Re: Can relational alegbra perform bulk operations?
Date: Wed, 30 Sep 2009 16:34:09 +1000
> exclusively, but my puzzlement definitely dealt with the 'if relational
> theory is supposed to help with this, then why has SQL strayed so far
> from the relational theory as understood in mathematics.')
I believe you've had a good answer in the existence of NULLs and duplicates, but I don't know that SQL is *that* far. The relational algebra doesn't cover the most common four ways to implement an inner join; implementation isn't its concern. But choice of looping, merge joins, hash joins, etc, definitely affects query performance.
Also you have to appreciate that SQL is essentially a verbal form of relational calculus. That gets translated to algebra, and progressively refined towards physical operations in the formulation of a query plan. As a calculus, it isn't going to look algebraic, as, for example, QUEL did.
>> The change was triggered in part at least by the work of Ken J McDonell >> on the MUSBUS benchmarking tools, who was able to point out the glaring >> differences in actual behaviour of the RDBMS he benchmarked.
> Thank you. I may look his works up and learn a bit about that. It does
> provide a hint (?) toward why the actual implementations is quite
> divorced from the relational theory.
I wish more of his work was still available - I heard him speak about it - but he's still around, see <http://www.kenj.com.au/>. He doesn't live that far from me, and I've thought about looking him up. Perhaps he has some archived material he'd email you?
After MUSBUS, he continued the same kind of work at Pyramid Computers, with their fantastic multi-processor MIPS machines. They had a policy of being RDBMS agnostic, but liaising with the vendors closely on performance analysis so their hardware ran every RDBMS better than competitive h/w. I wish they were still around.
-- Clifford Heath, Data Constellation, http://dataconstellation.com Agile Information Management and DesignReceived on Wed Sep 30 2009 - 08:34:09 CEST