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Because I'm currently struggling to learn IBM Rational ClearCase, I'd like to hear your professional opinion.
I'm particularly interested in advantages/disadvantages compared to other version-control-systems like Subversion or Git.
You can find a good comparison between ClearCase and Git in my SO answer:
"What are the basic ClearCase concepts every developer should know?", illustrating some major differences (and some shortcomings of ClearCase)
File-centric operations
The most single important shortcoming of ClearCase is its old "file-centric" approach (as opposed to "repository-centric" like in SVN or Git or Perforce...)
That means each checkout or check-in is done file per file. The atomicity of operation is at file levels.
Combine that with a very verbose protocol and a network with potentially several nodes between the developer workstation and the VOB server, and you can end up with a fairly slow and inefficient file server (which ClearCase is at its core).
File-per-file operations means: slow recursive operations (like recursive checkout or recursive "add to source control", even by clearfsimport).
A fast LAN is mandatory to mitigate the side-effects of that chatty protocol.
Centralized VCS
The other aspect to take into account is its centralized aspect (even though it can be "distributed" with its multi-site replicated VOB feature)
If the network does not allow access to the VOBs, the developers can:
still work within snapshot views (but with hijacked files only)
wait for the restoration of the network if they are using dynamic views
Expensive Distributed VCS option
You can have some distributed VCS feature by replicating a Vob.
But:
you need a special kind of license to access it.
that license is expensive and add to the cost of the regular license
any vob that uses the replicated vob (admin vob, admin pvob, ...) must be replicated as well (meaning some projects not directly concerned with a distributed development will still have to pay multi-site license...)
Old and not user-friendly GUI
the GUI is very old school and impractical (mid-90's MFC look, completely synchronous GUI, meaning you have to wait for a refresh before clicking elsewhere): when browsing baselines, you cannot quickly look for one in particular.
the GUI on Unix is not exactly the same than on Windows (the latest 7.1 version is better but not there yet)
the installation process is quite complicated (although the latest Installer Manager introduced by CC7.1 is now a coherent GUI on Windows or Unix and does simplify the procedure)
the only real rich application has only been developed for CCRC (the Remote Client)
UCM inconsistencies and in coherencies
As mentioned in "How to Leverage ClearCase’s features", dynamic views are great (a way to see data through the network without having to copy them to the disk), but the main feature remain UCM: it can be a real asset if you have big project with complex workflow.
Some shortcomings on that front:
the dependencies between components is not well managed for a depth superior to one (because of the bug of "parasite baseline")
UCM still has some in coherencies and inconsistencies as documented in CM Crossroads
Limited policies with Base ClearCase
Using ClearCase without using UCM means having to define a policy to:
create branch (otherwise anyone can create any branch, and you end up with a gazillon of them, with merge workflow nightmare)
put labels (otherwise you forget to label some files, or you put a label where you were not supposed to, or you "move" (gasp) a label from one version to another: at least UCM baselines cannot be moved)
define changeset. ChangeSets only exist with UCM activities. With Base ClearCase, you are reduced to clever "cleartool find" requests...
No application rights
ClearCase right management is entirely built on system rights.
That means you need to register your user to the correct system group, which is not always easy to do when you have to enter a ticket to your IT service in order for them to make the proper registration.
Add to that an heterogeneous environment (users on Windows, and server on Unix), and you need to register your user on Unix as well as Windows! (with the same login/group name). Unless you put some sort of LDAP correspondence between the two world (like Centrify)
No advanced API
only CLI is complete ("cleartool" is the ClearCase Command Line Interface), meaning that any script (in Perl or other language) consists in parsing the output of those cleartool commands)
ClearCase Automation Library (CAL) exists, but is quite limited
Java API exists, but only for web views for the CCRC client.
View Storages not easily centralized/backed up
The View storages are the equivalent of the ".svn" of SubVersion, exept there is only one "view storage" per view instead of many .svn in all the directories of a SubVersion workspace. That is good.
What is bad is that each operations within a view (a simple "ls", checkout, checking, ...) will trigger a network request to the view_server process that manages your view server.
2 options:
declare your view storage on your workstation: great for scalability, you can have as many view as you want without taxing the LAN: all communications are directly done on your workstation. BUT if that machine dies on you, you loose your views.
declare your view storage on a centralized server: that means all view_server process will be created there and that all operations on a view by any user will have to communicate with that server. It can be done if the infrastructure is "right" (special high-speed LAN, dedicated server, constant monitoring), but in practice, your LAN will not support this mode.
The first mode means: you have to backup yourself your work in progress (private files or checked-out files)
The second mode means: your workstation can be unavailable, you can just log on another a get back your views (execpt for the private files of a snapshot view)
Side discussion about dynamic views:
To add to the "dynamic view" aspect, it has one advantage (it's dynamic) and one shortcoming (it's dynamic).
Dynamic views are great for setting a simple environment to quickly share a small development between a small team: for a small development effort, a dynamic view can help 2 or 3 developers to constantly stay in touch one with another, seeing instantly when one's commit breaks something in the other views.
For more complex development effort, the artificial "isolation" provided by snapshot view is preferable (you see changes only when you refresh - or "update" - your snapshot view)
For real divergent development effort or course, a branch is still required to achieve true code isolation (merges will be required at some point, which ClearCase handles very well, albeit slowly, file-by-file)
The point is, you can use both, for the right reasons.
Note: by small team I do not mean "small project". ClearCase is best used for large project, but if you want to use dynamic views, you need to setup up "task branches in order to isolate a small development effort per branch: that way a "small team" (a subset of your large team) can work efficiently, sharing quickly its work between its members.
If you use dynamic views on a "main" branch where everyone is doing anything, then any check-in would "kill you" as it could introduced some "build breaks" unrelated with your current development effort.
