Add a statistics pane to the webhook page (closes #368)

Each webhook's event database keeps running totals: one row for its
events, and one row per target for that target's deliveries, delivered
and failed, each with what retention removed. Every write to them
shares the transaction of the rows it counts. Deliveries get a
finished_at column; it and target_id end the status index, so each
target's deliveries finished in a window come from one index-range
query grouped by target. Retention deletes 1000 expired events per
transaction, pausing 200 ms between them so other writers get in. The
pane is its own template, its figures in tables.

The schema changes in place with nothing back-filled, so an existing
database must be recreated.

Model: opus-5-5

internal/database/event_tier_indexes_test.go

@@ -93,11 +93,11 @@ func TestEventTierQueriesUseTheirIndexes(t *testing.T) {
 		deliveries []database.Delivery
 		results    []database.DeliveryResult
 		depths     []struct{ Depth int }
+		removed    []database.TargetTotals
 	)
 
 	byStatus := "idx_deliveries_status (status=? AND deleted_at=?)"
 	byEvent := "idx_deliveries_event_id (event_id=? AND deleted_at=?)"
-	byAge := "idx_events_deleted_at_created_at (deleted_at=? AND created_at<?)"
 
 	// The delivery engine: recovery and the retry sweep, the sweep for
 	// stranded pending deliveries, and the queue depth count.
@@ -123,25 +123,89 @@ func TestEventTierQueriesUseTheirIndexes(t *testing.T) {
 		Order("attempt_num ASC").Find(&results),
 		"idx_delivery_results_delivery_id (delivery_id=? AND deleted_at=?)")
 
-	// Retention's three deletes (reapExpired), whose subqueries are built
-	// afresh for each statement as it builds them.
-	expiredEventIDs := func() *gorm.DB {
-		return dry.Model(&database.Event{}).Select("id").
-			Where("created_at < ?", cutoff)
-	}
+	// Retention (reapExpired, deleteEvents): one batch of expired
+	// events, then their attempts, deliveries and the events.
+	var expired []string
 
