Optimal size for TEMP tablespace tempfiles

Question

Hi all,
I've rumaged through Oracle documentation on the above topic but can't find the answer I'm seeking:
How do you determine the optimal size for your tempfiles? Are there rules to guide one in this area? For example for a 50G database, how do you determine if it's 2G, 3G or 4G that's best for the database? What about a 500G database?
Anwers will be appreciated.
Regards

Answer 1

It's the size of the sets, as you say. And in a data warehouse, the data sets can be very large. I'd say that in an OLTP database, then the useage of temp would (should) be low; but in a data warehouse, all bets are off: one-off end of month runs; director wants a monolithic report running; all that sort of DWH-related type of processing, which, by its nature, happens all the time. Similarly, a large number of users (e.g. users of, say, a Third Party BI tool) amy lead to lots of big sorts, owing to the ad hoc nature of their queries. Standard DWH stuff.
I don't often see tiddly-widdly bits of SQL in data warehouses, like your SELECT COUNT(*) FROM tab$ example. It could be done, sure, but more likely will be bit, fat queries, which a DWH is designed to deal with. And a lot of temp may be required.
From that 6-years old (but relevant) article (my emphasis): "For example, if you join two *large* tables, and Oracle cannot do the sort in memory (see SORT_AREA_SIZE initialisation parameter), *space will be allocated in a temporary tablespace for doing the sort operation*."
Regards - Don Lewis