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

Each webhook's event database keeps running totals: one row for its
events, with when the newest arrived, and one row per target for its
deliveries, delivered and failed, each with what retention removed.
Every write to them shares the transaction of the rows it counts, and
a delivery already delivered or failed is not settled again.
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, and stops between them on shutdown. 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

README.md

@@ -1075,7 +1075,7 @@ unconditionally against whatever files it finds:
 - the main database on connect — `Setting`, `User`, `APIKey`, `Webhook`,
   `Entrypoint`, `Target`
 - each event database when it is lazily opened — `Event`, `Delivery`,
-  `DeliveryResult`
+  `DeliveryResult`, `EventTotals`, `TargetTotals`
 - each archive database on every open and reopen
 
 There is no schema version table, no migration ledger, and no down
@@ -1392,7 +1392,7 @@ The codebase uses consistent naming throughout (rename completed in
 
 ### Data Model
 
-webhooker's data model has nine entities organized into two tiers: the
+webhooker's data model has eleven entities organized into two tiers: the
 **application tier** (user and webhook configuration) and the **event
 tier** (event ingestion, delivery, and logging).
 
@@ -1421,6 +1421,13 @@ tier** (event ingestion, delivery, and logging).
 │  ┌──────────┐       ┌──────────┐       ┌─────────────────┐  │
 │  │  Event   │──1:N──│ Delivery │──1:N──│ DeliveryResult  │  │
 │  └──────────┘       └──────────┘       └─────────────────┘  │
+│                                                             │
+│  ┌──────────────┐  (one row: running counts of events)      │
+│  │ EventTotals  │                                           │
+│  └──────────────┘                                           │
+│  ┌──────────────┐  (one row per target: running counts      │
+│  │ TargetTotals │   of its deliveries)                      │
+│  └──────────────┘                                           │
 └─────────────────────────────────────────────────────────────┘
 ```
 
@@ -1674,6 +1681,7 @@ status across potentially multiple attempts.
 | `event_id` | UUID           | Foreign key → Event |
 | `target_id`| UUID           | Foreign key → Target |
 | `status`   | DeliveryStatus | One of: `pending`, `delivered`, `failed`, `retrying` |
+| `finished_at` | timestamp   | When the delivery became `delivered` or `failed` (nullable; empty while `pending` or `retrying`) |
 
 **Relations:** Belongs to Event. Belongs to Target. Has many
 DeliveryResults.
@@ -1741,33 +1749,70 @@ retries) is individually logged for full observability.
 
 **Relations:** Belongs to Delivery.
 
+#### EventTotals and TargetTotals
+
+Running counts in each event database, read by the statistics pane at the
+top of the webhook page. `EventTotals` is one row:
+
+| Field            | Type      | Description |
+| ---------------- | --------- | ----------- |
+| `events`         | integer   | Events ever stored, resubmitted copies included |
+| `events_removed` | integer   | Events retention has deleted |
+| `last_event_at`  | timestamp | When the newest event arrived (nullable; empty before the first); retention leaves it as it is |
+
+`TargetTotals` is one row per target, created by the first delivery to it:
+
+| Field                | Type    | Description |
+| -------------------- | ------- | ----------- |
+| `target_id`          | UUID    | The target (primary key) |
+| `deliveries`         | integer | Deliveries to it ever created, replays included |
+| `delivered`          | integer | Of those, how many became `delivered` |
+| `failed`             | integer | Of those, how many became `failed` |
+| `deliveries_removed` | integer | Its deliveries retention has deleted |
+| `failed_removed`     | integer | Its failed deliveries retention has deleted |
+
+Each count changes in the transaction that writes or deletes the rows it
+counts. The pane's lifetime events are `events`, and its lifetime
+deliveries and failures are `deliveries` and `failed` summed over the
+targets; each figure within retention is the same less what retention
+removed, so neither needs the rows themselves. Its last event is
+`last_event_at`, written in the transaction that stores the event, so it
+still shows once retention has removed every event. Its last-10-minutes and
+last-24-hours figures are counted from the `events` and `deliveries`
+indexes over just that window, the deliveries in one query grouped by
+target. Its failure percentage for a window is the deliveries that became
+`failed` in it out of all that became `delivered` or `failed` in it, and
+a dash when none did.
+
 #### Event-tier indexes
 
 These indexes on the per-webhook event databases are declared in the model
-tags, so `AutoMigrate` creates them on a fresh and on an existing database:
+tags, so `AutoMigrate` creates them on a fresh database:
 
 | Table              | Columns                     | Serves |
 | ------------------ | --------------------------- | ------ |
-| `deliveries`       | `status`, `deleted_at`      | Startup recovery, the retry and pending sweeps every 60 seconds and the queue-depth sampler every 30 seconds, which select deliveries by status |
-| `deliveries`       | `event_id`, `deleted_at`    | The event log, which loads each event's deliveries, and retention, which selects and deletes the deliveries of expired events |
+| `deliveries`       | `status`, `deleted_at`, `finished_at`, `target_id` | Startup recovery, the retry and pending sweeps every 60 seconds and the queue-depth sampler every 30 seconds, which select deliveries by status, and the webhook page's statistics, which count each target's deliveries by status and when they finished |
+| `deliveries`       | `event_id`, `deleted_at`    | The event log, which loads each event's deliveries, and retention, which counts and deletes the deliveries of expired events |
 | `delivery_results` | `delivery_id`, `deleted_at` | The event log, which loads the attempts of a page's deliveries, and retention, which deletes the attempts of expired events |
-| `events`           | `deleted_at`, `created_at`  | Retention, which selects expired events by age |
-| `events`           | `created_at`                | Retention's delete of the expired events themselves |
+| `events`           | `deleted_at`, `created_at`  | The webhook page's statistics, which count recent events |
+| `events`           | `created_at`                | Retention, which selects expired events by age |
 
-GORM's soft delete adds `deleted_at IS NULL` to these queries; retention's
-deletes leave it out, but their lookups of expired rows keep it. SQLite keeps
-no statistics on these tables, and without them it rates the `deleted_at`
-index, which every live row matches, above an index on a column matched
-against several values or compared with `<`. So every index but the last also
-covers `deleted_at`. It comes second, so that retention's deletes can use the
-index without it, except in `events`, where `created_at` is compared with `<`
-and SQLite narrows by a `<` only on the last column it uses.
+GORM's soft delete adds `deleted_at IS NULL` to these queries; retention
+leaves it out. SQLite keeps no statistics on these tables, and without them it
+rates the `deleted_at` index, which every live row matches, above an index on
+a column matched against several values or compared with a range. So every
+index but the last also covers `deleted_at`. It comes second, so that
+retention can use the index without it, except in `events`, where the
+statistics compare `created_at` with a range (`>=`) and SQLite narrows by a
+range only on the last column it uses.
 
 #### Common Fields
 
-Every entity except `Setting` includes these fields from `BaseModel`.
-`Setting` is a bare key-value row with no `id`, no timestamps and no
-soft delete:
+Every entity except `Setting`, `EventTotals` and `TargetTotals` includes
+these fields from `BaseModel`. `Setting` is a bare key-value row with no
+`id`, no timestamps and no soft delete, and the two totals tables hold
+counts, plus `last_event_at` in `event_totals`, keyed by a numeric `id`
+and by `target_id`:
 
 | Field        | Type      | Description |
 | ------------ | --------- | ----------- |
@@ -1809,6 +1854,8 @@ encryption key is generated and stored, and an `admin` user is created.
 - **Events** — captured incoming webhook payloads
 - **Deliveries** — event-to-target pairings and their status
 - **DeliveryResults** — individual delivery attempt logs
+- **EventTotals** and **TargetTotals** — running counts of the above,
+  the deliveries per target, kept through retention
 
 Per-webhook databases are created automatically when a webhook is
 created (and lazily on first access for webhooks that predate this
@@ -2788,6 +2835,7 @@ webhooker/
 │   │   ├── model_event.go     # Event entity (per-webhook DB)
 │   │   ├── model_delivery.go  # Delivery entity (per-webhook DB)
 │   │   ├── model_delivery_result.go  # DeliveryResult entity (per-webhook DB)
+│   │   ├── model_totals.go    # EventTotals and TargetTotals (per-webhook DB)
 │   │   ├── model_apikey.go    # APIKey entity
 │   │   ├── password.go        # Argon2id hashing and verification
 │   │   ├── retention.go       # Retention reaper (per-webhook event expiry)
@@ -3052,7 +3100,8 @@ check, see [The login endpoint](#the-login-endpoint).
   before the app starts; the image's health check; and `docker exec`,
   unless given `--user`
 - GORM soft deletes on every entity that carries `BaseModel`, which is
-  all of them but `Setting` (data preserved for audit)
+  all of them but `Setting`, `EventTotals` and `TargetTotals` (data
+  preserved for audit)
 
 ### Shutdown
 

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 +123,80 @@ 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.Unscoped().Model(&database.Delivery{}).
+			Select("id").Where("event_id IN ?", ids),
+	).Delete(&database.DeliveryResult{}),
+		"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=?)")
 }
 
-	assertPlanUses(t, db, dry.Unscoped().Where(
-		"delivery_id IN (?)", dry.Model(&database.Delivery{}).
-			Select("id").Where("event_id IN (?)", expiredEventIDs()),
-	).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<?)")
+// 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, and events received since a time.
+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
+		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>?)")
 }
 
 // assertPlanUses asserts that SQLite's plan for a statement GORM built

internal/database/export_test.go

@@ -29,6 +29,10 @@ func NewTestRetentionReaper(
 	}
 }
 
+// ExportReapBatchSize exposes how many expired events one retention
+// transaction deletes.
+const ExportReapBatchSize = reapBatchSize
+
 // ExportSweep runs a single retention sweep synchronously for tests.
 func (r *RetentionReaper) ExportSweep(ctx context.Context) {
 	r.sweep(ctx)

internal/database/model_delivery.go

@@ -1,6 +1,10 @@
 package database
 
-import "gorm.io/gorm"
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
 
 // DeliveryStatus represents the status of a delivery
 type DeliveryStatus string
@@ -37,7 +41,7 @@ type Delivery struct {
 	BaseModel
 
 	EventID  string         `gorm:"type:uuid;not null;index:idx_deliveries_event_id,priority:1"       json:"eventId"`
-	TargetID string         `gorm:"type:uuid;not null"                                                json:"targetId"`
+	TargetID string         `gorm:"type:uuid;not null;index:idx_deliveries_status,priority:4"         json:"targetId"`
 	Status   DeliveryStatus `gorm:"not null;default:'pending';index:idx_deliveries_status,priority:1" json:"status"`
 
 	// DeletedAt repeats the BaseModel field only to be the second column
@@ -45,6 +49,13 @@ type Delivery struct {
 	// gives.
