public Process getProcess(String processId) throws IOException {
        if (StringUtils.isEmpty(processId)) {
            return null;
        }
        return getMetadataQueryDAO().getProcess(processId);
    }
@return all services, key is service id, value is services with different layers.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/query/MetadataQueryService.java