连接时的 BaseX 查询优化
BaseX query optimization on join
下面中的问题解决后，我在尝试进行如下连接时遇到另一个问题。最后一个查询大约需要 250 毫秒，而前两个查询只需要 16 毫秒。有没有更好的方法来执行两个项目之间的连接？
注：测试数据可以从这里找到link.
let $PlGeTys :=
/root/PlGeTys/PlGeTy[
isOfPlCt/@href=/root/PlCts/PlCt[
environment='AIR'
]/@id
]
let $PlSpTys :=
/root/PlSpTys/PlSpTy[
isOfPlGeTy/@href=$PlGeTys/@id
]
for $PlGeTy in $PlGeTys,
$PlSpTy in $PlSpTys
where $PlSpTy/isOfPlGeTy/@href=$PlGeTy/@id
return <done>{$PlGeTy, $PlSpTy }</done>
查询信息如下：
Compiling:
- applying attribute index for $PlGeTys_0/@*:id
- rewriting where clause(s)
Query:
let $PlGeTys := /root/PlGeTys/PlGeTy[ isOfPlCt/@href=/root/PlCts/PlCt[ environment='AIR' ]/@id ] let $PlSpTys := /root/PlSpTys/PlSpTy[ isOfPlGeTy/@href=$PlGeTys/@id ] for $PlGeTy in $PlGeTys, $PlSpTy in $PlSpTys where $PlSpTy/isOfPlGeTy/@href=$PlGeTy/@id return "done"
Optimized Query:
let $PlGeTys_0 := db:open-pre("Output6",0)/*:root/*:PlGeTys/*:PlGeTy[(*:isOfPlCt/@*:href = root()/*:root/*:PlCts/*:PlCt[(*:environment = "AIR")]/@*:id)] let $PlSpTys_1 := db:attribute("Output6", $PlGeTys_0/@*:id)/self::*:href/parent::*:isOfPlGeTy/parent::*:PlSpTy for $PlGeTy_2 in $PlGeTys_0 for $PlSpTy_3 in ($PlSpTys_1)[(isOfPlGeTy/@href = $PlGeTy_2/@*:id)] return "done"
Result:
- Hit(s): 3642 Items
- Updated: 0 Items
- Printed: 18209 Bytes
- Read Locking: local [Output6]
- Write Locking: none
Timing:
- Parsing: 0.77 ms
- Compiling: 0.47 ms
- Evaluating: 215.71 ms
- Printing: 0.17 ms
- Total Time: 217.11 ms
Query plan:
<QueryPlan compiled="true">
<GFLWOR>
<Let>
<Var name="$PlGeTys" id="0"/>
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
<IterStep axis="child" test="*:PlGeTys"/>
<IterStep axis="child" test="*:PlGeTy">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="*:isOfPlCt"/>
<IterStep axis="attribute" test="*:href"/>
</CachedPath>
<IterPath>
<Root/>
<IterStep axis="child" test="*:root"/>
<IterStep axis="child" test="*:PlCts"/>
<IterStep axis="child" test="*:PlCt">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="*:environment"/>
</CachedPath>
<Str value="AIR" type="xs:string"/>
</CmpG>
</IterStep>
<IterStep axis="attribute" test="*:id"/>
</IterPath>
</CmpG>
</IterStep>
</IterPath>
</Let>
<Let>
<Var name="$PlSpTys" id="1"/>
<CachedPath>
<ValueAccess data="Output6" type="ATTRIBUTE">
<CachedPath>
<VarRef>
<Var name="$PlGeTys" id="0"/>
</VarRef>
<IterStep axis="attribute" test="*:id"/>
</CachedPath>
</ValueAccess>
<IterStep axis="self" test="*:href"/>
<IterStep axis="parent" test="*:isOfPlGeTy"/>
<IterStep axis="parent" test="*:PlSpTy"/>
</CachedPath>
</Let>
<For>
<Var name="$PlGeTy" id="2"/>
<VarRef>
<Var name="$PlGeTys" id="0"/>
</VarRef>
</For>
<For>
<Var name="$PlSpTy" id="3"/>
<IterFilter>
<VarRef>
<Var name="$PlSpTys" id="1"/>
</VarRef>
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="isOfPlGeTy"/>
<IterStep axis="attribute" test="href"/>
</CachedPath>
<IterPath>
<VarRef>
<Var name="$PlGeTy" id="2"/>
</VarRef>
<IterStep axis="attribute" test="*:id"/>
</IterPath>
</CmpG>
</IterFilter>
</For>
<Str value="done" type="xs:string"/>
</GFLWOR>
</QueryPlan>
更新二：
以上问题已解决。但是当我想在下面的本地函数中使用它时，大约需要 700 毫秒。我做错了什么吗？
declare function local:result($root as element(root)) as element()* {
let $PlCts := $root/PlCts/PlCt[environment = 'AIR']/@id
for $PlGeTy in $root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts],
$PlSpTy in $root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id]
return <done>{ $PlGeTy, $PlSpTy }</done>
};
let $result := local:result(/root)
return $result
查询信息；
Compiling:
- removing redundant element()* cast.