That would then be a poor usage of dynamic views, and that would forget its other usages:
additional way of accessing data, in addition of snapshot views, meaning it is a great tool to just "see" the files (you can for example use a dynamic view to tweak its config spec until you see what you want and then copy those select rules into your usual snapshot view)
a side view to make merges: you work with your snapshot view, but for merges you can use your dynamic "sister-view" ("sister" as in "same config spec"), in order to avoid having a failed merge because of checked-out files (on which you would be currently working on your snapshot view), or because of a snapshot view not completely up-to-date. Once the merge is complete, you update your regular snapshot view and resume your work.
Developing directly in a dynamic view is not always the best option since all (non-checked-out) files are read over the network.
That means the dll or jar or exe needed by your IDE would be accessed over the network, which can slow down considerably the compilation process.
Possible solutions:
one snapshot view with all in it
a snapshot view with dll or jar or exe in it (files which do not changes every five minutes: one update per day), and dynamic view with only the sources visible.
The cost is a fairly obvious disadvantage. Not just the license cost, but also the cost of a ClearCase guru's salary. Almost every company I'm aware of that uses ClearCase seems to have at least one person whose only purpose is to tame the unruly beast.
The very fact that it's complicated enough to require a full-time nanny is also worrying.
An absolute nightmare of a system. It made me wish we could go back to VSS! (Never mind any modern source-control system like Subversion or Git!)
It's slooooow.
If you use dynamic views and the network goes down you cannot access your working copy of the source. You can do nothing but sit and wait for it to be fixed.
If you use snapshot views you seem to run into conflicts and "hijacked" files all the time, so the files in your working copy are never quite the same as in the source repository.
Whenever you try a large update or deliver operation it invariably FAILS for one reason or another, requiring your ClearCase guru to spend a few hour/days figuring it out. Oh yes, you must have a dedicated, full-time ClearCase guru!
When it fails you often cannot roll back the operation, either, so you're stuck with an operation in progress and the developers are blocked.
When you look past the pretty(?) icons, the GUI is very poor - right down to things like being unable to resize windows to see full file paths!
Their support staff are quite reluctant to fix anything. Their first response is always "this is by design" and "can you work around it?" If they do ultimately provide a fix (after much arguing) it will be the most basic possible fix to the most immediate problem.
Basically, it's slow, complicated and unreliable as hell. Oh, and did I mention it's ridiculously expensive? The only way they can possibly sell it is by talking to decision-makers who have never used the product and never will! I'm quite sure that no developer in the world would ever buy it.
Atomic commits and changesets are my biggest gripes against ClearCase. Let's say you check in five files as part of a bug fix or refactoring. Then it is discovered that something got messed up and you need to revert. Good luck finding which five files they are and what version each one needs to be on. But let's take a step back. You have just finished editing those five files, and it's time to commit. The first four go through just fine. That last one requires a massive merge. The other four files are already checked in. They don't wait for you to finish your necessary changes in the last file. I sure hope that no one updated or is using a dynamic view. A continuous integration build server is going to fail too.
Sometimes we make a whole new directory full of files that need to be checked in, but we don't want to check them in until they are done. It's early and everything is still volatile, so why check things in that you might delete very soon? OK, fine so far. Now it's time to check in. You add the newly created folder to source control. Well, ClearCase isn't recursive, so only that single folder is checked in. With SVN, that folder and everything below it is added, as you choose. The developer needs to remember to add everything, otherwise, a lot of files are going to be missing.
ClearCase owns the files and folders so you cannot modify anything unless you have checked it out first. The eclipse plugin takes away a lot of the nuisance here. I can't tell you how many times I opened a file in vi to make a quick change, only to find that I had forgotten to check it out first. Checkout isn't recursive either.
Updates can be painfully slow without changesets. When you update with a snapshot view, every file updates, not just the modified files. I worked on a project with 20,000+ files. I would remote in to my work machine, start the update, then drive to work; get coffee; go to my desk while it was finishing up. That might sound like an exaggeration, but it sadly isn't.
Dynamic views are terrible unless you are in a very small team. And if that's the case, why do you even have ClearCase? I have seen countless people's views getting hosed because someone checked in files that broke the views of everyone else. You should always update and merge any conflicts on your own view. That way, the changes only affect you. With a dynamic view, you cannot merge down before pushing back up; you just commit and hope.
I know cost probably isn't a big concern, but the developers who make the money for the company would enjoy spending the $50k-$100k (depending on ClearQuest license, which is a common addition) on either fun events or new equipment (chairs, monitors, etc.). IBM recommends having staff to keep ClearCase going. Why not re-purpose those people to generate revenue for the company, instead of making sure things don't crash and burn?
Some of the reasons that I have heard for not switching:
Learning will take time and money
Learning SVN or Mercurial should take no more than a day. Only ClearCase suggests having a certain ratio of admins to developers.
Migration will be painful
This is why tools exist: cc2svn
It's not as easy with Mercurial
Security
There are no known gaping holes in SVN AFAIK, and the development team is dedicated to fixing anything that is found quickly. The Department of Defense seems OK with SVN.
No real productivity gain afterwards
It takes forever trying to track down bugs without changesets. I love being able to roll back until I can't see the bug. You can't do that in ClearCase.
Multisite
WANdisco solves that problem. It's not free though.
The only thing that ClearCase does better than the rest is branching individual files, while keeping the others on the same track as another branch.
Everything I have done in Clearcase always seems hard. Whereas, I've never had that impression with other systems(except maybe CVS on occasion).
I've used SVN, CVS, Clearcase, and Mercurial.
My experience with ClearCase was a disaster, and I will second Don's statement that it requires a resident expert-- unfortunately we had more than one. I had experience with CVS and other version control systems, I was familiar with the concepts, but I found the ClearCase documentation incomprehensible and had to ask for help several times; different experts gave me conflicting advice to the point where we actually broke cd. That is, after I issued a ClearCase command in a UNIX shell, the "cd" command failed with an error message.
The basic task of a version control system is really pretty simple. Honestly, I think that half a dozen commands should suffice, using a file scheme that plays well with others. To me ClearCase looks like the result of a marketing exec deliberately complicating the hell out of things to make the product look sophisticated and powerful. I've heard that it can be configured to behave in a simple, safe, reliable way, but again that requires the services of an expert-- out of the box it's like a motorized swiss army knife.
