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/**
* Copyright (C) 2023-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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.
*/
#pragma once
#include "mongo/db/query/optimizer/defs.h"
#include "mongo/db/query/optimizer/node.h"
namespace mongo::optimizer {
/**
* If the input expression is a constant or a variable, or it is an EvalFilter/Path which has an
* identity path and input which itself is constant or variable, then return a pointer to the deepst
* simple expression.
*/
template <class T>
ABT::reference_type getTrivialExprPtr(const ABT& n) {
if (n.is<Constant>() || n.is<Variable>()) {
return n.ref();
}
if (const auto* ptr = n.cast<T>();
ptr != nullptr && ptr->getPath().template is<PathIdentity>()) {
return getTrivialExprPtr<T>(ptr->getInput());
}
return {};
}
/**
* Returns a vector all paths nested under conjunctions (PathComposeM) in the given path.
* For example, PathComposeM(PathComposeM(Foo, Bar), Baz) returns [Foo, Bar, Baz].
* If the given path is not a conjunction, returns a vector with the given path.
*/
std::vector<ABT::reference_type> collectComposed(const ABT& n);
/**
* Like collectComposed() but bounded by a maximum number of composed paths.
* If the given path has more PathComposeM;s than specified by maxDepth, then return a vector
* with the given path. Otherwise, returns the result of collectComposed().
*
* This is useful for preventing the optimizer from unintentionally creating a very deep tree which
* causes stack-overflow on a recursive traversal.
*/
std::vector<ABT::reference_type> collectComposedBounded(const ABT& n, size_t maxDepth);
/**
* De-compose a path and an input to an EvalFilter into sequence of Filter nodes. If we have a path
* with a prefix of PathGet's followed by a series of nested PathComposeM, then split into two or
* more filter nodes at the composition and retain the prefix for each. The result is a tree of
* chained filter nodes. We return an empty result if we have less than "minDepth" sub-tress which
* are composed. If "minDepth" = 1, then we are guaranteed to return a result, which will consist of
* a single Filter node.
*
* If the number of compositions exceeds "maxDepth" then we return the a single FilterNode
* consisting of an EvalFilter over the original path and input.
*/
constexpr size_t kMaxPathConjunctionDecomposition = 20;
boost::optional<ABT> decomposeToFilterNodes(const ABT& input,
const ABT& path,
const ABT& pathInput,
size_t minDepth,
size_t maxDepth = kMaxPathConjunctionDecomposition);
/**
* Returns true if the path represented by 'node' is of the form PathGet "field" PathId
*/
bool isSimplePath(const ABT& node);
template <class Element = PathComposeM>
inline void maybeComposePath(ABT& composition, ABT child) {
if (child.is<PathIdentity>()) {
return;
}
if (composition.is<PathIdentity>()) {
composition = std::move(child);
return;
}
composition = make<Element>(std::move(composition), std::move(child));
}
/**
* Creates a balanced tree of composition elements over the input vector which it modifies in place.
* In the end at most one element remains in the vector.
*/
template <class Element = PathComposeM>
inline void maybeComposePaths(ABTVector& paths) {
while (paths.size() > 1) {
const size_t half = paths.size() / 2;
for (size_t i = 0; i < half; i++) {
maybeComposePath<Element>(paths.at(i), std::move(paths.back()));
paths.pop_back();
}
}
}
/**
* Appends a path to another path. Performs the append at PathIdentity elements.
*/
class PathAppender {
public:
PathAppender(ABT suffix) : _suffix(std::move(suffix)) {}
void transport(ABT& n, const PathIdentity& node) {
n = _suffix;
}
template <typename T, typename... Ts>
void transport(ABT& /*n*/, const T& /*node*/, Ts&&...) {
// noop
}
/**
* Concatenate 'prefix' and 'suffix' by modifying 'prefix' in place.
*/
static void appendInPlace(ABT& prefix, ABT suffix) {
PathAppender instance{std::move(suffix)};
algebra::transport<true>(prefix, instance);
}
/**
* Return the concatenation of 'prefix' and 'suffix'.
*/
[[nodiscard]] static ABT append(ABT prefix, ABT suffix) {
appendInPlace(prefix, std::move(suffix));
return prefix;
}
private:
ABT _suffix;
};
/**
* Given a path and a MultikeynessTrie describing the path's input,
* removes any Traverse nodes that we know will never encounter an array.
*
* Returns true if any changes were made to the ABT.
*/
bool simplifyTraverseNonArray(ABT& path, const MultikeynessTrie& multikeynessTrie);
/**
* Fuses an index path and a query path to determine a residual path to apply over the index
* results. Checks if one index path is a prefix of another. Considers only Get, Traverse, and Id.
* Return the suffix that doesn't match.
*/
struct IndexFusionResult {
boost::optional<ABT::reference_type> _suffix;
size_t _numTraversesSkipped = 0;
size_t _numTraversesFused = 0;
};
IndexFusionResult fuseIndexPath(const ABT& node, const ABT& candidatePrefix);
/**
* Check if a path contains a Traverse element.
*/
bool checkPathContainsTraverse(const ABT& path);
/**
* This helper checks to see if we have a PathTraverse + PathId at the end of the path.
*/
bool pathEndsInTraverse(const optimizer::ABT& path);
} // namespace mongo::optimizer
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