- inlining local:result#1
- inlining $root_5 as element(root)
- simplifying flwor expression
Query:
declare function local:result($root as element(root)) as element()* { let $PlCts := $root/PlCts/PlCt[environment = 'AIR']/@id for $PlGeTy in $root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts], $PlSpTy in $root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id] return <done>{ $PlGeTy, $PlSpTy }</done> }; let $result := local:result(/root) return $result
Optimized Query:
let $PlCts_6 := ((: element(root), true :) db:open-pre("Output6",0)/*:root)/PlCts/PlCt[(environment = "AIR")]/@id let $result_4 := for $PlGeTy_7 in ((: element(root), true :) db:open-pre("Output6",0)/*:root)/PlGeTys/PlGeTy[(isOfPlCt/@href = $PlCts_6)] for $PlSpTy_8 in ((: element(root), true :) db:open-pre("Output6",0)/*:root)/PlSpTys/PlSpTy[(isOfPlGeTy/@href = $PlGeTy_7/@id)] return element done { (($PlGeTy_7, $PlSpTy_8)) } return $result_4
Result:
- Hit(s): 3642 Items
- Updated: 0 Items
- Printed: 553 KB
- Read Locking: local [Output6]
- Write Locking: none
Timing:
- Parsing: 1.41 ms
- Compiling: 2.9 ms
- Evaluating: 581.5 ms
- Printing: 8.34 ms
- Total Time: 594.15 ms
Query plan:
<QueryPlan compiled="true">
<GFLWOR>
<Let>
<Var name="$PlCts" id="6"/>
<IterPath>
<TypeCheck type="element(root)" function="true">
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
</IterPath>
</TypeCheck>
<IterStep axis="child" test="PlCts"/>
<IterStep axis="child" test="PlCt">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="environment"/>
</CachedPath>
<Str value="AIR" type="xs:string"/>
</CmpG>
</IterStep>
<IterStep axis="attribute" test="id"/>
</IterPath>
</Let>
<Let>
<Var name="$result" id="4"/>
<GFLWOR>
<For>
<Var name="$PlGeTy" id="7"/>
<IterPath>
<TypeCheck type="element(root)" function="true">
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
</IterPath>
</TypeCheck>
<IterStep axis="child" test="PlGeTys"/>
<IterStep axis="child" test="PlGeTy">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="isOfPlCt"/>
<IterStep axis="attribute" test="href"/>
</CachedPath>
<VarRef>
<Var name="$PlCts" id="6"/>
</VarRef>
</CmpG>
</IterStep>
</IterPath>
</For>
<For>
<Var name="$PlSpTy" id="8"/>
<IterPath>
<TypeCheck type="element(root)" function="true">
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
</IterPath>
</TypeCheck>
<IterStep axis="child" test="PlSpTys"/>
<IterStep axis="child" test="PlSpTy">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="isOfPlGeTy"/>
<IterStep axis="attribute" test="href"/>
</CachedPath>
<IterPath>
<VarRef>
<Var name="$PlGeTy" id="7"/>
</VarRef>
<IterStep axis="attribute" test="id"/>
</IterPath>
</CmpG>
</IterStep>
</IterPath>
</For>
<CElem>
<QNm value="done" type="xs:QName"/>
<List>
<VarRef>
<Var name="$PlGeTy" id="7"/>
</VarRef>
<VarRef>
<Var name="$PlSpTy" id="8"/>
</VarRef>
</List>
</CElem>
</GFLWOR>
</Let>
<VarRef>
<Var name="$result" id="4"/>
</VarRef>
</GFLWOR>
</QueryPlan>
更新三：
现在，当我使用额外的 "Cont" 项扩展查询时，我遇到了另一个问题，查询执行持续大约 600 毫秒。但是如果没有 "Cont" 项，它只需要 35 毫秒。
您对优化此查询有什么建议吗？
let $PlCts := /root/PlCts/PlCt[environment = 'AIR']/@id
for $PlGeTy in /root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts],