Everything I've experienced related in any capacity to ClearCase is inefficient, ugly, overly complex, slow, confusing, expensive and inconvenient.
It seems to attract managers and engineers that JUST HAVE GOT IT ALL WRONG.
Damn, IBM and Rational must have amazing sales guys to sell such a crappy product.
We are just migrating off CC onto Git for many of the reasons given here. I would like to add one reason to stay away from CC or any other commercial source control system.
Your vital business data is hostage to ClearCase. You can't get it out.
Your vital business data is the code, its version history and all metadata such as commit comments, who checked in and when.
All software will have a limited useful life. You should always ask yourself when you introduce a new system that swallows important business data, whether it is code, bugs, customer data or what not: How do I get my data out again? If you can't answer that question, you should not introduce that system.
When we migrated out we lost most of our history and all of our metadata. Essentially we only have history corresponding to released versions, but information about what changes were done in response to what customer requests is lost (we have that data in the customer support and bug ticket system, so it is not completely lost, but the coupling to the source code is gone).
This will be somewhere between a nuisance and a problem for us on short to medium term. In a couple of years time, it is not important anymore, but perhaps for 1-3 years it will matter.
(There are commercial tools to migrate CC to other SCM, but they were not deemed adequate to our needs, and I doubt it would have been feasible. The minimal export we did took long enough.)
The lesson learnt is: Never entrust vital business data to proprietary systems.
No atomic commits
Once you checked in files it is very hard to revert to a certain state, because atomic commits aren’t supported. When checking in multiple files, each file gets a new revision (similar to CVS) and not the check-in itself. I think this is a crucial feature, because you hardly want revert single files but complete commit actions (which should map tasks). With ClearCase you can only revert to certain states by using Labels. In practice using ClearCase Labels for each check-in is overkill and thus not done.
Crappy user interface
The GUI of ClearCase Explorer is just a big joke. Horrible in usability and ugly looking. Different and often necessary functions aren’t provided (e.g. recursively checking in worked on artifacts). Command line tool cleartool used with cygwin is much better, but still some things aren’t available like recursively adding new files/folders to source control. I have to laugh my head off if I read a 50 lines of code long script to workaround this.
High administration efforts
Administrating ClearCase beast is far from obvious or lightweight (in difference to other scm-systems like CVS, subversion or Git). Expect to put quite a few dedicated ClearCase experts to just keep it running.
Horrible performance
Nothing is worse as making your developers wait while interfacing with SCM-tool, it is like driving with hand brakes enabled. It slows down your brain and also your work. Getting fresh new files to your snapshot view takes around 30 minutes for 10K artifacts. An update (no artifacts were changed) for the same amount takes roughly 5 minutes. When experimenting a lot and jumping between different up-to-date views means a lot of waiting. It gets even worse, when you’re working on files and you want to check-in or update them. Check-out, check-in and adding to source control cycles take around 10-15 seconds which is obviously a nightmare. It gets very annoying when you’re refactoring renaming/moving types or methods (many files can be affected).
Lack of support of distributed development
Today software development is often a distributed thing (developers are spread around the world working on the same product/project). ClearCase definetely isn’t suitable for this, because it is badly suited for offline work. Doing a check-out (action before you can edit a file/folder) requires that you are network connected. Here you could use the hijack option but this is rather a workaround as a feature (you basically just unlock the file on the filesystem). If your development sites are far away from your ClearCase server the check-in/check-out latency can even increase so dramatically that it is not usable at all. There are workarounds for that like using ClearCase Multisite (scm DB replica technology), but you have to pay extra for it and is not trivial to adminstrate.
Git as alternative
Though being a big fan+supporter of Open Source I am still willing to pay money for good software. But looking at IBM-monster ClearCase I wouldn’t invest my money here, it has all these discussed shortcomings, and further more IBM doesn’t seem to invest money to improve their product significantly. Recently I had a look a Git scm which looks very good, especially for its branching+merging features, where ClearCase has its major strengths.
This information taken from http://www.aldana-online.de/2009/03/19/reasons-why-you-should-stay-away-from-clearcase/
Possibly the worst software ever made. I will not work for any firm that uses rational anything. Aside from CC completely crashing and restarting my workstation frequently on dynamic builds. What happens when you are pushing something to source control and CC does what it does best, crash? Is your code then put in lost+found, backed up somewhere maybe? No, it is gone forever. So if you are ever in the god-awful situation of using this giant piece of expensive software, keep duplicates of everything. Good job Rational / IBM. Way to capture the most important part of source control, reliability. Die slow.
Downsides of ClearCase - an addition to the most in-depth post here.
The merge tool is not worthwhile. It barely helps you, remembers no decisions you made, its just a glorified diff.
The merge tool has to check out directories to even CHECK if they need a merge. Its a bit insane.
I use BitKeeper at work (let's assume Git), and merging two repositories even if there are conflicts is so trivial and user friendly even with command line, while ClearCase having tons of GUI tools is a long and laborious process which is also extremely error prone.
All GUI tools require a ton of latency. Even seeing what can be done on a file requires a high speed connection. So right-clicking in the ClearCase tool on a file working from home could take a minute or two having high speed internet because of the extreme amount of networking requirements.
Someone can completely mess up the repository or check-ins if they make their view spec different than the team. Which is quite insane that nobody can just check out some branch; they need the appropriate view spec which will incidentally give them the right stuff. The whole concept can be nice and flexible but 99% of the time it just causes lots of pain. Did I mention you can't email your spec via Microsoft Outlook since CC tools don't accept UTF-8 so you can't copy-paste it?
I have absolutely nothing nice to say about CC. I used it for 2 years at 2 companies and dropped it in a heartbeat feeling happy the entire time. It is also impossible to just experiment with at home with your own projects, so you will still learn SVN or Git at home, and be forced to go through ClearCase pains at work. Nobody I know has ever used CC voluntarily. They only use it because some manager at work decided CC is the path to salvation and forced everyone to migrate to it. In fact my last company migrated from CVS to ClearCase, and after one year from ClearCase to SVN. It was that hated.
