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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 "mongo/platform/basic.h"
#include <boost/intrusive_ptr.hpp>
#include <boost/optional.hpp>
#include <functional>
#include <list>
#include <memory>
#include <string>
#include <vector>
#include "mongo/base/init.h"
#include "mongo/bson/simple_bsonobj_comparator.h"
#include "mongo/db/collection_index_usage_tracker.h"
#include "mongo/db/commands.h"
#include "mongo/db/exec/document_value/document.h"
#include "mongo/db/exec/document_value/value.h"
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/exec/scoped_timer.h"
#include "mongo/db/generic_cursor.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/pipeline/dependencies.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/field_path.h"
#include "mongo/db/pipeline/lite_parsed_document_source.h"
#include "mongo/db/pipeline/pipeline.h"
#include "mongo/db/pipeline/stage_constraints.h"
#include "mongo/db/query/explain_options.h"
#include "mongo/util/intrusive_counter.h"
namespace mongo {
class Document;
/**
* Registers a DocumentSource to have the name 'key'.
*
* 'liteParser' takes an AggregateCommand and a BSONElement and returns a
* LiteParsedDocumentSource. This is used for checks that need to happen before a full parse,
* such as checks about which namespaces are referenced by this aggregation.
*
* 'fullParser' is either a DocumentSource::SimpleParser or a DocumentSource::Parser.
* In both cases, it takes a BSONElement and an ExpressionContext and returns fully-executable
* DocumentSource(s), for optimization and execution. In the common case it's a SimpleParser,
* which returns a single DocumentSource; in the general case it's a Parser, which returns a whole
* std::list to support "multi-stage aliases" like $bucket.
*
* Stages that do not require any special pre-parse checks can use
* LiteParsedDocumentSourceDefault::parse as their 'liteParser'.
*
* As an example, if your stage DocumentSourceFoo looks like {$foo: <args>} and does *not* require
* any special pre-parse checks, you should implement a static parser like
* DocumentSourceFoo::createFromBson(), and register it like so:
* REGISTER_DOCUMENT_SOURCE(foo,
* LiteParsedDocumentSourceDefault::parse,
* DocumentSourceFoo::createFromBson);
*/
#define REGISTER_DOCUMENT_SOURCE(key, liteParser, fullParser, allowedWithApiStrict) \
REGISTER_DOCUMENT_SOURCE_CONDITIONALLY( \
key, liteParser, fullParser, allowedWithApiStrict, boost::none, true)
/**
* Like REGISTER_DOCUMENT_SOURCE, except the parser will only be enabled when FCV >= minVersion.
* We store minVersion in the parserMap, so that changing FCV at runtime correctly enables/disables
* the parser.
*/
#define REGISTER_DOCUMENT_SOURCE_WITH_MIN_VERSION( \
key, liteParser, fullParser, allowedWithApiStrict, minVersion) \
REGISTER_DOCUMENT_SOURCE_CONDITIONALLY( \
key, liteParser, fullParser, allowedWithApiStrict, minVersion, true)
/**
* Like REGISTER_DOCUMENT_SOURCE_WITH_MIN_VERSION, except you can also specify a condition,
* evaluated during startup, that decides whether to register the parser.
*
* For example, you could check a feature flag, and register the parser only when it's enabled.
*
* Note that the condition is evaluated only once, during a MONGO_INITIALIZER. Don't specify
* a condition that can change at runtime, such as FCV. (Feature flags are ok, because they
* cannot be toggled at runtime.)
*
* This is the most general REGISTER_DOCUMENT_SOURCE* macro, which all others should delegate to.
*/
#define REGISTER_DOCUMENT_SOURCE_CONDITIONALLY( \
key, liteParser, fullParser, allowedWithApiStrict, minVersion, ...) \
MONGO_INITIALIZER(addToDocSourceParserMap_##key)(InitializerContext*) { \
if (!__VA_ARGS__) { \
return; \
} \
LiteParsedDocumentSource::registerParser("$" #key, liteParser, allowedWithApiStrict); \
DocumentSource::registerParser("$" #key, fullParser, minVersion); \
}
/**
* Like REGISTER_DOCUMENT_SOURCE, except the parser is only enabled when test-commands are enabled.