 	DeletedAt gorm.DeletedAt `gorm:"index:idx_deliveries_event_id,priority:2;index:idx_deliveries_status,priority:2" json:"deletedAt,omitzero"`
 
+	// FinishedAt is when the delivery became delivered or failed, and
+	// nil while it is pending or retrying. It and then TargetID end the
+	// status index, so the webhook page counts each target's deliveries
+	// that finished in a recent window by reading just that window from
+	// the index.
+	FinishedAt *time.Time `gorm:"index:idx_deliveries_status,priority:3" json:"finishedAt,omitempty"`
+
 	// Relations
 	Event           Event            `json:"event,omitzero"`
 	Target          Target           `json:"target,omitzero"`

internal/database/model_totals.go

@@ -0,0 +1,99 @@
+package database
+
+import (
+	"fmt"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// The running totals in a webhook's event database keep the webhook
+// page's lifetime figures right after retention has removed the rows
+// they count, and let the page show them without counting every row.
+// Each total changes in the transaction that writes or deletes the
+// rows it counts.
+
+// EventTotals is the single row counting a webhook's events: every
+// event ever stored, how many of them retention has deleted, and when
+// the newest arrived, which retention leaves as it is.
+type EventTotals struct {
+	ID int64 `gorm:"primaryKey"`
+
+	Events        int64 `gorm:"not null"`
+	EventsRemoved int64 `gorm:"not null"`
+
+	// LastEventAt is when the newest event arrived, or nil before the
+	// first.
+	LastEventAt *time.Time
+}
+
+// TableName names the table AddEventTotals updates.
+func (EventTotals) TableName() string {
+	return "event_totals"
+}
+
+// TargetTotals is one row per target counting its deliveries: every
+// delivery ever created, how many became delivered and how many
+// failed, and how many deliveries and failed deliveries retention has
+// deleted. The webhook's delivery figures are these rows summed.
+type TargetTotals struct {
+	TargetID string `gorm:"type:uuid;primaryKey"`
+
+	Deliveries int64 `gorm:"not null"`
+	Delivered  int64 `gorm:"not null"`
+	Failed     int64 `gorm:"not null"`
+
+	DeliveriesRemoved int64 `gorm:"not null"`
+	FailedRemoved     int64 `gorm:"not null"`
+}
+
+// TableName names the table AddTargetTotals updates.
+func (TargetTotals) TableName() string {
+	return "target_totals"
+}
+
+// AddEventTotals adds each count in add to the webhook's event totals,
+// and records add.LastEventAt as when the newest event arrived if it is
+// set. Call it on the transaction that writes or deletes the events it
+// counts.
+func AddEventTotals(tx *gorm.DB, add EventTotals) error {
+	err := tx.Exec(
+		`UPDATE event_totals SET
+			events = events + ?,
+			events_removed = events_removed + ?,
+			last_event_at = coalesce(?, last_event_at)`,
+		add.Events, add.EventsRemoved, add.LastEventAt,
+	).Error
+	if err != nil {
+		return fmt.Errorf("adding to event totals: %w", err)
+	}
+
+	return nil
+}
+
+// AddTargetTotals adds each count in add to the totals of the target
+// add.TargetID names, creating its row the first time. Call it on the
+// transaction that writes or deletes the deliveries it counts.
+func AddTargetTotals(tx *gorm.DB, add TargetTotals) error {
+	err := tx.Exec(
+		`INSERT INTO target_totals (target_id, deliveries, delivered,
+			failed, deliveries_removed, failed_removed)
+		VALUES (?, ?, ?, ?, ?, ?)
+		ON CONFLICT (target_id) DO UPDATE SET
+			deliveries = deliveries + excluded.deliveries,
+			delivered = delivered + excluded.delivered,
+			failed = failed + excluded.failed,
+			deliveries_removed =
+				deliveries_removed + excluded.deliveries_removed,
+			failed_removed = failed_removed + excluded.failed_removed`,
+		add.TargetID, add.Deliveries, add.Delivered,
+		add.Failed, add.DeliveriesRemoved, add.FailedRemoved,
+	).Error
+	if err != nil {
+		return fmt.Errorf(
+			"adding to totals of target %s: %w", add.TargetID, err,
+		)
+	}
+
+	return nil
+}

internal/database/models.go

@@ -2,7 +2,8 @@ package database
 
 // Migrate runs database migrations for the main application database.
 // Only configuration-tier models are stored in the main database.
-// Event-tier models (Event, Delivery, DeliveryResult) live in
+// Event-tier models (Event, Delivery, DeliveryResult, EventTotals,
+// TargetTotals) live in
 // per-webhook dedicated databases managed by WebhookDBManager.
 func (d *Database) Migrate() error {
 	return d.db.AutoMigrate(

internal/database/retention.go

@@ -18,6 +18,19 @@ import (
 // computation.
 const hoursPerDay = 24
 
+// reapBatchSize is how many expired events one retention transaction
+// deletes. A transaction holds the event database's write lock, which
+// the receiver and the delivery workers wait for, so a large prune is
+// split into transactions each short enough to finish well inside the
+// busy timeout.
+const reapBatchSize = 1000
+
+// reapBatchPause is how long retention waits after one batch before
+// starting the next. A writer waiting for the write lock checks for it
+// again after at most 100 ms, so a longer pause lets it in between two
+// batches instead of only after the whole prune.
+const reapBatchPause = 200 * time.Millisecond
+
 // RetentionReaperParams holds the fx dependencies for the
 // RetentionReaper.
 type RetentionReaperParams struct {
@@ -187,13 +200,15 @@ func (r *RetentionReaper) sweep(ctx context.Context) {
 			continue
 		}
 
-		r.reapWebhook(wh.ID, wh.RetentionDays)
+		r.reapWebhook(ctx, wh.ID, wh.RetentionDays)
 	}
 }
 
 // reapWebhook removes every expired event (and its dependents) from a
-// single webhook's database.
+// single webhook's database, or as many as it reaches before ctx is
+// cancelled.
 func (r *RetentionReaper) reapWebhook(
+	ctx context.Context,
 	webhookID string,
 	retentionDays int,
 ) {
@@ -213,7 +228,7 @@ func (r *RetentionReaper) reapWebhook(
 		return
 	}
 
-	deleted, err := reapExpired(db, cutoff)
+	deleted, err := reapExpired(ctx, db, cutoff)
 	if err != nil {
 		r.log.Error(
 			"retention sweep: failed to reap expired events",
@@ -265,57 +280,107 @@ func retentionCutoff(
 	), true
 }
 
-// reapExpired hard-deletes, in foreign-key-safe order, the delivery
-// results, deliveries, and events associated with events older than
-// cutoff. Deletes are unscoped so rows are physically removed rather
-// than soft-deleted, reclaiming disk. It returns the number of events
-// deleted.
-func reapExpired(db *gorm.DB, cutoff time.Time) (int64, error) {
-	// Fresh subqueries are built per statement to avoid reusing a
-	// mutated builder across executions.
-	expiredEventIDs := func() *gorm.DB {
-		return db.Model(&Event{}).
-			Select("id").
-			Where("created_at < ?", cutoff)
-	}
-	expiredDeliveryIDs := func() *gorm.DB {
-		return db.Model(&Delivery{}).
-			Select("id").
-			Where("event_id IN (?)", expiredEventIDs())
-	}
+// reapExpired hard-deletes the events older than cutoff, with their
+// deliveries and delivery results, reapBatchSize events per
+// transaction with reapBatchPause between transactions, until none is
+// left. Once ctx is cancelled it returns after the batch in hand,
+// leaving the rest to the next sweep, so stopping the app does not
+// wait for a long prune. It returns the number of events deleted.
+func reapExpired(
+	ctx context.Context, db *gorm.DB, cutoff time.Time,
+) (int64, error) {
+	var total int64
 
-	// 1. Delivery results whose delivery belongs to an expired event.
-	res := db.Unscoped().
-		Where("delivery_id IN (?)", expiredDeliveryIDs()).
-		Delete(&DeliveryResult{})
-	if res.Error != nil {
-		return 0, fmt.Errorf(
-			"deleting expired delivery results: %w",
-			res.Error,
-		)
-	}
+	for {
+		var eventIDs []string
 
-	// 2. Deliveries belonging to an expired event.
-	del := db.Unscoped().
-		Where("event_id IN (?)", expiredEventIDs()).
-		Delete(&Delivery{})
-	if del.Error != nil {
-		return 0, fmt.Errorf(
-			"deleting expired deliveries: %w",
-			del.Error,
-		)
-	}
-
-	// 3. The expired events themselves.
-	ev := db.Unscoped().
+		err := db.Transaction(func(tx *gorm.DB) error {
+			err := tx.Unscoped().Model(&Event{}).
 				Where("created_at < ?", cutoff).
-		Delete(&Event{})
-	if ev.Error != nil {
-		return 0, fmt.Errorf(
-			"deleting expired events: %w",
-			ev.Error,
-		)
+				Limit(reapBatchSize).
+				Pluck("id", &eventIDs).Error
+			if err != nil {
+				return fmt.Errorf("selecting expired events: %w", err)
 			}
 
-	return ev.RowsAffected, nil
+			if len(eventIDs) == 0 {
+				return nil
+			}
+
+			return deleteEvents(tx, eventIDs)
+		})
+		if err != nil {
+			return total, err
+		}
+
+		total += int64(len(eventIDs))
+
+		if len(eventIDs) < reapBatchSize {
+			return total, nil
+		}
+
+		select {
+		case <-ctx.Done():
+			return total, nil
+		case <-time.After(reapBatchPause):
+		}
+	}
+}
+
+// deleteEvents hard-deletes the given events and, in foreign-key-safe
+// order before them, their delivery results and deliveries, then adds
+// what it deleted to the running totals. It runs on reapExpired's
+// transaction, so the totals change exactly when the rows do. Deletes
+// are unscoped so rows are physically removed rather than
+// soft-deleted, reclaiming disk.
+func deleteEvents(tx *gorm.DB, eventIDs []string) error {
+	// 1. The delivery results of the events' deliveries.
+	err := tx.Unscoped().
+		Where("delivery_id IN (?)", tx.Unscoped().Model(&Delivery{}).
+			Select("id").
