I'm trying to debug a reverse proxy which occasionally takes longer than usual time to serve a client. I can see in the logs e.g. that the request took 10 times the usual amount of time for similar file, however I can't say whether it was caused by the origin side or client side (i.e. was the issue when retrieving content from origin or serving it to client).

Is there any way to get more detailed logs for response time? I'm looking at 'ttms' value, is there any log to indicate "origin connection time", "time between sending request to origin and finishing reading response", "time between starting and finishing serving response to client" etc. That would help with optimizing...

If there is nothing in the logs, maybe there is some useful statistic I should look into?