SERVER-23725 Aggregation now supports the graphLookup stage.

This commit is identical to a1253a94b82e65780d3aa3c4ddf92db02ec0b9d1.

1 files changed, 494 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/document_source_graph_lookup.cpp b/src/mongo/db/pipeline/document_source_graph_lookup.cpp
new file mode 100644
index 00000000000..f2821b9107c
--- /dev/null
+++ b/src/mongo/db/pipeline/document_source_graph_lookup.cpp
@@ -0,0 +1,494 @@
+/**
+ *    Copyright (C) 2016 MongoDB 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/platform/basic.h"
+
+#include "document_source.h"
+
+#include "mongo/base/init.h"
+#include "mongo/db/jsobj.h"
+#include "mongo/db/pipeline/document.h"
+#include "mongo/db/pipeline/expression.h"
+#include "mongo/db/pipeline/expression_context.h"
+#include "mongo/db/pipeline/value.h"
+#include "mongo/stdx/memory.h"
+
+namespace mongo {
+
+using boost::intrusive_ptr;
+using std::unique_ptr;
+
+REGISTER_DOCUMENT_SOURCE(graphLookup, DocumentSourceGraphLookUp::createFromBson);
+
+const char* DocumentSourceGraphLookUp::getSourceName() const {
+    return "$graphLookup";
+}
+
+boost::optional<Document> DocumentSourceGraphLookUp::getNext() {
+    pExpCtx->checkForInterrupt();
+
+    uassert(
+        40106, "from collection must have a unique _id index", _mongod->hasUniqueIdIndex(_from));
+
+    if (_unwind) {
+        return getNextUnwound();
+    }
+
+    // We aren't handling a $unwind, process the input document normally.
+    if (!(_input = pSource->getNext())) {
+        dispose();
+        return boost::none;
+    }
+
+    performSearch();
+
+    std::vector<Value> results;
+    while (!_visited.empty()) {
+        // Remove elements one at a time to avoid consuming more memory.
+        auto it = _visited.begin();
+        results.push_back(Value(it->second));
+        _visited.erase(it);
+    }
+
+    MutableDocument output(*_input);
+    output.setNestedField(_as, Value(std::move(results)));
+
+    _visitedUsageBytes = 0;
+
+    invariant(_visited.empty());
+
+    return output.freeze();
+}
+
+boost::optional<Document> DocumentSourceGraphLookUp::getNextUnwound() {
+    const boost::optional<FieldPath> indexPath((*_unwind)->indexPath());
+
+    // If the unwind is not preserving empty arrays, we might have to process multiple inputs before
+    // we get one that will produce an output.
+    while (true) {
+        if (_visited.empty()) {
+            // No results are left for the current input, so we should move on to the next one and
+            // perform a new search.
+            if (!(_input = pSource->getNext())) {
+                dispose();
+                return boost::none;
+            }
+
+            performSearch();
+            _visitedUsageBytes = 0;
+            _outputIndex = 0;
+        }
+        MutableDocument unwound(*_input);
+
+        if (_visited.empty()) {
+            if ((*_unwind)->preserveNullAndEmptyArrays()) {
+                // Since "preserveNullAndEmptyArrays" was specified, output a document even though
+                // we had no result.
+                unwound.setNestedField(_as, Value());
+                if (indexPath) {
+                    unwound.setNestedField(*indexPath, Value(BSONNULL));
+                }
+            } else {
+                // $unwind would not output anything, since the '_as' field would not exist. We
+                // should loop until we have something to return.
+                continue;
+            }
+        } else {
+            auto it = _visited.begin();
+            unwound.setNestedField(_as, Value(it->second));
+            if (indexPath) {
+                unwound.setNestedField(*indexPath, Value(_outputIndex));
+                ++_outputIndex;
+            }
+            _visited.erase(it);
+        }
+
+        return unwound.freeze();
+    }
+}
+
+void DocumentSourceGraphLookUp::dispose() {
+    _cache.clear();
+    _frontier.clear();
+    _visited.clear();
+    pSource->dispose();
+}
+
+void DocumentSourceGraphLookUp::doBreadthFirstSearch() {
+    long long depth = 0;
+    bool shouldPerformAnotherQuery;
+    do {
+        shouldPerformAnotherQuery = false;
+
+        // Check whether each key in the frontier exists in the cache or needs to be queried.
+        BSONObjSet cached;
+        auto query = constructQuery(&cached);
+
+        std::unordered_set<Value, Value::Hash> queried;
+        _frontier.swap(queried);
+        _frontierUsageBytes = 0;
+
+        // Process cached values, populating '_frontier' for the next iteration of search.
