What's faster? BEGIN ... EXCEPTION or CREATE TEMP TABLE IF NOT EXISTS?

For this, I need to store a couple of temporary session variables such as the ID of the user performing the change, which can be set at the start of the session.

Until now I have been using a permanent table to store the session variables, but it has been difficult to wipe the data properly at the end of the session.

So I have decided to try to implement them using temporary tables. 

The problem now is that for every row now, I need to check for the existence of the temporary table before I access it, in order to avoid exceptions.

Either I can do all such accesses within a BEGIN...EXCEPTION block, or I can precede any such accesses with CREATE TEMP TABLE IF NOT EXISTS.

Is one of these much faster than the other? Will I be slowing things down inordinately by doing this for every row?

Thanks.
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