Updating session id based on accesstimeout

Hi,

I want to set a session id based on a session timeout per user. I have a very large logfile with more than 1.3 Mio records and look for a very efficient solution - maybe with PL/pgSQL .

The important columns in the table are: access timestamp and userid sorted by userid and access time.
The logic for the session id is: when ever the userid changes or the time between two following records is greater than 60 sec create a new session id and update the record with this id.

I tried to solve this problem with Perl and the DBI interface - but it took about 12 hours to update all records.
The fastes solution I found until now was not to use any data base, sort the data with the unix command sort and process the logfile text directly with perl.

Thanks in advance!

Andreas