+        while (!cached.empty()) {
+            auto it = cached.begin();
+            shouldPerformAnotherQuery =
+                addToVisitedAndFrontier(*it, depth) || shouldPerformAnotherQuery;
+            cached.erase(it);
+            checkMemoryUsage();
+        }
+
+        if (query) {
+            // Query for all keys that were in the frontier and not in the cache, populating
+            // '_frontier' for the next iteration of search.
+            unique_ptr<DBClientCursor> cursor = _mongod->directClient()->query(_from.ns(), *query);
+
+            // Iterate the cursor.
+            while (cursor->more()) {
+                BSONObj result = cursor->nextSafe();
+                shouldPerformAnotherQuery =
+                    addToVisitedAndFrontier(result.getOwned(), depth) || shouldPerformAnotherQuery;
+                addToCache(result, queried);
+            }
+            checkMemoryUsage();
+        }
+
+        ++depth;
+    } while (shouldPerformAnotherQuery && depth < std::numeric_limits<long long>::max() &&
+             (!_maxDepth || depth <= *_maxDepth));
+
+    _frontier.clear();
+    _frontierUsageBytes = 0;
+}
+
+namespace {
+
+BSONObj addDepthFieldToObject(const std::string& field, long long depth, BSONObj object) {
+    BSONObjBuilder bob;
+    bob.appendElements(object);
+    bob.append(field, depth);
+    return bob.obj();
+}
+
+}  // namespace
+
+bool DocumentSourceGraphLookUp::addToVisitedAndFrontier(BSONObj result, long long depth) {
+    Value _id = Value(result.getField("_id"));
+
+    if (_visited.find(_id) != _visited.end()) {
+        // We've already seen this object, don't repeat any work.
+        return false;
+    }
+
+    // We have not seen this node before. If '_depthField' was specified, add the field to the
+    // object.
+    BSONObj fullObject =
+        _depthField ? addDepthFieldToObject(_depthField->getPath(false), depth, result) : result;
+
+    // Add the object to our '_visited' list.
+    _visited[_id] = fullObject;
+
+    // Update the size of '_visited' appropriately.
+    _visitedUsageBytes += _id.getApproximateSize();
+    _visitedUsageBytes += static_cast<size_t>(fullObject.objsize());
+
+    // Add the 'connectFrom' field of 'result' into '_frontier'. If the 'connectFrom' field is an
+    // array, we treat it as connecting to multiple values, so we must add each element to
+    // '_frontier'.
+    BSONElementSet recurseOnValues;
+    result.getFieldsDotted(_connectFromField.getPath(false), recurseOnValues);
+
+    for (auto&& elem : recurseOnValues) {
+        Value recurseOn = Value(elem);
+        if (recurseOn.isArray()) {
+            for (auto&& subElem : recurseOn.getArray()) {
+                _frontier.insert(subElem);
+                _frontierUsageBytes += subElem.getApproximateSize();
+            }
+        } else if (!recurseOn.missing()) {
+            // Don't recurse on a missing value.
+            _frontier.insert(recurseOn);
+            _frontierUsageBytes += recurseOn.getApproximateSize();
+        }
+    }
+
+    // We inserted into _visited, so return true.
+    return true;
+}
+
+void DocumentSourceGraphLookUp::addToCache(const BSONObj& result,
+                                           const unordered_set<Value, Value::Hash>& queried) {
+    BSONElementSet cacheByValues;
+    result.getFieldsDotted(_connectToField.getPath(false), cacheByValues);
+
+    for (auto&& elem : cacheByValues) {
+        Value cacheBy(elem);
+        if (cacheBy.isArray()) {
+            for (auto&& val : cacheBy.getArray()) {
+                if (queried.find(val) != queried.end()) {
+                    _cache.insert(val.getOwned(), result.getOwned());
+                }
+            }
+        } else if (!cacheBy.missing() && queried.find(cacheBy) != queried.end()) {
+            // It is possible that 'cacheBy' is a single value, but was not queried for. For
+            // instance, with a connectToField of "a.b" and a document with the structure:
+            // {a: [{b: 1}, {b: 0}]}, this document will be retrieved by querying for "{b: 1}", but
+            // the outer for loop will split this into two separate cacheByValues. {b: 0} was not
+            // queried for, and thus, we cannot cache under it.
