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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.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/commands/feature_compatibility_version_documentation.h"
#include "mongo/db/exec/document_value/value.h"
#include "mongo/db/matcher/expression_algo.h"
#include "mongo/db/pipeline/document_source_group.h"
#include "mongo/db/pipeline/document_source_internal_shard_filter.h"
#include "mongo/db/pipeline/document_source_match.h"
#include "mongo/db/pipeline/document_source_sample.h"
#include "mongo/db/pipeline/document_source_sequential_document_cache.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/field_path.h"
#include "mongo/db/pipeline/semantic_analysis.h"
#include "mongo/util/string_map.h"
namespace mongo {
using Parser = DocumentSource::Parser;
using boost::intrusive_ptr;
using std::list;
using std::string;
using std::vector;
DocumentSource::DocumentSource(const StringData stageName,
const intrusive_ptr<ExpressionContext>& pCtx)
: pSource(nullptr), pExpCtx(pCtx), _commonStats(stageName.rawData()) {}
namespace {
struct ParserRegistration {
Parser parser;
boost::optional<ServerGlobalParams::FeatureCompatibility::Version> requiredMinVersion;
};
// Used to keep track of which DocumentSources are registered under which name.
static StringMap<ParserRegistration> parserMap;
} // namespace
void DocumentSource::registerParser(
string name,
Parser parser,
boost::optional<ServerGlobalParams::FeatureCompatibility::Version> requiredMinVersion) {
auto it = parserMap.find(name);
massert(28707,
str::stream() << "Duplicate document source (" << name << ") registered.",
it == parserMap.end());
parserMap[name] = {parser, requiredMinVersion};
}
list<intrusive_ptr<DocumentSource>> DocumentSource::parse(
const intrusive_ptr<ExpressionContext>& expCtx, BSONObj stageObj) {
uassert(16435,
"A pipeline stage specification object must contain exactly one field.",
stageObj.nFields() == 1);
BSONElement stageSpec = stageObj.firstElement();
auto stageName = stageSpec.fieldNameStringData();
// Get the registered parser and call that.
auto it = parserMap.find(stageName);
uassert(16436,
str::stream() << "Unrecognized pipeline stage name: '" << stageName << "'",
it != parserMap.end());
uassert(ErrorCodes::QueryFeatureNotAllowed,
str::stream() << stageName
<< " is not allowed in the current feature compatibility version. See "
<< feature_compatibility_version_documentation::kCompatibilityLink
<< " for more information.",
!expCtx->maxFeatureCompatibilityVersion || !it->second.requiredMinVersion ||
(*it->second.requiredMinVersion <= *expCtx->maxFeatureCompatibilityVersion));
return it->second.parser(stageSpec, expCtx);
}
const char* DocumentSource::getSourceName() const {
static const char unknown[] = "[UNKNOWN]";
return unknown;
}
intrusive_ptr<DocumentSource> DocumentSource::optimize() {
return this;
}
namespace {
/**
* Returns a pair of pointers to $match stages, either of which can be null. The first entry in the
* pair is a $match stage that can be moved before this stage, the second is a $match stage that
* must remain after this stage.
*/
std::pair<boost::intrusive_ptr<DocumentSourceMatch>, boost::intrusive_ptr<DocumentSourceMatch>>
splitMatchByModifiedFields(const boost::intrusive_ptr<DocumentSourceMatch>& match,
const DocumentSource::GetModPathsReturn& modifiedPathsRet) {
// Attempt to move some or all of this $match before this stage.
std::set<std::string> modifiedPaths;
switch (modifiedPathsRet.type) {
case DocumentSource::GetModPathsReturn::Type::kNotSupported:
// We don't know what paths this stage might modify, so refrain from swapping.
return {nullptr, match};
case DocumentSource::GetModPathsReturn::Type::kAllPaths:
// This stage modifies all paths, so cannot be swapped with a $match at all.
