Recent Posts by Poonam Parhar

If the terms 'Stuck Threads' or 'Hang' sound familiar and scary to you, please read on. We can sometimes come across situations where the Weblogic Server (WLS) reports some threads as being 'Stuck' or 'not making any progress', but the stack traces of those threads and others in the process look absolutely normal, showing no signs why and how those threads could get stuck. I got to analyze such a situation recently. The threads in the application were reported to be Stuck....

I was recently involved in a performance issue where the application's response times were decreasing over time, and I was tasked to determine if GC was playing any role in that. Well, as we all know that misconfiguration of the java heap space and its generations can lead to unexpected/frequent/longer garbage collection cycles causing inferior performance and longer response times of the application, and that indeed was the cause of this performance issue. I want to share some...

In this blog, I am going to talk about two confusions around Java Flight Recordings that I have come across from multiple users/customers. Let's take a look at them one by one. Flight Recordings Interval A number of Java Flight Recorder users seem to have a confusion around the 'start-time' and the 'interval' of the flight recordings. The complaint is that the flight recordings in the Java Mission Control show longer recording interval than their actual recorded data. For...

This question comes up every now and then that how can I find what the minor/young collections are promoting to the old generation of my Java application. Recently, there was a case where the customer wanted to know the types of objects getting promoted to the old generation at different input loads for their application. Well, one longer and a little bit tedious way is to use -XX:+TraceScavenge option. This is a non-product JVM option and hence you would need to build a debug...

I was recently asked a question that why my Java application runs out of Java Heap when there is still so much memory available to use? Here is the question in detail - I am running my application with -Xmx1600m but the logs show that it runs out of memory without fully using the 1600mb. 2017-03-21T13:15:39.478+0000: 289274.599: [Full GC [PSYoungGen: 338944K->0K(425472K)] [ParOldGen: 1092073K->1055276K(1092096K)] 1431017K->1055276K(1517568K) [PSPermGen:...

I was recently working on a memory growth issue involving WeakReferences, and I came across this great blog post on how non-strong references can affect the heap usage and the garbage collection: https://plumbr.eu/blog/garbage-collection/weak-soft-and-phantom-references-impact-on-gcIt has a demo application that demonstrates an increase in the number of objects getting promoted from young to old generation when WeakReferences are used. That made me deeply interested...

In this post, I am going to discuss a couple of scenarios where the Java process hangs are actually NOT because of a Java/JVM issue but happen due to the OS problems. Both the hangs being discussed here occur on the Linux operating system. Lets take a look at the first case where a thread seems to be stuck in the Java Thread.sleep() call. From the process stack trace, the two threads of interest are: Thread 26755: (state = IN_VM)  - java.lang.Thread.interrupt0() @bci=0...

Recently there was a report from a customer that they observed performance degradation while using JFR with G1 when they used it along with -XX:FlightRecorderOptions=stackdepth=512, but didn't see any performance impact when using the same setting for the stackdepth with the Parallel Collector. The flight recordings revealed that the poor performance was due to the long pauses introduced by the JFRCheckpoint operations. The long JFRCheckpoints occurred only for the recordings...

Recently, received quite a few reports of the application crashes from different customers and product groups with the stack trace looking like this: Stack: [0xb0c00000,0xb0c80000], sp=0xb0c7c890, free space=498kNative frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)C [libc_psr.so.1+0x700] memcpy+0x2f8C [libzip.so+0xd19c]C [libzip.so+0x2380] ZIP_GetEntry+0xe4C [libzip.so+0x2800] Java_java_util_zip_ZipFile_getEntry+0xc4j ...