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/**
* Copyright (C) 2013 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#include "mongo/db/query/index_tag.h"
#include "mongo/db/matcher/expression_array.h"
#include "mongo/db/matcher/expression_tree.h"
#include "mongo/db/query/indexability.h"
#include "mongo/platform/unordered_map.h"
#include <algorithm>
#include <limits>
namespace mongo {
using TagType = MatchExpression::TagData::Type;
namespace {
bool TagComparison(const MatchExpression* lhs, const MatchExpression* rhs) {
IndexTag* lhsTag = static_cast<IndexTag*>(lhs->getTag());
size_t lhsValue = (NULL == lhsTag) ? IndexTag::kNoIndex : lhsTag->index;
size_t lhsPos = (NULL == lhsTag) ? IndexTag::kNoIndex : lhsTag->pos;
IndexTag* rhsTag = static_cast<IndexTag*>(rhs->getTag());
size_t rhsValue = (NULL == rhsTag) ? IndexTag::kNoIndex : rhsTag->index;
size_t rhsPos = (NULL == rhsTag) ? IndexTag::kNoIndex : rhsTag->pos;
// First, order on indices.
if (lhsValue != rhsValue) {
// This relies on kNoIndex being larger than every other possible index.
return lhsValue < rhsValue;
}
// Next, order so that if there's a GEO_NEAR it's first.
if (MatchExpression::GEO_NEAR == lhs->matchType()) {
return true;
} else if (MatchExpression::GEO_NEAR == rhs->matchType()) {
return false;
}
// Ditto text.
if (MatchExpression::TEXT == lhs->matchType()) {
return true;
} else if (MatchExpression::TEXT == rhs->matchType()) {
return false;
}
// Next, order so that the first field of a compound index appears first.
if (lhsPos != rhsPos) {
return lhsPos < rhsPos;
}
// Next, order on fields.
int cmp = lhs->path().compare(rhs->path());
if (0 != cmp) {
return 0;
}
// Finally, order on expression type.
return lhs->matchType() < rhs->matchType();
}
// Sorts the tree using its IndexTag(s). Nodes that use the same index will sort so that they are
// adjacent to one another.
void sortUsingTags(MatchExpression* tree) {
for (size_t i = 0; i < tree->numChildren(); ++i) {
sortUsingTags(tree->getChild(i));
}
std::vector<MatchExpression*>* children = tree->getChildVector();
if (NULL != children) {
std::sort(children->begin(), children->end(), TagComparison);
}
}
// Attaches 'node' to 'target'. If 'target' is an AND, adds 'node' as a child of 'target'.
// Otherwise, creates an AND that is a child of 'targetParent' at position 'targetPosition', and
// adds 'target' and 'node' as its children. Tags 'node' with 'tagData'.
void attachNode(MatchExpression* node,
MatchExpression* target,
OrMatchExpression* targetParent,
size_t targetPosition,
std::unique_ptr<MatchExpression::TagData> tagData) {
auto clone = node->shallowClone();
if (clone->matchType() == MatchExpression::NOT) {
IndexTag* indexTag = static_cast<IndexTag*>(tagData.get());
clone->setTag(new IndexTag(indexTag->index));
clone->getChild(0)->setTag(tagData.release());
} else {
clone->setTag(tagData.release());
}
if (MatchExpression::AND == target->matchType()) {
AndMatchExpression* andNode = static_cast<AndMatchExpression*>(target);
andNode->add(clone.release());
} else {
std::unique_ptr<AndMatchExpression> andNode = stdx::make_unique<AndMatchExpression>();
IndexTag* indexTag = static_cast<IndexTag*>(clone->getTag());
andNode->setTag(new IndexTag(indexTag->index));
andNode->add(target);
andNode->add(clone.release());
targetParent->getChildVector()->operator[](targetPosition) = andNode.release();
}
}
// Partitions destinations according to the first element of the destination's route. Trims the
// first element off of each destination's route.
unordered_map<size_t, std::vector<OrPushdownTag::Destination>> partitionChildDestinations(
std::vector<OrPushdownTag::Destination> destinations) {
unordered_map<size_t, std::vector<OrPushdownTag::Destination>> childDestinations;
for (auto&& dest : destinations) {
invariant(!dest.route.empty());
auto index = dest.route.front();
dest.route.pop_front();
childDestinations[index].push_back(std::move(dest));
}
return childDestinations;
}
// Finds the node within 'tree' that is an indexed OR, if one exists.
MatchExpression* getIndexedOr(MatchExpression* tree) {
if (MatchExpression::OR == tree->matchType() && tree->getTag()) {
return tree;
}
for (size_t i = 0; i < tree->numChildren(); ++i) {
if (auto indexedOrChild = getIndexedOr(tree->getChild(i))) {
return indexedOrChild;
}
}
return nullptr;
}
// Pushes down 'node' along the routes in 'target' specified in 'destinations'. Each value in the
// route is the index of a child in an indexed OR. Returns true if 'node' is moved to every indexed
// descendant of 'target'.
bool pushdownNode(MatchExpression* node,
MatchExpression* target,
std::vector<OrPushdownTag::Destination> destinations) {
if (MatchExpression::OR == target->matchType()) {
OrMatchExpression* orNode = static_cast<OrMatchExpression*>(target);
bool moveToAllChildren = true;
auto childDestinationsMap = partitionChildDestinations(std::move(destinations));
for (size_t i = 0; i < orNode->numChildren(); ++i) {
auto childDestinations = childDestinationsMap.find(i);
if (childDestinations == childDestinationsMap.end()) {
// This child was not specified by any route in 'destinations'.
moveToAllChildren = false;
} else {
invariant(!childDestinations->second.empty());
if (childDestinations->second[0].route.empty()) {
// There should only be one destination if we have reached the end of a route.
