[Tiered Caching] Stats rework (1/3): Interfaces and implementations for individual tiers

[peteralfonsi]

Description

As part of tiered caching stats, changes the common ICache interface to use ICacheKey as its key. This key contains dimensions (for example, shard ID, index name, or tier) that can be used to aggregate stats. Also changes the CacheStats interface to store the necessary cache stats, and to support getting stats either as a total or aggregated by these dimensions.

Integrates these changes with OpenSearchOnHeapCache and EhcacheDiskCache. The stats implementation for the TieredSpilloverCache will be in a followup PR.

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• [N/A] Public documentation issue/PR created

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[github-actions]

❌ Gradle check result for 50da5dc: FAILURE

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[github-actions]

❌ Gradle check result for 2f59ee7: FAILURE

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[github-actions]

❌ Gradle check result for da9e485: FAILURE

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[github-actions]

❌ Gradle check result for f60fb08: FAILURE

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[github-actions]

❌ Gradle check result for 5330225: FAILURE

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[github-actions]

❌ Gradle check result for f465a22: FAILURE

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[github-actions]

✅ Gradle check result for 5283470: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 92.70073% with 30 lines in your changes are missing coverage. Please review.

Project coverage is 71.62%. Comparing base (b15cb0c) to head (54e12a3).
Report is 158 commits behind head on main.

Files	Patch %	Lines
...in/java/org/opensearch/common/cache/ICacheKey.java	75.75%	3 Missing and 5 partials ⚠️
.../org/opensearch/common/cache/stats/CacheStats.java	87.50%	4 Missing and 3 partials ⚠️
...pensearch/common/cache/stats/CacheStatsHolder.java	95.32%	1 Missing and 4 partials ⚠️
.../opensearch/cache/store/disk/EhcacheDiskCache.java	93.75%	2 Missing and 1 partial ⚠️
...h/common/cache/serializer/ICacheKeySerializer.java	91.17%	3 Missing ⚠️
...search/cache/common/tier/TieredSpilloverCache.java	83.33%	1 Missing ⚠️
...search/common/cache/stats/ImmutableCacheStats.java	96.42%	0 Missing and 1 partial ⚠️
.../common/cache/stats/ImmutableCacheStatsHolder.java	96.55%	1 Missing ⚠️
...arch/common/cache/store/OpenSearchOnHeapCache.java	96.96%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #12531      +/-   ##
============================================
+ Coverage     71.42%   71.62%   +0.19%     
- Complexity    59978    60706     +728     
============================================
  Files          4985     5039      +54     
  Lines        282275   285316    +3041     
  Branches      40946    41326     +380     
============================================
+ Hits         201603   204344    +2741     
- Misses        63999    64092      +93     
- Partials      16673    16880     +207     

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[github-actions]

❕ Gradle check result for 54e12a3: UNSTABLE

• TEST FAILURES:

      2 org.opensearch.cluster.MinimumClusterManagerNodesIT.testThreeNodesNoClusterManagerBlock
      1 org.opensearch.repositories.azure.AzureBlobStoreRepositoryTests.testSnapshotWithLargeSegmentFiles

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.