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From "Winnebeck, Jason" <Jason.Winneb...@windstream.com>
Subject RE: Very Odd/Random JVM Slowdown With Indy
Date Tue, 15 Mar 2016 12:40:15 GMT
Method handles are a relatively new component to the JVM. One thing to consider is whether
or not you are running the latest JVM version.

If I ignore for a moment your finding of that method on the top of the stack, when I’ve
seen the JVM get very slow without any apparent deadlocks I’ve also seen GC as an issue.
I would just double check to make sure there’s not a leak (in heap or permgen/metaspace)
going on, it might be possible that the MethodHandle code is more susceptible to GC pauses
and appears more often in your stack dumps. Same thing with your underlying OS as well, I
would just double check that you aren’t in a swap condition or (on Linux) in iowait states.
Your note about removing indy fixing this seems to suggest that is not the case but it’s
also a common condition I see with “JVM starts running order of magnitudes slower until
you restart” issues. It may also be possible that Groovy indy or JVM invokedynamic has a
leak that shows up as a memory scaling problem as well.

Jason

From: David Clark [mailto:plotinussmith@gmail.com]
Sent: Monday, March 14, 2016 5:31 PM
To: users@groovy.apache.org
Subject: Very Odd/Random JVM Slowdown With Indy

I've been chasing a slowdown in our application for a couple of months now. I have what I
believe is a solution (no slowdown for 4 days now). But I'm having difficulty understanding
why the solution works.

Symptoms:

At random intervals and a random times our web servers will go from serving responses in the
300 ms range to taking 30 seconds or more. Sometimes the servers will recover, sometimes they
require a restart of the webserver (spring boot/tomcat). When the applications slow down we
always see the tomcat thread pool hit the maximum size. Every single thread in the thread
pool is in the RUNNABLE state but appears to be making no progress. Successive thread dumps
show that the stacks are changing, but VERY slowly. The top of the stack is always this method:

at java.lang.invoke.MethodHandleNatives.setCallSiteTargetNormal(Native Method).

The other common condition is that whatever application code is on the stack is always dynamically
compiled. Code that is @CompileStatic is NEVER on the stack when we see these slowdowns.

The thread dumps showed that the application code is never waiting on locks, socket reads,
db connections, etc.

Solution:

The solution to the problem was to disable Indy compilation and return to non-Indy compilation.
However, I don't think Indy is the problem here. I noticed that our Spring Boot executable
jar contained BOTH groovy-all-2.4.5.jar AND groovy-all-indy-2.4.5.jar. Someone forgot to exclude
the non-indy jars.

My theory:

Having both indy and non-indy jars on the classpath is confusing the JIT compiler. Code will
be continuously JIT-ed as different methods fight over which class files to JIT, those loaded
from the groovy-all jar or those loaded from the groovy-all-indy jar. If this is true then
the compiler threads will be continuously running and applying native locks which are invisible
to tools like VisualVM. The result would be random slowdowns because only certain combinations
of code paths would result in slowdowns. It would also cause application code to go very slowly
as the JIT compiler continuously re-compiles code over and over again. Application code would
be stuck mostly waiting for JIT operations to complete as invalidated code is continuously
removed and replaced.

For now I will be leaving Indy disabled until we can do more accurate load testing in non
production environments.

My Question:

Is this theory possible? Am I going in a direction that is possible or likely?

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