Ram Lakshmanan, the founder and the architect of yCrash talked about how to diagnose and solve issues when a app crashes due to a memory leak, thread leak, CPU spike, unresponsiveness, BLOCKED threads, Deadlocks, and Heavy I/O activity.

1. Lets crash our
applications!
Jax london - 2022
Ram Lakshmanan | Architect

2. Young old metaspace others
-Xmx -XX:MaxMetaspaceSize
Young: Newly created Objects
Old: New objects that survived one or more minor
GC promoted here
Metaspace: Classes, Methods, metadata
Others Description
Thread Stacks Each thread has a separate memory space.
Controlled by -Xss
Garbage
Collection
Threads, Memory to store GC info
Code Generation Converting bytecode to native code
Socket Buffers TCP Connections (Receive buffer ~37k, Send
Buffer ~2.5k)
JNI JNI program also allocate memory
Can Java process memory consumption
go beyond –Xmx?

3. main( )
a( )
b( )
c( )
x=1
y*
z=2.11
public class SimpleExample {
public static void main(String args[]) {
a();
}
public static void a() {
int x = 1;
b();
}
public static void b() {
Car y = new Car();
c();
}
public static void c() {
float z = 2.11f;
}
}
Thread’s stack
Young old metaspace
car
-Xss
car
metada
How java program is executed?

4. 1. stackoverflowERROR
https://blog.ycrash.io/2021/04/09/chaos-engineering-stackoverflow-error/

5. HOW TO SIMULATE?
Source code: https://github.com/ycrash/buggyapp
public class StackOverflowDemo {
public void start() {
start( );
}
}
Thread’s stack
frame
Infinite times start( )
is present in the
stack
start( )
start( )
start( )
start( )
start( )
start( )

6. 2. Cpu spike
https://blog.ycrash.io/2021/02/10/chaos-engineering-simulating-cpu-spike/

7. HOW TO SIMULATE?
Open Source: https://github.com/ycrash/buggyapp
public class CPUSpikerThread extends Thread
{
@Override
public void run( ) {
while (true) {
}
}
}

8. 3. OUTOFMEMORYERROR
https://blog.ycrash.io/2021/02/10/chaos-engineering-simulating-cpu-spike/

9. HOW TO SIMULATE?
Open Source: https://github.com/ycrash/buggyapp
public class OOMDemo {
static HashMap<Object, Object> myMap = new HashMap<>();
public static void start() throws Exception {
long counter = 0;
while (true) {
myMap.put("key" + counter,
"Large stringgggggggggggggggggggggggggggggggggggg“ + counter);
++counter;
}
}
}

10. Hashmap in memory
Key0 Large stringggggggggggggggggggggggggggggggggggg0
Key1 Large stringggggggggggggggggggggggggggggggggggg1
Key2 Large stringggggggggggggggggggggggggggggggggggg2
Key3 Large stringggggggggggggggggggggggggggggggggggg3
: :
: :
: :
: :
: :

11. 4 . BLOCKED Threads
https://blog.ycrash.io/2021/04/09/chaos-engineering-blocked-threads/

12. HOW TO SIMULATE?
public synchronized getData() {
makeDBCall();
}
T1: Runnable
T2
T3
T4
Tn
Blocked

13. 5. Thread leak
https://blog.ycrash.io/2021/04/09/chaos-engineering-thread-leak/

14. HOW TO SIMULATE?
public class ThreadLeakDemo {
public static void start() {
while (true) {
new ForeverThread().start();
}
}
}
public class ForeverThread extends Thread {
@Override
public void run() {
while (true) { // Put the thread to sleep forever, so they don't die.
try {
Thread.sleep(10 * 60 * 1000); // Sleeping for 10 minutes repeatedly
} catch (Exception e) {}
}
}
}
Source code: https://github.com/ycrash/buggyapp

15. Oom: unable to create new native thread
Java Heap + metaspace
Physical memory
Threads
Key: Threads are created outside heap,
metaspace
Java Heap + metaspace
Physical memory
Process
-1
Process
-2
Solution:
1. Fix thread leak
2. Increase the Thread Limits Set at
Operating System(ulimit –u)
3. Reduce Java Heap Size
4. Kills other processes
5. Increase physical memory size
6. Reduce thread stack size (-Xss).
Note: can cause StackOverflowError

16. 360° DATA (16 artifacts)
open-source script: https://github.com/ycrash/yc-data-script

17. Live Demo!

18. Thank you friends
Ram Lakshmanan
ram@tier1app.com
@yCrash
https://www.linkedin.com/company/gceasy
This deck will be published in: https://blog.ycrash.io
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