> **WARNING:** This document describes only the change applied in this PR.
> It may already be outdated once the next PR is merged.
> Historic PR-documentation is not maintained along with new PRs — treat it as a snapshot, not as current documentation.

## Problem

PR#146 put the seven tiles of the System page into one row.
They are narrow there, so their values had to shrink to 16 px.
Two rows would give them room, but seven tiles cannot fill two rows evenly.

The OOM kills are sampled since RFC 0004, but no page shows them.
Their aggregated buckets also held the average per sample, not the count, so no range could be added up.

## Non-Goals

- The OOM kills are shown, not judged: the counter is machine-wide, so on a shared hive it counts the neighbours' kills too.
- The cards keep their one row from PR#146.
- The home rail keeps its five tiles.

## Specification

### Feature: OOM kills tile, tiles in full rows

#### Scenario#147.01: The OOM kills are summed per bucket

So that a minute and a quarter hour hold the kills that happened in them, not the kills per sample.

- **Given** one OOM kill per minute for an hour
- **When** the history aggregates the samples into minutes and quarter hours
- **Then** every minute holds 1 and every quarter hour 15
- **And** a level such as `cpuUsed` is still averaged

##### Verified by

- [MetricsHistoryUnitTest](../../src/test/kotlin/de/hoennig/werkator/metrics/MetricsHistoryUnitTest.kt) — Scenario#147.01

#### Scenario#147.02: A range adds up its OOM kills

So that the tile can say how many kills the selected range holds, and `n/a` where the series was not yet sampled.

- **Given** one OOM kill per minute for an hour, a range without the series, and a quiet range
- **When** the total of each range is computed
- **Then** it is 60, no total, and 0

##### Verified by

- [MetricsHistoryUnitTest](../../src/test/kotlin/de/hoennig/werkator/metrics/MetricsHistoryUnitTest.kt) — Scenario#147.02

#### Scenario#147.03: The history endpoint serves the OOM kills as a total, not as an average

So that the page reads the count of the range, and no mean of bucket sums whose unit changes with the range.

- **Given** samples with 0, 2 and 1 OOM kills
- **When** `GET /api/system/history` is asked for `1h` and for `24h`
- **Then** `totals.oomKills` is 3 in both, and `averages` has no `oomKills`
- **And** for a range without the series `totals.oomKills` is `null`

##### Verified by

- [SystemApiControllerRestTest](../../src/test/kotlin/de/hoennig/werkator/server/SystemApiControllerRestTest.kt) — Scenario#147.03

#### Scenario#147.04: The server renders the OOM kills tile without a count

So that the tile never shows the count of a range other than the selected one; `werkator.js` fills in the count of the selected range.

- **Given** a snapshot of the machine
- **When** the server renders the System page
- **Then** the OOM kills tile reads `n/a` and `in the last 1 h`
- **And** the tile has no colour

##### Verified by

- [UiViewsUnitTest](../../src/test/kotlin/de/hoennig/werkator/server/UiViewsUnitTest.kt) — Scenario#147.04
- the count filled in by `werkator.js` for the 1 h and 24 h ranges, checked by hand in the browser

#### Scenario#147.05: The tiles stand in two full rows of four

So that the tiles look tidy and have room for their values.

- **Given** the System page with its eight tiles
- **When** it is shown on a screen wider than 680 px
- **Then** Load, CPU pressure, RAM pressure and OOM kills form the first row, Disk pressure, Repositories, Builds and PR targets the second
- **And** on a phone they stand in four rows of two

##### Verified by

- [UiViewsUnitTest](../../src/test/kotlin/de/hoennig/werkator/server/UiViewsUnitTest.kt) — Scenario#147.05, and the updated Scenario#27.05, Scenario#101.01 and Scenario#146.03
- the layout checked by hand in the browser at 1280 and 390 px

## Solution

- `MetricsHistory.COUNTED_KEYS` names the series that count events, so far `oomKills`; `HistoryTier.aggregate` sums them instead of averaging.
  The bucket's field is `points` now, not `averages`, since it holds either.
  Every OOM kills point recorded on mih09 until now is 0, so no stored bucket changes its meaning.
- `HistoryTotals.of` adds up a counted series over a range; `GET /api/system/history` serves it as `totals`.
  `HistoryAverages` leaves the counted series out: a mean of bucket sums would be kills per minute in one range and per quarter hour in the next.
- The tile row is now processor and memory — Load, CPU pressure, RAM pressure, OOM kills — and the second row the disk and the builds.
- The server renders the OOM kills tile as `n/a`, since it knows no range; `werkator.js` fills in the count and the range label with every history fetch, like the peak line under a card.
- `.tiles` is a grid of four columns, two up to 680 px; the 16 px tile values of PR#146 are 18 px again.

## Additional Changes

- The architecture skill describes the counted series and the tile rows; its system-metrics paragraph has one sentence per line now.
- Version 1.40.0 with its release note.

## Prerequisite PRs

- [PR#146](https://git.javagil.de/mi/werkator/pulls/146): the swap-out card and the one-row layout this PR changes.