agent used a 24-hour CPU window - it called the weekend-low database idle and the Monday morning queue blew up

TL;DR

Stretch the lookback to 14 to 30 days and judge weekdays separately from weekends. A database that sleeps on Sunday and works on Monday is not idle; it is weekly. The Monday-morning queue blowup is the receipt for a 24-hour window.

agent used a 24-hour CPU window  -  it called the weekend-low database idle and the Monday morning queue blew up

Steps

1. Re-pull the flagged database's CPU over 30 days:

aws cloudwatch get-metric-statistics --namespace AWS/RDS --metric-name CPUUtilization --dimensions Name=DBInstanceIdentifier,Value=[db-id] --start-time 2026-09-08T00:00:00Z --end-time 2026-10-08T00:00:00Z --period 86400 --statistics Average,Maximum

Expected: weekday averages far above the weekend ones. The weekend low was the whole story the agent read.

1. Change the rule: idle requires low CPU on weekdays too, over at least 14 days, with no weekday maximum above the burst cap.

Expected: weekly-pattern databases stop being flagged.

1. Add a Monday-morning check: queue depth, connection count, or replica lag at 9am local time before any action on a database.

Expected: the action that would have caused the blowup gets blocked by live evidence.

1. Require the flag to survive two consecutive weekly cycles before it becomes a recommendation.

Expected: one quiet weekend can never again produce a shutdown plan.

Use this when

• idle flags appear on weekends or Mondays
• databases flagged "idle" are busy on weekdays
• the lookback window is a day or less

Not for this skill when

• the database is quiet on weekdays too across weeks (it may genuinely be idle)
• the workload is monthly batch (you need a 60-day window, not 14)
• you are chasing a live incident rather than a rightsizing candidate

Variant phrasings

• "RDS flagged idle on weekend but busy Monday"
• "24 hour CPU window false idle database"
• "weekly pattern mistaken for idle"

Why it happens

24 hours is the default lookback in every quick script, and it samples exactly one phase of a weekly cycle. Run it on Sunday and the database looks dead; the agent cannot know Monday exists because it never looked. Weekly seasonality is the most common shape in business databases and the easiest to miss with a short window.

Edge cases

• Month-end close creates a monthly spike that a 14-day window still misses. Check the calendar for monthly jobs before acting.
• Read replicas can look idle while the primary is busy. Judge the cluster, not the node.
• A database quiet for 30 straight days including weekdays is a real candidate. Do not let this skill talk you out of genuine finds.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstba6ekbx6TN-Kb9NQE_YmQ