Re: Convert SAP Oracle Database to IBM DB2 Database??

From: Serge Rielau <srielau_at_ca.ibm.com>
Date: Fri, 08 Feb 2008 07:51:18 -0500
Message-ID: <6131igF1tkikoU1@mid.individual.net>

Mark Townsend wrote:
>

>>>
>>> What I'm saying is that it is not just superficial ... from a 
>>> technical point-of-view it is mostly incorrect. He needs to learn how 
>>> to read the
>>> on-line docs.
>> Well the nice thing about BLOGs is the ability to give feedback.
>> You are a teacher, no? Teach!
>>
>> Cheers
>> Serge

>
> Eaton's blog is basically correct. However he mentions the negatives of
> the Oracle design, and does not mention the advantages. The greatest
> advantage of having the symbol table local to the page is that you do
> not have to do another I/O to read the symbol table - the single block
> I/O gets the compressed data and the symbols required to uncompress it.
> Our testing in large scale environments shows that to me more beneficial
> than the IBM design.

The compression dictionary is part of the table's meta-data, thus it is cached. There is no I/O after the first touch.

> There are also additional benefits accrued from not
> having to expand a single symbol table when the data values grow, etc.
That works both way. Harms vs. benefit depend on the distribution of the data. If data values are highly localized, then having local dictionaries can be helpful. Otherwise they inevitably also cause a great deal of repetition.

> So it's horses for courses. We just think our horses are better. YMMV,
> and as always, test well.

Amen, and that's what keeps our jobs interesting.

Cheers
Serge

-- 
Serge Rielau
DB2 Solutions Development
IBM Toronto Lab

Received on Fri Feb 08 2008 - 06:51:18 CST