Jenkins comes with the remoting library that it uses to communicate between a master and slaves.  This is a pretty awesome library, I think, which served us well. 

One of the things this remoting layer does it to transfer the Java byte code on demand from the master to slaves on demand.  This approach helps us keep slave deployment simple, as you don't have to keep the master and all the slaves in sync, but it also made the slave start-up slower, because none of the byte code loaded to slaves are kept around.  It was all forgotten once the slave gets disconnected. 

When slaves are static and stays online for hours, this wasn't a problem at all.  But as more and more slaves become elastic (think EC2 or CloudBees DEV@cloud), This delay is becoming more and more noticeable.  A similar issue happens when the Maven project type, which uses the same remoting library to talk to the running Maven build. 

Git plugin is one of the most popular plugins out there, and it's been around for quite some time.  Combine that with the fact that there are so many different ways to use Git, it was inevitable that Git plugin became quite a capable but complex plugin over time.  It has more than a dozen options and switches, and it was becoming harder to use and harder to maintain. 

As early as 2010, some of us have already been saying that we should refactor this plugin, but none of us have managed.  The good news is, I finally started tackling this problem last month while I was in London, and I've made a steadily progress since then and I'm ready for a wider review. 

As the usage of Jenkins expands, we started seeing users who run multiple 100s of slaves on one master, and thus it became a lot more important for us to scale well to even larger number of slaves. 

While I was looking at the thread dump of a large system, I started noticing that there are a large number of threads lying around pumping InputStream and writing to another OutputStream.  On Linux, each thread occupies 2MB just for its stack size, so if we can eliminate some of them, it'd be a good saving. 

To cut the long story short, I was able to eliminate two pump threads per every SSH connection.  Furthermore, when it runs on the upcoming Jenkins 1.521, it'll save one more thread per every SSH connection.  So if you have 100 slaves connected through SSH, this alone saves up 600MB of memory.  That's pretty good for a few hours work! 

With more than 600 plugins, Jenkins has a vibrant community and we're dependent on YOU to keep it that way.  Here are 3 ways you can give back to the community to ensure that everyone benefits and Jenkins keeps growing...

Giving it back to the community #1: vendor+community=win

Jenkins is becoming ubiquitous enough that tool vendors and service providers often find their users asking them to provide Jenkins plugins.  The challenge for these companies is that they don’t necessarily possess the necessary Jenkins expertise to do one. 

Here at the Jenkins project, what we are trying to do is to work with these people to deliver a plugin.  It gets the job done a whole lot more quickly if the vendor brings in their expertise on their tool/services and we bring in our expertise on Jenkins plugin development. 

For example, we recently worked with SOASTA to help them open-source the plugin they developed in house, then help them add a whole bunch of new functionalities.  By open-sourcing a plugin in the Jenkins project, vendors win as the community helps fix bugs and improve plugins.  The Jenkins project wins by building relationship with vendors.  And finally the users win by having more integrations.