[wildfly-dev] Speeding up WildFly boot time

[J Pai]

Not to undermine these efforts (in fact, this thread has actually brought up a couple of really interesting details), but one of the things I have always seen when we spent time trying to add relatively complex ways to squeeze some milli seconds out of the boot time, is that for the end users, most of the times it really didn’t matter in a noticeable way.I am not talking about the major improvements we have made from AS5/AS6 to the WildFly boot times today. 

What I have experienced is that for end users, they are mostly interested in seeing their (usually large) deployments show noticeable improvements in deployment time, not necessarily from a cold boot of the server, but when the server is already up and they either want to deploy something new or re-deploy their application.
 
All in all, as a developer, I will be curiously following how these experiments go, but as an end user, I am not sure this will show up as something noticeable. Of course, the place where this would probably make a difference (even from an end user perspective) is something like maybe WildFly Swarm, but then again I haven’t been following that project to understand if these efforts will directly end up somehow in WildFly Swarm.

-Jaikiran 

On 15-May-2017, at 5:06 AM, Stuart Douglas <stuart.w.douglas at gmail.com> wrote:

When JIRA was being screwy on Friday I used the time to investigate an idea I have had for a while about improving our boot time performance. According to Yourkit the majority of our time is spent in class loading. It seems very unlikely that we will be able to reduce the number of classes we load on boot (or at the very least it would be a massive amount of work) so I investigated a different approach.

I modified ModuleClassLoader to spit out the name and module of every class that is loaded at boot time, and stored this in a properties file. I then created a simple Service that starts immediately that uses two threads to eagerly load every class on this list (I used two threads because that seemed to work well on my laptop, I think Runtime.availableProcessors()/4 is probably the best amount, but that assumption would need to be tested on different hardware). 

The idea behind this is that we know the classes will be used at some point, and we generally do not fully utilise all CPU's during boot, so we can use the unused CPU to pre load these classes so they are ready when they are actually required.

Using this approach I saw the boot time for standalone.xml drop from ~2.9s to ~2.3s on my laptop. The (super hacky) code I used to perform this test is at https://github.com/wildfly/wildfly-core/compare/master...stuartwdouglas:boot-performance-hack

I think these initial results are encouraging, and it is a big enough gain that I think it is worth investigating further.

Firstly it would be great if I could get others to try it out and see if they see similar gains to boot time, it may be that the gain is very system dependent.

Secondly if we do decide to do this there are two approach that we can use that I can see:

1) A hard coded list of class names that we generate before a release (basically what the hack already does), this is simplest, but does add a little bit of additional work to the release process (although if it is missed it would be no big deal, as ClassNotFoundException's would be suppressed, and if a few classes are missing the performance impact is negligible as long as the majority of the list is correct).

2) Generate the list dynamically on first boot, and store it in the temp directory. This would require the addition of a hook into JBoss Modules to generate the list, but is the approach I would prefer (as first boot is always a bit slower anyway).

Thoughts?

Stuart
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