app/vlinsert/opentelemetry: explicitly clear references to the underlying byte slice before returning logstorage.Fields to the pool

This is yet another attempt to fix the increased memory usage at VictoriaLogs v1.40.0.

The previous attempt at 8997983 was unsuccessful.
See #869 (comment)

Author: valyala

app/vlinsert/opentelemetry/pb.go

@@ -54,7 +54,14 @@ func decodeResourceLogs(src []byte, pushLogs pushLogsHandler) (err error) {
 	defer putFmtBuffer(fb)
 
 	fs := logstorage.GetFields()
-	defer logstorage.PutFields(fs)
+	defer func() {
+		// Manually clear all the fields up to capacity in order to remove references to src and help GC freeing up the used memory.
+		// The logstorage.PutFields() clears only the references up to len(fs.Fields).
+		clear(fs.Fields[:cap(fs.Fields)])
+		fs.Fields = fs.Fields[:0]
+
+		logstorage.PutFields(fs)
+	}()
 
 	// Decode resource
 	resourceData, ok, err := easyproto.GetMessageData(src, 1)
@@ -88,9 +95,7 @@ func decodeResourceLogs(src []byte, pushLogs pushLogsHandler) (err error) {
 				return fmt.Errorf("cannot decode ScopeLogs: %w", err)
 			}
 
-			clear(fs.Fields[streamFieldsLen:])
 			fs.Fields = fs.Fields[:streamFieldsLen]
-
 			fb.buf = fb.buf[:fbLen]
 		}
 	}
@@ -175,13 +180,10 @@ func decodeScopeLogs(src []byte, fs *logstorage.Fields, fb *fmtBuffer, pushLogs
 				pushLogs(timestamp, fs.Fields, streamFieldsLen+1)
 
 				// Return back common fields to their places before the next iteration
-				fieldsLen := len(fs.Fields)
 				fs.Fields = append(fs.Fields[:streamFieldsLen], fs.Fields[streamFieldsLen+1:commonFieldsLen+1]...)
-				clear(fs.Fields[commonFieldsLen:fieldsLen])
 			} else {
 				pushLogs(timestamp, fs.Fields, streamFieldsLen)
 
-				clear(fs.Fields[commonFieldsLen:])
 				fs.Fields = fs.Fields[:commonFieldsLen]
 			}