$PlSpTy in /root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id],
$Cont in /root/Conts/Cont[@id=$PlSpTy/isOfCont/@href]
return <done>{ $PlGeTy, $PlSpTy, $Cont }</done>
这是link最新的XML个测试数据。
查询信息：
Compiling:
- applying text index for "AIR"
- applying attribute index for $PlCts_0
- applying attribute index for $PlGeTy_1/@id
- applying attribute index for $PlSpTy_2/isOfCont/@href
- inlining $PlCts_0
Query:
let $PlCts := /root/PlCts/PlCt[environment = 'AIR']/@id for $PlGeTy in /root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts], $PlSpTy in /root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id], $Cont in /root/Conts/Cont[@id=$PlSpTy/isOfCont/@href] return <done>{ $PlGeTy, $PlSpTy, $Cont }</done>
Optimized Query:
for $PlGeTy_1 in db:attribute("Output7", db:text("Output7", "AIR")/parent::*:environment/parent::*:PlCt/@*:id)/self::*:href/parent::*:isOfPlCt/parent::*:PlGeTy for $PlSpTy_2 in db:attribute("Output7", $PlGeTy_1/@id)/self::*:href/parent::*:isOfPlGeTy/parent::*:PlSpTy for $Cont_3 in db:attribute("Output7", $PlSpTy_2/isOfCont/@href)/self::*:id/parent::*:Cont return element done { (($PlGeTy_1, $PlSpTy_2, $Cont_3)) }
Result:
- Hit(s): 3642 Items
- Updated: 0 Items
- Printed: 1159 KB
- Read Locking: local [Output7]
- Write Locking: none
Timing:
- Parsing: 0.39 ms
- Compiling: 0.68 ms
- Evaluating: 585.29 ms
- Printing: 14.36 ms
- Total Time: 600.72 ms
Query plan:
<QueryPlan compiled="true">
<GFLWOR>
<For>
<Var name="$PlGeTy" id="1"/>
<CachedPath>
<ValueAccess data="Output7" type="ATTRIBUTE">
<CachedPath>
<ValueAccess data="Output7" type="TEXT" name="*:environment">
<Str value="AIR" type="xs:string"/>
</ValueAccess>
<IterStep axis="parent" test="*:PlCt"/>
<IterStep axis="attribute" test="*:id"/>
</CachedPath>
</ValueAccess>
<IterStep axis="self" test="*:href"/>
<IterStep axis="parent" test="*:isOfPlCt"/>
<IterStep axis="parent" test="*:PlGeTy"/>
</CachedPath>
</For>
<For>
<Var name="$PlSpTy" id="2"/>
<CachedPath>
<ValueAccess data="Output7" type="ATTRIBUTE">
<IterPath>
<VarRef>
<Var name="$PlGeTy" id="1"/>
</VarRef>
<IterStep axis="attribute" test="id"/>
</IterPath>
</ValueAccess>
<IterStep axis="self" test="*:href"/>
<IterStep axis="parent" test="*:isOfPlGeTy"/>
<IterStep axis="parent" test="*:PlSpTy"/>
</CachedPath>
</For>
<For>
<Var name="$Cont" id="3"/>
<CachedPath>
<ValueAccess data="Output7" type="ATTRIBUTE">
<IterPath>
<VarRef>
<Var name="$PlSpTy" id="2"/>
</VarRef>
<IterStep axis="child" test="isOfCont"/>
<IterStep axis="attribute" test="href"/>
</IterPath>
</ValueAccess>
<IterStep axis="self" test="*:id"/>
<IterStep axis="parent" test="*:Cont"/>
</CachedPath>
</For>
<CElem>
<QNm value="done" type="xs:QName"/>
<List>
<VarRef>
<Var name="$PlGeTy" id="1"/>
</VarRef>
<VarRef>
<Var name="$PlSpTy" id="2"/>
</VarRef>
<VarRef>
<Var name="$Cont" id="3"/>
</VarRef>
</List>
</CElem>
</GFLWOR>
</QueryPlan>
在那些 for 循环中，两个 "large" XPath 表达式的结果已被优化器缓存。此外，您实际上是在比较 href/id 属性两次。
清理查询消除了这种双重努力，将执行时间减少了大约 90%。
let $PlCts := /root/PlCts/PlCt[environment = 'AIR']/@id
for $PlGeTy in /root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts],
$PlSpTy in /root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id]
return <done>{ $PlGeTy, $PlSpTy }</done>
下面
注：测试数据可以从这里找到link.
