db-jdo-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Jörg von Frantzius <joerg.von.frantz...@artnology.com>
Subject Re: [Fwd: last issue with completeness test]
Date Thu, 20 Apr 2006 12:40:36 GMT
Hello Craig,

I think that if we have includeSubclasses==true that the WHERE clause 
generated by JPOX will OR all possible values of the discriminator 
column. Won't that also be sped up by an index on the discriminator column?

Regards,
Jörg

Craig L Russell schrieb:
> Hi Jörg,
>
> Just to be clear: this improves performance only in the case that you 
> know what specific class you are looking for (you have a relationship 
> to a specific most-derived subclass) and there is not another more 
> appropriate index to optimize on. So it's worthless in the generic 
> query use case because there will typically be a more restrictive 
> index, and of little value in the navigation case because you are 
> joining on a foreign key anyway. So it's only useful for a table scan 
> of a most-derived subclass or superclass Extent with 
> includeSubclasses==false.
>
> This came out more harshly than I thought it would when I started. Is 
> there a good use case for indexing the discriminator column?
>
> Regards,
>
> Craig
>
> On Apr 18, 2006, at 9:22 AM, Jörg von Frantzius wrote:
>
>> Craig Russell schrieb:
>>> Hi Erik,
>>>
>>> It's probably not related to the problem, but why do you declare an
>>> index defined on the discriminator columns in the metadata?
>>>   
>> Yes I'm not Erik but still: in our production system we do that to 
>> increase performance of queries. We'd even like to have that by default.


Mime
  • Unnamed multipart/mixed (inline, None, 0 bytes)
View raw message