ClearCase is not just one thing that makes you say no. It's like living in a house infested with ants. Each ant is just a minor inconvenience at best, but the infestation will drive you mad.
I'm trying to consolidate a few comments into an actual post here. I'm not really here to persuade you that one is better than the other, except by way of making a few points:
If you're comparing git and ClearCase, I respectfully submit that you need to better define your needs - if you are considering ClearCase for a "good" reason, the git probably isn't even in the equation - it's far too new to trust for enterprise-level source control, imo.
ClearCase introduces a lot of concepts into the version control space that other systems don't have, so it can be pretty daunting and confusing. Especially if the only experience you have is reading the documentation, as appears to be the case for a few people here.
ClearCase is definitely not well suited to huge code bases supported by developers who are not on a LAN with a VOB server. You can have many replicated (multi-site) VOB servers to get them close to remote developers, but this isn't necessarily practical if those remote sites are just a single developer.
Do you want file versioning or repository versioning? This is a pretty important question, and one that will necessarily filter out an entire set of tools, making your job easier. Repository versioning has a lot of advantages (and it's not "new", like some posters claimed - commercial tools like Perforce have been around for more than a dozen years, and there may have been tools that did repository versioning even before Perforce), but it isn't a panacea.
With a sufficiently large installation of any source control system, you're going to need help. When considering tools, you need to consider how easy it will be to find people to help you (either job applicants who have experience, or consultants who will be there at a moments' notice to address any issues). There's no such thing as a maintenance-free SCM system, and assuming you have one will get you into more trouble than picking one that requires "too much" administration.
Don't pay too much attention to people who talk about how bad "dynamic views" are - bad SCM policies are bad, regardless of the tool you're using. Your configuration management policies and practices have to be separate from your choice of tool - no tool will stop people from smashing all over your codebase if you don't define sensible branching and merging policies. If someone suggests that having developers directly commit onto /main is ever a sensible idea, you might want to walk away from that conversation.
ClearCase is a fine tool, but it is a complicated tool. There is no getting around this - it does not have an "easy install" mode. :-) From a technical standpoint, there's nothing that git or SVN can do that ClearCase cannot (although often the terminology is different, since Open Source projects tend to just invent new taxonomy where there already existed one), but some things are definitely easier/harder for a given system, depending on their design. ClearCase "snapshot" views are basically the same thing you would have if you checked out a repository from SVN or CVS - it's a local copy of the source code on your machine, with pointers back into the central server for tools to query version history, etc. You can work with these views without any network connection to the ClearCase server at all once they have been created, and you can "recycle" them to avoid downloading your entire repository again when you want to move to work on another branch, for example. "Dynamic Views" are basically a ClearCase invention, and the standard operating mode for a LAN. They appear the same as checking out an SVN repository, but they don't actually copy any files until you make changes. In this way the view is available immediately, but it obviously cannot be worked with if the main clearcase server is unavailable, and is unpleasant to work with over a high-latency connection. They also have the convenience of being able to be mounted as a network drive on any machine with access to the server on which they were created, so if your windows workstation dies, you can just log onto another one, mount your view, and get back to work, since all the files are stored either in the VOB server (for files you haven't modified on this branch), or the view_server (for files you have created or modified just in this view).
Also, and this deserves its' own paragraph....clearmerge is nearly worth the price of admission alone. It's hands down the best merge tool that I've ever used in my life. I firmly believe a lot of bad practice in SCM has developed because of a lack of high-quality merge tools, so CVS users never learned to use branches properly and this fear of branching has propagated to the current day for no particularly good reason.
Ok, all that being said, if you're looking for reasons not to use ClearCase, they're not hard to find, although I think that's the wrong way to go about it. Really you should need to come up with good reasons TO use ClearCase, not reasons for NOT using ClearCase. You should come into any SCM situation assuming that ClearCase is too much tool or too complicated a tool for the job, and then see if you have some situation that encourages you to use it anyhow. Having IBM or Rational logos is not a good reason.. :-)
I would not even consider ClearCase unless you could say yes to all the following statements:
You do now, or will eventually have, more than 50 developers working on the same codebase.
Most of those developers are centrally located, or have high-throughput low-latency connections to a central location.
You have a set of SCM policies and can identify how to use ClearCase to enforce those policies (really you should consider this for any tool)
Money really is no object
My experience is mostly limited by CC, CVS and SVN. In principle, CC is technologically capable, enterprise ready and comparable by features with any modern VCS. But it has several flaws that make it unusable in any people-oriented environment. For process oriented environments it is probably more appropriate, though I doubt that such environments are appropriate by themselves. Maybe, in military, cosmic or medical software, I don't know. Anyway, I believe that even for these domains there are appropriate and still more friendly tools.
Beside being technically capable VCS, CC has several distinctive advantages:
Dynamic views
Nice version tree
Triggers
Good merge versioning, including renames
In my opinion, their use is limited excepting last one; and they don't compensate flaws. Dynamic view nice in theory, but not always available in practice. Version tree has much less use in other VCS, while necessary in CC because of proliferation of branches (see 6). Triggers, as I know, very detailed and capable, but I think that for most practical tasks SVN hooks are good enough. And now about disadvantages that mostly concerns usability:
CC totally fails in sense of usability for main user group: for developers. And that is the main reason why I think that it should never be used in any environment, be it enterprise or not. Even if it were free, it would nevertheless suck your company's money by wasting time of your developers and frustrating them. This point is composed from:
"Check out-Check In" with strict locking approach - it is counter-productive, refactoring unfriendly, and dangerous in repository organizations with single development branch for multiple developers. Meanwhile, the advantages of strict locking are negligible.
Poor performance and high load
It effectively cannot be used remotely without multi-site (due to 2). Multisite is expensive too. ClearCase Remote client is very limited. It don't even have cleartool (before version 7.1), leaving alone dynamic views.
