Experience with parallel query option

I have played around a little bit with the parallel query option of ORACLE 7.1.4.
I found out that for short queries there is a performance decrease when using the parallel queries. This seems logical as there must be some overhead for splitting the query over several processors.

The query I used was very simple:

        select count(*) from table,table;

I used table,table in order to get the cartesian product. This allowed me to have a big result set without having to have very big tables. I executed this query and then I gradually incremented the number of rows in table. In SQL*PLUS with "set timing on" I measured the times once without parallel once with parallel (degree 2 as my server has 2 processors). To change to parallel I used "alter table table parallel (degree 2)".

As I said before at the beginning the queries were faster without the parallel query option. From the approx. count(*)=12000000 on, the parallel query started to be faster than the normal one.

Questions:

1. Does this suggest that the parallel option is only useful for huge queries (very many rows or long running queries)?
2. Is it useful to set the degree to a value higher than the number of processors on the server?
3. Has anyone made other experiences with this option?
4. Was this the correct way of testing the option?

Thanx for any comments Received on Tue Apr 11 1995 - 00:00:00 CEST