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Continuously samples event-loop delay via perf_hooks.monitorEventLoopDelay() (C++-backed histogram; cheap). Each window persists mean/p50/p99/max to a new event_loop_lag table and recomputes a coarse load band (normal/elevated/critical) from the window p99. Standalone value: current lag is exposed on /api/status and band changes are logged, so site lag is diagnosable independent of throttling. The band feeds the #142 reconnect throttle (next commit) but ships first as its own subsystem. - event_loop_lag is bounded from day one: indexed on sampled_at + scheduled prune (LAG_TELEMETRY_RETENTION_DAYS, small default) modeled on the play_logs prune. Deliberately NOT another unbounded-growth table. - Band transitions are asymmetric: jump up immediately (tighten fast), release one level at a time after N calm samples below a deadband (release slow, no flap). Pure nextBand() function, unit-tested deterministically. - config: LAG_SAMPLE_INTERVAL_MS, LAG_RESOLUTION_MS, LAG_TELEMETRY_RETENTION_DAYS, LAG_PRUNE_INTERVAL_MS, LAG_ELEVATED_MS, LAG_CRITICAL_MS, LAG_RELEASE_SAMPLES. - tests: band-transition unit tests; integration proves sampling persists, stays bounded under the prune, and surfaces on /api/status. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
58 lines
2.8 KiB
JavaScript
58 lines
2.8 KiB
JavaScript
'use strict';
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// #142 step 2 — deterministic unit tests for the event-loop-lag band transitions.
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// Pure function, no sockets/timing. Isolate the DB to a temp dir BEFORE requiring
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// the module (requiring it pulls in db/database, which initialises a DB on load).
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const os = require('node:os');
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const path = require('node:path');
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const crypto = require('node:crypto');
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process.env.DATA_DIR = path.join(os.tmpdir(), 'st-lag-unit-' + crypto.randomBytes(4).toString('hex'));
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const { test } = require('node:test');
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const assert = require('node:assert/strict');
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const { nextBand } = require('../services/loop-lag');
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// config defaults exercised here: elevated=100ms, critical=250ms, releaseSamples=5,
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// deadband=0.5 -> release-below thresholds: elevated@50ms, critical@125ms.
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test('UP is immediate and can skip a level (tighten fast)', () => {
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assert.deepEqual(nextBand('normal', 50, 0), ['normal', 0], 'below elevated stays normal');
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assert.deepEqual(nextBand('normal', 100, 0), ['elevated', 0], 'crossing elevated up-threshold jumps immediately');
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assert.deepEqual(nextBand('normal', 250, 0), ['critical', 0], 'a big spike jumps normal->critical in one sample');
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assert.deepEqual(nextBand('elevated', 250, 0), ['critical', 0]);
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});
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test('deadband holds the band for small fluctuations (no flap)', () => {
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// elevated, p99 between release(50) and up(100) -> hold elevated, calm reset
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assert.deepEqual(nextBand('elevated', 80, 3), ['elevated', 0]);
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// critical, p99 between release(125) and up(250) -> hold critical
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assert.deepEqual(nextBand('critical', 200, 4), ['critical', 0]);
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});
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test('DOWN is slow: requires lagReleaseSamples calm samples below the deadband', () => {
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// elevated -> normal only after 5 consecutive calm samples
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let band = 'elevated', calm = 0;
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for (let i = 0; i < 4; i++) {
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[band, calm] = nextBand(band, 20, calm);
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assert.equal(band, 'elevated', `still elevated after ${i + 1} calm sample(s)`);
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}
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[band, calm] = nextBand(band, 20, calm); // 5th
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assert.deepEqual([band, calm], ['normal', 0], 'drops to normal on the 5th calm sample');
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});
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test('DOWN releases one level at a time: critical -> elevated -> normal', () => {
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let band = 'critical', calm = 0;
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for (let i = 0; i < 5; i++) [band, calm] = nextBand(band, 10, calm);
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assert.equal(band, 'elevated', 'critical releases to elevated, never straight to normal');
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for (let i = 0; i < 5; i++) [band, calm] = nextBand(band, 10, calm);
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assert.equal(band, 'normal', 'then elevated releases to normal');
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});
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test('a single calm sample does not release (calm counter resets on a non-calm sample)', () => {
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let [band, calm] = nextBand('elevated', 20, 0); // calm=1
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assert.deepEqual([band, calm], ['elevated', 1]);
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[band, calm] = nextBand(band, 80, calm); // back inside deadband -> reset
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assert.deepEqual([band, calm], ['elevated', 0], 'one blip resets the release counter');
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});
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