*/
#define REGISTER_TEST_DOCUMENT_SOURCE(key, liteParser, fullParser) \
REGISTER_DOCUMENT_SOURCE_CONDITIONALLY( \
key, \
liteParser, \
fullParser, \
LiteParsedDocumentSource::AllowedWithApiStrict::kNeverInVersion1, \
boost::none, \
::mongo::getTestCommandsEnabled())
class DocumentSource : public RefCountable {
public:
// In general a parser returns a list of DocumentSources, to accomodate "multi-stage aliases"
// like $bucket.
using Parser = std::function<std::list<boost::intrusive_ptr<DocumentSource>>(
BSONElement, const boost::intrusive_ptr<ExpressionContext>&)>;
// But in the common case a parser returns only one DocumentSource.
using SimpleParser = std::function<boost::intrusive_ptr<DocumentSource>(
BSONElement, const boost::intrusive_ptr<ExpressionContext>&)>;
using ChangeStreamRequirement = StageConstraints::ChangeStreamRequirement;
using HostTypeRequirement = StageConstraints::HostTypeRequirement;
using PositionRequirement = StageConstraints::PositionRequirement;
using DiskUseRequirement = StageConstraints::DiskUseRequirement;
using FacetRequirement = StageConstraints::FacetRequirement;
using StreamType = StageConstraints::StreamType;
using TransactionRequirement = StageConstraints::TransactionRequirement;
using LookupRequirement = StageConstraints::LookupRequirement;
using UnionRequirement = StageConstraints::UnionRequirement;
/**
* This is what is returned from the main DocumentSource API: getNext(). It is essentially a
* (ReturnStatus, Document) pair, with the first entry being used to communicate information
* about the execution of the DocumentSource, such as whether or not it has been exhausted.
*/
class GetNextResult {
public:
enum class ReturnStatus {
// There is a result to be processed.
kAdvanced,
// There will be no further results.
kEOF,
// There is not a result to be processed yet, but there may be more results in the
// future. If a DocumentSource retrieves this status from its child, it must propagate
// it without doing any further work.
kPauseExecution,
};
static GetNextResult makeEOF() {
return GetNextResult(ReturnStatus::kEOF);
}
static GetNextResult makePauseExecution() {
return GetNextResult(ReturnStatus::kPauseExecution);
}
/**
* Shortcut constructor for the common case of creating an 'advanced' GetNextResult from the
* given 'result'. Accepts only an rvalue reference as an argument, since DocumentSources
* will want to move 'result' into this GetNextResult, and should have to opt in to making a
* copy.
*/
/* implicit */ GetNextResult(Document&& result)
: _status(ReturnStatus::kAdvanced), _result(std::move(result)) {}
/**
* Gets the result document. It is an error to call this if isAdvanced() returns false.
*/
const Document& getDocument() const {
dassert(isAdvanced());
return _result;
}
/**
* Releases the result document, transferring ownership to the caller. It is an error to
* call this if isAdvanced() returns false.
*/
Document releaseDocument() {
dassert(isAdvanced());
return std::move(_result);
}
ReturnStatus getStatus() const {
return _status;
}
bool isAdvanced() const {
return _status == ReturnStatus::kAdvanced;
}
bool isEOF() const {
return _status == ReturnStatus::kEOF;
}
bool isPaused() const {
return _status == ReturnStatus::kPauseExecution;
}
private:
GetNextResult(ReturnStatus status) : _status(status) {}
ReturnStatus _status;
Document _result;
};
/**
* A struct representing the information needed to execute this stage on a distributed
* collection. Describes how a pipeline should be split for sharded execution.
