Re: Monitoring parallelism

Rick Denoire <100.17706_at_germanynet.de> wrote in message news:<peu2muk9g5eu5jg95ghordebsc67bk1k6f_at_4ax.com>...
> afilonov_at_yahoo.com (Alex Filonov) wrote:
>
>
> >If you are using 8i, you also need to set
> >optimizer_percent_parallel to something greater than 0. You can do it in init.ora
> >or at a session level. It's also a good idea to increase hash_area_size to 8M at
> >least (Oracle recommended value).
>
> OK, I will try that. Does this parameter have an influence on Oracle's
> tendence to do full table scans? It seems that when parallelizing
> things, Oracle will more likely do full table scans - bad.

Full table scans are not always bad.
As far as I understand, parallel query is good for full table scans only.
I don't know if Oracle can actually parallelize anything but full table scans.
If you can have reasonably good execution plan using indexes, there is no place for parallel query in it. The whole idea of parallel query is to read and filter rows from huge table in parallel. I mean huge, 100M at least.

>
> >Table should be created or altered to use parallel query. Or you can hint your
> >query to use parallel query. Hints work on base tables only, they don't work on
> >views (at least with 7.3.3, 8.0, 8.1, don't know about 9 yet).
>
> As I wrote in other parts of this thread, I found out that it is
> enough to parallelize tables to get things done in parallel, without
> changing any init.ora parameter.
>

What version of server do you have? init.ora parameters are different in different versions.

> If I use PARALLEL_AUTOMATIC_TUNING, should then the degree of
> parallelism for the particular table be set to default? (Since it
> should work *automatically*). I could not really understand the
> meaning of the default degree of parallelism for a table.
Received on Tue Aug 20 2002 - 10:57:37 CDT