+			Where("event_id IN ?", eventIDs)).
+		Delete(&DeliveryResult{}).Error
+	if err != nil {
+		return fmt.Errorf("deleting expired delivery results: %w", err)
+	}
+
+	// 2. The events' deliveries, after counting them, and the failed
+	// ones among them, per target. The status is tested in the select
+	// list rather than the WHERE clause: there, SQLite would read every
+	// failed delivery the webhook has through the status index,
+	// instead of only these through the event_id index.
+	var removed []TargetTotals
+
+	err = tx.Unscoped().Model(&Delivery{}).
+		Select("target_id, count(*) AS deliveries_removed, "+
+			"count(CASE WHEN status = ? THEN 1 END) AS failed_removed",
+			DeliveryStatusFailed).
+		Where("event_id IN ?", eventIDs).
+		Group("target_id").
+		Find(&removed).Error
+	if err != nil {
+		return fmt.Errorf("counting expired deliveries: %w", err)
+	}
+
+	err = tx.Unscoped().
+		Where("event_id IN ?", eventIDs).
+		Delete(&Delivery{}).Error
+	if err != nil {
+		return fmt.Errorf("deleting expired deliveries: %w", err)
+	}
+
+	// 3. The events themselves.
+	ev := tx.Unscoped().Where("id IN ?", eventIDs).Delete(&Event{})
+	if ev.Error != nil {
+		return fmt.Errorf("deleting expired events: %w", ev.Error)
+	}
+
+	for i := range removed {
+		err = AddTargetTotals(tx, removed[i])
+		if err != nil {
+			return err
+		}
+	}
+
+	return AddEventTotals(tx, EventTotals{EventsRemoved: ev.RowsAffected})
 }

internal/database/totals_test.go

@@ -0,0 +1,410 @@
+package database_test
+
+import (
+	"context"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/gorm"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// readEventTotals reads a webhook database's row of event totals,
+// asserting that it has exactly one.
+func readEventTotals(t *testing.T, db *gorm.DB) database.EventTotals {
+	t.Helper()
+
+	var rows []database.EventTotals
+
+	require.NoError(t, db.Find(&rows).Error)
+	require.Len(t, rows, 1)
+
+	return rows[0]
+}
+
+// readTargetTotals reads a webhook database's target totals, keyed by
+// target.
+func readTargetTotals(
+	t *testing.T, db *gorm.DB,
+) map[string]database.TargetTotals {
+	t.Helper()
+
+	var rows []database.TargetTotals
+
+	require.NoError(t, db.Find(&rows).Error)
+
+	byTarget := make(map[string]database.TargetTotals, len(rows))
+	for _, row := range rows {
+		byTarget[row.TargetID] = row
+	}
+
+	return byTarget
+}
+
+// TestWebhookDBManager_TotalsSurviveReopen verifies that a new event
+// database starts with one row of zero event totals and no target
+// totals, that adding to a target twice adds to the one row, and that
+// opening the database again keeps everything added.
+func TestWebhookDBManager_TotalsSurviveReopen(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)) }()
+
+	webhookID := uuid.New().String()
+
+	db, err := mgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	fresh := readEventTotals(t, db)
+	assert.Equal(t, database.EventTotals{ID: fresh.ID}, fresh)
+	assert.Empty(t, readTargetTotals(t, db))
+
+	first, second := uuid.New().String(), uuid.New().String()
+
+	require.NoError(t, database.AddEventTotals(db, database.EventTotals{
+		Events: 2,
+	}))
+	require.NoError(t, database.AddTargetTotals(db, database.TargetTotals{
+		TargetID: first, Deliveries: 2, Delivered: 1,
+	}))
+	require.NoError(t, database.AddTargetTotals(db, database.TargetTotals{
+		TargetID: first, Failed: 1,
+	}))
+	require.NoError(t, database.AddTargetTotals(db, database.TargetTotals{
+		TargetID: second, Deliveries: 1,
+	}))
+
+	// Drop the cached connection so the next open reopens the file,
+	// as a restart would.
+	require.NoError(t, mgr.CloseAll())
+
+	db, err = mgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	assert.Equal(t, database.EventTotals{ID: fresh.ID, Events: 2},
+		readEventTotals(t, db))
+	assert.Equal(t, map[string]database.TargetTotals{
+		first: {
+			TargetID: first, Deliveries: 2, Delivered: 1, Failed: 1,
+		},
+		second: {TargetID: second, Deliveries: 1},
+	}, readTargetTotals(t, db))
+}
+
+// seedExpiredEvents stores count events created at the given time,
+// each with a delivered delivery to one target and a failed delivery
+// to the other, and one attempt for each delivery.
+func seedExpiredEvents(
+	t *testing.T,
+	db *gorm.DB,
+	webhookID string,
+	count int,
+	createdAt time.Time,
+	delivered, failed string,
+) {
+	t.Helper()
+
+	events := make([]database.Event, count)
+	deliveries := make([]database.Delivery, 0, 2*count)
+
+	for i := range events {
+		events[i] = database.Event{
+			WebhookID:    webhookID,
+			EntrypointID: uuid.New().String(),
+			Method:       http.MethodPost,
+		}
+		events[i].ID = uuid.New().String()
+		events[i].CreatedAt = createdAt
+
+		deliveries = append(deliveries,
+			database.Delivery{
+				EventID:  events[i].ID,
+				TargetID: delivered,
+				Status:   database.DeliveryStatusDelivered,
+			},
+			database.Delivery{
+				EventID:  events[i].ID,
+				TargetID: failed,
+				Status:   database.DeliveryStatusFailed,
+			},
+		)
+	}
+
+	require.NoError(t, db.CreateInBatches(events, 500).Error)
+	require.NoError(t, db.CreateInBatches(deliveries, 500).Error)
+
+	results := make([]database.DeliveryResult, len(deliveries))
+	for i := range deliveries {
+		results[i] = database.DeliveryResult{
+			DeliveryID: deliveries[i].ID, AttemptNum: 1,
+		}
+	}
+
+	require.NoError(t, db.CreateInBatches(results, 500).Error)
+}
+
+// seedBareEvents stores count events created at the given time, with
+// no deliveries.
+func seedBareEvents(
+	t *testing.T,
+	db *gorm.DB,
+	webhookID string,
+	count int,
+	createdAt time.Time,
+) {
+	t.Helper()
+
+	events := make([]database.Event, count)
+	for i := range events {
+		events[i] = database.Event{
+			WebhookID:    webhookID,
+			EntrypointID: uuid.New().String(),
+			Method:       http.MethodPost,
+		}
+		events[i].CreatedAt = createdAt
+	}
+
+	require.NoError(t, db.CreateInBatches(events, 500).Error)
+}
+
+// TestRetentionReaper_PrunesMoreThanOneBatch verifies that a prune
+// larger than one transaction's batch removes every expired event with
+// its deliveries and delivery results, keeps the recent event, and
+// adds what it removed to the event and target totals, so the totals
+// within retention match the rows still stored.
+func TestRetentionReaper_PrunesMoreThanOneBatch(t *testing.T) {
+	t.Parallel()
+
+	env := setupRetentionTest(t)
+
+	webhookID := createWebhook(t, env.mainDB.DB(), 30)
+
+	db, err := env.mgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	expired := database.ExportReapBatchSize + 1
+	delivered, failed := uuid.New().String(), uuid.New().String()
+	seedExpiredEvents(t, db, webhookID, expired,
+		time.Now().Add(-40*24*time.Hour), delivered, failed)
+
+	// One recent event, delivered to the first target.
+	recent := seedEventChain(t, db, webhookID, time.Now())
+	require.NoError(t, db.Model(&database.Delivery{}).
+		Where("id = ?", recent.deliveryID).
+		Update("target_id", delivered).Error)
+
+	// The totals storing those rows would have left.
+	n := int64(expired)
+	require.NoError(t, database.AddEventTotals(db, database.EventTotals{
+		Events: n + 1,
+	}))
+	require.NoError(t, database.AddTargetTotals(db, database.TargetTotals{
+		TargetID: delivered, Deliveries: n + 1, Delivered: n + 1,
+	}))
+	require.NoError(t, database.AddTargetTotals(db, database.TargetTotals{
+		TargetID: failed, Deliveries: n, Failed: n,
+	}))
+
+	env.reaper.ExportSweep(context.Background())
+
+	// Only the recent event's rows are left.
+	for _, model := range []any{
+		&database.Event{}, &database.Delivery{}, &database.DeliveryResult{},
+	} {
+		var count int64
+
+		require.NoError(t, db.Model(model).Count(&count).Error)
+		assert.Equal(t, int64(1), count, "%T rows left", model)
+	}
+
+	assertChainPresent(t, db, recent)
+
+	eventTotals := readEventTotals(t, db)
+	assert.Equal(t, database.EventTotals{
+		ID: eventTotals.ID, Events: n + 1, EventsRemoved: n,
+	}, eventTotals)
+
+	targetTotals := readTargetTotals(t, db)
+	assert.Equal(t, map[string]database.TargetTotals{
+		delivered: {
+			TargetID: delivered, Deliveries: n + 1, Delivered: n + 1,
+			DeliveriesRemoved: n,
+		},
+		failed: {
+			TargetID: failed, Deliveries: n, Failed: n,
+			DeliveriesRemoved: n, FailedRemoved: n,
+		},
+	}, targetTotals)
+
+	// A sweep with nothing left to remove changes nothing.
+	env.reaper.ExportSweep(context.Background())
+
+	assert.Equal(t, eventTotals, readEventTotals(t, db))
+	assert.Equal(t, targetTotals, readTargetTotals(t, db))
+}
+
+// TestRetentionReaper_WriteDuringPruneSucceeds verifies that a prune
+// of several batches lets other writers in between its batches: an
+// event stored once the first batch is deleted is stored while expired
+// events are still left, not only after the prune has finished.
+func TestRetentionReaper_WriteDuringPruneSucceeds(t *testing.T) {
+	t.Parallel()
+
+	env := setupRetentionTest(t)
+
+	webhookID := createWebhook(t, env.mainDB.DB(), 30)
+
+	db, err := env.mgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	// Three batches of expired events, with nothing else stored: only
+	// the number of batches matters here.
+	expired := 3 * database.ExportReapBatchSize
+	seedBareEvents(t, db, webhookID, expired,
+		time.Now().Add(-40*24*time.Hour))
+
+	cutoff := time.Now().Add(-30 * 24 * time.Hour)
+	countExpired := func() int64 {
+		var count int64
+
+		require.NoError(t, db.Model(&database.Event{}).
