From 1250c591b7318747e562d8c5cc747d6b9ba7e51a Mon Sep 17 00:00:00 2001 From: mkelvers Date: Sun, 21 Jun 2026 17:18:52 +0200 Subject: [PATCH] feat: expose jikan cache metrics --- internal/observability/metrics.go | 92 +++++++++++++++++++++++++- internal/observability/metrics_test.go | 4 ++ 2 files changed, 95 insertions(+), 1 deletion(-) diff --git a/internal/observability/metrics.go b/internal/observability/metrics.go index d9ee2f1..0419b0c 100644 --- a/internal/observability/metrics.go +++ b/internal/observability/metrics.go @@ -37,6 +37,11 @@ type histogramSample struct { sum float64 } +type gaugeSample struct { + labels map[string]string + value float64 +} + type counterVec struct { mu sync.Mutex labelNames []string @@ -50,6 +55,12 @@ type histogramVec struct { samples map[string]*histogramSample } +type gaugeVec struct { + mu sync.Mutex + labelNames []string + samples map[string]*gaugeSample +} + type Metrics struct { httpRequests *counterVec httpRequestLatency *histogramVec @@ -59,6 +70,8 @@ type Metrics struct { dbQueryLatency *histogramVec workerTicks *counterVec cacheOperations *counterVec + jikanCacheRows *gaugeVec + jikanCacheOldest *gaugeVec } func NewMetrics() *Metrics { @@ -71,6 +84,8 @@ func NewMetrics() *Metrics { dbQueryLatency: newHistogramVec(defaultDurationBuckets, "operation", "result"), workerTicks: newCounterVec("worker", "result"), cacheOperations: newCounterVec("cache", "result"), + jikanCacheRows: newGaugeVec("state"), + jikanCacheOldest: newGaugeVec(), } } @@ -119,6 +134,12 @@ func (m *Metrics) ObserveCache(cache string, result string) { m.cacheOperations.Inc(cache, result) } +func (m *Metrics) ObserveJikanCacheStats(totalRows int64, expiredRows int64, oldestExpiresAtSeconds int64) { + m.jikanCacheRows.Set(float64(totalRows), "total") + m.jikanCacheRows.Set(float64(expiredRows), "expired") + m.jikanCacheOldest.Set(float64(oldestExpiresAtSeconds)) +} + func (m *Metrics) writePrometheus(w http.ResponseWriter) error { if err := writeCounterMetric(w, "mal_http_requests_total", "Total HTTP requests by method, route, and status.", m.httpRequests.snapshot()); err != nil { return err @@ -141,7 +162,13 @@ func (m *Metrics) writePrometheus(w http.ResponseWriter) error { if err := writeCounterMetric(w, "mal_worker_ticks_total", "Total background worker ticks by worker and result.", m.workerTicks.snapshot()); err != nil { return err } - return writeCounterMetric(w, "mal_cache_operations_total", "Total cache hits and misses by cache name.", m.cacheOperations.snapshot()) + if err := writeCounterMetric(w, "mal_cache_operations_total", "Total cache hits and misses by cache name.", m.cacheOperations.snapshot()); err != nil { + return err + } + if err := writeGaugeMetric(w, "mal_jikan_cache_rows", "Current jikan_cache row count by state.", m.jikanCacheRows.snapshot()); err != nil { + return err + } + return writeGaugeMetric(w, "mal_jikan_cache_oldest_expires_at_seconds", "Unix timestamp for the oldest jikan_cache expires_at value, or 0 when empty.", m.jikanCacheOldest.snapshot()) } func newCounterVec(labelNames ...string) *counterVec { @@ -237,6 +264,45 @@ func (h *histogramVec) snapshot() []histogramSample { return out } +func newGaugeVec(labelNames ...string) *gaugeVec { + return &gaugeVec{ + labelNames: append([]string(nil), labelNames...), + samples: make(map[string]*gaugeSample), + } +} + +func (g *gaugeVec) Set(value