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Subject DO NOT REPLY [Bug 53022] session is expired/removed/not found by unknown reason
Date Tue, 03 Apr 2012 02:20:59 GMT

--- Comment #7 from Leonardo Uribe <> 2012-04-03 02:20:59 UTC ---
After evaluating the probabilities, it seems to be the size of the key is
critical. Since by default sessionIdLength is 16, there are 2^128 = 3.4e38
possible combinations. So, the possible number of sessions in a single tomcat
instance and the ammount of request a tomcat instance is capable to handle in a
reasonable frame of time is much more less. The duplicate check is useless,
because it will not affect significantly the probability, but a single lookup
over a ConcurrentHashMap is cheap enough to let it (because the duplicate
should happen in a even shorter frame of time). Anyway, a simple check taking
the value returned by put() operation, could easily detect the occurrence, and
it is not necessary to do anything more than restore the old session in the
map, and throw an exception for the new one. It will be enough to prevent the
duplicate session effect at 100% and they are just some few lines of code.

Other different history will happen if the user reduce sessionIdLength, but
there is nothing to do in that case, maybe a check for a minimal
sessionIdLength is reasonable, but it is questionable because usually you want
that key be large enough to make computationally infeasible to find it by brute

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