*/
struct DistributedPlanLogic {
// A stage which executes on each shard in parallel, or nullptr if nothing can be done in
// parallel. For example, a partial $group before a subsequent global $group.
boost::intrusive_ptr<DocumentSource> shardsStage = nullptr;
// A stage which executes after merging all the results together, or nullptr if nothing is
// necessary after merging. For example, a $limit stage.
boost::intrusive_ptr<DocumentSource> mergingStage = nullptr;
// If set, each document is expected to have sort key metadata which will be serialized in
// the '$sortKey' field. 'inputSortPattern' will then be used to describe which fields are
// ascending and which fields are descending when merging the streams together.
boost::optional<BSONObj> inputSortPattern = boost::none;
};
virtual ~DocumentSource() {}
/**
* The main execution API of a DocumentSource. Returns an intermediate query result generated by
* this DocumentSource.
*
* For performance reasons, a streaming stage must not keep references to documents across calls
* to getNext(). Such stages must retrieve a result from their child and then release it (or
* return it) before asking for another result. Failing to do so can result in extra work, since
* the Document/Value library must copy data on write when that data has a refcount above one.
*/
GetNextResult getNext() {
pExpCtx->checkForInterrupt();
if (MONGO_likely(!pExpCtx->shouldCollectDocumentSourceExecStats())) {
return doGetNext();
}
auto serviceCtx = pExpCtx->opCtx->getServiceContext();
invariant(serviceCtx);
auto fcs = serviceCtx->getFastClockSource();
invariant(fcs);
invariant(_commonStats.executionTimeMillis);
ScopedTimer timer(fcs, _commonStats.executionTimeMillis.get_ptr());
++_commonStats.works;
GetNextResult next = doGetNext();
if (next.isAdvanced()) {
++_commonStats.advanced;
}
return next;
}
/**
* Returns a struct containing information about any special constraints imposed on using this
* stage. Input parameter Pipeline::SplitState is used by stages whose requirements change
* depending on whether they are in a split or unsplit pipeline.
*/
virtual StageConstraints constraints(
Pipeline::SplitState = Pipeline::SplitState::kUnsplit) const = 0;
/**
* Informs the stage that it is no longer needed and can release its resources. After dispose()
* is called the stage must still be able to handle calls to getNext(), but can return kEOF.
*
* This is a non-virtual public interface to ensure dispose() is threaded through the entire
* pipeline. Subclasses should override doDispose() to implement their disposal.
*/
void dispose() {
doDispose();
if (pSource) {
pSource->dispose();
}
}
/**
* Get the CommonStats for this DocumentSource.
*/
const CommonStats& getCommonStats() const {
return _commonStats;
}
/**
* Get the stats specific to the DocumentSource. It is legal for the DocumentSource to return
* nullptr to indicate that no specific stats are available.
*/
virtual const SpecificStats* getSpecificStats() const {
return nullptr;
}
/**
* Get the stage's name.
*/
virtual const char* getSourceName() const;
/**
* Set the underlying source this source should use to get Documents from. Must not throw
* exceptions.
*/
virtual void setSource(DocumentSource* source) {
pSource = source;
}
/**
* In the default case, serializes the DocumentSource and adds it to the std::vector<Value>.
*
* A subclass may choose to overwrite this, rather than serialize, if it should output multiple
* stages (eg, $sort sometimes also outputs a $limit).
*
* The 'explain' parameter indicates the explain verbosity mode, or is equal boost::none if no
* explain is requested.
*/
virtual void serializeToArray(
std::vector<Value>& array,
boost::optional<ExplainOptions::Verbosity> explain = boost::none) const;
/**
* If this stage uses additional namespaces, adds them to 'collectionNames'. These namespaces
* should all be names of collections, not views.
*/
virtual void addInvolvedCollections(
stdx::unordered_set<NamespaceString>* collectionNames) const {}
virtual void detachFromOperationContext() {}
virtual void reattachToOperationContext(OperationContext* opCtx) {}
virtual bool usedDisk() {
return false;
};
/**
* Create a DocumentSource pipeline stage from 'stageObj'.
