private int getLimitNum(Optional<Integer> limitParam, MatcherSetResult parseResult) {
        String limitLabel = parseResult.getLabelMap().getOrDefault(LabelName.LIMIT.getLabel(), "100");
        int limitNum = Integer.parseInt(limitLabel);
        if (limitParam.isPresent()) {
            limitNum = Integer.min(limitParam.get(), Integer.parseInt(limitLabel));
        }
        return limitNum;
    }
OAP adopt time step by start/end,
reserve step/timeout param to keep consistent with API protocol.
oap-server/server-query-plugin/promql-plugin/src/main/java/org/apache/skywalking/oap/query/promql/handler/PromQLApiHandler.java