+			Where("created_at < ?", cutoff).
+			Count(&count).Error)
+
+		return count
+	}
+
+	pruned := make(chan struct{})
+
+	go func() {
+		defer close(pruned)
+
+		env.reaper.ExportSweep(context.Background())
+	}()
+
+	t.Cleanup(func() { <-pruned })
+
+	// Every stored event is expired until the write below.
+	require.Eventually(t, func() bool {
+		var count int64
+
+		err := db.Model(&database.Event{}).Count(&count).Error
+
+		return err == nil && count < int64(expired)
+	}, 10*time.Second, 10*time.Millisecond)
+
+	event := &database.Event{
+		WebhookID:    webhookID,
+		EntrypointID: uuid.New().String(),
+		Method:       http.MethodPost,
+	}
+	require.NoError(t, db.Create(event).Error)
+
+	assert.Positive(t, countExpired(),
+		"the event was stored only after the whole prune")
+
+	<-pruned
+
+	assert.Zero(t, countExpired())
+
+	var stored database.Event
+
+	require.NoError(t, db.First(&stored, "id = ?", event.ID).Error)
+}
+
+// TestRetentionReaper_StopDuringPruneLeavesTheRest verifies that
+// stopping the reaper during a prune of several batches returns
+// between two batches, well inside the stop timeout, leaving the
+// remaining expired events for the next sweep, and that the totals
+// match the rows left.
+func TestRetentionReaper_StopDuringPruneLeavesTheRest(t *testing.T) {
+	t.Parallel()
+
+	env := setupRetentionTest(t)
+
+	webhookID := createWebhook(t, env.mainDB.DB(), 30)
+
+	db, err := env.mgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	// Two batches and one more of expired events, a few of them with a
+	// delivered and a failed delivery for the target totals to count.
+	// Most carry nothing else, to keep the test quick.
+	const withDeliveries = 10
+
+	expiredAt := time.Now().Add(-40 * 24 * time.Hour)
+	delivered, failed := uuid.New().String(), uuid.New().String()
+	seedExpiredEvents(t, db, webhookID, withDeliveries, expiredAt,
+		delivered, failed)
+	seedBareEvents(t, db, webhookID,
+		2*database.ExportReapBatchSize+1-withDeliveries, expiredAt)
+
+	n := int64(2*database.ExportReapBatchSize + 1)
+	require.NoError(t, database.AddEventTotals(db, database.EventTotals{
+		Events: n,
+	}))
+	require.NoError(t, database.AddTargetTotals(db, database.TargetTotals{
+		TargetID: delivered, Deliveries: withDeliveries,
+		Delivered: withDeliveries,
+	}))
+	require.NoError(t, database.AddTargetTotals(db, database.TargetTotals{
+		TargetID: failed, Deliveries: withDeliveries,
+		Failed: withDeliveries,
+	}))
+
+	env.reaper.ExportSetInterval(time.Millisecond)
+	env.reaper.ExportStart()
+
+	// Stop once the first batch is deleted. The stop lands in the pause
+	// after it, or at worst during the second batch, so at least the
+	// last event is left.
+	require.Eventually(t, func() bool {
+		var count int64
+
+		err := db.Model(&database.Event{}).Count(&count).Error
+
+		return err == nil && count < n
+	}, 10*time.Second, 10*time.Millisecond)
+
+	// The app's stop timeout.
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	require.NoError(t, env.reaper.ExportStop(ctx))
+
+	var events int64
+
+	require.NoError(t, db.Model(&database.Event{}).Count(&events).Error)
+	assert.Positive(t, events, "the stop waited for the whole prune")
+
+	eventTotals := readEventTotals(t, db)
+	assert.Equal(t, events, eventTotals.Events-eventTotals.EventsRemoved)
+
+	targetTotals := readTargetTotals(t, db)
+	require.Len(t, targetTotals, 2)
+
+	for target, totals := range targetTotals {
+		var deliveries, failures int64
+
+		require.NoError(t, db.Model(&database.Delivery{}).
+			Where("target_id = ?", target).
+			Count(&deliveries).Error)
+		require.NoError(t, db.Model(&database.Delivery{}).
+			Where("target_id = ? AND status = ?",
+				target, database.DeliveryStatusFailed).
+			Count(&failures).Error)
+
+		assert.Equal(t, deliveries,
+			totals.Deliveries-totals.DeliveriesRemoved, target)
+		assert.Equal(t, failures, totals.Failed-totals.FailedRemoved,
+			target)
+	}
+}

internal/database/webhook_db_manager.go

@@ -35,7 +35,8 @@ var errInvalidCachedDBType = errors.New(
 
 // WebhookDBManager manages per-webhook SQLite database files
 // for event storage. Each webhook gets its own dedicated
-// database containing Events, Deliveries, and DeliveryResults.
+// database containing Events, Deliveries, DeliveryResults and the
+// running totals of them (EventTotals, TargetTotals).
 // Database connections are opened lazily and cached.
 type WebhookDBManager struct {
 	dataDir string
@@ -295,6 +296,7 @@ func (m *WebhookDBManager) openDB(
 	// Run migrations for event-tier models only
 	err = db.AutoMigrate(
 		&Event{}, &Delivery{}, &DeliveryResult{},
+		&EventTotals{}, &TargetTotals{},
 	)
 	if err != nil {
 		_ = sqlDB.Close()
@@ -305,6 +307,18 @@ func (m *WebhookDBManager) openDB(
 		)
 	}
 
+	// A new database gets its row of event totals, all zero. Target
+	// totals rows are created by the first delivery to each target.
+	err = db.FirstOrCreate(&EventTotals{}).Error
+	if err != nil {
+		_ = sqlDB.Close()
+
+		return nil, fmt.Errorf(
+			"creating event totals for webhook database %s: %w",
+			webhookID, err,
+		)
+	}
+
 	m.log.Info(
 		"opened per-webhook database",
 		"webhook_id", webhookID,

internal/delivery/delivery_totals_test.go

@@ -0,0 +1,177 @@
+package delivery_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/gorm"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// targetTotals reads one target's totals from a webhook database, all
+// zero when it has no row.
+func targetTotals(
+	t *testing.T, db *gorm.DB, targetID string,
+) database.TargetTotals {
+	t.Helper()
+
+	var rows []database.TargetTotals
+
+	require.NoError(t, db.Where("target_id = ?", targetID).
+		Find(&rows).Error)
+
+	if len(rows) == 0 {
+		return database.TargetTotals{TargetID: targetID}
+	}
+
+	return rows[0]
+}
+
+// TestUpdateDeliveryStatus_FinishTimeAndTargetTotals pins what a status
+// write records for the webhook page's statistics: the time a delivery
+// finished, set only when it becomes delivered or failed, and one more
+// on its target's delivered or failed total.
+func TestUpdateDeliveryStatus_FinishTimeAndTargetTotals(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		status    database.DeliveryStatus
+		finished  bool
+		delivered int64
+		failed    int64
+	}{
+		{database.DeliveryStatusRetrying, false, 0, 0},
+		{database.DeliveryStatusDelivered, true, 1, 0},
+		{database.DeliveryStatusFailed, true, 0, 1},
+	}
+
+	for _, tt := range tests {
+		t.Run(string(tt.status), func(t *testing.T) {
+			t.Parallel()
+
+			db := testWebhookDB(t)
+			e := testEngine(t, 1)
+			event := seedEvent(t, db, `{}`)
+			targetID := uuid.New().String()
+			d := seedDelivery(
+				t, db, event.ID, targetID,
+				database.DeliveryStatusPending,
+			)
+
+			before := time.Now()
+
+			require.NoError(t, e.ExportUpdateDeliveryStatus(
+				db, &d, tt.status,
+			))
+
+			var stored database.Delivery
+
+			require.NoError(t, db.First(&stored, "id = ?", d.ID).Error)
+			assert.Equal(t, tt.status, stored.Status)
+
+			if tt.finished {
+				require.NotNil(t, stored.FinishedAt)
+				assert.False(t, stored.FinishedAt.Before(before))
+			} else {
+				assert.Nil(t, stored.FinishedAt)
+			}
+
+			assert.Equal(t, database.TargetTotals{
+				TargetID:  targetID,
+				Delivered: tt.delivered,
+				Failed:    tt.failed,
+			}, targetTotals(t, db, targetID))
+		})
+	}
+}
+
+// TestUpdateDeliveryStatus_DeletedDeliveryIsNotCounted covers a
+// delivery retention deleted while the engine still held it. Failing
+// it afterwards writes no row, so it adds no failure either: retention
+// has already counted what it removed.
+func TestUpdateDeliveryStatus_DeletedDeliveryIsNotCounted(t *testing.T) {
+	t.Parallel()
+
+	db := testWebhookDB(t)
+	e := testEngine(t, 1)
+	event := seedEvent(t, db, `{}`)
+	targetID := uuid.New().String()
+	d := seedDelivery(
+		t, db, event.ID, targetID,
+		database.DeliveryStatusRetrying,
+	)
+
+	require.NoError(t, db.Unscoped().
+		Delete(&database.Delivery{}, "id = ?", d.ID).Error)
+
+	require.NoError(t, e.ExportUpdateDeliveryStatus(
+		db, &d, database.DeliveryStatusFailed,
+	))
+
+	assert.Equal(t, database.TargetTotals{TargetID: targetID},
+		targetTotals(t, db, targetID))
+}
+
+// TestUpdateDeliveryStatus_FinishedDeliveryIsNotSettledAgain covers a
+// delivery settled a second time, as recovery can do when a worker has
+// settled it since recovery read it. Neither status writes over the
+// first, and the totals do not move.
+func TestUpdateDeliveryStatus_FinishedDeliveryIsNotSettledAgain(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	finished := []database.DeliveryStatus{
+		database.DeliveryStatusDelivered,
+		database.DeliveryStatusFailed,
+	}
+
+	for _, first := range finished {
+		t.Run(string(first), func(t *testing.T) {
+			t.Parallel()
+
+			db := testWebhookDB(t)
+			e := testEngine(t, 1)
+			event := seedEvent(t, db, `{}`)
+			targetID := uuid.New().String()
+			d := seedDelivery(
+				t, db, event.ID, targetID,
+				database.DeliveryStatusRetrying,
+			)
+
+			// The delivery as recovery read it, before the worker
+			// settled it.
