coherence-operator

Produce and Extract Heap Dump

Some of the debugging techniques described in Debugging in Coherence require the creation of files, such as log files and JVM heap dumps, for analysis. You can also create and extract these files in the Coherence Operator.

This sample shows how to collect a .hprof file for a heap dump. A single-command technique is also included at the end of this sample.

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Prerequisites

Ensure you have installed the Coherence Operator using the instructions here.

Installation Steps

Install the Coherence cluster

Install a Coherence cluster if you don’t have one running:

$ helm install \
   --namespace sample-coherence-ns \
   --name storage \
   --set clusterSize=3 \
   --set cluster=coherence-cluster \
   --set imagePullSecrets=sample-coherence-secret \
   --set logCaptureEnabled=false \
   coherence/coherence

Ensure the pods are running:

$ kubectl get pods -n sample-coherence-ns

NAME                                  READY   STATUS    RESTARTS   AGE
coherence-operator-66f9bb7b75-hqk4l   1/1     Running   0          13m
storage-coherence-0                   1/1     Running   0          3m
storage-coherence-1                   1/1     Running   0          2m
storage-coherence-2                   1/1     Running   0          44s

Open a terminal window in one of the storage nodes:
```
$ kubectl exec -it storage-coherence-0 -n sample-coherence-ns -- bash
```
Obtain the PID of the Coherence process. Generally, the PID is 1. You can also use jps to get the actual PID.
```
# /usr/java/default/bin/jps
1 DefaultCacheServer
4230 Jps
```

Use the jcmd command to extract the heap dump:

$ rm /tmp/heap.hprof
$ /usr/java/default/bin/jcmd 1 GC.heap_dump /tmp/heap.hprof
$ exit

Copy the heap dump to local machine:
```
$ kubectl cp sample-coherence-ns/storage-coherence-0:/tmp/heap.hprof heap.hprof 
```
Deepending upon whether the Kubernetes cluster is local or remote, this might take some time.

Single command usage

Assuming that the Coherence PID is 1, you can use this repeatable single-command technique to extract the heap dump:

$ (kubectl exec storage-coherence-0 -n sample-coherence-ns  -- /bin/bash -c "rm -f /tmp/heap.hprof; /usr/java/default/bin/jcmd 1 GC.heap_dump /tmp/heap.hprof; cat /tmp/heap.hprof > /dev/stderr" ) 2> heap.hprof

Note that we redirect the heap dump output to stderr to prevent the unsuppressable.

1:
Heap dump file created

Uninstall the Charts

Use the following command to delete the chart installed in this sample:

$ helm delete storage --purge

Before starting another sample, ensure that all the pods are removed from previous sample.

If you want to remove the coherence-operator, then include it in the helm delete command.

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