let $PlGeTys :=
/root/PlGeTys/PlGeTy[
isOfPlCt/@href=/root/PlCts/PlCt[
environment='AIR'
]/@id
]
let $PlSpTys :=
/root/PlSpTys/PlSpTy[
isOfPlGeTy/@href=$PlGeTys/@id
]
for $PlGeTy in $PlGeTys,
$PlSpTy in $PlSpTys
where $PlSpTy/isOfPlGeTy/@href=$PlGeTy/@id
return <done>{$PlGeTy, $PlSpTy }</done>
查询信息如下：
Compiling:
- applying attribute index for $PlGeTys_0/@*:id
- rewriting where clause(s)
Query:
let $PlGeTys := /root/PlGeTys/PlGeTy[ isOfPlCt/@href=/root/PlCts/PlCt[ environment='AIR' ]/@id ] let $PlSpTys := /root/PlSpTys/PlSpTy[ isOfPlGeTy/@href=$PlGeTys/@id ] for $PlGeTy in $PlGeTys, $PlSpTy in $PlSpTys where $PlSpTy/isOfPlGeTy/@href=$PlGeTy/@id return "done"
Optimized Query:
let $PlGeTys_0 := db:open-pre("Output6",0)/*:root/*:PlGeTys/*:PlGeTy[(*:isOfPlCt/@*:href = root()/*:root/*:PlCts/*:PlCt[(*:environment = "AIR")]/@*:id)] let $PlSpTys_1 := db:attribute("Output6", $PlGeTys_0/@*:id)/self::*:href/parent::*:isOfPlGeTy/parent::*:PlSpTy for $PlGeTy_2 in $PlGeTys_0 for $PlSpTy_3 in ($PlSpTys_1)[(isOfPlGeTy/@href = $PlGeTy_2/@*:id)] return "done"
Result:
- Hit(s): 3642 Items
- Updated: 0 Items
- Printed: 18209 Bytes
- Read Locking: local [Output6]
- Write Locking: none
Timing:
- Parsing: 0.77 ms
- Compiling: 0.47 ms
- Evaluating: 215.71 ms
- Printing: 0.17 ms
- Total Time: 217.11 ms
Query plan:
<QueryPlan compiled="true">
<GFLWOR>
<Let>
<Var name="$PlGeTys" id="0"/>
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
<IterStep axis="child" test="*:PlGeTys"/>
<IterStep axis="child" test="*:PlGeTy">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="*:isOfPlCt"/>
<IterStep axis="attribute" test="*:href"/>
</CachedPath>
<IterPath>
<Root/>
<IterStep axis="child" test="*:root"/>
<IterStep axis="child" test="*:PlCts"/>
<IterStep axis="child" test="*:PlCt">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="*:environment"/>
</CachedPath>
<Str value="AIR" type="xs:string"/>
</CmpG>
</IterStep>
<IterStep axis="attribute" test="*:id"/>
</IterPath>
</CmpG>
</IterStep>
</IterPath>
</Let>
<Let>
<Var name="$PlSpTys" id="1"/>
<CachedPath>
<ValueAccess data="Output6" type="ATTRIBUTE">
<CachedPath>
<VarRef>
<Var name="$PlGeTys" id="0"/>
</VarRef>
<IterStep axis="attribute" test="*:id"/>
</CachedPath>
</ValueAccess>
<IterStep axis="self" test="*:href"/>
<IterStep axis="parent" test="*:isOfPlGeTy"/>
<IterStep axis="parent" test="*:PlSpTy"/>
</CachedPath>
</Let>
<For>
<Var name="$PlGeTy" id="2"/>
<VarRef>
<Var name="$PlGeTys" id="0"/>
</VarRef>
</For>
<For>
<Var name="$PlSpTy" id="3"/>
<IterFilter>
<VarRef>
<Var name="$PlSpTys" id="1"/>
</VarRef>
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="isOfPlGeTy"/>
<IterStep axis="attribute" test="href"/>
</CachedPath>
<IterPath>
<VarRef>
<Var name="$PlGeTy" id="2"/>
</VarRef>
<IterStep axis="attribute" test="*:id"/>
</IterPath>
</CmpG>
</IterFilter>
</For>
<Str value="done" type="xs:string"/>
</GFLWOR>
</QueryPlan>
更新二：
以上问题已解决。但是当我想在下面的本地函数中使用它时，大约需要 700 毫秒。我做错了什么吗？
declare function local:result($root as element(root)) as element()* {
let $PlCts := $root/PlCts/PlCt[environment = 'AIR']/@id
for $PlGeTy in $root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts],
$PlSpTy in $root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id]
return <done>{ $PlGeTy, $PlSpTy }</done>
};
let $result := local:result(/root)
return $result
查询信息；
Compiling:
- removing redundant element()* cast.
