logstash-input-azureblob plugin retrieve NSG flow log very slow

I have installed logstash-input-azureblob with logstash 5.6 and open-jdk8 in ubuntu 18. I read NSG flow log from storage account container, however, the read in logs is very slow. Sometimes, the process will get stuck and need to restart logstash to resume reading NSG flow log again. What can I do to improve the performance of NSG flow log read in? Thank you very much.