HDFS-17789. Add NormalUnderReplBlocksCount and BadlyDistributedBlocksCount to getStats() NN RPC

[aswinmprabhu]

Description of PR

Reopening PR: #7963

At LinkedIn, we use the stats from the getStats() NN RPC call to evaluate safety checks that ensure that various maintenance ops are safe to run.

Due to a migration we are undertaking, the badly distributed block count is very high for the cluster undergoing migration. This is not a safety problem. However, to distinguish it from the actual low redundancy block count, we need both these values to be available from the getStats() RPC. The current low redundancy blocks count value available is the sum of all the different types of low redundancy blocks, including normal low redundancy blocks and badly distributed blocks.

This PR adds these 2 values separately to the array returned by getStats() RPC.

How was this patch tested?

Trivial change. It has been running in our prod cluster for a bit now.
Build passes:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  42:50 min
[INFO] Finished at: 2025-05-19T14:51:09+05:30
[INFO] ------------------------------------------------------------------------

Ran a RPC testing script manually:

Raw stats array: [863531924404371456, 593154736167663129, 269347053575775718, 0, 0, 0, 0, 0, 0, 0, 0]

=== NameNode Stats ===
[ 0] Capacity (bytes)                              : 863,531,924,404,371,456
[ 1] Used (bytes)                                  : 593,154,736,167,663,129
[ 2] Remaining (bytes)                             : 269,347,053,575,775,718
[ 3] Under-replicated blocks                       : 0
[ 4] Corrupt blocks                                : 0
[ 5] Missing blocks                                : 0
[ 6] Missing blocks with replication factor 1      : 0
[ 7] Bytes in future blocks                        : 0
[ 8] Pending deletion blocks                       : 0
[ 9] Badly distributed blocks                      : 0
[10] Normal under-replicated blocks                : 0

Code:

long[] stats = namenode.getStats();

System.out.println("Raw stats array: " + Arrays.toString(stats));
System.out.println();
...

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[ctrezzo]

@aswinmprabhu can you address the failing check-style issues? Thank you!

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 43s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+0 🆗	mvndep	9m 16s		Maven dependency ordering for branch
+1 💚	mvninstall	26m 55s		trunk passed
+1 💚	compile	3m 32s		trunk passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	compile	4m 1s		trunk passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	checkstyle	0m 46s		trunk passed
+1 💚	mvnsite	1m 43s		trunk passed
+1 💚	javadoc	1m 20s		trunk passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	javadoc	1m 21s		trunk passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	spotbugs	4m 34s		trunk passed
-1 ❌	shadedclient	17m 56s		branch has errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+0 🆗	mvndep	0m 19s		Maven dependency ordering for patch
-1 ❌	mvninstall	0m 20s	/patch-mvninstall-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
-1 ❌	mvninstall	0m 21s	/patch-mvninstall-hadoop-hdfs-project_hadoop-hdfs-client.txt	hadoop-hdfs-client in the patch failed.
-1 ❌	compile	0m 20s	/patch-compile-hadoop-hdfs-project-jdkUbuntu-21.0.7+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs-project in the patch failed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04.
-1 ❌	javac	0m 20s	/patch-compile-hadoop-hdfs-project-jdkUbuntu-21.0.7+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs-project in the patch failed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04.
-1 ❌	compile	0m 21s	/patch-compile-hadoop-hdfs-project-jdkUbuntu-17.0.15+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs-project in the patch failed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04.
-1 ❌	javac	0m 21s	/patch-compile-hadoop-hdfs-project-jdkUbuntu-17.0.15+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs-project in the patch failed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04.
+1 💚	blanks	0m 0s		The patch has no blanks issues.
-0 ⚠️	checkstyle	0m 19s	/buildtool-patch-checkstyle-hadoop-hdfs-project.txt	The patch fails to run checkstyle in hadoop-hdfs-project
-1 ❌	mvnsite	0m 21s	/patch-mvnsite-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
-1 ❌	mvnsite	0m 20s	/patch-mvnsite-hadoop-hdfs-project_hadoop-hdfs-client.txt	hadoop-hdfs-client in the patch failed.
-1 ❌	javadoc	0m 21s	/patch-javadoc-hadoop-hdfs-project_hadoop-hdfs-jdkUbuntu-21.0.7+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs in the patch failed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04.
-1 ❌	javadoc	0m 20s	/patch-javadoc-hadoop-hdfs-project_hadoop-hdfs-client-jdkUbuntu-21.0.7+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs-client in the patch failed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04.
-1 ❌	javadoc	0m 21s	/patch-javadoc-hadoop-hdfs-project_hadoop-hdfs-jdkUbuntu-17.0.15+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs in the patch failed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04.
-1 ❌	javadoc	0m 21s	/patch-javadoc-hadoop-hdfs-project_hadoop-hdfs-client-jdkUbuntu-17.0.15+6-Ubuntu-0ubuntu120.04.txt	hadoop-hdfs-client in the patch failed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04.
-1 ❌	spotbugs	0m 21s	/patch-spotbugs-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
-1 ❌	spotbugs	0m 20s	/patch-spotbugs-hadoop-hdfs-project_hadoop-hdfs-client.txt	hadoop-hdfs-client in the patch failed.
+1 💚	shadedclient	5m 49s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	0m 21s	/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
-1 ❌	unit	0m 21s	/patch-unit-hadoop-hdfs-project_hadoop-hdfs-client.txt	hadoop-hdfs-client in the patch failed.
+0 🆗	asflicense	0m 21s		ASF License check generated no output?
		80m 43s

Subsystem	Report/Notes
Docker	ClientAPI=1.53 ServerAPI=1.53 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8190/2/artifact/out/Dockerfile
GITHUB PR	#8190
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux 10bb20d61b28 5.15.0-164-generic #174-Ubuntu SMP Fri Nov 14 20:25:16 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 20f5e88
Default Java	Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
Multi-JDK versions	/usr/lib/jvm/java-21-openjdk-amd64:Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04 /usr/lib/jvm/java-17-openjdk-amd64:Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8190/2/testReport/
Max. process+thread count	258 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs hadoop-hdfs-project/hadoop-hdfs-client U: hadoop-hdfs-project
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8190/2/console
versions	git=2.25.1 maven=3.9.11 spotbugs=4.9.7
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