- inlining local:result#1
- inlining $root_5 as element(root)
- simplifying flwor expression
Query:
declare function local:result($root as element(root)) as element()* { let $PlCts := $root/PlCts/PlCt[environment = 'AIR']/@id for $PlGeTy in $root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts], $PlSpTy in $root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id] return <done>{ $PlGeTy, $PlSpTy }</done> }; let $result := local:result(/root) return $result
Optimized Query:
let $PlCts_6 := ((: element(root), true :) db:open-pre("Output6",0)/*:root)/PlCts/PlCt[(environment = "AIR")]/@id let $result_4 := for $PlGeTy_7 in ((: element(root), true :) db:open-pre("Output6",0)/*:root)/PlGeTys/PlGeTy[(isOfPlCt/@href = $PlCts_6)] for $PlSpTy_8 in ((: element(root), true :) db:open-pre("Output6",0)/*:root)/PlSpTys/PlSpTy[(isOfPlGeTy/@href = $PlGeTy_7/@id)] return element done { (($PlGeTy_7, $PlSpTy_8)) } return $result_4
Result:
- Hit(s): 3642 Items
- Updated: 0 Items
- Printed: 553 KB
- Read Locking: local [Output6]
- Write Locking: none
Timing:
- Parsing: 1.41 ms
- Compiling: 2.9 ms
- Evaluating: 581.5 ms
- Printing: 8.34 ms
- Total Time: 594.15 ms
Query plan:
<QueryPlan compiled="true">
<GFLWOR>
<Let>
<Var name="$PlCts" id="6"/>
<IterPath>
<TypeCheck type="element(root)" function="true">
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
</IterPath>
</TypeCheck>
<IterStep axis="child" test="PlCts"/>
<IterStep axis="child" test="PlCt">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="environment"/>
</CachedPath>
<Str value="AIR" type="xs:string"/>
</CmpG>
</IterStep>
<IterStep axis="attribute" test="id"/>
</IterPath>
</Let>
<Let>
<Var name="$result" id="4"/>
<GFLWOR>
<For>
<Var name="$PlGeTy" id="7"/>
<IterPath>
<TypeCheck type="element(root)" function="true">
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
</IterPath>
</TypeCheck>
<IterStep axis="child" test="PlGeTys"/>
<IterStep axis="child" test="PlGeTy">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="isOfPlCt"/>
<IterStep axis="attribute" test="href"/>
</CachedPath>
<VarRef>
<Var name="$PlCts" id="6"/>
</VarRef>
</CmpG>
</IterStep>
</IterPath>
</For>
<For>
<Var name="$PlSpTy" id="8"/>
<IterPath>
<TypeCheck type="element(root)" function="true">
<IterPath>
<DBNode name="Output6" pre="0"/>
<IterStep axis="child" test="*:root"/>
</IterPath>
</TypeCheck>
<IterStep axis="child" test="PlSpTys"/>
<IterStep axis="child" test="PlSpTy">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="isOfPlGeTy"/>
<IterStep axis="attribute" test="href"/>
</CachedPath>
<IterPath>
<VarRef>
<Var name="$PlGeTy" id="7"/>
</VarRef>
<IterStep axis="attribute" test="id"/>
</IterPath>
</CmpG>
</IterStep>
</IterPath>
</For>
<CElem>
<QNm value="done" type="xs:QName"/>
<List>
<VarRef>
<Var name="$PlGeTy" id="7"/>
</VarRef>
<VarRef>
<Var name="$PlSpTy" id="8"/>
</VarRef>
</List>
</CElem>
</GFLWOR>
</Let>
<VarRef>
<Var name="$result" id="4"/>
</VarRef>
</GFLWOR>
</QueryPlan>
更新三： 现在，当我使用额外的 "Cont" 项扩展查询时，我遇到了另一个问题，查询执行持续大约 600 毫秒。但是如果没有 "Cont" 项，它只需要 35 毫秒。 您对优化此查询有什么建议吗？
let $PlCts := /root/PlCts/PlCt[environment = 'AIR']/@id
for $PlGeTy in /root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts],
