XML please, I don’t want to recompile

There’s one quite naive argument that sometimes determines the technology choice. I want to write about it because this argument I’ve been hearing on and off for years. It’s about favouring XML to avoid recompilation.

I remember in the late days of EJB2, one of the selling points of Spring was that you can reconfigure the wiring of your beans without recompilation. At that time I was quite enthusiastic about this feature… even though the argument was almost completely negligible.

My friend said today:

“Another advantage [of XML workflow] is you can do some modification to the flow without recompiling the whole app”

It’s true that you don’t need to recompile. However, if you want fully implement the change to the XML workflow you probably still have to:

• run tests
• validate the app works
• check-in the change to your VCS (new revision created)
• make sure the integration build on newly created revision works OK
• validate the application (built with the new revision) works on the integration box
• …

In most cases, updating XML by hand on the integration/prod box is not practical. Don’t fall for the ‘no recompilation’ argument because it is negligable. Usually you still need a build & QA cycle.

This post is not intended to claim that XML is bad for you (although I probably agree with that statement =)). This post claims that ‘no recompilation’ argument is void.

Nevertheless, If I have to use a workflow in my java app it will declared in java and not in xml. I’m great fan of fluent, type-safe & intellisense-ready configurations!

Developer! rid your wip!

I’m big on eliminating waste, I’m big on minimizing Work In Progress (WIP).

Here’s my story: a colleague asked me to pair with him because he broke the application and he didn’t know why. So we sat together. My first question was:

– “Did the app work before you made your changes?”
– “Yes”
– “Ok, show me the changes you made”

I saw ~150 hundred unknown files, ~20 modified or added files. I said:

– “That’s a lot of changes. I bet you started doing too many changes at once so you ended up with a lot of WIP. Can we revert all the changes you made?”
– “Errr… I guess so. I know what refactoring I wanted to do. We can do it again”
– “Excellent, let’s clean your workspace now”

We reverted the changes. We also discovered that there were some core “VCS ignores” missing (hence so many unknown files in the working copy). We fixed that problem by adding necessary “VCS ignores”. I continued:

– “Ok, the working copy is clean and the application works OK. Let’s kick off the refactoring you wanted to do. However this time, we will do the refactoring in small steps. We will keep the WIP small by doing frequent check-ins on the way.”
– “Sounds good”

Guess what. We didn’t encounter the initial problem at all. We completed the refactoring in ~1 hour doing several check-ins in the process. Previous attempt to the refactoring took much more time due to few hours spent on debugging the issue.

Here’s my advice for a developer who wants to debug less & smile more:

1. Understand what is your work in progress; keep WIP under control; keep it small.
2. Develop code in small steps.
3. Keep your workspace clean, avoid unknown or modified files between check-ins.

Hudson is a cunning beast

Build failed today:

ERROR: Failed to update http://svn.dev.sabre.com/svn/apd_centiva2/trunk
org.tmatesoft.svn.core.SVNException: svn: blah blah blah

‘Bummer, I need to log in to the ci box and figure out what’s wrong with svn.’ – I thought. Being in the middle of something I didn’t get to it immediately. Then I got another notification from Hudson:


Updated failed due to local files. Getting a fresh workspace
...
Finished: SUCCESS

Apparently, hudson figured out that there’s been an issue with svn update so during the next build he simply did a full checkout. It worked just fine. I do like Hudson.

hgsubversion on windows

Who likes mercurial? I do. Lately, I even started using mercurial as a client for subversion repositories. Let me describe the hgsubversion installation steps that worked for me; on my laptop that is boldly supplied with The Only Right operation system…

I heavily borrow from excellent entry by Ben Collins-Sussman and from outrageously diligent post by Dave Cameron. I want to focus on the smallest possible installation routine on windows. Also, I want to emphasize that you don’t have to build anything on windows. All the prepackaged installables or binaries are ready, waiting for you to grab them.

Oh right, here are the steps that worked for me:

1. Install mercurial (TortoiseHg)
2. Clone hgsubversion
3. Configure hgsubversion extension
4. Start cloning svn repos!
5. Understand the gotchas
6. Stay happy

1. Install mercurial (TortoiseHg). I installed TortoiseHg (mercurial + tortoise). Your cmd should nicely take: hg version.

In theory you can install different Mercurial client. However, there is a huge advantage of installing TortoiseHg: you don’t have to install python, svn python bindings & make your Mercurial use it. All because TortoiseHg comes with python+svn bindings (thanks Afriza for a hint!).

2. Clone hgsubversion:

hg clone http://bitbucket.org/durin42/hgsubversion SomeFantasticFolder

In my case SomeFantasticFolder is c:\projects\open-source\hgsubversion. At the moment I cloned hgsubversion the tip was the changeset 500.

3. Configure hgsubversion extension. Add extensions to your USER_HOME/.hgrc, which on windows is Documents and Settings\SomeFabulousName. In my case SomeFabulousName is sg0897xxx (after years in IT industry I’m still just a number…). Note that hgsubversion is duplicated at the end – that’s fine. Your .hgrc should contain something like:

[extensions]
rebase=
#do not quote the path if it has spaces!
svn=c:\projects\open-source\hgsubversion\hgsubversion

Your cmd should print enabled extensions at the bottom of the screen when you do: hg help extensions

4. Start cloning svn repos!

Instead of cloning repos with “hg clone” I suggest to “hg pull” instead. Pull is better because it can continue in case something breaks (cloning very large repo can takes hours).

hg init example
cd example
hg pull http://example-for-hgsubversion.googlecode.com/svn example-for-hgsubversion

5. Understand the gotchas.

• gotcha 1. If svn requires authentication, you may be asked to enter user/password… 3 times. Don’t worry, just enter correct credentials patiently. Three shall be the number thou shalt count, and the number of the counting shall be three. (update) Augie Fackler, the mastermind of hgsubversion points out svn+http or svn+https can be used to work around this gotcha
• gotcha 2: After updating changes from svn (hg pull, hg update) never use ‘hg merge’, instead use ‘hg rebase’. Merges are not yet supported by hgsubversion I heard. If you accidentally do hg merge you probably have to rollback the merge in order to push.
• gotcha 3: (new) From my experience it is better to clone entire repo, not only trunk. Cloning trunk worked for me but I noticed exceptions thrown during unsuccessful rebase. Working with full repo clone was smooth for me so far.
• gotcha 4: (new) Commands you should know:

  hg help svn
  hg rebase --svn
  hg svn info
  hg svn rebuildmeta
  

• last gotcha: I’m not a mercurial expert so feel free to comment & give feedback. Also, newer (different) versions of before mentioned installables should work as well. If links to binaries are dead then get creative and google for it – I don’t guarantee all links will work forever.

6. Stay happy. Are you kidding me? You know what to do =)