+            _cache.insert(cacheBy.getOwned(), result.getOwned());
+        }
+    }
+}
+
+boost::optional<BSONObj> DocumentSourceGraphLookUp::constructQuery(BSONObjSet* cached) {
+    // Add any cached values to 'cached' and remove them from '_frontier'.
+    for (auto it = _frontier.begin(); it != _frontier.end();) {
+        if (auto entry = _cache[*it]) {
+            for (auto&& obj : *entry) {
+                cached->insert(obj);
+            }
+            size_t valueSize = it->getApproximateSize();
+            it = _frontier.erase(it);
+
+            // If the cached value increased in size while in the cache, we don't want to underflow
+            // '_frontierUsageBytes'.
+            invariant(valueSize <= _frontierUsageBytes);
+            _frontierUsageBytes -= valueSize;
+        } else {
+            it = std::next(it);
+        }
+    }
+
+    // Create a query of the form {_connectToField: {$in: [...]}}.
+    BSONObjBuilder query;
+    BSONObjBuilder subobj(query.subobjStart(_connectToField.getPath(false)));
+    BSONArrayBuilder in(subobj.subarrayStart("$in"));
+
+    for (auto&& value : _frontier) {
+        in << value;
+    }
+
+    in.doneFast();
+    subobj.doneFast();
+
+    return _frontier.empty() ? boost::none : boost::optional<BSONObj>(query.obj());
+}
+
+void DocumentSourceGraphLookUp::performSearch() {
+    // Make sure _input is set before calling performSearch().
+    invariant(_input);
+
+    _variables->setRoot(*_input);
+    Value startingValue = _startWith->evaluateInternal(_variables.get());
+    _variables->clearRoot();
+
+    // If _startWith evaluates to an array, treat each value as a separate starting point.
+    if (startingValue.isArray()) {
+        for (auto value : startingValue.getArray()) {
+            _frontier.insert(value);
+            _frontierUsageBytes += value.getApproximateSize();
+        }
+    } else {
+        _frontier.insert(startingValue);
+        _frontierUsageBytes += startingValue.getApproximateSize();
+    }
+
+    doBreadthFirstSearch();
+}
+
+Pipeline::SourceContainer::iterator DocumentSourceGraphLookUp::optimizeAt(
+    Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
+    invariant(*itr == this);
+
+    // If we are not already handling an $unwind stage internally, we can combine with the following
+    // $unwind stage.
+    auto nextUnwind = dynamic_cast<DocumentSourceUnwind*>((*std::next(itr)).get());
+    if (nextUnwind && !_unwind && nextUnwind->getUnwindPath() == _as.getPath(false)) {
+        _unwind = std::move(nextUnwind);
+        container->erase(std::next(itr));
+        return itr;
+    }
+    return std::next(itr);
+}
+
+BSONObjSet DocumentSourceGraphLookUp::getOutputSorts() {
+    std::set<std::string> fields{_as.getPath(false)};
+    if (_depthField) {
+        fields.insert(_depthField->getPath(false));
+    }
+    if (_unwind && (*_unwind)->indexPath()) {
+        fields.insert((*_unwind)->indexPath()->getPath(false));
+    }
+
+    return DocumentSource::truncateSortSet(pSource->getOutputSorts(), fields);
+}
+
+void DocumentSourceGraphLookUp::checkMemoryUsage() {
+    // TODO SERVER-23980: Implement spilling to disk if allowDiskUse is specified.
+    uassert(40099,
+            "$graphLookup reached maximum memory consumption",
+            (_visitedUsageBytes + _frontierUsageBytes) < _maxMemoryUsageBytes);
+    _cache.evictDownTo(_maxMemoryUsageBytes - _frontierUsageBytes - _visitedUsageBytes);
+}
+
+void DocumentSourceGraphLookUp::serializeToArray(std::vector<Value>& array, bool explain) const {
+    // Serialize default options.
+    MutableDocument spec(DOC("from" << _from.coll() << "as" << _as.getPath(false)
+                                    << "connectToField" << _connectToField.getPath(false)
+                                    << "connectFromField" << _connectFromField.getPath(false)
+                                    << "startWith" << _startWith->serialize(false)));
+
+    // depthField is optional; serialize it if it was specified.
+    if (_depthField) {
+        spec["depthField"] = Value(_depthField->getPath(false));
+    }
+
+    if (_maxDepth) {
+        spec["maxDepth"] = Value(*_maxDepth);
+    }
+
+    // If we are explaining, include an absorbed $unwind inside the $graphLookup specification.
