![]() ![]() We can actually tweak OpenJDK to be less aggressive by forcing it to only use the simplest part of its JIT, We pay a large cost at startup in trade for reducing In fact, the JVM is actually a little too aggressive, spending many CPU cycles during this 1.6 seconds optimizingĪnd emitting code that will only be used briefly. The JVM does optimize some of our code, but it’s too little, too JIT anything until after baseline startup. I say this is a worst case because it really gives us no time at all to optimize any code. Yikes! Both implementations are doing roughly the same work here: setting up the core classes and booting the This first example compares ruby -e 1 times on CRuby 2.6.4 versus JRuby 9.2.9 (from master) on OpenJDK 8. Let’s take a look at some worst-case numbers. Interpreter…which itself is also running in the JVM interpreter! How bad is it? Running during the first few seconds after launching JRuby is running in the JVM interpreter or the JRuby Methods, for example) as well as the actual core method implementations also start out “cold”. Making matters worse, all of the logic to set up the core classes (defining String or Array and their Run lots of Ruby code on every startup, mostly to boot up the RubyGems subsystem Contrast this to CRuby, where all of these stagesĪre written in C and precompiled to native code long before the runtime is launched. ![]() Ruby apps are distributed as source code, which means they must firstįirst pass through a parser and compiler before being executed with an interpreter – all of which start out as It hitsĬompare JRuby with CRuby at startup. Modern JVMs do start executing very quickly, but if your application needs to run lots ofĬode at boot, before it can do useful work, startup time will reflect the fact that the bytecode interpreterĪnyone familiar with deploying JVM-based applications will know this as the dreaded “warmup curve”. Immediately, we save some startup time by not running an expensive JIT compiler before execution. The idea is that since the interpreter can start executing Instructions that the system CPU can execute directly. As that code gets “hot”, the JVM will usually compile it to native Most JVMs initially execute that bytecode using an interpreter, similar to how CRubyĮxecutes its “instruction sequences”. JRuby is an implementation of Ruby that runs on the JVM, and as you’d expect a large part of our codebase starts This, JRuby needs to have acceptable startup time. Rubyists do the great majority of their work using two tools: an editor, and a terminal. Line, be they installing libraries, generating code, or starting up interactive consoles and application Most non-coding development tasks involve running Ruby at a command In the Ruby world, things are very different. Recently with the rise of small services and cloud “functions” has the issue of Java startup time really become Startup time issue for years because most developers built their apps using an always-on IDE that transparentlyĬompiled code in the background and often restarted or redeployed to local development servers automatically. The actual development experience of different languages varies greatly. While this is usually true (ignoring continuous deployment for now), right? Even the most aggressive organizations usually won’t Most applications are deployed pretty rarely. Startup time is important!īefore we get started running numbers and tweaking flags, you may be wondering why startup time is such a bigĭeal. Today we’ll cover a topic that never gets old: JRuby’s startup performance. Hello friends! How long has it been? Too long! This post marks the beginning of a return to blogging about JRuby, the JVM, and everything in between. ![]()
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