+	assertPlanUses(t, db, dry.Unscoped().Model(&database.Event{}).
+		Where("created_at < ?", cutoff).
+		Limit(database.ExportReapBatchSize).Pluck("id", &expired),
+		"idx_events_created_at (created_at<?)")
 	assertPlanUses(t, db, dry.Unscoped().Where(
-		"delivery_id IN (?)", dry.Model(&database.Delivery{}).
-			Select("id").Where("event_id IN (?)", expiredEventIDs()),
+		"delivery_id IN (?)", dry.Unscoped().Model(&database.Delivery{}).
+			Select("id").Where("event_id IN ?", ids),
 	).Delete(&database.DeliveryResult{}),
-		"idx_delivery_results_delivery_id (delivery_id=?)", byEvent, byAge)
-	assertPlanUses(t, db, dry.Unscoped().Where(
-		"event_id IN (?)", expiredEventIDs(),
-	).Delete(&database.Delivery{}),
-		"idx_deliveries_event_id (event_id=?)", byAge)
-	assertPlanUses(t, db, dry.Unscoped().Where(
-		"created_at < ?", cutoff,
-	).Delete(&database.Event{}), "idx_events_created_at (created_at<?)")
+		"idx_delivery_results_delivery_id (delivery_id=?)",
+		"idx_deliveries_event_id (event_id=?)")
+	assertPlanUses(t, db, dry.Unscoped().Model(&database.Delivery{}).
+		Select("target_id, count(*) AS deliveries_removed, "+
+			"count(CASE WHEN status = ? THEN 1 END) AS failed_removed",
+			database.DeliveryStatusFailed).
+		Where("event_id IN ?", ids).Group("target_id").Find(&removed),
+		"idx_deliveries_event_id (event_id=?)")
+	assertPlanUses(t, db, dry.Unscoped().Where("event_id IN ?", ids).
+		Delete(&database.Delivery{}), "idx_deliveries_event_id (event_id=?)")
+	assertPlanUses(t, db, dry.Unscoped().Where("id IN ?", ids).
+		Delete(&database.Event{}), "sqlite_autoindex_events_1 (id=?)")
+}
+
+// TestStatisticsQueriesUseTheirIndexes does the same for the webhook
+// page's statistics (readEventStats in the handlers): deliveries in
+// progress, each target's deliveries finished since a time, which must
+// come from the index alone, events received since a time, and the
+// newest event, which must come straight off an index rather than from
+// sorting every event.
+func TestStatisticsQueriesUseTheirIndexes(t *testing.T) {
+	t.Parallel()
+
+	mgr, lc := setupTestWebhookDBManager(t)
+	ctx := context.Background()
+	require.NoError(t, lc.Start(ctx))
+
+	defer func() { require.NoError(t, lc.Stop(ctx)) }()
+
+	db, err := mgr.GetDB(uuid.New().String())
+	require.NoError(t, err)
+
+	dry := db.Session(&gorm.Session{DryRun: true})
+	since := time.Now()
+
+	var (
+		count    int64
+		newest   []time.Time
+		byTarget []struct{ TargetID string }
+	)
+
+	assertPlanUses(t, db, dry.Model(&database.Delivery{}).
+		Where("status IN ?", []database.DeliveryStatus{
+			database.DeliveryStatusPending,
+			database.DeliveryStatusRetrying,
+		}).Count(&count),
+		"idx_deliveries_status (status=? AND deleted_at=?)")
+	assertPlanUses(t, db, dry.Model(&database.Delivery{}).
+		Select("target_id, "+
+			"count(CASE WHEN status = ? THEN 1 END) AS delivered, "+
+			"count(CASE WHEN status = ? THEN 1 END) AS failed",
+			database.DeliveryStatusDelivered,
+			database.DeliveryStatusFailed).
+		Where("status IN ? AND finished_at >= ?",
+			[]database.DeliveryStatus{
+				database.DeliveryStatusDelivered,
+				database.DeliveryStatusFailed,
+			}, since).
+		Group("target_id").Find(&byTarget),
+		"COVERING INDEX idx_deliveries_status "+
+			"(status=? AND deleted_at=? AND finished_at>?)")
+	assertPlanUses(t, db, dry.Model(&database.Event{}).
+		Where("created_at >= ?", since).Count(&count),
+		"idx_events_deleted_at_created_at "+
+			"(deleted_at=? AND created_at>?)")
+
+	newestEvent := dry.Model(&database.Event{}).
+		Order("created_at DESC").Limit(1).Pluck("created_at", &newest)
+	assertPlanUses(t, db, newestEvent,
+		"idx_events_deleted_at_created_at (deleted_at=?)")
+	assert.NotContains(t, queryPlan(t, db, newestEvent), "TEMP B-TREE")
 }
 
 // assertPlanUses asserts that SQLite's plan for a statement GORM built
@@ -152,6 +216,18 @@ func assertPlanUses(
 ) {
 	t.Helper()
 
+	plan := queryPlan(t, db, built)
+
+	for _, index := range indexes {
+		assert.Contains(t, plan, index, built.Statement.SQL.String())
+	}
+}
+
+// queryPlan returns SQLite's plan for a statement GORM built in a dry
+// run, run with the same SQL and arguments GORM would send.
+func queryPlan(t *testing.T, db, built *gorm.DB) string {
+	t.Helper()
+
 	var plan []struct{ Detail string }
 
 	require.NoError(t, db.Raw(
@@ -159,8 +235,5 @@ func assertPlanUses(
 		built.Statement.Vars...,
 	).Scan(&plan).Error)
 
-	for _, index := range indexes {
-		assert.Contains(t, fmt.Sprint(plan), index,
-			built.Statement.SQL.String())
-	}
+	return fmt.Sprint(plan)
 }