perf(s3stream): compute compaction delay using min timestamp instead of sorting

[JasirVoriya]

Issue Title
Performance: avoid sorting when computing compactionDelayTime; use min timestamp

Description
In CompactionManager.start()’s periodic monitor task, compactionDelayTime is computed by sorting server objects by committedTimestamp and then taking the first element. This sorting is unnecessary because we only need the minimum timestamp. Sorting costs O(n log n) time; finding the minimum is O(n). With large object lists, the sort introduces avoidable CPU overhead and potential GC pressure.

Affected Code

• Path: s3stream/src/main/java/com/automq/stream/s3/compact/CompactionManager.java
• Method: start()
• Current logic:

data.sort(Comparator.comparingLong(S3ObjectMetadata::committedTimestamp));
this.compactionDelayTime = System.currentTimeMillis() - data.get(0).committedTimestamp();

Benefits

• Reduce time complexity from O(n log n) to O(n).
• Lower CPU usage and reduce GC pressure from sorting.
• Improve efficiency of the periodic monitoring task in high-object-count scenarios.

Behavior

• Semantics unchanged: the delay is still based on the earliest committedTimestamp.
• Edge cases unchanged: when data is null/empty or an exception occurs, delay is set to 0.

Validation

• Build s3stream module: ./gradlew :s3stream:compileJava -x test should pass.
• Run regular builds/integration tests to confirm no functional regressions.
• Optional: profile CPU/time of the monitor task with large object lists to confirm reduction.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

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Pull Request Overview

This PR optimizes the computation of compactionDelayTime by replacing a sort-based approach with a single-pass minimum finding algorithm. This improves performance when calculating the delay time metric for compaction monitoring.

Key Changes:

• Replaces List.sort() followed by get(0) with a manual iteration to find the minimum committedTimestamp
• Eliminates unnecessary sorting overhead when only the minimum value is needed

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[Gezi-lzq]

Thank you for your contribution @JasirVoriya . It looks fine overall, but I noticed there are some CI errors that could be resolved.

[JasirVoriya]

Thank you for your contribution @JasirVoriya . It looks fine overall, but I noticed there are some CI errors that could be resolved.

Fixed it, thanks for the heads-up @Gezi-lzq .

[Gezi-lzq]

LGTM

[woshigaopp]

LGTM

[Mixficsol]

LGTM