subsequence and streaming

[William Candillon]

I'm writing the following query which streams fine:
 let $raw-data as xs:string := http:send-request(<http:request
href="http://cf.zorba-xquery.com.s3.amazonaws.com/forecasts.xml"
method="GET" override-media-type="text/plain" />)[2]
 let $data := p:parse($raw-data,
<opt:options><opt:parse-external-parsed-entity
opt:skip-root-nodes="1"/></opt:options>)
 for $node in $data
 where $node/@site-id = "3"
 return
   $node

However if I write:
let $result :=
 let $raw-data as xs:string := http:send-request(<http:request
href="http://cf.zorba-xquery.com.s3.amazonaws.com/forecasts.xml"
method="GET" override-media-type="text/plain" />)[2]
 let $data := p:parse($raw-data,
<opt:options><opt:parse-external-parsed-entity
opt:skip-root-nodes="1"/></opt:options>)
 for $node in $data
 where $node/@site-id = "3"
 return
   $node
return subsequence($result, 1, 1)
The query result is extremely long to compute.

[Matthias Brantner (matthias-brantner)]

The problem is not string-streaming but related to inlining a let variable that is only used once. The problem can be reproduced using the following much smaller query:

let $result := (1 to 10000000)
return subsequence($result, 1, 1)

The plan for this query is (note materialize="true" in the LetVariable)

<flwor::FLWORIterator id="1006">
  <LetVariable name="result" materialize="true" referenced-by="1003">
    <OpToIterator id="1002">
      <SingletonIterator value="xs:integer(1)" id="1000"/>
      <SingletonIterator value="xs:integer(100000000)" id="1001"/>
    </OpToIterator>
  </LetVariable>
  <ReturnClause>
    <LetVarIterator varname="result" id="1003">
      <SingletonIterator value="xs:integer(1)" id="1004"/>
      <SingletonIterator value="xs:integer(1)" id="1005"/>
    </LetVarIterator>
  </ReturnClause>
</flwor::FLWORIterator>

I'm assigning this to Markos for further investigation.

[Chris Hillery (ceejatec)]

It seems like this may be related to bug 1204362.