It can hardly be used offline. Dynamic views are just not work. Snapshot views are effectively read only, because you cannot check out without access to repository (see 1). Hijack is poor option which in fact means that CC gives up any responsibility for hijacked file. And CC cannot show you difference with previous revision when offline. SVN is able to show difference with previous revision even being offline.
Overly complicated model, especially with UCM: VOBs, PVOBs, Projects, streams, branches, views, deliver, update, load, restore, rebase, merge, baseline, check in, check out. I think that half of this concepts are just superfluous and doesn't add value, while increasing both technical and conceptual complexity. Few developers understand even basic stuff about CC.
Proliferation of branches. For example, repository often organized with stream per developer (due to 1). It just has no sense in SVN or most other VCSs.
No repository wide revisions. Well, there are such revisions as understand, they called baselines. But when I see some file revision and want to get repository snapshot at the moment of that file revision, I will get some problems. I will need to do black magic with config spec to create a snapshot view, or find somehow through dynamic view if it is available.
Crappy user GUI. Version tree, even being nice, has mediocre usability. Merge tool is just a pity. Other "features": not resizeable windows, absence of incremental search in some places, mouse-centric interface, look and feel in 1995 style, strange work flow distributed between Client and Project Explorer etc.
CC provokes rare and vast check ins. You all know, that check ins must be small and frequent. But developers usually refrains from additional interactions with CC, hijack files and work in local VCS or even without VCS at all (which is more often, unfortunately). And then, after two weeks of development they begin commit comlex feature that adds 20 files and affects another 20 files. It lasts for a day or two, because they hijacked files and now need to perform manual merge with all new changes from repo and resolve all conflicts and discrepancies. During that process, code lies not compilable, because several files successfully got checked in and others do not. And after that it still lies not compilable because they forgot to add another 2 files to CC.
It is very expensive
It is very complex in terms of infrastructure and requires dedicated administrators
ClearCase seems extremely powerful, from the outside. But really, it's just that the number of commands and options you need to use for basic workflow is so high that these get hidden behind a few aliases or scripts, and you end up with something less powerful than CVS, with the usability of Visual Source Safe. And any time you want to do something a little more complicated than your scripts allow, you get a sick feeling in your stomach.
Compare this with Git, which seems complicated from the outside, but after a week working with it you feel completely in control. The repository model is simple to understand, and incredibly powerful. Because it's easy to get at the nuts and bolts, it's actually enjoyable to dig below the surface of your daily workflow.
For example, figuring out a trivial task such as how to just view a non-HEAD version of a file in a snapshot view took me a couple of hours and what I ended up with was a complete hack. Not the enjoyable sort of hack either.
But in Git, figuring out a seemingly complicated task such as how to interactively commit only some changes, (and leave the rest for later) was great fun, and all the time I have the feeling that the VCS is allowing me to organise code and history in a way that suits me, rather than history being an accident of how we used the VCS. "Git means never having to say 'you should have'".
At my work, I use Git for all sorts of lightweight tasks, even within ClearCase. For instance, I do TDD, and I commit to Git whenever a bunch of tests pass and I'm about to refactor. When the task's eventually done, I check in to ClearCase, and Git helps me review exactly what I'm changing. Just try to get ClearCase to produce a diff across a couple of files - it can't! Use Google to find out the various hacks people have tried to work around this. This is something version control should do out of the box, and it should be easy! CVS has had this for decades!
Nightmare to administer in secure environments
Outdated technology
Non-intuitive GUI
Expensive
Resource monster
Sellout to Microsoft
In my opinion? Only reason to have it? If you are religiously following RUP.
The support is terrible. We've had tickets open for years. Our eclipse guru actually fixed a bug in their eclipse plugin locally in about 30 minutes by disassembling the java file. But the ticket still hasn't got past level one support. Every so often they either try to sneakily close it or ping it back to us 'to try on the latest version' (even though we sent them a reproduction recipe which they could try for themselves.).
Do not touch with a barge pole.
Performance.
ClearCase is powerful, stable (IF properly maintained and supervised) but it's slow.
Geological sometimes.
Dynamic views views lead to horrible build times, snapshot views can take ages to update (lunch break for large projects) or checkout (go home for the day).
Clearcase is so annoying it actually drives people to write poetry about it:
http://digital-compulsion.blogspot.com/2007/01/poetic-pathetic-version-control.html
http://grahamis.com/blog/2007/01/24/if-it-was-free-no-one-would-download-it/
The developers will spend 1/2 their time figuring out clearcase before doing any work and once they've figured it out they'll install git locally and only push to the clearcase repo as needed.
You'll have to employ a dedicated Clearcase admin.
I would suggest SVN for toolset and Git for scaling/workflow. I'd also suggest avoiding CC where possible. (Not counting money, the fact it is such a pain to use that is requires a full time admin is a total joke)
I recently had to wrangle with a similar situation. Maybe you can learn from my story.
The team I was newly assigned to was using a heavyweight tool in an convoluted, error-prone manner. I first attempted to sell them on my tools and processes of choice. This attempt failed miserably. I was flabbergasted that they would pick such a burdensome environment over one that was both easier and more effective. Turns out that they wanted to be disciplined, and using a painful process felt disciplined to them. It sounds wierd, but it's true. They had a lot of other misconceptions too. After I figured out what they were after, we actually stuck with the same tool suite (Serena), but massively changed how it was configured.
My advice to you is to figure out what matters to your team. Ripping on ClearCase won't get you anywhere unless you speak to their interests. Also, find out why they don't want to use alternatives. Basically do a little requirements gathering and fit your tool choices to your needs. Depending on your options, who knows, Clear Case may end up being the best option after all.
I'm not totally against ClearCase ( it does have it's advantages ), but to list out the disadvantages:
License Limitations - I can't easily work from home, because I don't have access to the license server. Even with a snapshot view on my laptop I have to play tricks because I can't get a license. There is a special remote client, but adds tons of its own limitations to the mix
License Limitations again - Only so many seats to go around, and then no one can use it.
