0.2.79 - Slow api fixes

server/internal/api/related.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"net/http"
@@ -10,6 +11,7 @@ import (
 	"github.com/ponzischeme89/memby/server/internal/emby"
 	"github.com/ponzischeme89/memby/server/internal/recommend"
 	"github.com/ponzischeme89/memby/server/internal/store"
+	"github.com/ponzischeme89/memby/server/internal/timing"
 )
 
 // fieldsRelated is the detail set. It once added Studios on its own account — the
@@ -50,7 +52,24 @@ func (s *Server) handleRelated(w http.ResponseWriter, r *http.Request, sess stor
 		return
 	}
 
-	reasons, related, err := s.recommender.RelatedTo(ctx, credentials(sess), item, relatedRowSize)
+	// Coalesced, because this route is asked for twice for the same title as a matter of
+	// course: the launcher warms it while a card is focused and the detail page asks for
+	// it again the moment somebody presses. Those two requests used to build the answer
+	// twice, and building it is the same Emby fan-out the home rows pay for.
+	body, err := s.buildCached(ctx, key, relatedTTL(s.cfg.ItemTTL),
+		func(ctx context.Context) (json.RawMessage, error) {
+			reasons, related, err := s.recommender.RelatedTo(
+				timing.WithLabel(ctx, "emby.related"), credentials(sess), item, relatedRowSize)
+			if err != nil {
+				return nil, err
+			}
+			items := nonNilRaws(recommend.Raws(related))
+			s.decorateItemRatings(ctx, items)
+			return json.Marshal(relatedResponse{
+				Reasons: nonNilStrings(reasons),
+				Items:   items,
+			})
+		})
 	if err != nil {
 		// RelatedTo degrades rather than failing, so the only error it returns is the
 		// viewer having navigated on. That is the television saving work, not a fault.
@@ -61,29 +80,20 @@ func (s *Server) handleRelated(w http.ResponseWriter, r *http.Request, sess stor
 		s.writeUpstreamError(ctx, w, err, "could not load related titles")
 		return
 	}
+	writeCached(w, false, body)
+}
 
-	items := nonNilRaws(recommend.Raws(related))
-	s.decorateItemRatings(ctx, items)
-	body, err := json.Marshal(relatedResponse{
-		Reasons: nonNilStrings(reasons),
-		Items:   items,
-	})
-	if err != nil {
-		writeError(w, http.StatusInternalServerError, "could not encode related titles")
-		return
+// relatedTTL keeps an empty carousel briefly rather than for the item lifetime: it
+// usually means something upstream was unwell, and the ten-minute answer would otherwise
+// outlive the minute of trouble that produced it.
+func relatedTTL(itemTTL time.Duration) func(json.RawMessage) time.Duration {
+	return func(body json.RawMessage) time.Duration {
+		var decoded relatedResponse
+		if json.Unmarshal(body, &decoded) == nil && len(decoded.Items) == 0 {
+			return relatedEmptyTTL
+		}
+		return itemTTL
 	}
-	// An empty carousel is cached briefly rather than for the item lifetime: it usually
-	// means something upstream was unwell, and the ten-minute answer would otherwise
-	// outlive the minute of trouble that produced it.
-	ttl := s.cfg.ItemTTL
-	if len(items) == 0 {
-		ttl = relatedEmptyTTL
-	}
-	if err := s.cache.Set(ctx, key, body, ttl); err != nil {
-		s.loggerFor(ctx).Warn("related cache write failed", "error", err)
-	}
-	w.Header().Set("X-Memby-Cache", "miss")
-	writeRaw(w, http.StatusOK, body)
 }
 
 // relatedRowSize is a carousel's worth. The strip scrolls, but a viewer who reaches the