snapshot of https://github.com/centrifugal/centrifugo.git (master, 2026-09-16; blobs > 131072B omitted)

internal/pgmapbroker/sampler.go

@@ -0,0 +1,73 @@
+package pgmapbroker
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/centrifugal/centrifugo/v6/internal/metrics"
+)
+
+// mapMetricsSampler periodically samples PG-specific gauge metrics: outbox
+// cursor lag per shard and partition count on the stream table.
+type mapMetricsSampler struct {
+	broker        *PostgresMapBroker
+	mu            sync.Mutex
+	cursorByShard map[int]int64
+}
+
+func newMapMetricsSampler(b *PostgresMapBroker) *mapMetricsSampler {
+	return &mapMetricsSampler{
+		broker:        b,
+		cursorByShard: make(map[int]int64),
+	}
+}
+
+func (s *mapMetricsSampler) storeCursor(shard int, cursor int64) {
+	s.mu.Lock()
+	s.cursorByShard[shard] = cursor
+	s.mu.Unlock()
+}
+
+func (s *mapMetricsSampler) sample(ctx context.Context) {
+	if metrics.MapBrokerPostgresPartitions == nil {
+		return
+	}
+	brokerName := s.broker.conf.Name
+
+	// Sample partition count on the stream table.
+	var partitionCount int
+	err := s.broker.pool.QueryRow(ctx, `
+		SELECT COUNT(*) FROM pg_inherits i
+		 JOIN pg_class c ON c.oid = i.inhparent
+		 WHERE c.relname = $1
+	`, s.broker.names.stream).Scan(&partitionCount)
+	if err == nil {
+		metrics.MapBrokerPostgresPartitions.WithLabelValues(brokerName).Set(float64(partitionCount))
+	}
+
+	// Sample cursor lag per shard.
+	s.mu.Lock()
+	cursors := make(map[int]int64, len(s.cursorByShard))
+	for k, v := range s.cursorByShard {
+		cursors[k] = v
+	}
+	s.mu.Unlock()
+	for shard, cursor := range cursors {
+		var createdAt time.Time
+		err := s.broker.pool.QueryRow(ctx, fmt.Sprintf(
+			`SELECT created_at FROM %s WHERE id = $1 LIMIT 1`,
+			s.broker.names.stream,
+		), cursor).Scan(&createdAt)
+		if err != nil {
+			metrics.MapBrokerPostgresOutboxCursorLagSeconds.WithLabelValues(brokerName, fmt.Sprintf("%d", shard)).Set(0)
+			continue
+		}
+		lag := time.Since(createdAt).Seconds()
+		if lag < 0 {
+			lag = 0
+		}
+		metrics.MapBrokerPostgresOutboxCursorLagSeconds.WithLabelValues(brokerName, fmt.Sprintf("%d", shard)).Set(lag)
+	}
+}