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From hwellmann <harald.wellm...@multi-m.de>
Subject Re: How to avoid sequential scans in queries
Date Fri, 15 Oct 2010 10:43:16 GMT


Alexander Klimetschek wrote:
> 
> On Fri, Oct 15, 2010 at 12:18, hwellmann <harald.wellmann@multi-m.de>
> wrote:
>> I've started with a simple example, creating a repository with 50000
>> nodes
> 
> Are these nodes directly under one node in a flat hierarchy? Note that
> you should not have more than ~10k nodes per child node (search the
> mailing list for "flat hierarchy" for more info).
> 

It's a flat hierarchy currently, but even so there should be no need to scan
all the nodes....?



>> select * from 'nt:unstructured' where myProp = 'myValue'
> 
> This is JCR-SQL from the JCR 1.0 spec, right?
> 

It's supposed to be Query.JCR_SQL2.



> Could you try an Xpath query and compare the execution times?
> 
> //element(*, nt:unstructured)[@myProp='myValue']
> 
> 

I did, and this is extremely fast. I also tried a Query.SQL with slightly
modified syntax:

select * from nt:unstructured where myProp = 'myValue'

The XPath and SQL queries return almost instantly. I started with SQL2 since
the other query languages are marked as deprecated. 

Is there a problem with the SQL2 query engine? Should I use XPath instead?

Best regards,
Harald

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