$PlSpTy in /root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id],
$Cont in /root/Conts/Cont[@id=$PlSpTy/isOfCont/@href]
return <done>{ $PlGeTy, $PlSpTy, $Cont }</done>
这是link最新的XML个测试数据。
查询信息：
Compiling:
- applying text index for "AIR"
- applying attribute index for $PlCts_0
- applying attribute index for $PlGeTy_1/@id
- applying attribute index for $PlSpTy_2/isOfCont/@href
- inlining $PlCts_0
Query:
let $PlCts := /root/PlCts/PlCt[environment = 'AIR']/@id for $PlGeTy in /root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts], $PlSpTy in /root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id], $Cont in /root/Conts/Cont[@id=$PlSpTy/isOfCont/@href] return <done>{ $PlGeTy, $PlSpTy, $Cont }</done>
Optimized Query:
for $PlGeTy_1 in db:attribute("Output7", db:text("Output7", "AIR")/parent::*:environment/parent::*:PlCt/@*:id)/self::*:href/parent::*:isOfPlCt/parent::*:PlGeTy for $PlSpTy_2 in db:attribute("Output7", $PlGeTy_1/@id)/self::*:href/parent::*:isOfPlGeTy/parent::*:PlSpTy for $Cont_3 in db:attribute("Output7", $PlSpTy_2/isOfCont/@href)/self::*:id/parent::*:Cont return element done { (($PlGeTy_1, $PlSpTy_2, $Cont_3)) }
Result:
- Hit(s): 3642 Items
- Updated: 0 Items
- Printed: 1159 KB
- Read Locking: local [Output7]
- Write Locking: none
Timing:
- Parsing: 0.39 ms
- Compiling: 0.68 ms
- Evaluating: 585.29 ms
- Printing: 14.36 ms
- Total Time: 600.72 ms
Query plan:
<QueryPlan compiled="true">
<GFLWOR>
<For>
<Var name="$PlGeTy" id="1"/>
<CachedPath>
<ValueAccess data="Output7" type="ATTRIBUTE">
<CachedPath>
<ValueAccess data="Output7" type="TEXT" name="*:environment">
<Str value="AIR" type="xs:string"/>
</ValueAccess>
<IterStep axis="parent" test="*:PlCt"/>
<IterStep axis="attribute" test="*:id"/>
</CachedPath>
</ValueAccess>
<IterStep axis="self" test="*:href"/>
<IterStep axis="parent" test="*:isOfPlCt"/>
<IterStep axis="parent" test="*:PlGeTy"/>
</CachedPath>
</For>
<For>
<Var name="$PlSpTy" id="2"/>
<CachedPath>
<ValueAccess data="Output7" type="ATTRIBUTE">
<IterPath>
<VarRef>
<Var name="$PlGeTy" id="1"/>
</VarRef>
<IterStep axis="attribute" test="id"/>
</IterPath>
</ValueAccess>
<IterStep axis="self" test="*:href"/>
<IterStep axis="parent" test="*:isOfPlGeTy"/>
<IterStep axis="parent" test="*:PlSpTy"/>
</CachedPath>
</For>
<For>
<Var name="$Cont" id="3"/>
<CachedPath>
<ValueAccess data="Output7" type="ATTRIBUTE">
<IterPath>
<VarRef>
<Var name="$PlSpTy" id="2"/>
</VarRef>
<IterStep axis="child" test="isOfCont"/>
<IterStep axis="attribute" test="href"/>
</IterPath>
</ValueAccess>
<IterStep axis="self" test="*:id"/>
<IterStep axis="parent" test="*:Cont"/>
</CachedPath>
</For>
<CElem>
<QNm value="done" type="xs:QName"/>
<List>
<VarRef>
<Var name="$PlGeTy" id="1"/>
</VarRef>
<VarRef>
<Var name="$PlSpTy" id="2"/>
</VarRef>
<VarRef>
<Var name="$Cont" id="3"/>
</VarRef>
</List>
</CElem>
</GFLWOR>
</QueryPlan>
在那些 for 循环中，两个 "large" XPath 表达式的结果已被优化器缓存。此外，您实际上是在比较 href/id 属性两次。
清理查询消除了这种双重努力，将执行时间减少了大约 90%。
let $PlCts := /root/PlCts/PlCt[environment = 'AIR']/@id
for $PlGeTy in /root/PlGeTys/PlGeTy[isOfPlCt/@href = $PlCts],
$PlSpTy in /root/PlSpTys/PlSpTy[isOfPlGeTy/@href = $PlGeTy/@id]
return <done>{ $PlGeTy, $PlSpTy }</done>