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| <h1 title="程序包" class="title">程序包 org.apache.calcite.plan.volcano</h1> |
| <div class="docSummary"> |
| <div class="block">Optimizes relational expressions.</div> |
| </div> |
| <p>请参阅: <a href="#package.description">说明</a></p> |
| </div> |
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| <ul class="blockList"> |
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| <table class="typeSummary" border="0" cellpadding="3" cellspacing="0" summary="接口概要表, 列表接口和解释"> |
| <caption><span>接口概要</span><span class="tabEnd"> </span></caption> |
| <tr> |
| <th class="colFirst" scope="col">接口</th> |
| <th class="colLast" scope="col">说明</th> |
| </tr> |
| <tbody> |
| <tr class="altColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlannerPhaseRuleMappingInitializer.html" title="org.apache.calcite.plan.volcano中的接口">VolcanoPlannerPhaseRuleMappingInitializer</a></td> |
| <td class="colLast"> |
| <div class="block">VolcanoPlannerPhaseRuleMappingInitializer describes an interface for |
| initializing the mapping of <a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlannerPhase.html" title="org.apache.calcite.plan.volcano中的枚举"><code>VolcanoPlannerPhase</code></a>s to sets of rule |
| descriptions.</div> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </li> |
| <li class="blockList"> |
| <table class="typeSummary" border="0" cellpadding="3" cellspacing="0" summary="类概要表, 列表类和解释"> |
| <caption><span>类概要</span><span class="tabEnd"> </span></caption> |
| <tr> |
| <th class="colFirst" scope="col">类</th> |
| <th class="colLast" scope="col">说明</th> |
| </tr> |
| <tbody> |
| <tr class="altColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/AbstractConverter.html" title="org.apache.calcite.plan.volcano中的类">AbstractConverter</a></td> |
| <td class="colLast"> |
| <div class="block">Converts a relational expression to any given output convention.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/AbstractConverter.ExpandConversionRule.html" title="org.apache.calcite.plan.volcano中的类">AbstractConverter.ExpandConversionRule</a></td> |
| <td class="colLast"> |
| <div class="block">Rule which converts an <a href="../../../../../org/apache/calcite/plan/volcano/AbstractConverter.html" title="org.apache.calcite.plan.volcano中的类"><code>AbstractConverter</code></a> into a chain of |
| converters from the source relation to the target traits.</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/ChainedPhaseRuleMappingInitializer.html" title="org.apache.calcite.plan.volcano中的类">ChainedPhaseRuleMappingInitializer</a></td> |
| <td class="colLast"> |
| <div class="block">ChainedPhaseRuleMappingInitializer is an abstract implementation of |
| <a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlannerPhaseRuleMappingInitializer.html" title="org.apache.calcite.plan.volcano中的接口"><code>VolcanoPlannerPhaseRuleMappingInitializer</code></a> that allows additional |
| rules to be layered on top of those configured by a subordinate |
| <a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlannerPhaseRuleMappingInitializer.html" title="org.apache.calcite.plan.volcano中的接口"><code>VolcanoPlannerPhaseRuleMappingInitializer</code></a>.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/RelSubset.html" title="org.apache.calcite.plan.volcano中的类">RelSubset</a></td> |
| <td class="colLast"> |
| <div class="block">Subset of an equivalence class where all relational expressions have the |
| same physical properties.</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlanner.html" title="org.apache.calcite.plan.volcano中的类">VolcanoPlanner</a></td> |
| <td class="colLast"> |
| <div class="block">VolcanoPlanner optimizes queries by transforming expressions selectively |
| according to a dynamic programming algorithm.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/VolcanoRelMetadataProvider.html" title="org.apache.calcite.plan.volcano中的类">VolcanoRelMetadataProvider</a></td> |
| <td class="colLast"> |
| <div class="block">VolcanoRelMetadataProvider implements the <a href="../../../../../org/apache/calcite/rel/metadata/RelMetadataProvider.html" title="org.apache.calcite.rel.metadata中的接口"><code>RelMetadataProvider</code></a> |
| interface by combining metadata from the rels making up an equivalence class.</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/VolcanoRuleCall.html" title="org.apache.calcite.plan.volcano中的类">VolcanoRuleCall</a></td> |
