Return early if push payload does not contain data (#5229)

Optimize for:

* payload does not contain any streams
* a stream does not contain any entries
* none of the streams contain any entries

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

pkg/distributor/distributor.go

@@ -222,18 +222,28 @@ func (d *Distributor) Push(ctx context.Context, req *logproto.PushRequest) (*log
 		return nil, err
 	}
 
+	// Return early if request does not contain any streams
+	if len(req.Streams) == 0 {
+		return &logproto.PushResponse{}, nil
+	}
+
 	// First we flatten out the request into a list of samples.
 	// We use the heuristic of 1 sample per TS to size the array.
 	// We also work out the hash value at the same time.
 	streams := make([]streamTracker, 0, len(req.Streams))
 	keys := make([]uint32, 0, len(req.Streams))
-	var validationErr error
 	validatedSamplesSize := 0
 	validatedSamplesCount := 0
 
+	var validationErr error
 	validationContext := d.validator.getValidationContextForTime(time.Now(), userID)
 
 	for _, stream := range req.Streams {
+		// Return early if stream does not contain any entries
+		if len(stream.Entries) == 0 {
+			continue
+		}
+
 		// Truncate first so subsequent steps have consistent line lengths
 		d.truncateLines(validationContext, &stream)
 
@@ -262,16 +272,11 @@ func (d *Distributor) Push(ctx context.Context, req *logproto.PushRequest) (*log
 		}
 		stream.Entries = stream.Entries[:n]
 
-		if len(stream.Entries) == 0 {
-			continue
-		}
-
 		keys = append(keys, util.TokenFor(userID, stream.Labels))
-		streams = append(streams, streamTracker{
-			stream: stream,
-		})
+		streams = append(streams, streamTracker{stream: stream})
 	}
 
+	// Return early if none of the streams contained entries
 	if len(streams) == 0 {
 		return &logproto.PushResponse{}, validationErr
 	}