Performance problems upgrading from 2.3.10 to 2.4.11

Question

I have written code (in Java) which tracks "delta-versions" of XML files (labelled with an id attribute) in different sandboxes (sandbox attribute). For example if we set sandbox "B" as a sub-sandbox of sandbox "A" we can write the following pseudo code :-
for (int i=0; i<1000000; i++) {
// add <object sandbox="A" id="i" /> to the container
for (int j=0; j<10000; j++) {
// add <object sandbox="B" id="i" /> to the container
This represents a system with a million objects (in A) of which 10000 in B have been "checked out". The physical checked-out sandbox would thus consist of all elements in B plus all elements in A which have not been checked out to B. This can be achieved as follows.
let $A := container(...)/object[@sandbox="A"]
let $B := container(...)/object[@sandbox="B"]
let $base = $B union ($A except $A{./@id = $B/@id])
@sandbox and @id are appropriately indexed.
$base is thus a nice definition of an appropriately sandboxed environment which can then be used as the universe of objects in a sandboxed XQuery environment. For example to fetch the unique object with id = "ID" we can write:
$base[@id = "ID"]
Unfortunately, for the above test query, version 2.3 executes in under 0.3 seconds on my workstation. The same query in the same environment in 2.4 takes almost 15 seconds.
Could you please let me know what is happening here and how I might be able to fix the problem.

Answer 1

The experiment is "clean" in the sense that everything is created from scratch in each environment and indexed with the same indexes.
The queryplan is as follows:
<XQuery>
<Return>
<LetTuple uri="" name="C">
<LetTuple uri="" name="D">
<LetTuple uri="" name="B">
<LetTuple uri="" name="A">
<ContextTuple/>
<QueryPlanToAST>
<LevelFilterQP>
<StepQP axis="parent-of-attribute" name="object" nodeType="element">
<ValueQP container="e:\contentfactory 2007\security.dbxml" index="edge-attribute-equality-string" operation="eq" parent="object" child="sandbox" value="A"/>
</StepQP>
</LevelFilterQP>
</QueryPlanToAST>
</LetTuple>
<QueryPlanToAST>
<LevelFilterQP>
<NodePredicateFilterQP uri="" name="#tmp6">
<StepQP axis="parent-of-attribute" name="object" nodeType="element">
<ValueQP container="e:\contentfactory 2007\security.dbxml" index="edge-attribute-equality-string" operation="prefix" parent="object" child="id" value="1"/>
</StepQP>
<AttributeJoinQP>
<VariableQP name="#tmp6"/>
<ValueQP container="e:\contentfactory 2007\security.dbxml" index="edge-attribute-equality-string" operation="eq" parent="object" child="sandbox" value="B"/>
</AttributeJoinQP>
</NodePredicateFilterQP>
</LevelFilterQP>
</QueryPlanToAST>
</LetTuple>
<QueryPlanToAST>
<ExceptQP>
<VariableQP name="A"/>
<ParentOfAttributeJoinQP>
<ValueQP container="e:\contentfactory 2007\security.dbxml" index="edge-attribute-equality-string" operation="eq" parent="object" child="id">
<Atomize>
<QueryPlanToAST>
<StepQP axis="attribute" name="id" nodeType="attribute">
<VariableQP name="B"/>
</StepQP>
</QueryPlanToAST>
</Atomize>
</ValueQP>
<VariableQP name="A"/>
</ParentOfAttributeJoinQP>
</ExceptQP>
</QueryPlanToAST>
</LetTuple>
<QueryPlanToAST>
<UnionQP>
<VariableQP name="B"/>
<VariableQP name="D"/>
</UnionQP>
</QueryPlanToAST>
</LetTuple>
<QueryPlanToAST>
<ParentOfAttributeJoinQP>
<ValueQP container="e:\contentfactory 2007\security.dbxml" index="edge-attribute-equality-string" operation="eq" parent="object" child="id" value="120"/>
<VariableQP name="C"/>
</ParentOfAttributeJoinQP>
</QueryPlanToAST>
</Return>
</XQuery>