perf(crons): Prefetch some queries in clock tasks consumer

[wedamija]

When we're backlogged we are making a lot of queries here attempting to catch up. We can instead preload a bunch of them for the batch and pass them along.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Prefetch snapshot skips live miss guard

Medium Severity

When prefetch is on, mark_environment_missing applies the next_checkin_latest guard to a batch-start snapshot instead of a live row, and mark_checkin_timeout does the same for has_newer_status_affecting_checkin. An ingest check-in that lands after prefetch can advance next_checkin_latest or add a newer OK, but the clock task still writes a miss or incident and can overwrite last_checkin, next_checkin, and status. That window is largest exactly when clock-tasks is backlogged.

Additional Locations (2)

• src/sentry/monitors/clock_tasks/check_timeout.py#L100-L104
• src/sentry/monitors/clock_tasks/prefetch.py#L67-L89

 

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[sentry-warden]

Prefetched newer-check-in guard can miss concurrent OK/ERROR

When prefetch is set, has_newer uses a batch-start snapshot instead of the live exists() query, so an OK/ERROR check-in inserted after prefetch still lets this timeout call mark_failed and incorrectly flip the monitor to ERROR.

Evidence

• In this hunk, prefetch is not None replaces monitor_has_newer_status_affecting_checkins() with prefetch.has_newer_status_affecting_checkin().
• That helper only reads ClockTaskPrefetch.newest_status_affecting, populated once in prefetch_clock_tasks() before the thread pool runs.
• A concurrent monitor-consumer OK/ERROR for the same environment after prefetch is invisible to the snapshot, so has_newer stays false.
• Execution continues into mark_failed(), unlike the non-prefetch path which re-queries date_added__gt=checkin.date_added at decision time.

_{Identified by Warden · sentry-backend-bugs · W8E-ACM}