Unix tools out of date - ClearCase seems to run best on Unix systems, but the GUI tools suck there. Windows/Unix integration of ClearCase introduces all sorts of its own pains.
The biggest downfall for me is both the performance (especially if your VOB is multisite or offsite), and potentially lengthy downtimes.
If you're like me and work in a relatively small office as part of a large company (with no onsite IT), Clearcase servers going down can cost you the better part of a workday in non-productivity as well as getting the right people to get it fixed.
Bottom line, use it only if you really need it for what you are doing and make sure you have a beefy IT budget to maintain it.
ClearCase is perfectly usable if your willing to also use another version control system on top of it! personally I find using mercurial ontop of CC to work quite well.
no atomic checkins
As of the new version of version 7.1 CC provides atomic checkin as functionality IF you like that. Personally I would really not want it but apparently some people see that as "an essential feature". I NEVER would want one big bulk in one go as a sort of massive version. Then again... if you want it just turn it on.
so... no longer an argument.
We used UCM ClearCase integrated with ClearQuest (DR Tracking/change request system) for the last 4 years with more than 50 developers. We have over 50 UCM projects over thousand of streams that handled over 35K DRs and change requests. During this period we have officially made over 600 integration deliveries and while having up to 6 concurrent development and release efforts.
I am the main CM/ClearCase guy with a backup who is able to perform the regular delivery/merge and integration builds. The network and servers are supported by the IT team. All I can say is we have had virtually no problems coming from the CM side of this huge development effort and were never a show stopper. Our developers where trained with just the basic stuff and a simple steps were given to them whenever a new project (branch) was created at the request from the project management.
Too many developer complained about ClearCase because they lack the proper CM/IT/ClearCase/Process/Management support. Developers should focus on development not SCM or be a tool specialist. For a large software development, at least 5-7% of the budget should be spent on CM and tool support.
Running a JDK from a VOB in Linux.
Try it, you need to play with the LD_PRELOAD variable (I know!)
the point of "it needs a dedicated person" and "it is complicated" etc....
The core issue here with finding this a problem is that you have to define if you want to have configuration management performed in your organization (which is NOT version management). Configuration Management is like Project Management: even without a tool you still can do project managment and without a tool you can do Configuration Management. Lots of people have a hard time understanding this and lots of people think Configuration Management is equal to a tool which versions sources of software or something...... (therefore comparisons with subversions or other VERSION management systems)
ClearCase is a solution that is build for usage in a Configuration Management environment ERGO: there is a configuration manager (just like "there is a project manager").
So... if in your perception that dedicated person is there to manage a tool I think there is something very wrong. In my perception there is a dedicated person who does configuration management who from an end-user perpective only shows up when there is a problem with the tool but regards this as only 1% of his job.
So what you need to do (like in any other software project) go back to your requirements and put a list of requirements together on what your organisation wants with configuration management. AND YES like in any other software project you will have users (like e.g. developers) who totally not agree with other users (like e.g. management) on certain requirements. There lies the key imho on some reactions I read here.
And IMHO if you have the organization list of requirements AND a configuration manager in the mix.... the choice is pretty clear (see also the forum on www.cmcrossroads.com)
ClearCase is not a tool only for end-users entering their sources under version control like subversion or git. That is only 1% of why a configuration manager really wants a mature configuration management tool.
And... I think the choice of a CM system should never lay with developers equal to choosing the right project management tool or the right CRM system. Developers are end-users of a certain part of the functionality of the tool.
I will be maybe alone here, but ClearCase is not that bad as everyone says. It can handle huge repositeories. Dynamic view are pretty cool and powerful feature too. It is reliable, can be customized by adding triggers and constraints on a pef file basis, permissions, etc.
Unfortunatelly, it comes with a price, big price. It is costly, and to operate properly needs to be properly configured and maintained by dedicated IT team. It makes it really good for BigCo, but not so wise choice for SmallFirm.
I'm a big fan of DVCS and git, but can understand why would BigCo choose ClearCase over SVN and Git. What I can't understand why would anyone choose SVN over Git ;>
Dynamic Views. Must admire a fully functional translucent file system.
One big benefit is that the Intellectual Property is always in the corporate network. A laptop can be lost/stolen and no source code in jeopardy.
Another is the instant access to source code and changed files, no time is ever spent downloading anything.
It serves well for the purpose it has.
I'd like to hear from people who are using distributed version control (aka distributed revision control, decentralized version control) and how they are finding it. What are you using, Mercurial, Darcs, Git, Bazaar? Are you still using it? If you've used client/server rcs in the past, are you finding it better, worse or just different? What could you tell me that would get me to jump on the bandwagon? Or jump off for that matter, I'd be interested to hear from people with negative experiences as well.
I'm currently looking at replacing our current source control system (Subversion) which is the impetus for this question.
I'd be especially interested in anyone who's used it with co-workers in other countries, where your machines may not be on at the same time, and your connection is very slow.
If you're not sure what distributed version control is, here are a couple articles:
Intro to Distributed Version Control
Wikipedia Entry
I've been using Mercurial both at work and in my own personal projects, and I am really happy with it. The advantages I see are:
Local version control. Sometimes I'm working on something, and I want to keep a version history on it, but I'm not ready to push it to the central repositories. With distributed VCS, I can just commit to my local repo until it's ready, without branching. That way, if other people make changes that I need, I can still get them and integrate them into my code. When I'm ready, I push it out to the servers.
Fewer merge conflicts. They still happen, but they seem to be less frequent, and are less of a risk, because all the code is checked in to my local repo, so even if I botch the merge, I can always back up and do it again.
Separate repos as branches. If I have a couple development vectors running at the same time, I can just make several clones of my repo and develop each feature independently. That way, if something gets scrapped or slipped, I don't have to pull pieces out. When they're ready to go, I just merge them together.
Speed. Mercurial is much faster to work with, mostly because most of your common operations are local.