// Otherwise, we started with duplicate routes.
invariant(childDestinations->second.size() == 1);
// We have reached the position at which to attach 'node'.
attachNode(node,
orNode->getChild(i),
orNode,
i,
std::move(childDestinations->second[0].tagData));
} else {
// This child was specified by a non-trivial route in destinations, so we recur.
moveToAllChildren = pushdownNode(node,
orNode->getChild(i),
std::move(childDestinations->second)) &&
moveToAllChildren;
}
}
}
return moveToAllChildren;
}
if (MatchExpression::AND == target->matchType()) {
auto indexedOr = getIndexedOr(target);
invariant(indexedOr);
return pushdownNode(node, indexedOr, std::move(destinations));
}
MONGO_UNREACHABLE;
}
// Populates 'out' with all descendants of 'node' that have OrPushdownTags, assuming the initial
// input is an ELEM_MATCH_OBJECT.
void getElemMatchOrPushdownDescendants(MatchExpression* node, std::vector<MatchExpression*>* out) {
if (node->getTag() && node->getTag()->getType() == TagType::OrPushdownTag) {
out->push_back(node);
} else if (node->matchType() == MatchExpression::ELEM_MATCH_OBJECT ||
node->matchType() == MatchExpression::AND) {
for (size_t i = 0; i < node->numChildren(); ++i) {
getElemMatchOrPushdownDescendants(node->getChild(i), out);
}
}
}
// Finds all the nodes in the tree with OrPushdownTags and copies them to the Destinations specified
// in the OrPushdownTag, tagging them with the TagData in the Destination. Removes the node from its
// current location if possible.
void resolveOrPushdowns(MatchExpression* tree) {
if (tree->numChildren() == 0) {
return;
}
if (MatchExpression::AND == tree->matchType()) {
AndMatchExpression* andNode = static_cast<AndMatchExpression*>(tree);
MatchExpression* indexedOr = getIndexedOr(andNode);
for (size_t i = 0; i < andNode->numChildren(); ++i) {
auto child = andNode->getChild(i);
if (child->getTag() && child->getTag()->getType() == TagType::OrPushdownTag) {
invariant(indexedOr);
OrPushdownTag* orPushdownTag = static_cast<OrPushdownTag*>(child->getTag());
auto destinations = orPushdownTag->releaseDestinations();
auto indexTag = orPushdownTag->releaseIndexTag();
child->setTag(nullptr);
if (pushdownNode(child, indexedOr, std::move(destinations)) && !indexTag) {
// indexedOr can completely satisfy the predicate specified in child, so we can
// trim it. We could remove the child even if it had an index tag for this
// position, but that could make the index tagging of the tree wrong.
auto ownedChild = andNode->removeChild(i);
// We removed child i, so decrement the child index.
--i;
} else {
child->setTag(indexTag.release());
}
} else if (child->matchType() == MatchExpression::NOT && child->getChild(0)->getTag() &&
child->getChild(0)->getTag()->getType() == TagType::OrPushdownTag) {
invariant(indexedOr);
OrPushdownTag* orPushdownTag =
static_cast<OrPushdownTag*>(child->getChild(0)->getTag());
auto destinations = orPushdownTag->releaseDestinations();
auto indexTag = orPushdownTag->releaseIndexTag();
child->getChild(0)->setTag(nullptr);
// Push down the NOT and its child.
if (pushdownNode(child, indexedOr, std::move(destinations)) && !indexTag) {
// indexedOr can completely satisfy the predicate specified in child, so we can
// trim it. We could remove the child even if it had an index tag for this
// position, but that could make the index tagging of the tree wrong.
auto ownedChild = andNode->removeChild(i);
// We removed child i, so decrement the child index.
--i;
} else {
child->getChild(0)->setTag(indexTag.release());
}
} else if (child->matchType() == MatchExpression::ELEM_MATCH_OBJECT) {
// Push down all descendants of child with OrPushdownTags.
std::vector<MatchExpression*> orPushdownDescendants;
getElemMatchOrPushdownDescendants(child, &orPushdownDescendants);
if (!orPushdownDescendants.empty()) {
invariant(indexedOr);
}
for (auto descendant : orPushdownDescendants) {
OrPushdownTag* orPushdownTag =
static_cast<OrPushdownTag*>(descendant->getTag());
auto destinations = orPushdownTag->releaseDestinations();
auto indexTag = orPushdownTag->releaseIndexTag();
descendant->setTag(nullptr);
pushdownNode(descendant, indexedOr, std::move(destinations));
descendant->setTag(indexTag.release());
// We cannot trim descendants of an $elemMatch object, since the filter must
// be applied in its entirety.
}
}
}
}
for (size_t i = 0; i < tree->numChildren(); ++i) {
resolveOrPushdowns(tree->getChild(i));
}
}
} // namespace
const size_t IndexTag::kNoIndex = std::numeric_limits<size_t>::max();
void prepareForAccessPlanning(MatchExpression* tree) {
resolveOrPushdowns(tree);
sortUsingTags(tree);
}
} // namespace mongo
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