MM-27456: Use reflect-free serialization for hot structs (#15171)

Automatic Merge

services/cache/lru.go

@@ -8,6 +8,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/tinylib/msgp/msgp"
 	"github.com/vmihailenco/msgpack/v5"
 )
 
@@ -141,9 +143,21 @@ func (l *LRU) set(key string, value interface{}, ttl time.Duration) error {
 		expires = time.Now().Add(ttl)
 	}
 
-	buf, err := msgpack.Marshal(value)
-	if err != nil {
-		return err
+	var buf []byte
+	var err error
+
+	// We use a fast path for hot structs.
+	if msgpVal, ok := value.(msgp.Marshaler); ok {
+		buf, err = msgpVal.MarshalMsg(nil)
+		if err != nil {
+			return err
+		}
+	} else {
+		// Slow path for other structs.
+		buf, err = msgpack.Marshal(value)
+		if err != nil {
+			return err
+		}
 	}
 
 	// Check for existing item, ignoring expiry since we'd update anyway.
@@ -182,6 +196,34 @@ func (l *LRU) get(key string, value interface{}) error {
 
 		l.evictList.MoveToFront(ent)
 
+		// We use a fast path for hot structs.
+		if msgpVal, ok := value.(msgp.Unmarshaler); ok {
+			_, err := msgpVal.UnmarshalMsg(e.value)
+			return err
+		}
+
+		// This is ugly and makes the cache package aware of the model package.
+		// But this is due to 2 things.
+		// 1. The msgp package works on methods on structs rather than functions.
+		// 2. Our cache interface passes pointers to empty pointers, and not pointers
+		// to values. This is mainly how all our model structs are passed around.
+		// It might be technically possible to use values _just_ for hot structs
+		// like these and then return a pointer while returning from the cache function,
+		// but it will make the codebase inconsistent, and has some edge-cases to take care of.
+		switch v := value.(type) {
+		case **model.User:
+			var u model.User
+			_, err := u.UnmarshalMsg(e.value)
+			*v = &u
+			return err
+		case **model.Session:
+			var s model.Session
+			_, err := s.UnmarshalMsg(e.value)
+			*v = &s
+			return err
+		}
+
+		// Slow path for other structs.
 		return msgpack.Unmarshal(e.value, value)
 	}
 	return ErrKeyNotFound