*/
static std::list<boost::intrusive_ptr<DocumentSource>> parse(
const boost::intrusive_ptr<ExpressionContext>& expCtx, BSONObj stageObj);
/**
* Registers a DocumentSource with a parsing function, so that when a stage with the given name
* is encountered, it will call 'parser' to construct that stage.
*
* DO NOT call this method directly. Instead, use the REGISTER_DOCUMENT_SOURCE macro defined in
* this file.
*/
static void registerParser(
std::string name,
Parser parser,
boost::optional<ServerGlobalParams::FeatureCompatibility::Version> requiredMinVersion);
/**
* Convenience wrapper for the common case, when DocumentSource::Parser returns a list of one
* DocumentSource.
*
* DO NOT call this method directly. Instead, use the REGISTER_DOCUMENT_SOURCE macro defined in
* this file.
*/
static void registerParser(
std::string name,
SimpleParser simpleParser,
boost::optional<ServerGlobalParams::FeatureCompatibility::Version> requiredMinVersion);
/**
* Returns true if the DocumentSource has a query.
*/
virtual bool hasQuery() const;
/**
* Returns the DocumentSource query if it exists.
*/
virtual BSONObj getQuery() const;
private:
/**
* Attempt to push a match stage from directly ahead of the current stage given by itr to before
* the current stage. Returns whether the optimization was performed.
*/
bool pushMatchBefore(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container);
/**
* Attempt to push a sample stage from directly ahead of the current stage given by itr to
* before the current stage. Returns whether the optimization was performed.
*/
bool pushSampleBefore(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container);
public:
/**
* The non-virtual public interface for optimization. Attempts to do some generic optimizations
* such as pushing $matches as early in the pipeline as possible, then calls out to
* doOptimizeAt() for stage-specific optimizations.
*
* Subclasses should override doOptimizeAt() if they can apply some optimization(s) based on
* subsequent stages in the pipeline.
*/
Pipeline::SourceContainer::iterator optimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container);
/**
* Returns an optimized DocumentSource that is semantically equivalent to this one, or
* nullptr if this stage is a no-op. Implementations are allowed to modify themselves
* in-place and return a pointer to themselves. For best results, first optimize the pipeline
* with the optimizePipeline() method defined in pipeline.cpp.
*
* This is intended for any operations that include expressions, and provides a hook for
* those to optimize those operations.
*
* The default implementation is to do nothing and return yourself.
*/
virtual boost::intrusive_ptr<DocumentSource> optimize();
//
// Property Analysis - These methods allow a DocumentSource to expose information about
// properties of themselves, such as which fields they need to apply their transformations, and
// whether or not they produce or preserve a sort order.
//
// Property analysis can be useful during optimization (e.g. analysis of sort orders determines
// whether or not a blocking group can be upgraded to a streaming group).
//
struct GetModPathsReturn {
enum class Type {
// No information is available about which paths are modified.
kNotSupported,
// All fields will be modified. This should be used by stages like $replaceRoot which
// modify the entire document.
kAllPaths,
// A finite set of paths will be modified by this stage. This is true for something like
// {$project: {a: 0, b: 0}}, which will only modify 'a' and 'b', and leave all other
// paths unmodified.
kFiniteSet,
// This stage will modify an infinite set of paths, but we know which paths it will not
// modify. For example, the stage {$project: {_id: 1, a: 1}} will leave only the fields
// '_id' and 'a' unmodified, but all other fields will be projected out.
kAllExcept,
};
GetModPathsReturn(Type type,
std::set<std::string>&& paths,
StringMap<std::string>&& renames)
: type(type), paths(std::move(paths)), renames(std::move(renames)) {}
Type type;
std::set<std::string> paths;
// Stages may fill out 'renames' to contain information about path renames. Each entry in
// 'renames' maps from the new name of the path (valid in documents flowing *out* of this
// stage) to the old name of the path (valid in documents flowing *into* this stage).