+			readBefore := d
+
+			require.NoError(t, e.ExportUpdateDeliveryStatus(
+				db, &d, first,
+			))
+
+			var settled database.Delivery
+
+			require.NoError(t, db.First(&settled, "id = ?", d.ID).Error)
+			require.NotNil(t, settled.FinishedAt)
+
+			totals := targetTotals(t, db, targetID)
+
+			for _, again := range finished {
+				stale := readBefore
+
+				require.NoError(t, e.ExportUpdateDeliveryStatus(
+					db, &stale, again,
+				))
+			}
+
+			var stored database.Delivery
+
+			require.NoError(t, db.First(&stored, "id = ?", d.ID).Error)
+			assert.Equal(t, first, stored.Status)
+			require.NotNil(t, stored.FinishedAt)
+			assert.True(t, settled.FinishedAt.Equal(*stored.FinishedAt))
+			assert.Equal(t, totals, targetTotals(t, db, targetID))
+		})
+	}
+}

internal/delivery/engine.go

@@ -531,6 +531,11 @@ func (e *Engine) processRetryTask(
 		return
 	}
 
+	// Set before anything below can fail the delivery: the failure is
+	// added to this target's totals.
+	d.EventID = task.EventID
+	d.TargetID = task.TargetID
+
 	if d.Status != database.DeliveryStatusRetrying {
 		e.log.Debug(
 			"skipping retry for delivery "+
@@ -562,8 +567,6 @@ func (e *Engine) processRetryTask(
 	}
 
 	target := buildTargetFromTask(task)
-	d.EventID = task.EventID
-	d.TargetID = task.TargetID
 	d.Event = event
 	d.Target = target
 
@@ -1554,8 +1557,9 @@ func (e *Engine) updateDeliveryStatus(
 	targetType database.TargetType,
 	status database.DeliveryStatus,
 ) error {
-	err := webhookDB.Model(d).
-		Update("status", status).Error
+	err := webhookDB.Transaction(func(tx *gorm.DB) error {
+		return writeDeliveryStatus(tx, d, status)
+	})
 	if err != nil {
 		return fmt.Errorf(
 			"updating delivery %s to status %s: %w",
@@ -1574,6 +1578,43 @@ func (e *Engine) updateDeliveryStatus(
 	return nil
 }
 
+// writeDeliveryStatus writes a delivery's new status. A delivery that
+// becomes delivered or failed also gets the time it finished, and is
+// added to its target's delivered or failed total. That write changes
+// only a delivery not yet delivered or failed, and the total moves
+// only when it changed a row: retention may have deleted the delivery
+// while the engine was working on it, and a recovery path may settle
+// a delivery that a worker has already settled.
+func writeDeliveryStatus(
+	tx *gorm.DB,
+	d *database.Delivery,
+	status database.DeliveryStatus,
+) error {
+	if !status.Terminal() {
+		return tx.Model(d).Update("status", status).Error
+	}
+
+	res := tx.Model(d).
+		Where("status NOT IN ?", []database.DeliveryStatus{
+			database.DeliveryStatusDelivered,
+			database.DeliveryStatusFailed,
+		}).
+		Updates(map[string]any{
+			"status":      status,
+			"finished_at": time.Now(),
+		})
+	if res.Error != nil || res.RowsAffected == 0 {
+		return res.Error
+	}
+
+	add := database.TargetTotals{TargetID: d.TargetID, Delivered: 1}
+	if status == database.DeliveryStatusFailed {
+		add = database.TargetTotals{TargetID: d.TargetID, Failed: 1}
+	}
+
+	return database.AddTargetTotals(tx, add)
+}
+
 // settleStatus moves a delivery to its outcome status and reports a
 // failed write through bookkeepingFailed, which leaves the row
 // recoverable. It exists so the target call sites read as one

internal/delivery/engine_test.go

@@ -57,7 +57,10 @@ func testWebhookDB(t *testing.T) *gorm.DB {
 		&database.Event{},
 		&database.Delivery{},
 		&database.DeliveryResult{},
+		&database.EventTotals{},
+		&database.TargetTotals{},
 	))
+	require.NoError(t, db.Create(&database.EventTotals{}).Error)
 
 	return db
 }

internal/delivery/export_test.go

@@ -150,6 +150,16 @@ func (e *Engine) ExportDeliverSlack(
 	)
 }
 
+// ExportUpdateDeliveryStatus exposes updateDeliveryStatus. It passes no
+// target type, so no metric moves.
+func (e *Engine) ExportUpdateDeliveryStatus(
+	webhookDB *gorm.DB,
+	d *database.Delivery,
+	status database.DeliveryStatus,
+) error {
+	return e.updateDeliveryStatus(webhookDB, d, "", status)
+}
+
 // ExportProcessNewTask exposes processNewTask.
 func (e *Engine) ExportProcessNewTask(
 	ctx context.Context, task *Task,

internal/delivery/terminal_state_test.go

@@ -418,6 +418,38 @@ func TestProcessRetryTask_TargetDeleted_MakesNoAttempt(
 	assert.Zero(t, s.Engine.ExportInflightHeld())
 }
 
+// TestProcessRetryTask_TargetDeleted_CountsFailureOnTarget verifies
+// that the failure of a retry abandoned because its target is gone is
+// added to that target's own totals, not to a row with no target.
+func TestProcessRetryTask_TargetDeleted_CountsFailureOnTarget(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	s := newISetup(t)
+
+	var hits atomic.Int64
+
+	task, targetID := tRetryChainSetup(
+		t, s, "gone-counted", &hits,
+	)
+
+	require.NoError(t, s.MainDB.Delete(
+		&database.Target{}, "id = ?", targetID,
+	).Error)
+
+	s.Engine.ExportProcessRetryTask(
+		context.Background(), &task,
+	)
+
+	var rows []database.TargetTotals
+
+	require.NoError(t, s.WebhookDB.Find(&rows).Error)
+	assert.Equal(t, []database.TargetTotals{
+		{TargetID: targetID, Failed: 1},
+	}, rows)
+}
+
 // TestProcessRetryTask_TargetPresent_StillDelivers is the guard's
 // mutation check: a liveness check that refused every retry would pass
 // the test above and break every retry there is.

internal/handlers/delivery_replay.go

@@ -299,8 +299,9 @@ func countInFlightDeliveries(
 	return count, err
 }
 
-// createReplayDelivery writes the new pending delivery row and returns
-// the task that carries it to the delivery engine.
+// createReplayDelivery writes the new pending delivery row, adds it to
+// its target's totals in the same transaction, and returns the task
+// that carries it to the delivery engine.
 //
 // The row is written with associations omitted, and neither Event nor
 // Target is populated on it: GORM's SaveBeforeAssociations would
@@ -319,7 +320,16 @@ func createReplayDelivery(
 		Status:   database.DeliveryStatusPending,
 	}
 
-	err := webhookDB.Omit(clause.Associations).Create(dlv).Error
+	err := webhookDB.Transaction(func(tx *gorm.DB) error {
+		err := tx.Omit(clause.Associations).Create(dlv).Error
+		if err != nil {
+			return err
+		}
+
+		return database.AddTargetTotals(tx, database.TargetTotals{
+			TargetID: dlv.TargetID, Deliveries: 1,
+		})
+	})
 	if err != nil {
 		return delivery.Task{}, err
 	}

internal/handlers/export_test.go

@@ -4,7 +4,9 @@ import (
 	"html/template"
 	"log/slog"
 	"net/http"
+	"time"
 
+	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
 )
 
@@ -69,6 +71,29 @@ func (s *Handlers) LoadEventLogViewsForTest(
 	return views
 }
 
+// WebhookStatsForTest returns the figures the statistics pane on a
+// webhook's page shows, from the webhook's entrypoints and targets
+// loaded as that page loads them.
+func (s *Handlers) WebhookStatsForTest(webhookID string) *WebhookStats {
+	var entrypoints []database.Entrypoint
+
+	s.db.DB().Where("webhook_id = ?", webhookID).Find(&entrypoints)
+
+	var targets []database.Target
+
+	s.db.DB().Where("webhook_id = ?", webhookID).Find(&targets)
+
+	return s.loadWebhookStats(webhookID, entrypoints, targets)
+}
+
+// FinishedByTargetForTest exposes finishedByTarget for use in the
+// handlers_test package.
+func FinishedByTargetForTest(
+	webhookDB *gorm.DB, since time.Time,
+) ([]TargetFinished, error) {
+	return finishedByTarget(webhookDB, since)
+}
+
 // AddTemplateForTest registers a template under a page name so that
 // the handlers_test package can drive the render path with a
 // template of its own.

internal/handlers/handlers.go

@@ -91,18 +91,22 @@ type Handlers struct {
 
 // parsePageTemplate parses a page-specific template set from the
 // embedded FS. Each page template is combined with the shared
-// base, htmlheader, and navbar templates. The page file must be
-// listed first so that its root action ({{template "base" .}})
-// becomes the template set's entry point.
-func parsePageTemplate(pageFile string) *template.Template {
-	return template.Must(
-		template.ParseFS(
-			templates.Templates,
+// base, htmlheader, and navbar templates, and with any further files
+// the page includes. The page file must be listed first so that its
+// root action ({{template "base" .}}) becomes the template set's entry
+// point.
+func parsePageTemplate(
+	pageFile string, included ...string,
+) *template.Template {
+	files := append([]string{
 		pageFile,
 		"base.html",
 		"htmlheader.html",
 		"navbar.html",
-		),
+	}, included...)
+
+	return template.Must(
+		template.ParseFS(templates.Templates, files...),
 	)
 }
 
@@ -131,7 +135,7 @@ func New(
 		"profile.html":       parsePageTemplate("profile.html"),
 		"sources_list.html":  parsePageTemplate("sources_list.html"),
 		"sources_new.html":   parsePageTemplate("sources_new.html"),
-		"source_detail.html": parsePageTemplate("source_detail.html"),
+		"source_detail.html": parsePageTemplate("source_detail.html", "webhook_stats.html"),
 		"source_edit.html":   parsePageTemplate("source_edit.html"),
 		"source_logs.html":   parsePageTemplate("source_logs.html"),
 		"target_edit.html":   parsePageTemplate("target_edit.html"),

internal/handlers/source_management.go

@@ -457,6 +457,7 @@ func (h *Handlers) renderSourceDetail(
 		"Targets":     delivery.NewTargetViews(targets),
 		"Events":      events,
 		"BaseURL":     baseURL,
+		"Stats":       h.loadWebhookStats(webhook.ID, entrypoints, targets),
 	}
 
 	h.renderTemplate(w, r, "source_detail.html", data)

internal/handlers/webhook.go

@@ -253,11 +253,12 @@ func requestEventSource(
 	}
 }
 
-// createAndFanOut writes the event and one pending delivery per target
-// in a single transaction, then hands the tasks to the delivery
-// engine. It is the only path by which an event and its deliveries are
-// created, so a resubmitted event is retried, SSRF-guarded and
-// circuit-broken exactly as a received one is.