+    if (_unwind && explain) {
+        const boost::optional<FieldPath> indexPath = (*_unwind)->indexPath();
+        spec["unwinding"] =
+            Value(DOC("preserveNullAndEmptyArrays"
+                      << (*_unwind)->preserveNullAndEmptyArrays() << "includeArrayIndex"
+                      << (indexPath ? Value((*indexPath).getPath(false)) : Value())));
+    }
+
+    array.push_back(Value(DOC(getSourceName() << spec.freeze())));
+
+    // If we are not explaining, the output of this method must be parseable, so serialize our
+    // $unwind into a separate stage.
+    if (_unwind && !explain) {
+        (*_unwind)->serializeToArray(array);
+    }
+}
+
+DocumentSourceGraphLookUp::DocumentSourceGraphLookUp(
+    NamespaceString from,
+    std::string as,
+    std::string connectFromField,
+    std::string connectToField,
+    boost::intrusive_ptr<Expression> startWith,
+    boost::optional<FieldPath> depthField,
+    boost::optional<long long> maxDepth,
+    const boost::intrusive_ptr<ExpressionContext>& expCtx)
+    : DocumentSource(expCtx),
+      _from(std::move(from)),
+      _as(std::move(as)),
+      _connectFromField(std::move(connectFromField)),
+      _connectToField(std::move(connectToField)),
+      _startWith(std::move(startWith)),
+      _depthField(depthField),
+      _maxDepth(maxDepth) {}
+
+intrusive_ptr<DocumentSource> DocumentSourceGraphLookUp::createFromBson(
+    BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx) {
+    NamespaceString from;
+    std::string as;
+    boost::intrusive_ptr<Expression> startWith;
+    std::string connectFromField;
+    std::string connectToField;
+    boost::optional<FieldPath> depthField;
+    boost::optional<long long> maxDepth;
+
+    VariablesIdGenerator idGenerator;
+    VariablesParseState vps(&idGenerator);
+
+    for (auto&& argument : elem.Obj()) {
+        const auto argName = argument.fieldNameStringData();
+
+        if (argName == "startWith") {
+            startWith = Expression::parseOperand(argument, vps);
+            continue;
+        } else if (argName == "maxDepth") {
+            uassert(40100,
+                    str::stream() << "maxDepth must be numeric, found type: "
+                                  << typeName(argument.type()),
+                    argument.isNumber());
+            maxDepth = argument.safeNumberLong();
+            uassert(
+                40101,
+                str::stream() << "maxDepth requires a nonnegative argument, found: " << *maxDepth,
+                *maxDepth >= 0);
+            uassert(
+                40102,
+                str::stream() << "maxDepth could not be represented as a long long: " << *maxDepth,
+                *maxDepth == argument.number());
+            continue;
+        }
+
+        if (argName == "from" || argName == "as" || argName == "connectFromField" ||
+            argName == "depthField" || argName == "connectToField") {
+            // All remaining arguments to $graphLookup are expected to be strings.
+            uassert(40103,
+                    str::stream() << "expected string as argument for " << argName
+                                  << ", found: " << argument.toString(false, false),
+                    argument.type() == String);
+        }
+
+        if (argName == "from") {
+            from = NamespaceString(expCtx->ns.db().toString() + '.' + argument.String());
+        } else if (argName == "as") {
+            as = argument.String();
+        } else if (argName == "connectFromField") {
+            connectFromField = argument.String();
+        } else if (argName == "connectToField") {
+            connectToField = argument.String();
+        } else if (argName == "depthField") {
+            depthField = boost::optional<FieldPath>(FieldPath(argument.String()));
+        } else {
+            uasserted(40104,
+                      str::stream()
+                          << "Unknown argument to $graphLookup: " << argument.fieldName());
+        }
+    }
+
+    const bool isMissingRequiredField = from.ns().empty() || as.empty() || !startWith ||
+        connectFromField.empty() || connectToField.empty();
+
+    uassert(40105,
+            str::stream() << "$graphLookup requires 'from', 'as', 'startWith', 'connectFromField', "
+                          << "and 'connectToField' to be specified.",
+            !isMissingRequiredField);
+
+    intrusive_ptr<DocumentSourceGraphLookUp> newSource(
+        new DocumentSourceGraphLookUp(std::move(from),
+                                      std::move(as),
+                                      std::move(connectFromField),
+                                      std::move(connectToField),
+                                      std::move(startWith),
+                                      depthField,
+                                      maxDepth,
+                                      expCtx));
+
+    newSource->_variables.reset(new Variables(idGenerator.getIdCount()));
+
+    return std::move(newSource);
+}
+}  // namespace mongo