[hotfix][Metrics] Iterate a locked table-runtime snapshot in gauges - #4326
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…p gauges OptimizerGroupMetrics' five table-count gauges streamed over SchedulingPolicy's live HashMap on scrape threads without tableLock; concurrent addTable/removeTable (table onboarding, group migration) threw ConcurrentModificationException mid-scrape. getTableRuntimeMap() is @VisibleForTesting yet was the production access path. Add tableRuntimesSnapshot() (locked copy, same pattern as tableIdentifiersSnapshot) and point the gauges at it. Churn regression test: with the lock temporarily removed it fails 2 of 3 runs with CME; locked it is stable. Fix record: docs/fix-records/2026-08-16-fix-17-gauge-snapshot-cme.md
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Brief change log
Make optimizer-group metric gauges iterate a scheduling-policy snapshot instead of the live runtime map. The snapshot is taken under the policy lock, preventing concurrent modification failures while metrics are scraped.
How was this patch tested?
TestSchedulingPolicylocally with JDK 11 before creating this pull request.Documentation