Hi,

We have a doctype with an index defined over three fields (obra, par and posPar). The following XQuery
for $a in input()/A
where $a/obra=398 and $a/par=557 and $a/posPar>=2
return $a

is very slow, while this one:
for $a in input()/A
where $a/obra=398 and $a/par=557 and $a/posPar = (2, 3, 4, 5, 6, 7, 8, 9)
return $a

is executed inmediately.

The problem is the “>” operand (or “>=” or “ge”) What’s the correct way to write the first XQuery?

Thanks in advance?

Hi Pau,
A few extra info’s would be interesting:

1. what datatype and indextype has posPar ?

• is there an index ?

2. how many instances are there with values beyond 9 ?

• is the bulk of of hits > 9 then the explanation would be obvious

regards
Finn

Hi Finn,

1. what datatype and indextype has posPar ?
   The datatype is xs:integer and the indextype is standard

• is there an index ? Yes.

2. how many instances are there with values beyond 9? There are 8 (2, 3, 4, 5, 6, 7, 8 and 9)

The result set should be the same. I don’t understand this extremely slow behavior for “the same” XQuery…

regards,

Hi Pau,
So you mean there are no posPar values higher than 9 ?
What does the “explain” says about indexUsage ?

Finn

Hi Finn,

Yes, there are no posPar values higher than 9.

The “explain” says the same about indexUsage for both XQueries. I paste here the response:

• <ino:response xmlns:ino=“http://namespaces.softwareag.com/tamino/response2” xmlns:xql=“XQL FAQ (XML Query Language - Frequently Asked Questions)”>
• <xq:query xmlns:xq=“http://namespaces.softwareag.com/tamino/XQuery/result”>
• <![CDATA[

{?explain ?}
for $a in input()/A
where $a/obra=398 and $a/par=557 and $a/posPar lt 9
return $a

]]>
</xq:query>

• <xq:explanation mode=“optimizer” xmlns:xq=“http://namespaces.softwareag.com/tamino/XQuery/result”>
• <ino:message ino:returnvalue=“0”>
  ino:messagelineXQuery Explain Request processed</ino:messageline>
  </ino:message>
  </ino:response>

Thanks in advance,

Hi Pau,
May I recommend that you use the XQUERY tool which does a translation of the explain output into a more readable format
Finn

Hi Finn,

The “Explain Query” of the XQuery tool answers this:

"
This query compiles successfully.

This query will perform an index scan (details unknown).

The analyzed query:
{?explain?}
for $a in input()/Locali
where $a/obra=398 and $a/par=557 and $a/posPar = 2
return $a
"

And the “Response” tab shows the same message than the Interactive Interface.

regards,

Hi Pau,

• then I’m beginning to run out of suggestions !

How many hits do you get/want ?

• Have you tried specifying a position filter to see if this show the same difference in execution time ?

Finn

(for $a in input()/A
where $a/obra=398 and $a/par=557 and $a/posPar>=2
return $a ) [position() < 10 ]

Hi Finn,

I found another XQuery which executes efficiently. I just separated the criteria into two pieces. In one hand, the “equals” comparison, and in the other hand the “less than or equals” comparison. Just like this:

for $a in input()/A [posPar <= 9]
where $a/obra=398 and $a/par=557
return $a

I don’t know why Tamino likes this one but not the other one. But it works.

Thanks for your attention,

Best regards.