Re: Several CPUs and the parallel option

Hi Rick,

Just to add to what Sybrand has said.

For the novice, I would strongly recommend setting the parallel_automatic_tuning parameter to true. This sets other parameters to appropriate values and allows Oracle to automatically set appropriate parallel process depending on load.

As you become more experienced, you can tweak things if required.

The other thing to note is that tables and the such by default have the parallel clause set to noparallel (check degree in dba_tables). You might wish to change the default degree on specific tables (just supplying parallel is again recommended for the novice) else supply the appropriate parallel option or hint as required.

As Sybrand has noted not much point having (say) 8 people digging a hole if they've only got the one shovel to use. Appropriate data distribution, use of partitions etc. is essential to maximise parallel effectiveness.

Good Luck

Richard
"Sybrand Bakker" <postbus_at_sybrandb.demon.nl> wrote in message news:pch7ku4b4e1c6bgj1vbl2i0q2qb3n177q9_at_4ax.com...
> On Sun, 28 Jul 2002 12:09:56 +0200, Rick Denoire
> <100.17706_at_germanynet.de> wrote:
>
> >Hello
> >
> >Put simple, I would like a data mining application to take advantage
> >of the four CPUs of our E3500 (Solaris 2.7, Oracle 8.1.7 Enterprise
> >Edition). When it runs, it only uses effectively one CPU (which is
> >being switched of course). I assume that when using the parallel
> >feature of Oracle, it will then be possible to use several CPUs for
> >one and the same job.
> >
> >When I start instance, I get a message "...with the parallel option".
> >But when I set the parallel option on in the init.ora file, the
> >instance won't start.
> >
> >Is this a question of an additional installation that has not yet been
> >done? If so, what is the name of the missing software package?
> >We should have no license problems.
> >
> >If I finally get the instance started with the parallel option set to
> >true, will Oracle more or less automatically parallelize something?
> >Or are any changes in the application itself (PL/SQL) needed to
> >achieve parallelism?
> >
> >According to your experience, if changes in the application are
> >needed, are they usually complicated to code? And in general, what are
> >the chances that the parallel option will accelerate execution
> >proportionally to the number of CPUs?
> >
> >I do not expect a "lecture" about parallelism in Oracle, but since I
> >am complete unexperienced in this question, any hints will be
> >appreciated, before I go for it. Collegues are blaming me for being
> >unable to use the whole power of the server...
> >
> >Thanks
> >Rick
>
> When posting at least try not to make this a riddle game.
> 'When I set the parallel option on in init.ora' --> which parameters
> do you set
> 'The instance won't start' : any error message?
> Do you think people here can help you when you don't post the error
> message. Or should one just guess what is going on on that server?
>
> >Is this a question of an additional installation that has not yet been
> >done? If so, what is the name of the missing software package?
> >We should have no license problems.
> Select * from v$option will tell you all the options which are
> installed and not installed.
> Yes, it is possible to run Enterprise edition without the Parallel
> Query option installed (might also be called Parallel Execution now),
> but it should be very easy for you to find out what has been
> installed.
>
> >If I finally get the instance started with the parallel option set to
> >true, will Oracle more or less automatically parallelize something?
> If you set parallel_min_servers and parallel_max_servers,and
> especially parallel_min_percent and parallel_max_percent and other
> parallel parameters (just look them up in init.ora) : Yes.
> Please note: if you are not using CBO, you likely are going to create
> havoc. Using any parallel option will automatically turn on CBO. If
> you don't have analyzed your tables you are up for disaster.
>
> Please also note: Because you are using parallelism using FTS is now
> considered <number of CPUs> times *cheaper*
>
> >appreciated, before I go for it. Collegues are blaming me for being
> >unable to use the whole power of the server...
> Your colleagues seem to consider parallel query as a panacea for all
> their tuning problems. Just turn on parallel query, and discover this
> is not true. You might even see a decrease in performance.
> Generally speaking parallel query is useless if your data is not being
> striped across <number of CPUs> disks. Having 4 parallel query slaves
> hit the same disk will definitely not help.
>
>
> Hth
>
>
> Sybrand Bakker, Senior Oracle DBA
>
> To reply remove -verwijderdit from my e-mail address
Received on Sun Jul 28 2002 - 20:30:37 CDT