Of course, like any new system, there was some pain during the transition. You have to think about version control differently than you did when you were using SVN, but overall I think it's very much worth it.
At the place where I work, we decided to move from SVN to Bazaar (after evaluating git and mercurial). Bazaar was easy to start off, with simple commands (not like the 140 commands that git has)
The advantages that we see is the ability to create local branches and work on it without disturbing the main version. Also being able to work without network access, doing diffs is faster.
One command in bzr which I like is the shelve extension. If you start working on two logically different pieces of code in a single file and want to commit only one piece, you can use the shelve extension to literally shelve the other changes later. In Git you can do the same with playing around in the index(staging area) but bzr has a better UI for it.
Most of the people were reluctant to move over as they have to type in two commands to commit and push (bzr ci + bzr push). Also it was difficult for them to understand the concept of branches and merging (no one uses branches or merges them in svn).
Once you understand that, it will increase the developer's productivity. Till everyone understands that, there will be inconsistent behaviour among everyone.
At my workplace we switched to Git from CVS about two months ago (the majority of my experience is with Subversion). While there was a learning curve involved in becoming familiar with the distributed system, I've found Git to be superior in two key areas: flexibility of working environment and merging.
I don't have to be on our VPN, or even have network connectivity at all, to have access to full versioning capabilities. This means I can experiment with ideas or perform large refactorings wherever I happen to be when the urge strikes, without having to remember to check in that huge commit I've built up or worrying about being unable to revert when I make a mess.
Because merges are performed client-side, they are much faster and less error-prone than initiating a server-side merge.
My company currently uses Subversion, CVS, Mercurial and git.
When we started five years ago we chose CVS, and we still use that in my division for our main development and release maintenance branch. However, many of our developers use Mercurial individually as a way to have private checkpoints without the pain of CVS branches (and particularly merging them) and we are starting to use Mercurial for some branches that have up to about 5 people. There's a good chance we'll finally ditch CVS in another year. Our use of Mercurial has grown organically; some people still never even touch it, because they are happy with CVS. Everyone who has tried Mercurial has ended up being happy with it, without much of a learning curve.
What works really nicely for us with Mercurial is that our (home brewed) continuous integration servers can monitor developer Mercurial repositories as well as the mainline. So, people commit to their repository, get our continuous integration server to check it, and then publish the changeset. We support lots of platforms so it is not feasible to do a decent level of manual checks. Another win is that merges are often easy, and when they are hard you have the information you need to do a good job on the merge. Once someone gets the merged version to work, they can push their merge changesets and then no one else has to repeat the effort.
The biggest obstacle is that you need to rewire your developers and managers brains so that they get away from the single linear branch model. The best medicine for this is a dose of Linus Torvalds telling you you're stupid and ugly if you use centralised SCM. Good history visualisation tools would help but I'm not yet satisfied with what's available.
Mercurial and CVS both work well for us with developers using a mix of Windows, Linux and Solaris, and I've noticed no problems with timezones. (Really, this isn't too hard; you just use epoch seconds internally, and I'd expect all the major SCM systems get this right).
It was possible, with a fair amount of effort, to import our mainline CVS history into Mercurial. It would have been easier if people had not deliberately introduced corner cases into our mainline CVS history as a way to test history migration tools. This included merging some Mercurial branches into the CVS history, so the project looks like it was using from day one.
Our silicon design group chose Subversion. They are mainly eight timezones away from my office, and even over a fairly good dedicated line between our offices SUbversion checkouts are painful, but workable. A big advantage of centralised systems is that you can potentially check big binaries into it (e.g. vendor releases) without making all the distributed repositories huge.
We use git for working with Linux kernel. Git would be more suitable for us once a native Windows version is mature, but I think the Mercurial design is so simple and elegant that we'll stick with it.
Not using distributed source control myself, but maybe these related questions and answers give you some insights:
Distributed source control options
Why is git better than Subversion
I personnaly use Mercurial source control system. I've been using it for a bit more than a year right now. It was actually my first experience with a VSC.
I tried Git, but never really pushed into it because I found it was too much for what I needed. Mercurial is really easy to pick up if you're a Subversion user since it shares a lot of commands with it. Plus I find the management of my repositories to be really easy.
I have 2 ways of sharing my code with people:
I share a server with a co-worker and we keep a main repo for our project.
For some OSS project I work on, we create patches of our work with Mercurial (hg export) and the maintener of the project just apply them on the repository (hg import)
Really easy to work with, yet very powerful. But generally, choosing a VSC really depends on our project's needs...
Back before we switched off of Sun workstations for embedded systems development we were using Sun's TeamWare solution. TeamWare is a fully distribution solution using SCCS as the local repository file revision system and then wrappers that with a set of tools to handle the merging operations (done through branch renaming) back to the centralized repositories of which there can be many. In fact, because it is distributed, there really is no master repository per se' (except by convention if you want it) and all users have their own copies of the entire source tree and revisions. During "put back" operations, the merge tool using 3-way diffs algorithmically sorts out what is what and allows you combine the changes from different developers that have accumulated over time.
After switching to Windows for our development platform, we ended up switching to AccuRev. While AccuRev, because it depends on a centralized server, is not truely a distributed solution, logically from a workflow model comes very close. Where TeamWare would have had completely seperate copies of everything at each client, including all the revisions of all files, under AccuRev this is maintained in the central database and the local client machines only have the flat file current version of things for editing locally. However these local copies can be versioned through the client connection to the server and tracked completely seperately from any other changes (ie: branches) implicitly created by other developers
Personally, I think the distributed model implemented by TeamWare or the sort of hybrid model implemented by AccuRev is superior to completely centralized solutions. The main reason for this is that there is no notion of having to check out a file or having a file locked by another user. Also, users don't have to create or define the branches; the tools do this for you implicitly. When there are larger teams or different teams contributing to or maintaining a set of source files this resolves "tool generated" locking related collisions and allows the code changes to be coordinated more at the developer level who ultimately have to coordinate changes anyway. In a sense, the distributed model allows for a much finer grained "lock" rather than the course grained locking instituted by the centralized models.