+// createAndFanOut writes the event and one pending delivery per target,
+// and adds them to the webhook's running totals, in a single
+// transaction, then hands the tasks to the delivery engine. It is the
+// only path by which an event and its deliveries are created, so a
+// resubmitted event is retried, SSRF-guarded and circuit-broken
+// exactly as a received one is.
 //
 // The tasks are returned as well as queued, so a caller can report how
 // many targets the event went to.
@@ -297,6 +298,15 @@ func (h *Handlers) createAndFanOut(
 		return nil, nil, err
 	}
 
+	err = database.AddEventTotals(tx, database.EventTotals{
+		Events: 1, LastEventAt: &event.CreatedAt,
+	})
+	if err != nil {
+		tx.Rollback()
+
+		return nil, nil, err
+	}
+
 	err = tx.Commit().Error
 	if err != nil {
 		return nil, nil, fmt.Errorf(
@@ -355,8 +365,9 @@ func (h *Handlers) finishWebhookResponse(
 }
 
 // buildDeliveryTasks creates one pending delivery per target in the
-// transaction and returns the tasks for the delivery engine. The
-// caller owns the transaction and rolls it back on error.
+// transaction, adds each to its target's totals, and returns the tasks
+// for the delivery engine. The caller owns the transaction and rolls
+// it back on error.
 func buildDeliveryTasks(
 	tx *gorm.DB,
 	event *database.Event,
@@ -380,6 +391,13 @@ func buildDeliveryTasks(
 			)
 		}
 
+		err = database.AddTargetTotals(tx, database.TargetTotals{
+			TargetID: targets[i].ID, Deliveries: 1,
+		})
+		if err != nil {
+			return nil, err
+		}
+
 		tasks = append(tasks, delivery.Task{
 			DeliveryID:   dlv.ID,
 			EventID:      event.ID,

internal/handlers/webhook_stats.go

@@ -0,0 +1,259 @@
+package handlers
+
+import (
+	"fmt"
+	"time"
+
+	"gorm.io/gorm"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// The spans of the two recent windows the statistics pane reports on:
+// the last 10 minutes and the last 24 hours.
+const (
+	shortWindow = 10 * time.Minute
+	longWindow  = 24 * time.Hour
+)
+
+// percent turns a fraction into a percentage.
+const percent = 100
+
+// WebhookStats holds the figures in the statistics pane at the top of
+// the webhook page.
+type WebhookStats struct {
+	Entrypoints       int
+	ActiveEntrypoints int
+	Targets           int
+	ActiveTargets     int
+
+	// Lifetime counts every event, delivery and failure the webhook
+	// has had, and WithinRetention those still stored.
+	Lifetime        Counts
+	WithinRetention Counts
+
+	// InProgress counts the deliveries still pending or retrying.
+	InProgress int64
+
+	// LastEventAt is when the newest event arrived, or nil when none
+	// has. Retention does not change it.
+	LastEventAt *time.Time
+
+	Last10Minutes RecentWindow
+	Last24Hours   RecentWindow
+}
+
+// Counts holds a number of events, of deliveries and of failed
+// deliveries.
+type Counts struct {
+	Events     int64
+	Deliveries int64
+	Failures   int64
+}
+
+// RecentWindow holds what happened in one recent window: the events
+// received in it, and the deliveries that became delivered or failed in
+// it.
+type RecentWindow struct {
+	Events    int64
+	Delivered int64
+	Failed    int64
+}
+
+// TargetFinished is how many of one target's deliveries became
+// delivered, and how many failed, in a recent window.
+type TargetFinished struct {
+	TargetID  string
+	Delivered int64
+	Failed    int64
+}
+
+// FailurePercent is the share of the deliveries finished in the window
+// that failed, or a dash when none finished. Deliveries still pending
+// or retrying are not counted either way.
+func (w RecentWindow) FailurePercent() string {
+	finished := w.Delivered + w.Failed
+	if finished == 0 {
+		return "—"
+	}
+
+	return fmt.Sprintf(
+		"%.1f%%", percent*float64(w.Failed)/float64(finished),
+	)
+}
+
+// loadWebhookStats gathers the figures for the statistics pane from the
+// webhook's entrypoints and targets, as the page has already loaded
+// them, and from its event database. It returns nil, and logs why, when
+// the event database cannot be read.
+func (h *Handlers) loadWebhookStats(
+	webhookID string,
+	entrypoints []database.Entrypoint,
+	targets []database.Target,
+) *WebhookStats {
+	stats := &WebhookStats{
+		Entrypoints: len(entrypoints),
+		Targets:     len(targets),
+	}
+
+	for i := range entrypoints {
+		if entrypoints[i].Active {
+			stats.ActiveEntrypoints++
+		}
+	}
+
+	for i := range targets {
+		if targets[i].Active {
+			stats.ActiveTargets++
+		}
+	}
+
+	// Opening an event database that does not exist would create it,
+	// and it would hold nothing to count.
+	if !h.dbMgr.DBExists(webhookID) {
+		return stats
+	}
+
+	webhookDB, err := h.dbMgr.GetDB(webhookID)
+	if err == nil {
+		err = readEventStats(webhookDB, time.Now(), stats)
+	}
+
+	if err != nil {
+		h.log.Error(
+			"failed to read webhook statistics",
+			"webhook_id", webhookID,
+			"error", err,
+		)
+
+		return nil
+	}
+
+	return stats
+}
+
+// readEventStats fills in the figures that come from the webhook's
+// event database. None of them reads every stored row: the totals are
+// one row for the events and one per target for the deliveries, and
+// every other figure is read from an index, over only the rows it
+// counts.
+func readEventStats(
+	db *gorm.DB, now time.Time, stats *WebhookStats,
+) error {
+	err := readTotals(db, stats)
+	if err != nil {
+		return err
+	}
+
+	err = db.Model(&database.Delivery{}).
+		Where("status IN ?", []database.DeliveryStatus{
+			database.DeliveryStatusPending,
+			database.DeliveryStatusRetrying,
+		}).
+		Count(&stats.InProgress).Error
+	if err != nil {
+		return fmt.Errorf("counting deliveries in progress: %w", err)
+	}
+
+	stats.Last10Minutes, err = readRecentWindow(
+		db, now.Add(-shortWindow),
+	)
+	if err != nil {
+		return err
+	}
+
+	stats.Last24Hours, err = readRecentWindow(
+		db, now.Add(-longWindow),
+	)
+
+	return err
+}
+
+// readTotals fills in the lifetime and within-retention figures, and
+// when the last event arrived, from the running totals: the events'
+// row, and the targets' rows summed.
+func readTotals(db *gorm.DB, stats *WebhookStats) error {
+	var events database.EventTotals
+
+	err := db.Take(&events).Error
+	if err != nil {
+		return fmt.Errorf("reading event totals: %w", err)
+	}
+
+	var targets []database.TargetTotals
+
+	err = db.Find(&targets).Error
+	if err != nil {
+		return fmt.Errorf("reading target totals: %w", err)
+	}
+
+	stats.Lifetime.Events = events.Events
+	stats.WithinRetention.Events = events.Events - events.EventsRemoved
+	stats.LastEventAt = events.LastEventAt
+
+	for _, t := range targets {
+		stats.Lifetime.Deliveries += t.Deliveries
+		stats.Lifetime.Failures += t.Failed
+		stats.WithinRetention.Deliveries += t.Deliveries - t.DeliveriesRemoved
+		stats.WithinRetention.Failures += t.Failed - t.FailedRemoved
+	}
+
+	return nil
+}
+
+// readRecentWindow counts the events received, and the deliveries that
+// became delivered or failed, since the given time.
+func readRecentWindow(
+	db *gorm.DB, since time.Time,
+) (RecentWindow, error) {
+	var w RecentWindow
+
+	err := db.Model(&database.Event{}).
+		Where("created_at >= ?", since).
+		Count(&w.Events).Error
+	if err != nil {
+		return w, fmt.Errorf("counting recent events: %w", err)
+	}
+
+	byTarget, err := finishedByTarget(db, since)
+	if err != nil {
+		return w, err
+	}
+
+	for _, f := range byTarget {
+		w.Delivered += f.Delivered
+		w.Failed += f.Failed
+	}
+
+	return w, nil
+}
+
+// finishedByTarget counts, for each target, the deliveries that became
+// delivered and those that failed since the given time, in one query
+// over just that window of the deliveries' status index. A target with
+// neither is left out.
+func finishedByTarget(
+	db *gorm.DB, since time.Time,
+) ([]TargetFinished, error) {
+	var byTarget []TargetFinished
+
+	err := db.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).Error
+	if err != nil {
+		return nil, fmt.Errorf(
+			"counting deliveries finished by target: %w", err,
+		)
+	}
+
+	return byTarget, nil
+}

internal/handlers/webhook_stats_test.go

@@ -0,0 +1,530 @@
+package handlers_test
+
+import (
+	"net/http"
+	"regexp"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/fx/fxtest"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/handlers"
+	"sneak.berlin/go/webhooker/internal/logger"
+	"sneak.berlin/go/webhooker/internal/session"
+)
+
+// statsEntrypoint adds an entrypoint to a webhook and returns its path.
+func statsEntrypoint(
+	t *testing.T, db *database.Database, webhookID string, active bool,
+) string {
+	t.Helper()
+
+	ep := &database.Entrypoint{
+		WebhookID: webhookID,
+		Path:      uuid.New().String(),
+	}
+
+	require.NoError(t, db.DB().Omit(clause.Associations).Create(ep).Error)
+	require.NoError(t, db.DB().Model(ep).Update("active", active).Error)
+
+	return ep.Path
+}
+
+// statsDelivery returns an event's delivery to a target.
+func statsDelivery(
+	t *testing.T, webhookDB *gorm.DB, eventID, targetID string,
+) database.Delivery {
+	t.Helper()
+
+	var d database.Delivery
+
+	require.NoError(t, webhookDB.Where(
+		"event_id = ? AND target_id = ?", eventID, targetID,
+	).First(&d).Error)
+
+	return d
+}
+
+// statsFinish settles a delivery as the delivery engine does: its
+// final status and the time it finished, and one more on its target's
+// delivered or failed total, in one transaction.