| <td class="colLast"> |
| <div class="block"><code>VolcanoRuleCall</code> implements the <a href="../../../../../org/apache/calcite/plan/RelOptRuleCall.html" title="org.apache.calcite.plan中的类"><code>RelOptRuleCall</code></a> interface |
| for VolcanoPlanner.</div> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
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| <li class="blockList"> |
| <table class="typeSummary" border="0" cellpadding="3" cellspacing="0" summary="枚举概要表, 列表枚举和解释"> |
| <caption><span>枚举概要</span><span class="tabEnd"> </span></caption> |
| <tr> |
| <th class="colFirst" scope="col">枚举</th> |
| <th class="colLast" scope="col">说明</th> |
| </tr> |
| <tbody> |
| <tr class="altColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlannerPhase.html" title="org.apache.calcite.plan.volcano中的枚举">VolcanoPlannerPhase</a></td> |
| <td class="colLast"> |
| <div class="block">VolcanoPlannerPhase represents the phases of operation that the |
| <a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlanner.html" title="org.apache.calcite.plan.volcano中的类"><code>VolcanoPlanner</code></a> passes through during optimization of a tree of |
| <a href="../../../../../org/apache/calcite/rel/RelNode.html" title="org.apache.calcite.rel中的接口"><code>RelNode</code></a> objects.</div> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </li> |
| </ul> |
| <a name="package.description"> |
| <!-- --> |
| </a> |
| <h2 title="程序包org.apache.calcite.plan.volcano的说明">程序包org.apache.calcite.plan.volcano的说明</h2> |
| <div class="block">Optimizes relational expressions.<p> </p> |
| |
| <h2>Overview</h2> |
| |
| <p>A <dfn>planner</dfn> (also known as an <dfn>optimizer</dfn>) finds the |
| most efficient implementation of a |
| <a href="../../../../../org/apache/calcite/rel/RelNode.html" title="org.apache.calcite.rel中的接口"><code>relational expression</code></a>.</p> |
| |
| <p>Interface <a href="../../../../../org/apache/calcite/plan/RelOptPlanner.html" title="org.apache.calcite.plan中的接口"><code>RelOptPlanner</code></a> defines a planner, |
| and class <a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlanner.html" title="org.apache.calcite.plan.volcano中的类"><code>VolcanoPlanner</code></a> is an |
| implementation which uses a dynamic programming technique. It is based upon |
| the Volcano optimizer [<a href="#graefe93">1</a>].</p> |
| |
| <p>Interface <a href="../../../../../org/apache/calcite/plan/RelOptCost.html" title="org.apache.calcite.plan中的接口"><code>RelOptCost</code></a> defines a cost |
| model; class <code>VolcanoCost</code> is |
| the implementation for a <code>VolcanoPlanner</code>.</p> |
| |
| <p>A <code>RelSet</code> is a set of equivalent |
| relational expressions. They are equivalent because they will produce the |
| same result for any set of input data. It is an equivalence class: two |
| expressions are in the same set if and only if they are in the same |
| <code>RelSet</code>.</p> |
| |
| <p>One of the unique features of the optimizer is that expressions can take |
| on a variety of physical traits. Each relational expression has a set of |
| traits. Each trait is described by an implementation of |
| <a href="../../../../../org/apache/calcite/plan/RelTraitDef.html" title="org.apache.calcite.plan中的类"><code>RelTraitDef</code></a>. Manifestations of the trait |
| implement <a href="../../../../../org/apache/calcite/plan/RelTrait.html" title="org.apache.calcite.plan中的接口"><code>RelTrait</code></a>. The most common example |
| of a trait is calling convention: the protocol used to receive and transmit |
| data. <a href="../../../../../org/apache/calcite/plan/ConventionTraitDef.html" title="org.apache.calcite.plan中的类"><code>ConventionTraitDef</code></a> defines the trait |
| and <a href="../../../../../org/apache/calcite/plan/Convention.html" title="org.apache.calcite.plan中的接口"><code>Convention</code></a> enumerates the |
| protocols. Every relational expression has a single calling convention by |
| which it returns its results. Some examples:</p> |
| |
| <ul> |
| <li><a href="../../../../../org/apache/calcite/adapter/jdbc/JdbcConvention.html" title="org.apache.calcite.adapter.jdbc中的类"><code>JdbcConvention</code></a> is a fairly |
| conventional convention; the results are rows from a |
