HDFS-15491. Fix misplaced NumTransactionsBatchedInSync metrics documentation.

[joseluisll]

Description of PR

HDFS-15491 reports that the NumTransactionsBatchedInSync* metrics documented for the JournalNode are absent from JournalNode JMX, and proposes adding the metric to JournalMetrics.java.

The metrics are not missing — they are documented in the wrong section.

The rows were added by HDFS-12320 (commit 423ebcaf510), which added the quantiles to NameNodeMetrics.java but documented them under JournalNode in Metrics.md. That issue was filed against the metrics, namenode components — the JournalNode was out of its scope, and no JournalNode change is needed here either.

The rows are also wrong in detail: the quantiles are registered with valueName = "count", so the emitted names end in ...thPercentileCount, not ...thPercentileLatencyMicros.

HDFS-13674 later documented the metric in the correct NameNodeActivity section but omitted the Num prefix, and left the JournalNode rows in place. The metric is currently documented twice, under two names, neither matching what is emitted.

Changes

1. Remove the 18 NumTransactionsBatchedInSync* rows from the JournalNode section.
2. Correct the NameNodeActivity row to `NumTransactionsBatchedInSync`*num*`s(50/75/90/95/99)thPercentileCount`.

Documentation only: 1 insertion, 19 deletions. No code or test changes.

How was this patch tested?

Documentation-only change; verified by inspection.

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? — N/A
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0? — N/A
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files? — N/A

AI Tooling

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Contains content generated by Claude Code.

[hadoop-yetus]

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+1 💚	@author	0m 0s		The patch does not contain any @author tags.
			_ trunk Compile Tests _
+1 💚	mvninstall	42m 22s		trunk passed
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+1 💚	shadedclient	75m 32s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 17s		the patch passed
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+1 💚	shadedclient	30m 20s		patch has no errors when building and testing our client artifacts.
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+1 💚	asflicense	0m 36s		The patch does not generate ASF License warnings.
		110m 50s

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Docker	ClientAPI=1.55 ServerAPI=1.55 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8646/1/artifact/out/Dockerfile
GITHUB PR	#8646
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uname	Linux ce142bda8eb1 5.15.0-181-generic #191-Ubuntu SMP Fri May 22 19:09:02 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux
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