Implement DB batch insertion instead of one insertion per event

Use db batching when inserting events instead of one insertion per
event. This offers a much more scalable database interaction with
reduced round-trip latency.

Later on we may look into batching further across multiple `POST`
requests if batches sent by the clients are too small still.

eventrecorder/recorder.go

@@ -9,6 +9,8 @@ import (
 	"strings"
 
 	"github.com/ipfs/go-log/v2"
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
@@ -100,9 +102,8 @@ func (r *EventRecorder) handleRetrievalEvents(res http.ResponseWriter, req *http
 
 	logger = logger.With("total", len(batch.Events))
 	ctx := req.Context()
-	errs := make([]error, 0, len(batch.Events))
+	var batchQuery pgx.Batch
 	for _, event := range batch.Events {
-		// TODO: use db batching; this will not be performant at scale.
 		query := `
 		INSERT INTO retrieval_events(
 			retrieval_id,
@@ -117,7 +118,7 @@ func (r *EventRecorder) handleRetrievalEvents(res http.ResponseWriter, req *http
 		)
 		VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
 		`
-		_, err := r.db.Exec(ctx, query,
+		batchQuery.Queue(query,
 			event.RetrievalId.String(),
 			event.InstanceId,
 			event.Cid,
@@ -127,21 +128,25 @@ func (r *EventRecorder) handleRetrievalEvents(res http.ResponseWriter, req *http
 			event.EventName,
 			event.EventTime,
 			event.EventDetails,
-		)
-		if err != nil {
-			logger.Errorw("Failed to insert retrieval event", "event", event, "err", err)
-			errs = append(errs, err)
-			continue
-		}
-		logger.Debug("Saved retrieval event")
+		).Exec(func(ct pgconn.CommandTag) error {
+			rowsAffected := ct.RowsAffected()
+			switch rowsAffected {
+			case 0:
+				logger.Warnw("Retrieval event insertion did not affect any rows", "event", event, "rowsAffected", rowsAffected)
+			default:
+				logger.Debugw("Inserted event successfully", "event", event, "rowsAffected", rowsAffected)
+			}
+			return nil
+		})
 	}
-
-	if len(errs) != 0 {
+	batchResult := r.db.SendBatch(ctx, &batchQuery)
+	if err := batchResult.Close(); err != nil {
 		http.Error(res, "", http.StatusInternalServerError)
-		logger.Infow("At least one retrieval event insertion failed", "failed", len(errs))
+		logger.Infow("At least one retrieval event insertion failed", "err", err)
 		return
+	} else {
+		logger.Infow("Successfully submitted batch event insertion")
 	}
-	logger.Infow("Successfully inserted events")
 }
 
 func (r *EventRecorder) Shutdown(ctx context.Context) error {