python - What is the "soft private memory limit" in GAE?

Question

A user of my application attempted to send a file as an email attachment using my application. However, doing so raised the following exception which I'm having trouble deciphering

Exceeded soft private memory limit with 192.023 MB after servicing 
2762 requests total

While handling this request, the process that handled this request was
found to be using too much memory and was terminated. This is likely to
cause a new process to be used for the next request to your application.

If you see this message frequently, you may have a memory leak in 
your application.

What is the "soft private memory limit" and what was likely to bring about this exception?

Answer 1

Waitting for answers