+func statsFinish(
+	t *testing.T,
+	webhookDB *gorm.DB,
+	d database.Delivery,
+	status database.DeliveryStatus,
+	at time.Time,
+) {
+	t.Helper()
+
+	add := database.TargetTotals{TargetID: d.TargetID, Delivered: 1}
+	if status == database.DeliveryStatusFailed {
+		add = database.TargetTotals{TargetID: d.TargetID, Failed: 1}
+	}
+
+	require.NoError(t, webhookDB.Transaction(func(tx *gorm.DB) error {
+		err := tx.Model(&database.Delivery{}).
+			Where("id = ?", d.ID).
+			Updates(map[string]any{"status": status, "finished_at": at}).
+			Error
+		if err != nil {
+			return err
+		}
+
+		return database.AddTargetTotals(tx, add)
+	}))
+}
+
+// statsAge moves an event's arrival back to the given time.
+func statsAge(
+	t *testing.T, webhookDB *gorm.DB, eventID string, at time.Time,
+) {
+	t.Helper()
+
+	require.NoError(t, webhookDB.Model(&database.Event{}).
+		Where("id = ?", eventID).
+		Update("created_at", at).Error)
+}
+
+// statsTargetTotals reads a webhook database's target totals, keyed by
+// target.
+func statsTargetTotals(
+	t *testing.T, webhookDB *gorm.DB,
+) map[string]database.TargetTotals {
+	t.Helper()
+
+	var rows []database.TargetTotals
+
+	require.NoError(t, webhookDB.Find(&rows).Error)
+
+	byTarget := make(map[string]database.TargetTotals, len(rows))
+	for _, row := range rows {
+		byTarget[row.TargetID] = row
+	}
+
+	return byTarget
+}
+
+// statsHistory is the webhook seedStatsHistory builds: its event
+// database, its newest event, and its two active targets.
+type statsHistory struct {
+	webhook       *database.Webhook
+	webhookDB     *gorm.DB
+	newest        database.Event
+	first, second string
+}
+
+// seedStatsHistory builds the webhook the statistics test checks: one
+// day of retention, five entrypoints (one inactive) and three targets
+// (one inactive). Six events arrive through the receiver, and so each
+// has a delivery to the two active targets. The oldest event is past
+// retention, the next six hours old, the other four just in. Five
+// deliveries are settled as the delivery engine would, the rest left
+// pending, and a replay adds a pending delivery to the oldest event.
+// Once retention has removed the oldest event, no two figures in the
+// pane's top row, or in the same table, are equal.
+func seedStatsHistory(
+	t *testing.T,
+	h *handlers.Handlers,
+	sess *session.Session,
+	db *database.Database,
+	dbMgr *database.WebhookDBManager,
+) statsHistory {
+	t.Helper()
+
+	wh := &database.Webhook{
+		UserID: deleteTestUserID, Name: "stats", RetentionDays: 1,
+	}
+	require.NoError(t, db.DB().Omit(clause.Associations).Create(wh).Error)
+
+	path := statsEntrypoint(t, db, wh.ID, true)
+	for range 3 {
+		statsEntrypoint(t, db, wh.ID, true)
+	}
+
+	statsEntrypoint(t, db, wh.ID, false)
+
+	first := seedConfiguredTarget(
+		t, db, wh.ID, database.TargetTypeHTTP,
+		`{"url":"`+replayTargetURL+`"}`,
+	)
+	second := seedTarget(t, db, wh.ID, database.TargetTypeLog)
+	inactive := seedTarget(t, db, wh.ID, database.TargetTypeLog)
+	require.NoError(t, db.DB().Model(inactive).
+		Update("active", false).Error)
+
+	router := receiverRouter(h)
+
+	for range 6 {
+		require.Equal(t, http.StatusOK, postReceiver(t, router, path))
+	}
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	events := listEvents(t, webhookDB)
+	require.Len(t, events, 6)
+
+	oldest, middle, newest := events[0], events[1], events[5]
+	now := time.Now()
+
+	statsAge(t, webhookDB, oldest.ID, now.Add(-50*time.Hour))
+	statsAge(t, webhookDB, middle.ID, now.Add(-6*time.Hour))
+
+	oldestFailure := statsDelivery(t, webhookDB, oldest.ID, first.ID)
+	statsFinish(t, webhookDB, oldestFailure,
+		database.DeliveryStatusFailed, now.Add(-49*time.Hour))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, oldest.ID, second.ID),
+		database.DeliveryStatusDelivered, now.Add(-49*time.Hour))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, middle.ID, first.ID),
+		database.DeliveryStatusFailed, now.Add(-5*time.Hour))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, middle.ID, second.ID),
+		database.DeliveryStatusFailed, now.Add(-time.Minute))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, newest.ID, first.ID),
+		database.DeliveryStatusDelivered, now.Add(-2*time.Minute))
+
+	require.Equal(t, http.StatusSeeOther,
+		postReplay(t, h, sess, wh.ID, oldestFailure.ID).Code)
+
+	return statsHistory{
+		webhook:   wh,
+		webhookDB: webhookDB,
+		newest:    newest,
+		first:     first.ID,
+		second:    second.ID,
+	}
+}
+
+// statsPrune runs the real retention reaper until it has removed one
+// event from the webhook's database, then stops it.
+func statsPrune(
+	t *testing.T,
+	db *database.Database,
+	dbMgr *database.WebhookDBManager,
+	log *logger.Logger,
+	webhookDB *gorm.DB,
+) {
+	t.Helper()
+
+	lc := fxtest.NewLifecycle(t)
+	database.NewRetentionReaper(lc, database.RetentionReaperParams{
+		Config: &config.Config{
+			RetentionSweepInterval: 10 * time.Millisecond,
+		},
+		Database:  db,
+		DBManager: dbMgr,
+		Logger:    log,
+	})
+
+	lc.RequireStart()
+
+	require.Eventually(t, func() bool {
+		var totals database.EventTotals
+
+		err := webhookDB.Take(&totals).Error
+
+		return err == nil && totals.EventsRemoved == 1
+	}, 10*time.Second, 10*time.Millisecond)
+
+	lc.RequireStop()
+}
+
+// statsPane returns the text of the statistics pane in a rendered
+// webhook page, everything from its heading to the next heading on the
+// page, with the markup taken out and each run of space made one
+// space. A table then reads header by header and row by row, each
+// row's label followed by its figures in column order.
+func statsPane(t *testing.T, page string) string {
+	t.Helper()
+
+	_, pane, found := strings.Cut(page, ">Statistics</h2>")
+	require.True(t, found, "the page has no statistics pane")
+
+	pane, _, _ = strings.Cut(pane, "<h2")
+	pane = regexp.MustCompile(`<[^>]*>`).ReplaceAllString(pane, " ")
+
+	return strings.Join(strings.Fields(pane), " ")
+}
+
+// assertStatsTargets checks, for the history seedStatsHistory builds,
+// each target's totals and its deliveries finished in the last 24
+// hours. The first target has six deliveries and the replay, the
+// second six; the inactive target has none and so no row.
+func assertStatsTargets(t *testing.T, hist statsHistory) {
+	t.Helper()
+
+	first, second := hist.first, hist.second
+
+	assert.Equal(t, map[string]database.TargetTotals{
+		first: {TargetID: first, Deliveries: 7, Delivered: 1, Failed: 2},
+		second: {
+			TargetID: second, Deliveries: 6, Delivered: 1, Failed: 1,
+		},
+	}, statsTargetTotals(t, hist.webhookDB))
+
+	lastDay, err := handlers.FinishedByTargetForTest(
+		hist.webhookDB, time.Now().Add(-24*time.Hour),
+	)
+	require.NoError(t, err)
+	assert.ElementsMatch(t, []handlers.TargetFinished{
+		{TargetID: first, Delivered: 1, Failed: 1},
+		{TargetID: second, Failed: 1},
+	}, lastDay)
+}
+
+// assertStatsPaneAfterPrune checks the rendered statistics pane for the
+// history seedStatsHistory builds, once retention has removed the
+// oldest event: each figure after its label, in its column.
+func assertStatsPaneAfterPrune(
+	t *testing.T,
+	h *handlers.Handlers,
+	sess *session.Session,
+	hist statsHistory,
+) {
+	t.Helper()
+
+	pane := statsPane(t, renderSourceDetailPage(t, h, sess, hist.webhook.ID))
+	lastEvent := hist.newest.CreatedAt.Format("2006-01-02 15:04:05 UTC")
+
+	assert.Contains(t, pane, "Entrypoints 5 (4 active) "+
+		"Targets 3 (2 active) "+
+		"Deliveries in progress 7 "+
+		"Last event "+lastEvent+" "+
+		"Retention 1 day")
+	assert.Contains(t, pane, "Lifetime Within retention "+
+		"Events 6 5 "+
+		"Deliveries 13 10 "+
+		"Failures 3 2")
+	assert.Contains(t, pane, "Last 10 minutes Last 24 hours "+
+		"Events 4 5 "+
+		"Failures 1 2 "+
+		"Failure percentage 50.0% 66.7%")
+}
+
+// TestWebhookStats_EveryFigureAcrossRetentionPrune checks every figure
+// the statistics pane shows for the history seedStatsHistory builds,
+// and each target's totals and recent figures, before and after the
+// real retention reaper removes the oldest event.
+func TestWebhookStats_EveryFigureAcrossRetentionPrune(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+		log   *logger.Logger
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &log)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	hist := seedStatsHistory(t, h, sess, db, dbMgr)
+	first, second := hist.first, hist.second
+
+	stats := h.WebhookStatsForTest(hist.webhook.ID)
+	require.NotNil(t, stats)
+
+	assert.Equal(t, 5, stats.Entrypoints)
+	assert.Equal(t, 4, stats.ActiveEntrypoints)
+	assert.Equal(t, 3, stats.Targets)
+	assert.Equal(t, 2, stats.ActiveTargets)
+	assert.Equal(t, handlers.Counts{Events: 6, Deliveries: 13, Failures: 3},
+		stats.Lifetime)
+	assert.Equal(t, stats.Lifetime, stats.WithinRetention)
+	assert.Equal(t, int64(8), stats.InProgress)
+	require.NotNil(t, stats.LastEventAt)
+	assert.True(t, hist.newest.CreatedAt.Equal(*stats.LastEventAt))
+	assert.Equal(t, handlers.RecentWindow{
+		Events: 4, Delivered: 1, Failed: 1,
+	}, stats.Last10Minutes)
+	assert.Equal(t, handlers.RecentWindow{
+		Events: 5, Delivered: 1, Failed: 2,
+	}, stats.Last24Hours)
+	assert.Equal(t, "50.0%", stats.Last10Minutes.FailurePercent())
+	assert.Equal(t, "66.7%", stats.Last24Hours.FailurePercent())
+
+	assertStatsTargets(t, hist)
+
+	// Retention removes the oldest event with its three deliveries:
+	// the first target's failed one and the pending replay, and the
+	// second target's delivered one.
