Occupancy of SSL connections?

Edward Hibbert Edward.Hibbert at metaswitch.com
Mon Nov 9 20:34:12 MSK 2009

Sorry, typo.   "takes about 1GB for 10L connections" should have read "takes about 1GB for 10K connections", i.e. almost an order of magnitude more than without SSL.

-----Original Message-----
From: Edward Hibbert 
Sent: 09 November 2009 17:29
To: 'nginx at sysoev.ru'
Cc: 'Leo P.'
Subject: Occupancy of SSL connections?

Has anyone done any measurement of SSL occupancy with NGINX, both for the existance of an SSL connection and for an outstanding request?  

I'm doing development on COMET polls, where a GET request is outstanding in the server for a long period.  This is using Leo's module (http://github.com/slact/nginx_http_push_module).

For HTTP connections, I can get about 20K connections and outstanding requests in 116MB, which is pretty respectable.

However with HTTPS, what I see is that:
- having the connection open takes 261MB for about 16K connections
- having the connection open with an outstanding request takes about 1GB for 10L connections.

So the occupancy hit for an outstanding HTTPS request is much higher than for HTTP. I'd be surprised if the extra occupancy is in Leo's module, because I'd expect that to be isolated from whether the connection is SSL or not.  

I don't have 100% confidence in these numbers, but they should be roughly right.  Can anyone think of why an outstanding request might consume a lot of memory in HTTPS compared to HTTP?  Has anyone done anything similar?



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