//
// For example, consider the stage
//
// {$project: {_id: 0, a: 1, b: "$c"}}
//
// This stage should return kAllExcept, since it modifies all paths other than "a". It can
// also fill out 'renames' with the mapping "b" => "c".
StringMap<std::string> renames;
};
/**
* Returns information about which paths are added, removed, or updated by this stage. The
* default implementation uses kNotSupported to indicate that the set of modified paths for this
* stage is not known.
*
* See GetModPathsReturn above for the possible return values and what they mean.
*/
virtual GetModPathsReturn getModifiedPaths() const {
return {GetModPathsReturn::Type::kNotSupported, std::set<std::string>{}, {}};
}
/**
* Returns the expression context from the stage's context.
*/
const boost::intrusive_ptr<ExpressionContext>& getContext() const {
return pExpCtx;
}
/**
* Get the dependencies this operation needs to do its job. If overridden, subclasses must add
* all paths needed to apply their transformation to 'deps->fields', and call
* 'deps->setNeedsMetadata()' to indicate what metadata (e.g. text score), if any, is required.
*
* See DepsTracker::State for the possible return values and what they mean.
*/
virtual DepsTracker::State getDependencies(DepsTracker* deps) const {
return DepsTracker::State::NOT_SUPPORTED;
}
/**
* If this stage can be run in parallel across a distributed collection, returns boost::none.
* Otherwise, returns a struct representing what needs to be done to merge each shard's pipeline
* into a single stream of results. Must not mutate the existing source object; if different
* behaviour is required, a new source should be created and configured appropriately. It is an
* error for the returned DistributedPlanLogic to have identical pointers for 'shardsStage' and
* 'mergingStage'.
*/
virtual boost::optional<DistributedPlanLogic> distributedPlanLogic() = 0;
/**
* Returns true if it would be correct to execute this stage in parallel across the shards in
* cases where the final stage is a stage which can perform a write operation, such as $merge.
* For example, a $group stage which is just merging the groups from the shards can be run in
* parallel since it will preserve the shard key.
*/
virtual bool canRunInParallelBeforeWriteStage(
const std::set<std::string>& nameOfShardKeyFieldsUponEntryToStage) const {
return false;
}
protected:
DocumentSource(const StringData stageName,
const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
/**
* The main execution API of a DocumentSource. Returns an intermediate query result generated by
* this DocumentSource. See comment at getNext().
*/
virtual GetNextResult doGetNext() = 0;
/**
* Attempt to perform an optimization with the following source in the pipeline. 'container'
* refers to the entire pipeline, and 'itr' points to this stage within the pipeline.
*
* The return value is an iterator over the same container which points to the first location
* in the container at which an optimization may be possible, or the end of the container().
*
* For example, if a swap takes place, the returned iterator should just be the position
* directly preceding 'itr', if such a position exists, since the stage at that position may be
* able to perform further optimizations with its new neighbor.
*/
virtual Pipeline::SourceContainer::iterator doOptimizeAt(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
return std::next(itr);
};
/**
* Release any resources held by this stage. After doDispose() is called the stage must still be
* able to handle calls to getNext(), but can return kEOF.
*/
virtual void doDispose() {}
/*
Most DocumentSources have an underlying source they get their data
from. This is a convenience for them.
The default implementation of setSource() sets this; if you don't
need a source, override that to verify(). The default is to
verify() if this has already been set.
*/
DocumentSource* pSource;
boost::intrusive_ptr<ExpressionContext> pExpCtx;
private:
CommonStats _commonStats;
/**
* Create a Value that represents the document source.
*
* This is used by the default implementation of serializeToArray() to add this object
* to a pipeline being serialized. Returning a missing() Value results in no entry
* being added to the array for this stage (DocumentSource).
*
* The 'explain' parameter indicates the explain verbosity mode, or is equal boost::none if no
* explain is requested.
*/
virtual Value serialize(
boost::optional<ExplainOptions::Verbosity> explain = boost::none) const = 0;
};
} // namespace mongo
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