Performance critical technical key

Hi folks

I'm designing a table to be used for web session management. If all
goes well with the project, the table should have 100,000+ records and
be getting hammered with SELECTS, INSERTS and UPDATES.

The table will need a technical key. The question is, what is the most
efficient way to do this?

a) Generate a random 24 character string in the application. Very
quick for the INSERTs, but will the longer key slow down the the
SELECTs and UPDATES?

b) Use a sequence. Faster for the SELECTS and UPDATES, I guess, but
how much will the sequence slow down the INSERTS on a medium sized
record-set?

There will probably be 6-8 SELECTs & UPDATEs for each INSERT.

I appreciate that I could set up some tests, but I am under the hammer
time-wise. Some rule-of-thumb advice from the list would be most
welcome.

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Geoff Caplan
Vario Software Ltd
(+44) 121-515 1154