Size for TEMP tablespace

Question

I don't know if this is a "valid" question. We have users running reports on our production system. The sometimes complain about the temp space being too small (due to their queries crashing when using too much temp space).
But I also have a feeling that you can keep throwing disks at TEMP space, and that it will never be enough.
What should the size of a database's TEMP space be - is there a rule of thumb for this ?
Dirk

Answer 1

There are several considerations that you should take into account when you try to size your temporary tablespace:
First, how much sort does you average transaction need and how many concurrent transactions does your system need to support. This number gives you a starting point for the minimum workable size for normal operations.
Now, how big is the largest table on your system and do you wish to be able to support select * from biggest order by ? Supporting an unqualified select on your largest table may not be required.
How big is the largest index in your system? It is likely that you need to have enough temp space available to recreate this index in the event of corruption without having to take special action to allocate more space to temp on a temporary basis. But having to add space in the event of a diaster might be acceptable.
Figure out what the largest sort operation you need to be able to support is and then add enough space to handle the number of concurrent average transactions that would be expected to be on the system at the same time. This is the size you should use for your temporary tablespace.
It is better to have all the space you will need for any normal and for any maintenance operation available at all time rather than trying to find additional file space to support special maintenance tasks or diaster recovery operations.
HTH -- Mark D Powell --