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From Daniel Noll <dan...@nuix.com.au>
Subject Re: "generated by default" question
Date Fri, 16 Jun 2006 01:52:58 GMT
Michael Segel wrote:
>> Presumably he column would be indexed if you're doing operations like
>> max() on it anyway, so efficiency isn't the problem.  I suspect the
>> problem would be what to do when two users tried to insert rows at
>> around the same time.  The second would fail to commit the transaction
>> and have to try again.
>> Daniel
> No.
> First, you're still returning a value from the sequence that will cause an 
> exception.  So  you have overhead. Also you'd have a lot harder time trying 
> to manage the inserts. Also, you have to consider that its cheaper to get a 
> value from memory than it is to apply the max() function on a value from the 
> index.

Ah.  I was making the assumption that the indexes were implemented 
"properly."  For instance, an index should keep a certain amount in 
memory in order to have a reasonable chance of running quickly.  So the 
max and min should already be in-memory.

I take it that Derby doesn't do this?


Daniel Noll

Nuix Pty Ltd
Suite 79, 89 Jones St, Ultimo NSW 2007, Australia    Ph: +61 2 9280 0699
Web: http://www.nuix.com.au/                        Fax: +61 2 9212 6902

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