Have used darcs on a big project (GHC) and for lots of small projects. I have a love/hate relationship with darcs.
Pluses: incredibly easy to set up repository. Very easy to move changes around between repositories. Very easy to clone and try out 'branches' in separate repositories. Very easy to make 'commits' in small coherent groups that makes sense. Very easy to rename files and identifiers.
Minuses: no notion of history---you can't recover 'the state of things on August 5'. I've never really figured out how to use darcs to go back to an earlier version.
Deal-breaker: darcs does not scale. I (and many others) have gotten into big trouble with GHC using darcs. I've had it hang with 100% CPU usage for 9 days trying to pull in
3 months' worth of changes. I had a bad experience last summer where I lost two weeks
trying to make darcs function and eventually resorted to replaying all my changes by hand into a pristine repository.
Conclusion: darcs is great if you want a simple, lightweight way to keep yourself from shooting yourself in the foot for your hobby projects. But even with some of the performance problems addressed in darcs 2, it is still not for industrial strength stuff. I will not really believe in darcs until the vaunted 'theory of patches' is something a bit more than a few equations and some nice pictures; I want to see a real theory published in a refereed venue. It's past time.
I really love Git, especially with GitHub. It's so nice being able to commit and roll back locally. And cherry-picking merges, while not trivial, is not terribly difficult, and far more advanced than anything Svn or CVS can do.
My group at work is using Git, and it has been all the difference in the world. We were using SCCS and a steaming pile of csh scripts to manage quite large and complicated projects that shared code between them (attempted to, anyway).
With Git, submodule support makes a lot of this stuff easy, and only a minimum of scripting is necessary. Our release engineering effort has gone way, way down because branches are easy to maintain and track. Being able to cheaply branch and merge really makes it reasonably easy to maintain a single collection of sources across several projects (contracts), whereas before, any disruption to the typical flow of things was very, very expensive. We've also found the scriptabability of Git to be a huge plus, because we can customize its behavior through hooks or through scripts that do . git-sh-setup, and it doesn't seem like a pile of kludges like before.
We also sometimes have situations in which we have to maintain our version control across distributed, non-networked sites (in this case, disconnected secure labs), and Git has mechanisms for dealing with that quite smoothly (bundles, the basic clone mechanism, formatted patches, etc).
Some of this is just us stepping out of the early 80s and adopting some modern version control mechanisms, but Git "did it right" in most areas.
I'm not sure of the extent of answer you're looking for, but our experience with Git has been very, very positive.
Using Subversion with SourceForge and other servers over a number of different connections with medium sized teams and it's working very well.
I am a huge proponent of centralized source control for a lot of reasons, but I did try BitKeeper on a project briefly. Perhaps after years of using a centralized model in one format or another (Perforce, Subversion, CVS) I just found distributed source control difficult to use.
I am of the mindset that our tools should never get in the way of the actual work; they should make work easier. So, after a few head pounding experiences, I bailed. I would advise doing some really hardy tests with your team before rocking the boat because the model is very different than what most devs are probably accustomed to in the SCM world.
I've used bazaar for a little while now and love it. Trivial branching and merging back in give great confidence in using branches as they should be used. (I know that central vcs tools should allow this, but the common ones including subversion don't allow this easily).
bzr supports quite a few different workflows from solo, through working as a centralised repository to fully distributed. With each branch (for a developer or a feature) able to be merged independently, code reviews can be done on a per branch basis.
bzr also has a great plugin (bzr-svn) allowing you to work with a subversion repository. You can make a copy of the svn repo (which initially takes a while as it fetches the entire history for your local repo). You can then make branches for different features. If you want to do a quick fix to the trunk while half way through your feature, you can make an extra branch, work in that, and then merge back to trunk, leaving your half done feature untouched and outside of trunk. Wonderful. Working against subversion has been my main use so far.
Note I've only used it on Linux, and mostly from the command line, though it is meant to work well on other platforms, has GUIs such as TortoiseBZR and a lot of work is being done on integration with IDEs and the like.
I'm playing around with Mercurial for my home projects. So far, what I like about it is that I can have multiple repositories. If I take my laptop to the cabin, I've still got version control, unlike when I ran CVS at home. Branching is as easy as hg clone and working on the clone.
Using Subversion
Subversion isn't distributed, so that makes me think I need a wikipedia link in case people aren't sure what I'm talking about :)
Been using darcs 2.1.0 and its great for my projects. Easy to use. Love cherry picking changes.
I use Git at work, together with one of my coworkers. The main repository is SVN, though. We often have to switch workstations and Git makes it very easy to just pull changes from a local repository on another machine. When we're working as a team on the same feature, merging our work is effortless.
The git-svn bridge is a little wonky, because when checking into SVN it rewrites all the commits to add its git-svn-id comment. This destroys the nice history of merges between my coworker's repo an mine. I predict that we wouldn't use a central repository at all if every teammember would be using Git.
You didn't say what os you develop on, but Git has the disadvantage that you have to use the command line to get all the features. Gitk is a nice gui for visualizing the merge history, but the merging itself has to be done manually. Git-Gui and the Visual Studio plugins are not that polished yet.
We use distributed version control (Plastic SCM) for both multi-site and disconnected scenarios.
1- Multi-site: if you have distant groups, sometimes you can't rely on the internet connection, or it's not fast enough and slows down developers. Then having independent server which can synchronize back (Plastic replicates branches back and forth) is very useful and speed up things. It's probably one of the most common scenarios for companies since most of them are still concerned of "totally distributed" practices where each developer has its own replicated repository.
2- Disconnected (or truly distributed if you prefer): every developer has his own repository which is replicated back and forth with his peers or the central location. It's very convenient to go to a customer's location or just go home with your laptop, and continue being able to switch branches, checkout and checkin code, look at the history, run annotates and so on, without having to access the remote "central" server. Then whenever you go back to the office you just replicate your changes (normally branches) back with a few clicks.