return {nullptr, match};
case DocumentSource::GetModPathsReturn::Type::kFiniteSet:
modifiedPaths = std::move(modifiedPathsRet.paths);
break;
case DocumentSource::GetModPathsReturn::Type::kAllExcept: {
DepsTracker depsTracker;
match->getDependencies(&depsTracker);
auto preservedPaths = modifiedPathsRet.paths;
for (auto&& rename : modifiedPathsRet.renames) {
preservedPaths.insert(rename.first);
}
modifiedPaths =
semantic_analysis::extractModifiedDependencies(depsTracker.fields, preservedPaths);
}
}
return match->splitSourceBy(modifiedPaths, modifiedPathsRet.renames);
}
/**
* Verifies whether or not a $group is able to swap with a succeeding $match stage. While ordinarily
* $group can swap with a $match, it cannot if the following $match has an $exists predicate on _id,
* and the $group has exactly one field as the $group key. This is because every document will have
* an _id field following such a $group stage, including those whose group key was missing before
* the $group. As an example, the following optimization would be incorrect as the post-optimization
* pipeline would handle documents that had nullish _id fields differently. Thus, given such a
* $group and $match, this function would return false.
* {$group: {_id: "$x"}}
* {$match: {_id: {$exists: true}}
* ---->
* {$match: {x: {$exists: true}}
* {$group: {_id: "$x"}}
*/
bool groupMatchSwapVerified(const DocumentSourceMatch& nextMatch,
const DocumentSourceGroup& thisGroup) {
if (thisGroup.getIdFields().size() != 1) {
return true;
}
return !expression::hasExistencePredicateOnPath(*(nextMatch.getMatchExpression()), "_id"_sd);
}
} // namespace
bool DocumentSource::pushMatchBefore(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) {
auto nextMatch = dynamic_cast<DocumentSourceMatch*>((*std::next(itr)).get());
auto thisGroup = dynamic_cast<DocumentSourceGroup*>(this);
if (constraints().canSwapWithMatch && nextMatch && !nextMatch->isTextQuery() &&
(!thisGroup || groupMatchSwapVerified(*nextMatch, *thisGroup))) {
// We're allowed to swap with a $match and the stage after us is a $match. Furthermore, the
// $match does not contain a text search predicate, which we do not attempt to optimize
// because such a $match must already be the first stage in the pipeline. We can attempt to
// swap the $match or part of the $match before ourselves.
auto splitMatch = splitMatchByModifiedFields(nextMatch, getModifiedPaths());
invariant(splitMatch.first || splitMatch.second);
if (splitMatch.first) {
// At least part of the $match can be moved before this stage. Erase the original $match
// and put the independent part before this stage. If splitMatch.second is not null,
// then there is a new $match stage to insert after ourselves which is dependent on the
// modified fields.
container->erase(std::next(itr));
container->insert(itr, std::move(splitMatch.first));
if (splitMatch.second) {
container->insert(std::next(itr), std::move(splitMatch.second));
}
return true;
}
}
return false;
}
bool DocumentSource::pushSampleBefore(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) {
auto nextSample = dynamic_cast<DocumentSourceSample*>((*std::next(itr)).get());
if (constraints().canSwapWithLimitAndSample && nextSample) {
container->insert(itr, std::move(nextSample));
container->erase(std::next(itr));
return true;
}
return false;
}
Pipeline::SourceContainer::iterator DocumentSource::optimizeAt(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
invariant(*itr == this);
// Attempt to swap 'itr' with a subsequent $match or subsequent $sample.
if (std::next(itr) != container->end() &&
(pushMatchBefore(itr, container) || pushSampleBefore(itr, container))) {
// The stage before the pushed before stage may be able to optimize further, if there is
// such a stage.
return std::prev(itr) == container->begin() ? std::prev(itr) : std::prev(std::prev(itr));
}
return doOptimizeAt(itr, container);
}
void DocumentSource::serializeToArray(vector<Value>& array,
boost::optional<ExplainOptions::Verbosity> explain) const {
Value entry = serialize(explain);
if (!entry.missing()) {
array.push_back(entry);
}
}
} // namespace mongo
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