| <a href="https://docs.oracle.com/javase/8/docs/api/java/sql/ResultSet.html?is-external=true" title="java.sql中的类或接口"><code>JDBC result set</code></a>. |
| </li> |
| <li><a href="../../../../../org/apache/calcite/plan/Convention.html#NONE"><code>Convention.NONE</code></a> means that a |
| relational |
| expression cannot be implemented; typically there are rules which can |
| transform it to equivalent, implementable expressions. |
| </li> |
| <li><a href="../../../../../org/apache/calcite/adapter/enumerable/EnumerableConvention.html" title="org.apache.calcite.adapter.enumerable中的枚举"><code>EnumerableConvention</code></a> |
| implements the expression by |
| generating Java code. The code places the current row in a Java |
| variable, then |
| calls the piece of code which implements the consuming relational |
| expression. |
| For example, a Java array reader of the <code>names</code> array |
| would generate the following code: |
| <blockquote> |
| <pre>String[] names; |
| for (int i = 0; i < names.length; i++) { |
| String name = names[i]; |
| // ... code for consuming relational expression ... |
| }</pre> |
| </blockquote> |
| </li> |
| </ul> |
| |
| <p>New traits are added to the planner in one of two ways:</p> |
| <ol> |
| <li>If the new trait is integral to Calcite, then each and every |
| implementation of <a href="../../../../../org/apache/calcite/rel/RelNode.html" title="org.apache.calcite.rel中的接口"><code>RelNode</code></a> should include |
| its manifestation of the trait as part of the |
| <a href="../../../../../org/apache/calcite/plan/RelTraitSet.html" title="org.apache.calcite.plan中的类"><code>RelTraitSet</code></a> passed to |
| <a href="../../../../../org/apache/calcite/rel/AbstractRelNode.html" title="org.apache.calcite.rel中的类"><code>AbstractRelNode</code></a>'s constructor. It may be |
| useful to provide alternate <code>AbstractRelNode</code> constructors |
| if most relational expressions use a single manifestation of the |
| trait.</li> |
| |
| <li>If the new trait describes some aspect of a Farrago extension, then |
| the RelNodes passed to |
| <a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlanner.html#setRoot-org.apache.calcite.rel.RelNode-"><code>VolcanoPlanner.setRoot(org.apache.calcite.rel.RelNode)</code></a> |
| should have their trait sets expanded before the |
| <code>setRoot(RelNode)</code> call.</li> |
| |
| </ol> |
| |
| <p>The second trait extension mechanism requires that implementations of |
| <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#clone--" title="java.lang中的类或接口"><code>Object.clone()</code></a> must not assume the |
| type and quantity of traits in their trait set. In either case, the new |
| <code>RelTraitDef</code> implementation must be |
| <a href="../../../../../org/apache/calcite/plan/volcano/VolcanoPlanner.html#addRelTraitDef-org.apache.calcite.plan.RelTraitDef-"><code>VolcanoPlanner.addRelTraitDef(org.apache.calcite.plan.RelTraitDef)</code></a> |
| registered with the planner.</p> |
| |
| <p>A <a href="../../../../../org/apache/calcite/plan/volcano/RelSubset.html" title="org.apache.calcite.plan.volcano中的类"><code>RelSubset</code></a> is a subset of a |
| <code>RelSet</code> containing expressions which are equivalent and which |
| have the same <code>Convention</code>. Like <code>RelSet</code>, it is an |
| equivalence class.</p> |
| |
| <h2>Related packages</h2> |
| <ul> |
| <li><code><a href="../rel/package-summary.html">org.apache.calcite.rel</a></code> |
| defines <a href="../../../../../org/apache/calcite/rel/RelNode.html" title="org.apache.calcite.rel中的接口"><code>relational expressions</code></a>. |
| </li> |
| </ul> |
| |
| <h2>Details</h2> |
| |
| <p>...</p> |
| |
| <p>Sets merge when the result of a rule already exists in another set. This |
| implies that all of the expressions are equivalent. The RelSets are |
| merged, and so are the contained RelSubsets.</p> |
| |
| <p>Expression registration.</p> |
| <ul> |
| <li>Expression is added to a set. We may find that an equivalent |
| expression already exists. Otherwise, this is the moment when an |
| expression becomes public, and fixed. Its digest is assigned, which |
| allows us to quickly find identical expressions.</li> |
| |
| <li>We match operands, figure out which rules are applicable, and |
| generate rule calls. The rule calls are placed on a queue, and the |
| important ones are called later.</li> |
| |
