How much temp / sort space is reasonable for a medium-large reporting db?

Question

I have 16G which is not enough for a user running a distcint against a complexly written view and it is the only query running at the time. About 500K rows returned from the base view. which is then joined to an additional table(14 rows). The view runs against 2 tables and 3 other views, it also use case statements and aggregate functions. The user who had written the base view is query savy, don't know that it could be improved. Could possisbly benefit from some index tuning... Thoughts? How much sort space is enough? Are there general guidelines? small 1G/ medium 8G / large 16/32G...

Answer 1

Ummmm
It kinda depends on how much sorting you need to do. Sorting comes from
- select: order by, group by
- select: distinct
- select: union (not union all)
- sort-merge joins
And it also depends on how effective is your PGA management and whether you use PGA_AGGREGATE_TARGET to your advantage. And whether you starve the PGA (aggregate) on the machine.
As a general rule of thumb, I'd start with sum of all (PGA_AGGREGATE_TARGET + SGA) at 95% of machine (or less if needed to allow 250M RAM for operating system), set PGA_AGGREGATE_TARGET to 40% of that figure and set TEMP tablespace size to 3x the PGA_AGGREGATE_TARGET.
Of course, every Rule of Thumb has assumptions, and if the assumptions are not valid, the Rule Of Thumb degenerates to plain ROT. Therefore the assumptions need to be validated (continuously) by using the methods shown at http://download-east.oracle.com/docs/cd/B19306_01/server.102/b14211/memory.htm#sthref668
Basically that means resize the PGA_AGGREGATE_TARGET to get 85% of all sorting "in memory or 1-pass", and resize the TEMP tablespace accordingly.
My analogy for your question: Can you tell me how big a snow shovel I should get for a small, medium or large yard? You would probably say "it depends on the amount of snow fall".