关于连接的BaseX查询优化

时间：2015-06-16 10:41:49

标签： query-optimization basex

修复了以下Stackoverflow中的问题后，当我尝试按以下方式进行加入时，我遇到了另一个问题。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。有没有更好的方法在两个项目之间执行连接？

注意：您可以从此link找到测试数据。

  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>

以下是查询信息：

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：

上述问题已修复。但是当我想在本地函数中使用它时，它需要大约700毫秒。我做错了吗？

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，当我使用附加的＆＃34; Cont＆＃34;扩展查询时，我还有另一个问题。 items，查询执行大约持续600毫秒。但没有＆＃34;续＆＃34;项目，只需35毫秒。 您对优化此查询有任何建议吗？

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>

这是用于测试的最新XML数据的link。

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>

1 个答案:

答案 0 :(得分：1)

在那些for循环中，两个＆＃34;大＆＃34;的结果。 XPath表达式已由优化程序缓存。此外，您实际上两次比较href / id属性。

清理查询消除此双重操作可将执行时间减少约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>
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