suggested change

flow/activities/flowable.go

@@ -160,10 +160,39 @@ func (a *FlowableActivity) CreateNormalizedTable(
 	return conn.SetupNormalizedTables(config)
 }
 
+func (a *FlowableActivity) recordSlotSizePeriodically(
+	ctx context.Context,
+	done <-chan struct{},
+	peerName string,
+	slotInfo []*protos.SlotInfo,
+) {
+	timeout := 10 * time.Minute
+	ticker := time.NewTicker(timeout)
+
+	defer ticker.Stop()
+	for {
+		if len(slotInfo) == 0 {
+			continue
+		}
+
+		select {
+		case <-ticker.C:
+			a.CatalogMirrorMonitor.AppendSlotSizeInfo(ctx, peerName, slotInfo[0])
+		case <-done:
+			a.CatalogMirrorMonitor.AppendSlotSizeInfo(ctx, peerName, slotInfo[0])
+		}
+		ticker.Stop()
+		ticker = time.NewTicker(timeout)
+	}
+
+}
+
 // StartFlow implements StartFlow.
 func (a *FlowableActivity) StartFlow(ctx context.Context,
 	input *protos.StartFlowInput) (*model.SyncResponse, error) {
 	activity.RecordHeartbeat(ctx, "starting flow...")
+	done := make(chan struct{})
+	defer close(done)
 	conn := input.FlowConnectionConfigs
 
 	ctx = context.WithValue(ctx, shared.CDCMirrorMonitorKey, a.CatalogMirrorMonitor)
@@ -205,6 +234,16 @@ func (a *FlowableActivity) StartFlow(ctx context.Context,
 	}
 	defer connectors.CloseConnector(srcConn)
 
+	slotNameForMetrics := fmt.Sprintf("peerflow_slot_%s", input.FlowConnectionConfigs.FlowJobName)
+	if input.FlowConnectionConfigs.ReplicationSlotName != "" {
+		slotNameForMetrics = input.FlowConnectionConfigs.ReplicationSlotName
+	}
+	slotInfo, err := srcConn.GetSlotInfo(slotNameForMetrics)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get slot info: %w", err)
+	}
+
+	go a.recordSlotSizePeriodically(ctx, done, input.FlowConnectionConfigs.Source.Name, slotInfo)
 	// start a goroutine to pull records from the source
 	errGroup.Go(func() error {
 		return srcConn.PullRecords(&model.PullRecordsRequest{
@@ -222,16 +261,6 @@ func (a *FlowableActivity) StartFlow(ctx context.Context,
 		})
 	})
 
-	slotNameForMetrics := fmt.Sprintf("peerflow_slot_%s", input.FlowConnectionConfigs.FlowJobName)
-	slotInfo, err := srcConn.GetSlotInfo(slotNameForMetrics)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get slot info: %w", err)
-	}
-
-	if len(slotInfo) == 1 {
-		a.CatalogMirrorMonitor.AppendSlotSizeInfo(ctx, input.FlowConnectionConfigs.Source.Name, slotInfo[0])
-	}
-
 	hasRecords := !recordBatch.WaitAndCheckEmpty()
 	log.WithFields(log.Fields{
 		"flowName": input.FlowConnectionConfigs.FlowJobName,
@@ -339,6 +368,7 @@ func (a *FlowableActivity) StartFlow(ctx context.Context,
 
 	pushedRecordsWithCount := fmt.Sprintf("pushed %d records", numRecords)
 	activity.RecordHeartbeat(ctx, pushedRecordsWithCount)
+	done <- struct{}{}
 
 	return res, nil
 }

flow/connectors/postgres/client.go

@@ -198,6 +198,8 @@ func (c *PostgresConnector) checkSlotAndPublication(slot string, publication str
 }
 
 // GetSlotInfo gets the information about the replication slot size and LSNs
+// If slotName input is empty, all slot info rows are returned - this is for UI.
+// Else, only the row pertaining to that slotName will be returned.
 func (c *PostgresConnector) GetSlotInfo(slotName string) ([]*protos.SlotInfo, error) {
 	specificSlotClause := ""
 	if slotName != "" {

flow/connectors/utils/monitoring/monitoring.go

@@ -258,7 +258,7 @@ func (c *CatalogMirrorMonitor) AppendSlotSizeInfo(
 	_, err := c.catalogConn.Exec(ctx,
 		"INSERT INTO peerdb_stats.peer_slot_size"+
 			"(peer_name, slot_name, restart_lsn, redo_lsn, confirmed_flush_lsn, slot_size) "+
-			"VALUES($1,$2,$3,$4,$5,$6);",
+			"VALUES($1,$2,$3,$4,$5,$6) ON CONFLICT DO NOTHING;",
 		peerName,
 		slotInfo.SlotName,
 		slotInfo.RestartLSN,

nexus/catalog/migrations/V12__slot_size.sql

@@ -1,4 +1,5 @@
 CREATE TABLE IF NOT EXISTS peerdb_stats.peer_slot_size (
+    id SERIAL PRIMARY KEY,
     slot_name TEXT NOT NULL,
     peer_name TEXT NOT NULL,
     redo_lsn TEXT,
@@ -7,3 +8,5 @@ CREATE TABLE IF NOT EXISTS peerdb_stats.peer_slot_size (
     slot_size BIGINT,
     updated_at TIMESTAMP NOT NULL DEFAULT NOW()
 );
+
+CREATE INDEX index_slot_name ON peerdb_stats.peer_slot_size (slot_name);