+	statsPrune(t, db, dbMgr, log, hist.webhookDB)
+
+	after := h.WebhookStatsForTest(hist.webhook.ID)
+	require.NotNil(t, after)
+
+	assert.Equal(t, stats.Lifetime, after.Lifetime)
+	assert.Equal(t, handlers.Counts{Events: 5, Deliveries: 10, Failures: 2},
+		after.WithinRetention)
+	assert.Equal(t, int64(7), after.InProgress)
+	assert.Equal(t, stats.LastEventAt, after.LastEventAt)
+	assert.Equal(t, stats.Last10Minutes, after.Last10Minutes)
+	assert.Equal(t, stats.Last24Hours, after.Last24Hours)
+
+	assert.Equal(t, map[string]database.TargetTotals{
+		first: {
+			TargetID: first, Deliveries: 7, Delivered: 1, Failed: 2,
+			DeliveriesRemoved: 2, FailedRemoved: 1,
+		},
+		second: {
+			TargetID: second, Deliveries: 6, Delivered: 1, Failed: 1,
+			DeliveriesRemoved: 1,
+		},
+	}, statsTargetTotals(t, hist.webhookDB))
+
+	assertStatsPaneAfterPrune(t, h, sess, hist)
+}
+
+// TestWebhookStats_LastEventSurvivesPruningEveryEvent checks that once
+// retention has removed every event, the pane still shows when the last
+// one arrived rather than "none".
+func TestWebhookStats_LastEventSurvivesPruningEveryEvent(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+		log   *logger.Logger
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &log)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := &database.Webhook{
+		UserID: deleteTestUserID, Name: "pruned", RetentionDays: 1,
+	}
+	require.NoError(t, db.DB().Omit(clause.Associations).Create(wh).Error)
+
+	path := statsEntrypoint(t, db, wh.ID, true)
+	require.Equal(t, http.StatusOK,
+		postReceiver(t, receiverRouter(h), path))
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	events := listEvents(t, webhookDB)
+	require.Len(t, events, 1)
+
+	arrived := events[0].CreatedAt
+
+	statsAge(t, webhookDB, events[0].ID, time.Now().Add(-50*time.Hour))
+	statsPrune(t, db, dbMgr, log, webhookDB)
+	require.Empty(t, listEvents(t, webhookDB))
+
+	stats := h.WebhookStatsForTest(wh.ID)
+	require.NotNil(t, stats)
+	require.NotNil(t, stats.LastEventAt)
+	assert.True(t, arrived.Equal(*stats.LastEventAt))
+
+	pane := statsPane(t, renderSourceDetailPage(t, h, sess, wh.ID))
+	assert.Contains(t, pane,
+		"Last event "+arrived.Format("2006-01-02 15:04:05 UTC"))
+}
+
+// TestWebhookStats_PaneShowsRetentionPeriod checks that the statistics
+// pane itself, not only the line at the foot of the page, shows the
+// webhook's retention period, for a finite one and for forever.
+func TestWebhookStats_PaneShowsRetentionPeriod(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h    *handlers.Handlers
+		sess *session.Session
+		db   *database.Database
+	)
+
+	app := newTestApp(t, &h, &sess, &db)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	tests := []struct {
+		retentionDays int
+		want          string
+	}{
+		{30, "30 days"},
+		{database.RetentionForeverDays, "forever"},
+	}
+
+	for _, tt := range tests {
+		wh := &database.Webhook{
+			UserID:        deleteTestUserID,
+			Name:          "retention",
+			RetentionDays: tt.retentionDays,
+		}
+		require.NoError(t,
+			db.DB().Omit(clause.Associations).Create(wh).Error)
+
+		pane := statsPane(t, renderSourceDetailPage(t, h, sess, wh.ID))
+		assert.Contains(t, pane, "Retention "+tt.want)
+	}
+}
+
+// TestWebhookStats_WebhookWithNoEvents covers a webhook whose event
+// database has never been opened: every count is zero, the
+// percentages are a dash, and showing the page does not create the
+// database.
+func TestWebhookStats_WebhookWithNoEvents(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+
+	assert.Equal(t, &handlers.WebhookStats{}, h.WebhookStatsForTest(wh.ID))
+	assert.Equal(t, "—", handlers.RecentWindow{}.FailurePercent())
+
+	pane := statsPane(t, renderSourceDetailPage(t, h, sess, wh.ID))
+	assert.Contains(t, pane, "Last event none")
+	assert.Contains(t, pane, "Failure percentage — —")
+	assert.False(t, dbMgr.DBExists(wh.ID))
+}
+
+// TestRecentWindow_FailurePercent pins the percentage: failed
+// deliveries out of all that finished in the window.
+func TestRecentWindow_FailurePercent(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		window handlers.RecentWindow
+		want   string
+	}{
+		{handlers.RecentWindow{}, "—"},
+		{handlers.RecentWindow{Events: 4}, "—"},
+		{handlers.RecentWindow{Delivered: 3, Failed: 1}, "25.0%"},
+		{handlers.RecentWindow{Failed: 2}, "100.0%"},
+		{handlers.RecentWindow{Delivered: 2}, "0.0%"},
+	}
+
+	for _, tt := range tests {
+		assert.Equal(t, tt.want, tt.window.FailurePercent(), tt.window)
+	}
+}

templates/source_detail.html

@@ -24,6 +24,8 @@
         </div>
     </div>
 
+    {{template "webhook_stats" .}}
+
     <div class="grid grid-cols-1 lg:grid-cols-2 gap-6">
         <!-- Entrypoints -->
         <div class="card">

templates/webhook_stats.html

@@ -0,0 +1,95 @@
+{{define "webhook_stats"}}
+<!-- Statistics pane at the top of the webhook page. -->
+<div class="card mb-6">
+    <div class="p-4 border-b border-gray-200">
+        <h2 class="text-lg font-medium text-gray-900">Statistics</h2>
+    </div>
+    {{with .Stats}}
+    <div class="p-4 flex flex-wrap gap-6 text-sm border-b border-gray-200">
+        <div>
+            <span class="text-gray-500">Entrypoints</span>
+            <span class="font-medium text-gray-900">{{.Entrypoints}}</span>
+            <span class="text-gray-500">({{.ActiveEntrypoints}} active)</span>
+        </div>
+        <div>
+            <span class="text-gray-500">Targets</span>
+            <span class="font-medium text-gray-900">{{.Targets}}</span>
+            <span class="text-gray-500">({{.ActiveTargets}} active)</span>
+        </div>
+        <div>
+            <span class="text-gray-500">Deliveries in progress</span>
+            <span class="font-medium text-gray-900">{{.InProgress}}</span>
+        </div>
+        <div>
+            <span class="text-gray-500">Last event</span>
+            <span class="font-medium text-gray-900">{{with .LastEventAt}}{{.Format "2006-01-02 15:04:05 UTC"}}{{else}}none{{end}}</span>
+        </div>
+        <div>
+            <span class="text-gray-500">Retention</span>
+            <span class="font-medium text-gray-900">{{$.Webhook.RetentionLabel}}</span>
+        </div>
+    </div>
+    <div class="p-4 grid grid-cols-1 lg:grid-cols-2 gap-6 text-sm">
+        <div>
+            <table class="w-full text-center text-gray-900">
+                <thead>
+                    <tr class="border-b border-gray-200 text-xs text-gray-500 uppercase tracking-wide">
+                        <th></th>
+                        <th class="py-2 font-medium">Lifetime</th>
+                        <th class="py-2 font-medium">Within retention</th>
+                    </tr>
+                </thead>
+                <tbody>
+                    <tr>
+                        <td class="py-2 text-left text-gray-600">Events</td>
+                        <td class="py-2">{{.Lifetime.Events}}</td>
+                        <td class="py-2">{{.WithinRetention.Events}}</td>
+                    </tr>
+                    <tr>
+                        <td class="py-2 text-left text-gray-600">Deliveries</td>
+                        <td class="py-2">{{.Lifetime.Deliveries}}</td>
+                        <td class="py-2">{{.WithinRetention.Deliveries}}</td>
+                    </tr>
+                    <tr>
+                        <td class="py-2 text-left text-gray-600">Failures</td>
+                        <td class="py-2">{{.Lifetime.Failures}}</td>
+                        <td class="py-2">{{.WithinRetention.Failures}}</td>
+                    </tr>
+                </tbody>
+            </table>
+        </div>
+        <div>
+            <table class="w-full text-center text-gray-900">
+                <thead>
+                    <tr class="border-b border-gray-200 text-xs text-gray-500 uppercase tracking-wide">
+                        <th></th>
+                        <th class="py-2 font-medium">Last 10 minutes</th>
+                        <th class="py-2 font-medium">Last 24 hours</th>
+                    </tr>
+                </thead>
+                <tbody>
+                    <tr>
+                        <td class="py-2 text-left text-gray-600">Events</td>
+                        <td class="py-2">{{.Last10Minutes.Events}}</td>
+                        <td class="py-2">{{.Last24Hours.Events}}</td>
+                    </tr>
+                    <tr>
+                        <td class="py-2 text-left text-gray-600">Failures</td>
+                        <td class="py-2">{{.Last10Minutes.Failed}}</td>
+                        <td class="py-2">{{.Last24Hours.Failed}}</td>
+                    </tr>
+                    <tr>
+                        <td class="py-2 text-left text-gray-600">Failure percentage</td>
+                        <td class="py-2">{{.Last10Minutes.FailurePercent}}</td>
+                        <td class="py-2">{{.Last24Hours.FailurePercent}}</td>
+                    </tr>
+                </tbody>
+            </table>
+            <p class="mt-2 text-xs text-gray-500">Failure percentage is the failed deliveries out of all deliveries that finished in the window. Deliveries still pending or retrying are not counted.</p>
+        </div>
+    </div>
+    {{else}}
+    <div class="p-4 text-sm text-gray-500">The statistics could not be read.</div>
+    {{end}}
+</div>
+{{end}}