussion and interaction with the audience, and the only Power Point slide used was the one showing the agenda.
He started out with sketching a naive traditional n-tier application (big ball of mud), and based on suggestions from the audience we explored different solutions which might improve the solution. Whatever suggestions we threw at him, he always had a thoroughly considered answer describing pros and cons with the suggested solution. He obviously has a lot of experience with real world enterprise SOA applications.”

Raphaël Wouters Raphaël Wouters, Owner/Managing Partner at Medinternals
“I attended Udi's excellent course 'Advanced Distributed System Design with SOA and DDD' at Skillsmatter. Few people can truly claim such a high skill and expertise level, present it using a pragmatic, concrete no-nonsense approach and still stay reachable.”

Nimrod Peleg Nimrod Peleg, Lab Engineer at Technion IIT
“One of the best programmers and software engineer I've ever met, creative, knows how to design and implemet, very collaborative and finally - the applications he designed implemeted work for many years without any problems!

Jose Manuel Beas
“When I attended Udi's SOA Workshop, then it suddenly changed my view of what Service Oriented Architectures were all about. Udi explained complex concepts very clearly and created a very productive discussion environment where all the attendees could learn a lot. I strongly recommend hiring Udi.”

Daniel Jin Daniel Jin, Senior Lead Developer at PJM Interconnection
“Udi is one of the top SOA guru in the .NET space. He is always eager to help others by sharing his knowledge and experiences. His blog articles often offer deep insights and is a invaluable resource. I highly recommend him.”

Pasi Taive Pasi Taive, Chief Architect at Tieto
“I attended both of Udi's "UI Composition Key to SOA Success" and "DDD in Enterprise Apps" sessions and they were exceptionally good. I will definitely participate in his sessions again. Udi is a great presenter and has the ability to explain complex issues in a manner that everyone understands.”

Eran Sagi, Software Architect at HP
“So far, I heard about Service Oriented architecture all over. Everyone mentions it – the big buzz word. But, when I actually asked someone for what does it really mean, no one managed to give me a complete satisfied answer. Finally in his excellent course “Advanced Distributed Systems”, I got the answers I was looking for. Udi went over the different motivations (principles) of Services Oriented, explained them well one by one, and showed how each one could be technically addressed using NService bus. In his course, Udi also explain the way of thinking when coming to design a Service Oriented system. What are the questions you need to ask yourself in order to shape your system, place the logic in the right places for best Service Oriented system.

I would recommend this course for any architect or developer who deals with distributed system, but not only. In my work we do not have a real distributed system, but one PC which host both the UI application and the different services inside, all communicating via WCF. I found that many of the architecture principles and motivations of SOA apply for our system as well. Enough that you have SW partitioned into components and most of the principles becomes relevant to you as well. Bottom line – an excellent course recommended to any SW Architect, or any developer dealing with distributed system.”

Consult with Udi

Guest Authored Books
Chapter: Introduction to SOA    Article: The Enterprise Service Bus and Your SOA

97 Things Every Software Architect Should Know



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