feat: time database queries

internal/observability/metrics_test.go

@@ -2,18 +2,22 @@ package observability
 
 import (
 	"context"
+	"database/sql"
 	"io"
 	"net/http"
 	"net/http/httptest"
 	"strings"
 	"testing"
 	"time"
+
+	_ "github.com/mattn/go-sqlite3"
 )
 
 func TestMetricsHandlerRendersPrometheusFamilies(t *testing.T) {
 	metrics := NewMetrics()
 	metrics.ObserveHTTPRequest(http.MethodGet, "/anime/:id", http.StatusOK, 125*time.Millisecond)
 	metrics.ObserveJikanRequest("/anime/{id}", http.StatusTooManyRequests, 800*time.Millisecond, assertErr{})
+	metrics.ObserveDBQuery("query", 25*time.Millisecond, nil)
 	metrics.ObserveWorkerTick("episodes_availability", nil)
 	metrics.ObserveCache("jikan", "hit")
 	metrics.ObserveCache("episode_availability", "miss")
@@ -32,10 +36,39 @@ func TestMetricsHandlerRendersPrometheusFamilies(t *testing.T) {
 	assertContains(t, text, `mal_http_request_duration_seconds_count{method="GET",route="/anime/:id",status="200"} 1`)
 	assertContains(t, text, `mal_jikan_upstream_requests_total{endpoint="/anime/{id}",status="429"} 1`)
 	assertContains(t, text, `mal_jikan_upstream_errors_total{endpoint="/anime/{id}",status="429"} 1`)
+	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`)
 }
 
+func TestInstrumentDBRecordsQueryLatency(t *testing.T) {
+	metrics := NewMetrics()
+	sqlDB, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	defer func() { _ = sqlDB.Close() }()
+
+	instrumented := InstrumentDB(sqlDB, metrics)
+	if _, err := instrumented.ExecContext(context.Background(), `CREATE TABLE item (id INTEGER PRIMARY KEY)`); err != nil {
+		t.Fatalf("create table: %v", err)
+	}
+	if _, err := instrumented.QueryContext(context.Background(), `SELECT id FROM item`); err != nil {
+		t.Fatalf("query table: %v", err)
+	}
+	if _, err := instrumented.QueryContext(context.Background(), `SELECT id FROM missing_table`); err == nil {
+		t.Fatal("expected missing table query to fail")
+	}
+
+	samples := metrics.dbQueryLatency.snapshot()
+	if len(samples) != 3 {
+		t.Fatalf("db samples = %d, want 3", len(samples))
+	}
+	assertHistogramSample(t, samples, "exec", "success")
+	assertHistogramSample(t, samples, "query", "success")
+	assertHistogramSample(t, samples, "query", "error")
+}
+
 type assertErr struct{}
 
 func (assertErr) Error() string { return "boom" }
@@ -46,3 +79,13 @@ func assertContains(t *testing.T, text string, want string) {
 		t.Fatalf("missing metric line %q in:\n%s", want, text)
 	}
 }
+
+func assertHistogramSample(t *testing.T, samples []histogramSample, operation string, result string) {
+	t.Helper()
+	for _, sample := range samples {
+		if sample.labels["operation"] == operation && sample.labels["result"] == result && sample.count == 1 {
+			return
+		}
+	}
+	t.Fatalf("missing db histogram sample operation=%q result=%q in %#v", operation, result, samples)
+}