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Date: Wed, 12 Nov 2008 03:38:59 -0800 (PST)
From: Reda134 <reda134@gmail.com>
To: derby-user@db.apache.org
Subject: Re: Derby optimizer for Table Function
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References: <20456636.post@talk.nabble.com> <wjo8fxlx2pfx.fsf@sun.com>


Thank you very much for your reply:)

Can you please explain me what derby developpers mean exactly with
"repeatable table functions" and "read once Streams" ? 

Many thanks in advance. 
 

Knut Anders Hatlen wrote:
> 
> Reda134 <reda134@gmail.com> writes:
> 
>> Hi all, 
>> The Derby devoloppers mentions in the documentation of table functions,
>> that
>> the optimizer takes 2 Assumtions : 
>>
>> 1 - It Assumes by default that table functions are repeatable and thus
>> place
>> them in the inner slot of a join.
>>
>> 2 -  It Assumes by default that table functions are expensice and thus
>> place
>> them in the outer slot of a join.
>>
>> Is this not paradoxal ?? Or i get it wrong ??
> 
> I assume you're talking about this section of the developer's guide:
> http://db.apache.org/derby/docs/10.4/devguide/cdevspecialtfoptimizer.html
> 
> The clue here is that it doesn't say "thus place them in the
> [outer/inner] slot", but rather that it is _likely_ that the optimizer
> will place the table function in an outer slot and that the optimizer
> _can_ place it in an inner slot. If you for example join two table
> functions, only one of them can be in the outer slot. The other one will
> go in the inner slot. If none of them can go in the inner slot because
> they are not repeatable, one of them will be stored in a temporary table
> which can go in the inner slot.
> 
> -- 
> Knut Anders
> 
> 

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