Performance comparison of using django signed cookie session over django db + cache based session?

Question

Django 1.4 offers several ways to maintain django sessions :

My viewpoint on using :

i) cache only : Not preferable, users sessions may get purged out of memcache.

ii) Db + cache (cached_db): Preferable , simple and secure solution.

iii) Signed cookie sessions : Preferable, no database hit .

Assuming that the session data is very small i.e. no problem in storing it in cookie. Is there any performance benefit of using signed cookie over a database + memcache driven session engine ? As for N concurrent new users, there would be order of N database hits saved. This will reduce total queries that the database server has to handle per unit time.

UPDATE : We found redis or aerospike as really robust and high throughput session backends for django. We are using redis as sessions backend

Answer 1

You must be able to handle N concurrent queries (N - concurrent new users).

You see the difference at a very large scale only. You must be pessimist (server is down, bad buckup, amazon bancrupcy ) and your database must be able to handle all users in rush hours.

• 10 000 000 users with cookie session will cost you 0$ extra, problems with iframes and mobiles
• 10 000 000 users with cache session will cost you hundreds or less than hundred of dollars daily, lost sessions in case of restart
• 10 000 000 users with cache_db session will cost you thousands of dollars daily (any persistent storage able to handle 1 000 000 hits in one time, 10% of users)

I use redis backend (periodic save to disk) with the possibility of switching to a cluster of memcached services.

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