While executing a Search Request Synchronous or Asynchronous Execution, which should we follow?

Elastic Stack Elasticsearch
1

1.In which case we will get the Response quickly?

Ex-Like if 500 people making request at the same time

2

That will be the same.

3

But when I perform a load test on my service (500 or 100 requests at a time).sometimes the service failed with 80,250 etc times But not all the times (sometimes it gives 100% result).

Can I do anything for this?

4

I don't know. Not sure I understood the problem though. Specifically without any logs it's hard to answer.

Anyway maybe someone else can help.