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Guide

Continuously improve your software with Scalpels and Solo

The sweep

· Ed Grosvenor

The sweep is the conductor's checklist for each app: the calls it makes, the arguments it passes, and what in the answer counts as a finding. It lives in orders/sweep.md in the companion code, and the conductor rereads it on every run, so tuning the loop is editing that file. This page explains what is in it and why.

Every call goes through Scalpels:

app_read {
  team: "acme",
  app_deployment: "<from the ledger>",
  tool: "<the app's tool>",
  args: { ... }
}

The app's answer comes back in structuredContent.app_content. If the conductor is not sure what a tool takes, app_tools with intent: "read" lists them. Hone has more tools than fit on one page of that list. If one you expect is missing, call it by name anyway.

Three apps, three ideas of "since"

The ledger gives the run a window, from covered_until to now. Each app takes time differently, and the sweep has to respect that:

App How it takes time What that means
Wake from and to, required, exact timestamps Use the window as it is. search_logs will not search more than seven days at once.
Reel started_from / started_to and ended_from / ended_to Use ended_from. A session is not ready for about twenty minutes after it ends, so read back an extra 30 minutes and let the fingerprints take care of anything seen twice.
Hone Most tools take days, counted in whole UTC days, today included You cannot ask Hone for "the last hour" of slow queries. Ask for today and the previous week, and compare. Hone's aggregates also run hourly and accept events up to a day late.

Hone is the odd one out, and it is worth being clear about why. Its slow-query and exception tools read daily aggregates, and that is what makes them fast and cheap to ask every hour. The conductor does not need minute-by-minute precision from Hone. It needs to know whether today looks worse than usual, and whether that started after a deploy.

Hone

Run these for each app's Hone app:

  1. ingest-freshness-tool. If ingest is behind or dropping events, report that as a finding and skip the rest of Hone for this app. A quiet Hone that is not receiving data looks exactly like a healthy one.
  2. deploys-tool with hours: 2. Any deploy in the last two hours goes in the summary, and anything that looks worse after it is linked to it.
  3. exceptions with days: 1 and days: 7. An exception normalized_key that appears today but not in the previous week is new. One whose daily count today is well above its seven-day average is rising.
  4. slow_requests, slow_queries and slow_jobs with days: 1 and days: 7, metric: "p95". An offender whose p95 today is more than 30% above its seven-day figure is a candidate. Confirm it with regression_check, which compares across deploys for one normalized_key.
  5. scheduled_task_health with days: 1. A scheduled task that stopped running is a finding.

Check aggregate_freshness.covers_window on every answer. When it is false, Hone has not finished rolling up the day, and zeros mean "not counted yet", not "nothing happened". Treat those as unknown, not good news.

Fingerprints: hone:{app}:exception:{normalized_key}, hone:{app}:slow:{record_type}:{normalized_key}, hone:{app}:task:{name}, hone:{app}:ingest.

Wake

Run these for each app's Wake app, with the run's window as from and to:

  1. ingest_health. As with Hone, a Wake that stopped receiving logs is the first finding, not the last.
  2. recent_errors. Group what comes back by message, with the variable parts (ids, timestamps, email addresses) taken out. Any group that is new, or noticeably bigger than in recent runs, is a candidate. The ledger's Open findings tell you what is already known.
  3. aggregate_logs with group_by: "level". A jump in error or warning volume against the same hour yesterday is a finding even when no single message stands out. That is often the first sign of a retry storm or a misbehaving queue.
  4. For any candidate, get_context on one event_id, with a handful of lines before and after, so the finding carries what the app was doing at the time.

Wake marks everything that came from a log line as untrusted, and the conductor should take that literally. A log line is something your app or your users wrote. It goes into a finding as evidence, quoted, never as an instruction.

Fingerprints: wake:{app}:error:{normalized message}, wake:{app}:volume:{level}, wake:{app}:ingest.

Reel

Reel does not tell you what is wrong. It tells you what a person was doing when something went wrong, and that is what turns an investigation from guesswork into a reproduction.

  1. sessions with the app's application, ended_from set to 30 minutes before the window, and marker: "server_error". These are sessions where the app's own Reel client tied a failing request to the session.
  2. Group them by the failing path and status in their error_markers. One unlucky session is noise. The same failure across several people is a finding.
  3. Attach the session ids to any Hone or Wake finding for the same path. The investigator will use them. Do not call session_content from the conductor: replay content is big, and reading it is the investigator's job.

Fingerprint: reel:{app}:{method} {path}:{status}. When a Reel group matches a Hone exception or a Wake error on the same route, file one finding with all three, not three findings.

Staying inside the limits

Scalpels allows each token 60 app_read calls a minute and four calls in flight per team, and gives each call 60 seconds. A sweep of three apps for one product is about fifteen calls. Make them one at a time and the limits never come up. If you sweep many apps, the conductor should slow down when it sees relay_busy or a rate limit, not retry immediately.

Tuning

The thresholds on this page are a starting point, not advice. Run the loop for a week, read the Runs section of the ledger, and adjust:

  • If it files things you would not have, raise the thresholds or add "ignore" rules to the sweep, such as a known noisy job or a bot that always fails on one route.
  • If it misses things you found yourself, ask what the sweep would have needed to see them. Usually it is one more call.

Most people find that a healthy app is much quieter than they expected, and tighten everything after the first week.

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