Re: [MonetDB-users] SQL exception during query resolving. Slow join? How to submit external variables?

27 Nov 2007

      Hi Huib,

to reproduce and investigate your problems, it would be very helpful for us
if you could provide us with (access to) (scaled-down versions of) your
documents (how big are they originally?) on which the problems (still) occur
for you.

Stefan

On Tue, Nov 27, 2007 at 10:53:43AM +0100, Huib Verweij wrote:
...
Hi everyone,
I'm new to MonetDB XQuery and have written a crude Cocoon generator for 
MonetDB using the example code for the JDBC client from the website.
I am using the latest Bug Fix Release of MonetDB as announced by Sjoerd 
Mullender on 24-10-2007. When I execute the following query I get an error:
---------------------------------------------------------
let $zz := doc('vogels.xml')//Vogels[data(Dwaalgast) = 'zeer zeldzaam']
return <vogeltjes>{$zz}</vogeltjes>
---------------------------------------------------------
throws:
java.sql.SQLException: ERROR:
ERROR: XML Generation: NULL BAT has a 4415 head, but tail is NULL.
ERROR:
ERROR: xquery_print_result_loop: operation failed.
However, when I change the XQuery to:
---------------------------------------------------------
let $zz := doc('vogels.xml')//Vogels[data(Dwaalgast) = 'zeer zeldzaam']
return <vogeltjes>{$zz}azaz</vogeltjes>
---------------------------------------------------------
everything's OK and I get the proper result. (The previous release threw 
the same error btw.)
Also, when I join the results from the above query with another table to 
resolve some codes to code-descriptions, the query takes from 8.5 up to 
11 seconds to execute, vs. <1 second for a query without the join. The 
result is a little over 1Mb in size. The query I use is this:
---------------------------------------------------------
let $zz := doc('vogels.xml')//Vogels[Ecotoop_x0020_nest]
return <vogeltjes>
        {for $vogel in doc('vogels.xml')//Vogels[Ecotoop_x0020_nest],
                $vc in 
doc('vogels-code.xml')//Vogels-code[data(Kolomnaam) = 'Ecotoop 
nest'][data(Code) = $vogel/Ecotoop_x0020_nest]/Codebeschrijving
                   return <vogel>
                               {$vogel/*}
                               {$vc}
                          </vogel>
        }
      </vogeltjes>
---------------------------------------------------------
The latest preview release of eXist handles the join in 3.1 seconds, any 
ideas on why this join takes almost three times as long?
I have a final question: how do I specify external variables using the 
JDBC client?
Regards,
Huib Verweij.
-- 
| Dr. Stefan Manegold | mailto:Stefan.Manegold@cwi.nl |
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