HTTP/2: allow unlimited number of requests in connection

[Maxim Dounin]

Hello!

On Mon, Jul 01, 2019 at 11:24:28AM +0200, Michael Würtinger wrote:

> thanks a lot for your reply. Could you please elaborate a little bit
> which memory resources need to be freed periodically? How much memory
> can be held by a connection? What's the worst case scenario?
> We are currently running it in production with http2_max_requests set
> to a value so high that the connection practically lives forever and
> so far we cannot spot any problems but maybe we're missing something?

And example of "wost case" can be seen here:

http://mailman.nginx.org/pipermail/nginx/2018-July/056525.html

Memory can be allocated from the connection memory pool.  And this 
memory have to be freed at some point - so you have to close 
the connection to do this.  And that's why number of requests in a 
particular connection is limited by default.

Whether or not memory allocations happens in your particular use 
case - doesn't really matter, especially given that things can 
change with seamingly minor configuration and/or client behaviour 
changes.

In most cases we try to limit allocations from the connection 
memory pool to a minimum, yet it is not always possible/convinient to 
completely avoid allocations from connection memory pool.  This 
allows processing of thousands of requests on a single connection 
without observable memory impact.  Likely millions will also work 
except may be in some specific use cases, yet I wouldn't recommend 
allowing that many requests, just to be on the safe side.

-- 
Maxim Dounin
http://mdounin.ru/