mirror of https://gitee.com/bigwinds/arangodb
79 lines
2.8 KiB
C++
79 lines
2.8 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2018 ArangoDB GmbH, Cologne, Germany
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///
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/// Licensed under the Apache License, Version 2.0 (the "License");
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/// you may not use this file except in compliance with the License.
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/// You may obtain a copy of the License at
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///
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/// http://www.apache.org/licenses/LICENSE-2.0
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///
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/// Unless required by applicable law or agreed to in writing, software
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/// distributed under the License is distributed on an "AS IS" BASIS,
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/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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/// See the License for the specific language governing permissions and
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/// limitations under the License.
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///
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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///
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/// @author Jan Steemann
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////////////////////////////////////////////////////////////////////////////////
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#include "PersistentIndexAttributeMatcher.h"
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#include "Aql/Ast.h"
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#include "Aql/AstNode.h"
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#include "Aql/SortCondition.h"
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#include "Aql/Variable.h"
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#include "Indexes/Index.h"
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#include "VocBase/vocbase.h"
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using namespace arangodb;
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bool PersistentIndexAttributeMatcher::supportsSortCondition(
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arangodb::Index const* idx, arangodb::aql::SortCondition const* sortCondition,
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arangodb::aql::Variable const* reference, size_t itemsInIndex,
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double& estimatedCost, size_t& coveredAttributes) {
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TRI_ASSERT(sortCondition != nullptr);
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if (!idx->sparse()) {
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// only non-sparse indexes can be used for sorting
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if (!idx->hasExpansion() && sortCondition->isUnidirectional() &&
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sortCondition->isOnlyAttributeAccess()) {
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coveredAttributes = sortCondition->coveredAttributes(reference, idx->fields());
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if (coveredAttributes >= sortCondition->numAttributes()) {
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// sort is fully covered by index. no additional sort costs!
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// forward iteration does not have high costs
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estimatedCost = itemsInIndex * 0.001;
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if (sortCondition->isDescending()) {
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// reverse iteration has higher costs than forward iteration
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estimatedCost *= 4;
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}
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return true;
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} else if (coveredAttributes > 0) {
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estimatedCost = (itemsInIndex / coveredAttributes) *
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std::log2(static_cast<double>(itemsInIndex));
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if (sortCondition->isAscending()) {
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// reverse iteration is more expensive
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estimatedCost *= 4;
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}
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return true;
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}
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}
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}
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coveredAttributes = 0;
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// by default no sort conditions are supported
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if (itemsInIndex > 0) {
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estimatedCost = itemsInIndex * std::log2(static_cast<double>(itemsInIndex));
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// slightly penalize this type of index against other indexes which
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// are in memory
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estimatedCost *= 1.05;
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} else {
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estimatedCost = 0.0;
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}
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return false;
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}
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