[xquery-talk] Re: The State of Native XML databases
john.snelson at oracle.com
Wed Aug 22 00:09:17 PDT 2007
Neither of us can really argue authoritatively about this without hard
timings - but I want to point out that 10000 date strings probably have
to come from 10000 nodes, and my money is on getting the nodes being the
Casts don't even make the radar on profiles of Berkeley DB XML, partly
because using the correct index avoids them, but also because parsing an
xs:date doesn't involve IO.
Jeff Dexter wrote:
> Parsing a date string, no, parsing 10,000 date strings, quite possibly. I
> would strongly suggest to query authors out there that if strong typing is
> available in the product they use that, for the sake of performance and to
> avoid runtime casting errors, they use it.
> That's not to say they have to, and in fact many use cases, such as querying
> streaming sources, are often forced to use weak typing, and it works quite
> well for those cases. Nonetheless the more up-front knowledge an engine has
> in regard to what it's querying and the types of the nodes involved the
> better it should perform, especially when using types like date, double,
> -----Original Message-----
> From: talk-bounces at x-query.com [mailto:talk-bounces at x-query.com] On Behalf
> Of John Snelson
> Sent: Tuesday, August 21, 2007 5:32 AM
> To: Andrew Welch
> Cc: talk at xquery.com
> Subject: Re: [xquery-talk] Re: The State of Native XML databases
> Andrew Welch wrote:
>> But it can only do any of those things if you tell it that the String
>> '2007-08-21' is a date, and not just a String?
>> Giving <date>2007-08-21</date> to the database can't be enough...
> Sure, that's why XSLT and XQuery allow you to cast values - there are even
> special rules that automatically cast values from an untyped XML document
> which make life easier in that case.
>> The way I was reading this thread was that if the type information was
>> stored in the database, the cost of creating the xs:date would be
>> incurred once and not once per query that uses the value?
> That's possible, but not mandatory. Besides, parsing a date string is
> probably not going to be the bottleneck in a well designed XML database.
> talk at x-query.com
> talk at x-query.com
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