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/**
* Copyright (C) 2018-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 <boost/optional.hpp>
#include <vector>
#include "mongo/base/status.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/query/collation/collator_interface.h"
#include "mongo/stdx/unordered_map.h"
#include "mongo/stdx/unordered_set.h"
#include "mongo/util/string_map.h"
namespace mongo {
class ViewDefinition;
/**
* Represents the dependencies of views on other namespaces and validates that this graph is acyclic
* and smaller than the maximum diameter. It also checks that the views in each connected component
* have compatible collations, and that all possible view pipelines stay within the maximum size in
* bytes.
*
* This is owned and managed by the ViewCatalog.
*/
class ViewGraph {
MONGO_DISALLOW_COPYING(ViewGraph);
public:
static const int kMaxViewDepth;
static const int kMaxViewPipelineSizeBytes;
ViewGraph() = default;
/**
* Inserts a new node for 'view' in the graph, which must not already be present. 'refs'
* contains the list of namespaces referred to by the view in its "viewOn" or "pipeline".
* 'pipelineSize' is the size of the view's pipeline, in bytes. If inserting the view would
* violate one of the graph's validity properties, the insertion is reverted and a non-OK status
* is returned.
*
* This method is intended for validating a view that is created or modified by a user
* operation.
*/
Status insertAndValidate(const ViewDefinition& view,
const std::vector<NamespaceString>& refs,
int pipelineSize);
/**
* Like insertAndValidate(), inserts a new node for 'view' in the graph, which must not already
* be present. However, no validation is performed. The insertion is not rolled back even if it
* puts the graph into an invalid state.
*
* This method is intended for quickly repopulating the graph with view definitions that are
* assumed to be already valid.
*/
void insertWithoutValidating(const ViewDefinition& view,
const std::vector<NamespaceString>& refs,
int pipelineSize);
/**
* Called when a view is removed from the catalog. If the view does not exist in the graph it is
* a no-op. The view may also have a cycle or max diameter through it.
*/
void remove(const NamespaceString& viewNss);
/**
* Deletes the view graph and all references to namespaces.
*/
void clear();
/**
* Returns the number of namespaces tracked by the view graph. Only exposed for testing.
*/
size_t size() const;
private:
// A graph node represents a namespace. We say that a node A is a parent of B if A is a view and
// it references B via its "viewOn" or $lookup/$graphLookup/$facet in its "pipeline".
//
// This node represents a view namespace if and only if 'children' is nonempty and 'collator' is
// set.
struct Node {
/**
* Returns true if this node represents a view.
*/
bool isView() const {
invariant(children.empty() == !static_cast<bool>(collator));
return !children.empty();
}
// The fully-qualified namespace that this node represents.
std::string ns;
// Represents the namespaces depended on by this view. A view may refer to the same child
// more than once, but we store the children as a set because each namespace need not be
// traversed more than once.
stdx::unordered_set<uint64_t> children;
// Represents the views that depend on this namespace.
stdx::unordered_set<uint64_t> parents;
// When set, this is an unowned pointer to the view's collation, or nullptr if the view has
// the binary collation. When not set, this namespace is not a view and we don't care about
// its collator.
boost::optional<const CollatorInterface*> collator;
// The size of this view's "pipeline", in bytes.
int size = 0;
};
// Bookkeeping for graph traversals.
struct NodeStats {
bool checked = false;
int height = 0;
int cumulativeSize = 0;
};
using StatsMap = stdx::unordered_map<uint64_t, NodeStats>;
/**
* Recursively validates the parents of 'currentId', filling out statistics about the node
* represented by that id in 'statsMap'. The recursion level is tracked in 'currentDepth' to
* limit recursive calls.
*
* A non-OK status is returned if 'currentId' or its parents violate any of the graph's
* validity properties.
*/
Status _validateParents(uint64_t currentId, int currentDepth, StatsMap* statsMap);
/**
* Recursively validates the children of 'currentId', filling out statistics about the node
* represented by that id in 'statsMap'. The recursion level is tracked in 'currentDepth' to
* limit recursive calls. Both 'startingId' and 'traversalIds' are used to detect cycles.
*
* A non-OK status is returned if 'currentId' or its children violate any of the graph's
* validity properties.
*/
Status _validateChildren(uint64_t startingId,
uint64_t currentId,
int currentDepth,
StatsMap* statsMap,
std::vector<uint64_t>* traversalIds);
/**
* Gets the id for this namespace, and creates an id if it doesn't exist.
*/
uint64_t _getNodeId(const NamespaceString& ns);
// Maps namespaces to an internal node id. A mapping exists for every namespace referenced,
// i.e. existing views, collections, and non-existing namespaces.
StringMap<uint64_t> _namespaceIds;
// Maps node ids to nodes. There is a 1-1 correspondence with _namespaceIds, hence the lifetime
// of a node is the same as the lifetime as its corresponding node id.
stdx::unordered_map<uint64_t, Node> _graph;
uint64_t _idCounter = 0;
};
} // namespace mongo
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