PHP Session ID Duplication? [duplicate]

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Possible Duplicate:

How unique is the php session id

Can there be a duplicate PHP Session ID?

I have not had this problem, but i want to see if this could be a issue in the future.

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It is possible, but unlikely in most cases.

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If I were one of php's developers I would check wether the generated session id matches any of existing ones, and generate a new one until I get unique data. And if I saw this way, I'm sure of php developers did indeed