fix(compression-coordinator): Ensure running Spider jobs always have a dispatch_time.

[Bill-hbrhbr]

Description

The compression coordinator can leave a Running job without a dispatch_time if it restarts after persist_spider_job_id changes the job from Pending to Running, but before the batched mark_jobs_dispatched update at the end of the polling interval.

On the next startup, the recovery process picks up Running jobs with a spider_id and resumes them via to_completion(), but does not populate the missing dispatch_time.

To keep dispatch_time representative of when the job was actually dispatched, persist_spider_job_id now also sets it if it has not already been set by the coordinator. This ensures the timestamp is recorded close to the actual dispatch rather than being reconstructed after a restart.

Checklist

• The PR satisfies the contribution guidelines.
• This is a breaking change and that has been indicated in the PR title, OR this isn't a
  breaking change.
• Necessary docs have been updated, OR no docs need to be updated.

Validation performed

• Benign SQL query string update that doesn't affect coordinator's functional correctness.

Summary by CodeRabbit

• Bug Fixes
  • Preserved existing job dispatch timestamps instead of overwriting them.
  • Ensured running compression jobs receive a dispatch timestamp when one is not already set.
  • Improved timestamp accuracy for jobs whose dispatch time is recorded by the job handler.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 268c81b2-04c6-4734-b97f-6906440b2d35

📥 Commits

Reviewing files that changed from the base of the PR and between 6aa5533 and 1df15e1.

📒 Files selected for processing (1)

• components/compression-coordinator/src/coordination.rs

💤 Files with no reviewable changes (1)

• components/compression-coordinator/src/coordination.rs

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Walkthrough

The compression coordinator now preserves existing dispatch_time values. The job handler and coordinator assign the current timestamp only when dispatch_time is unset. Documentation describes this behaviour.

Changes

Dispatch timestamp persistence

Layer / File(s)	Summary
Conditional dispatch timestamp updates components/compression-coordinator/src/job_handle.rs, components/compression-coordinator/src/coordination.rs	Both compression-job updates preserve existing dispatch_time values and assign the current timestamp only when the value is NULL. The method documentation reflects this behaviour.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related issues

• y-scope/clp issue 2461 — Both changes address dispatch_time handling in mark_jobs_dispatched and compression-job recovery.

Possibly related PRs

• y-scope/clp#2405 — This PR updates persist_spider_job_id, which was introduced by the related change.
• y-scope/clp#2417 — This PR refines the dispatch timestamp update in coordination.rs.
• y-scope/clp#2420 — Both PRs modify the compression-job timestamp update in job_handle.rs.

Suggested reviewers: linzhihao-723

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: ensuring running Spider jobs have a dispatch timestamp.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[LinZhihao-723]

One docstring update otherwise lgtm.