Re: What is Parallel DML?

From: Galen Boyer <galenboyer_at_hotpop.com>
Date: 27 Jul 2001 10:13:18 -0500
Message-ID: <uofq6tf64.fsf@verizon.net>

On Fri, 27 Jul 2001, vslabs_at_onwe.co.za wrote:

> Are you not thinking about rownum Galen? I know that does not
> like a BETWEEN clause or a GREATER THAN, but I'm sure that
> rowid can be treated like that without any problems in plain
> SQL.
Thanks, yes I was. Getting used to seeing and starting to answer that rownum FAQ/thought. Sorry for the misread.

>> How could we mimic PQ by splitting up the query ourselves into
>> 50 different queries and then running them all at the same
>> time?

>
> Why would you want to when Oracle PQ can do it for you?

Just as a test to try to understand what Oracle is doing in PQ. I bet Jonathan's book that I just bought explains it :-)

>> Could this be done and get the pretty much the same result
>> that Oracle does (Disregarding the final count, just get fifty
>> answers)?

>
> You mean perform an independant summarisation of a million rows
> at a time of a 50 million row table, resulting in 50 answers?
> Not sure what you want to achieve by this...

Just test to see how close we could get to how Oracle does it. Probably a silly idea.

> I think that you can emulate this when dealing with a table
> where you have some control over physical storage of data -
> partitioning for example. But when you deal with raw rowid's,
> it is likely going to be very difficult. You can use something
> like DBA_EXTENTS to get file id's and block numbers for the
> table in question.

Hm... Now getting to complicated. Do you think this is how PQ handles it.

-- 
Galen Boyer
It seems to me, I remember every single thing I know.

Received on Fri Jul 27 2001 - 10:13:18 CDT