| <li>RuleCalls allow us to defer the invocation of rules. When an |
| expression is registered </li> |
| </ul> |
| |
| <p>Algorithm</p> |
| |
| <p>To optimize a relational expression R:</p> |
| |
| <p>1. Register R.</p> |
| |
| <p>2. Create rule-calls for all applicable rules.</p> |
| |
| <p>3. Rank the rule calls by importance.</p> |
| |
| <p>4. Call the most important rule</p> |
| |
| <p>5. Repeat.</p> |
| |
| <p><b>Importance</b>. A rule-call is important if it is likely to produce |
| better implementation of a relexp on the plan's critical path. Hence (a) |
| it produces a member of an important RelSubset, (b) its children are |
| cheap.</p> |
| |
| <p>Conversion. Conversions are difficult because we have to work backwards |
| from the goal.</p> |
| |
| <p><b>Rule triggering</b></p> |
| |
| <p>The rules are:</p> |
| <ol> |
| <li><code>PushFilterThroughProjectRule</code>. Operands: |
| <blockquote> |
| <pre>Filter |
| Project</pre> |
| </blockquote> |
| </li> |
| <li><code>CombineProjectsRule</code>. Operands: |
| <blockquote> |
| <pre>Project |
| Project</pre> |
| </blockquote> |
| </li> |
| </ol> |
| |
| <p>A rule can be triggered by a change to any of its operands. Consider the |
| rule to combine two filters into one. It would have operands [Filter |
| [Filter]]. If I register a new Filter, it will trigger the rule in 2 |
| places. Consider:</p> |
| |
| <blockquote> |
| <pre>Project (deptno) [exp 1, subset A] |
| Filter (gender='F') [exp 2, subset B] |
| Project (deptno, gender, empno) [exp 3, subset C] |
| Project (deptno, gender, empno, salary) [exp 4, subset D] |
| TableScan (emp) [exp 0, subset X]</pre> |
| </blockquote> |
| <p>Apply <code>PushFilterThroughProjectRule</code> to [exp 2, exp 3]:</p> |
| <blockquote> |
| <pre>Project (deptno) [exp 1, subset A] |
| Project (deptno, gender, empno) [exp 5, subset B] |
| Filter (gender='F') [exp 6, subset E] |
| Project (deptno, gender, empno, salary) [exp 4, subset D] |
| TableScan (emp) [exp 0, subset X]</pre> |
| </blockquote> |
| |
| <p>Two new expressions are created. Expression 5 is in subset B (because it |
| is equivalent to expression 2), and expression 6 is in a new equivalence |
| class, subset E.</p> |
| |
| <p>The products of a applying a rule can trigger a cascade of rules. Even in |
| this simple system (2 rules and 4 initial expressions), two more rules |
| are triggered:</p> |
| |
| <ul> |
| |
| <li>Registering exp 5 triggers <code>CombineProjectsRule</code>(exp 1, |
| exp 5), which creates |
| |
| <blockquote> |
| <pre>Project (deptno) [exp 7, subset A] |
| Filter (gender='F') [exp 6, subset E] |
| Project (deptno, gender, empno, salary) [exp 4, subset D] |
| TableScan (emp) [exp 0, subset X]</pre> |
| </blockquote> |
| </li> |
| |
| <li>Registering exp 6 triggers |
| <code>PushFilterThroughProjectRule</code>(exp 6, exp 4), which |
| creates |
| |
| <blockquote> |
| <pre>Project (deptno) [exp 1, subset A] |
| Project (deptno, gender, empno) [exp 5, subset B] |
| Project (deptno, gender, empno, salary) [exp 8, subset E] |
| Filter (gender='F') [exp 9, subset F] |
| TableScan (emp) [exp 0, subset X]</pre> |
| </blockquote> |
| </li> |
| </ul> |
| |
| <p>Each rule application adds additional members to existing subsets. The |
| non-singleton subsets are now A {1, 7}, B {2, 5} and E {6, 8}, and new |
| combinations are possible. For example, |
| <code>CombineProjectsRule</code>(exp 7, exp 8) further reduces the depth |
| of the tree to:</p> |
| |
| <blockquote> |
| <pre>Project (deptno) [exp 10, subset A] |
| Filter (gender='F') [exp 9, subset F] |
| TableScan (emp) [exp 0, subset X]</pre> |
| </blockquote> |
| <p>Todo: show how rules can cause subsets to merge.</p> |
| |
| <p>Conclusion:</p> |
| <ol> |
| <li>A rule can be triggered by any of its operands.</li> |
| <li>If a subset is a child of more than one parent, it can trigger rule |
| matches for any of its parents. |
| </li> |
| |
| <li>Registering one relexp can trigger several rules (and even the same |
| rule several times).</li> |
| |
| <li>Firing rules can cause subsets to merge.</li> |
| </ol> |
| <h2>References</h2> |
| |
| <p>1. <a id="graefe93" href="http://citeseer.nj.nec.com/graefe93volcano.html">The |
| Volcano Optimizer |
| Generator: Extensibility and Efficient Search - Goetz Graefe, William J. |
| McKenna |
| (1993)</a>.</p></div> |
| </div> |
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