HBASE-30177 Make block caching configurable for MOB compaction reads

[liuxiaocs7]

• see: HBASE-30177

[Copilot]

Pull request overview

This PR (HBASE-30177) introduces a configuration knob to control whether MOB compaction reads should populate the block cache when resolving MOB references, allowing operators to avoid block-cache pollution from background compactions while preserving existing behavior by default.

Changes:

• Added hbase.mob.compaction.cache.blocks config (default true) and documented it in hbase-default.xml.
• Plumbed the config into DefaultMobStoreCompactor (and the test-only FaultyMobStoreCompactor) by passing it to HMobStore.resolve(...) instead of always caching.
• Added a small unit test validating the default and override behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
hbase-server/src/main/java/org/apache/hadoop/hbase/mob/DefaultMobStoreCompactor.java	Reads new config and uses it when resolving MOB references during compaction.
hbase-server/src/main/java/org/apache/hadoop/hbase/mob/MobConstants.java	Adds the new config key constant and default value.
hbase-common/src/main/resources/hbase-default.xml	Documents the new hbase.mob.compaction.cache.blocks property and its default.
hbase-server/src/test/java/org/apache/hadoop/hbase/mob/TestDefaultMobStoreCompactor.java	Adds unit tests for default true and configurable false.
hbase-server/src/test/java/org/apache/hadoop/hbase/mob/FaultyMobStoreCompactor.java	Ensures the test-only compactor respects the new caching config when resolving MOB refs.

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[VladRodionov]

Thanks for the patch. The change looks good to me. The new config is useful, and keeping the default as true preserves the existing behavior.

Minor: the current test verifies that the compactor reads the configuration value, which is probably enough for this change since the production code simply passes that field into mobStore.resolve(...). No blocker from my side.

[VladRodionov]

Minor naming/documentation question: the config name hbase.mob.compaction.cache.blocks is understandable, but the behavior is specifically about caching blocks while reading existing MOB files during compaction, not cache-on-write of compaction output. To avoid confusion with cache-on-write settings, would a more explicit name such as hbase.mob.compaction.read.cache.blocks or hbase.mob.compaction.cache.blocks.on.read be clearer?

[VladRodionov]

lgtm.