[SPARK-52654] Use ParallelGC by default

### What changes were proposed in this pull request?

This PR aims to use `ParallelGC` by default.

### Why are the changes needed?

Since `Spark K8s Operator` is not interactive application, we had better use `ParallelGC` because it is optimized for throughput in general.

### Does this PR introduce _any_ user-facing change?

No behavior change.

### How was this patch tested?

Manual review.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes apache#270 from dongjoon-hyun/SPARK-52654.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

build-tools/helm/spark-kubernetes-operator/values.yaml

@@ -41,7 +41,7 @@ operatorDeployment:
     # https://kubernetes.io/docs/concepts/scheduling-eviction/topology-spread-constraints/
     topologySpreadConstraints: [ ]
     operatorContainer:
-      jvmArgs: "-Dfile.encoding=UTF8 -XX:+ExitOnOutOfMemoryError"
+      jvmArgs: "-Dfile.encoding=UTF8 -XX:+ExitOnOutOfMemoryError -XX:+UseParallelGC"
       env:
         - name: "SPARK_USER"
           value: "spark"

docs/operations.md

@@ -76,7 +76,7 @@ following table:
 | operatorDeployment.operatorPod.volumes                           | Additional volumes to be added to the operator pod.                                                                                                                            |                                                                                                         |
 | operatorDeployment.operatorPod.priorityClassName                 | Priority class name to be used for the operator pod                                                                                                                            |                                                                                                         |
 | operatorDeployment.operatorPod.securityContext                   | Security context overrides for the operator pod                                                                                                                                |                                                                                                         |
-| operatorDeployment.operatorPod.operatorContainer.jvmArgs         | JVM arg override for the operator container.                                                                                                                                   | `"-Dfile.encoding=UTF8 -XX:+ExitOnOutOfMemoryError"`                                                    |
+| operatorDeployment.operatorPod.operatorContainer.jvmArgs         | JVM arg override for the operator container.                                                                                                                                   | `"-Dfile.encoding=UTF8 -XX:+ExitOnOutOfMemoryError -XX:+UseParallelGC"`                                                    |
 | operatorDeployment.operatorPod.operatorContainer.env             | Custom env to be added to the operator container.                                                                                                                              |                                                                                                         |
 | operatorDeployment.operatorPod.operatorContainer.envFrom         | Custom envFrom to be added to the operator container, e.g. for downward API.                                                                                                   |                                                                                                         |
 | operatorDeployment.operatorPod.operatorContainer.probes          | Probe config for the operator container.                                                                                                                                       |                                                                                                         |