Re: Dreaming About Redesigning SQL

Bob Badour wrote:

>"Lauri Pietarinen" <lauri.pietarinen@atbusiness.com> wrote in message
>news:bn3tve$qln$1@nyytiset.pp.htv.fi...
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>>Bob Badour wrote:
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>>>"Lauri Pietarinen" <lauri.pietarinen@atbusiness.com> wrote in message
>>>news:3F94BCBB.7030001@atbusiness.com...
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>>>>I could now denormalise OrderDetail so that it contains cust_id also
>>>>and cluster by cust_id
>>>>(might cause you trouble down the road, if you can change the customer
>>>>of an order), in which case, with 3 I/O's I would get
>>>>- 8 customer rows
>>>>- 16 order rows
>>>>- 24 order detail rows (which would all apply to one customer)
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>>>>
>>>Depending on block size, by clustering the three tables together, one
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>might
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>>>get all of those rows for a single read potentially improving on Wol's
>>>numbers by a factor of eight or more for this one query. Of course, doing
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>so
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>>>would increase the cost of a table scan on the customer table.
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>>Which DBMS'es support clustering of mutiple tables except for Oracle?
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>I don't know. Why would it matter?
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Just curious...

>>Is this feature really used any more?
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>If one has a hard performance requirement that only clustering can meet, one
>will use it.
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OK

>>I thought it was more trouble than worth.
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>All physical structures will bias performance for some operations and
>against others. In general, increasing the cost of customer scans will be
>sufficiently unpleasant to make clustering customers with orders
>undesirable. However, if one chooses to consider only one physical
>arrangement and one operations, as Wol is wont to do, I observe we can
>outperform his product by a factor of eight.
>
OK, right...

Lauri