float64, labelValues ...string) { + g.mu.Lock() + defer g.mu.Unlock() + + key, labels := buildLabelKey(g.labelNames, labelValues) + if labels == nil { + return + } + sample, ok := g.samples[key] + if !ok { + sample = &gaugeSample{labels: labels} + g.samples[key] = sample + } + sample.value = value +} + +func (g *gaugeVec) snapshot() []gaugeSample { + g.mu.Lock() + defer g.mu.Unlock() + + keys := sortedGaugeSampleKeys(g.samples) + out := make([]gaugeSample, 0, len(keys)) + for _, key := range keys { + sample := g.samples[key] + out = append(out, gaugeSample{ + labels: copyLabels(sample.labels), + value: sample.value, + }) + } + return out +} + func buildLabelKey(labelNames []string, labelValues []string) (string, map[string]string) { if len(labelNames) != len(labelValues) { return "", nil @@ -276,6 +342,15 @@ func sortedHistogramSampleKeys(samples map[string]*histogramSample) []string { return keys } +func sortedGaugeSampleKeys(samples map[string]*gaugeSample) []string { + keys := make([]string, 0, len(samples)) + for key := range samples { + keys = append(keys, key) + } + sort.Strings(keys) + return keys +} + func writeCounterMetric(w http.ResponseWriter, name string, help string, samples []counterSample) error { if _, err := fmt.Fprintf(w, "# HELP %s %s\n", name, help); err != nil { return err @@ -291,6 +366,21 @@ func writeCounterMetric(w http.ResponseWriter, name string, help string, samples return nil } +func writeGaugeMetric(w http.ResponseWriter, name string, help string, samples []gaugeSample) error { + if _, err := fmt.Fprintf(w, "# HELP %s %s\n", name, help); err != nil { + return err + } + if _, err := fmt.Fprintf(w, "# TYPE %s gauge\n", name); err != nil { + return err + } + for _, sample := range samples { + if _, err := fmt.Fprintf(w, "%s%s %s\n", name, formatLabels(sample.labels), formatFloat(sample.value)); err != nil { + return err + } + } + return nil +} + func writeHistogramMetric(w http.ResponseWriter, name string, help string, samples []histogramSample, bounds []float64) error { if _, err := fmt.Fprintf(w, "# HELP %s %s\n", name, help); err != nil { return err diff --git a/internal/observability/metrics_test.go b/internal/observability/metrics_test.go index 4998c16..6157c64 100644 --- a/internal/observability/metrics_test.go +++ b/internal/observability/metrics_test.go @@ -21,6 +21,7 @@ func TestMetricsHandlerRendersPrometheusFamilies(t *testing.T) { metrics.ObserveWorkerTick("episodes_availability", nil) metrics.ObserveCache("jikan", "hit") metrics.ObserveCache("episode_availability", "miss") + metrics.ObserveJikanCacheStats(12, 3, 1770000000) req := httptest.NewRequestWithContext(context.Background(), http.MethodGet, "/metrics", nil) rec := httptest.NewRecorder() @@ -39,6 +40,9 @@ func TestMetricsHandlerRendersPrometheusFamilies(t *testing.T) { assertContains(t, text, `mal_db_query_duration_seconds_count{operation="query",result="success"} 1`) assertContains(t, text, `mal_worker_ticks_total{result="success",worker="episodes_availability"} 1`) assertContains(t, text, `mal_cache_operations_total{cache="episode_availability",result="miss"} 1`) + assertContains(t, text, `mal_jikan_cache_rows{state="total"} 12`) + assertContains(t, text, `mal_jikan_cache_rows{state="expired"} 3`) + assertContains(t, text, `mal_jikan_cache_oldest_expires_at_seconds 1770000000`) } func TestInstrumentDBRecordsQueryLatency(t *testing.T) {