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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 <memory>
#include "mongo/base/status_with.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/s/query/cluster_query_result.h"
#include "mongo/util/time_support.h"
namespace mongo {
class OperationContext;
/**
* This is the lightweight mongoS analogue of the PlanStage abstraction used to execute queries on
* mongoD (see mongo/db/plan_stage.h).
*
* Each subclass is a query execution stage which executes on the merging node. In general, the
* execution plan on mongos could have a tree of execution stages, but currently each node has at
* most one child. The leaf stage of the pipeline receives query result documents merged from the
* shards. The pipeline may then transform the result set in various ways before being returned by
* the root stage.
*/
class RouterExecStage {
public:
enum class ExecContext {
kInitialFind,
kGetMoreNoResultsYet,
kGetMoreWithAtLeastOneResultInBatch,
};
RouterExecStage(OperationContext* opCtx) : _opCtx(opCtx) {}
RouterExecStage(OperationContext* opCtx, std::unique_ptr<RouterExecStage> child)
: _opCtx(opCtx), _child(std::move(child)) {}
virtual ~RouterExecStage() = default;
/**
* Returns the next query result, or an error.
*
* If there are no more results, returns an EOF ClusterQueryResult.
*
* All returned BSONObjs are owned. They may own a buffer larger than the object. If you are
* holding on to a subset of the returned results and need to minimize memory usage, call copy()
* on the BSONObjs.
*/
virtual StatusWith<ClusterQueryResult> next(ExecContext) = 0;
/**
* Must be called before destruction to abandon a not-yet-exhausted plan. May block waiting for
* responses from remote hosts.
*
* Note that 'opCtx' may or may not be the same as the operation context to which this cursor is
* currently attached. This is so that a killing thread may call this method with its own
* operation context.
*/
virtual void kill(OperationContext* opCtx) {
invariant(_child); // The default implementation forwards to the child stage.
_child->kill(opCtx);
}
/**
* Returns the number of remote hosts involved in this execution plan.
*/
virtual std::size_t getNumRemotes() const {
invariant(_child); // The default implementation forwards to the child stage.
return _child->getNumRemotes();
}
/**
* Returns whether or not all the remote cursors are exhausted.
*/
virtual bool remotesExhausted() {
invariant(_child); // The default implementation forwards to the child stage.
return _child->remotesExhausted();
}
/**
* Sets the maxTimeMS value that the cursor should forward with any internally issued getMore
* requests.
*
* Returns a non-OK status if this cursor type does not support maxTimeMS on getMore (i.e. if
* the cursor is not tailable + awaitData).
*/
Status setAwaitDataTimeout(Milliseconds awaitDataTimeout) {
if (_child) {
auto childStatus = _child->setAwaitDataTimeout(awaitDataTimeout);
if (!childStatus.isOK()) {
return childStatus;
}
}
return doSetAwaitDataTimeout(awaitDataTimeout);
}
/**
* Returns the postBatchResumeToken if this RouterExecStage tree is executing a $changeStream;
* otherwise, returns an empty BSONObj. Default implementation forwards to the stage's child.
*/
virtual BSONObj getPostBatchResumeToken() const {
return _child ? _child->getPostBatchResumeToken() : BSONObj();
}
/**
* Sets the current operation context to be used by the router stage.
*/
void reattachToOperationContext(OperationContext* opCtx) {
invariant(!_opCtx);
_opCtx = opCtx;
if (_child) {
_child->reattachToOperationContext(opCtx);
}
doReattachToOperationContext();
}
/**
* Discards the stage's current OperationContext, setting it to 'nullptr'.
*/
void detachFromOperationContext() {
invariant(_opCtx);
_opCtx = nullptr;
if (_child) {
_child->detachFromOperationContext();
}
doDetachFromOperationContext();
}
/**
* Returns a pointer to the current OperationContext, or nullptr if there is no context.
*/
OperationContext* getOpCtx() {
return _opCtx;
}
protected:
/**
* Performs any stage-specific reattach actions. Called after the OperationContext has been set
* and is available via getOpCtx().
*/
virtual void doReattachToOperationContext() {}
/**
* Performs any stage-specific detach actions. Called after the OperationContext has been set to
* nullptr.
*/
virtual void doDetachFromOperationContext() {}
/**
* Performs any stage-specific await data timeout actions.
*/
virtual Status doSetAwaitDataTimeout(Milliseconds awaitDataTimeout) {
return Status::OK();
}
/**
* Returns an unowned pointer to the child stage, or nullptr if there is no child.
*/
RouterExecStage* getChildStage() const {
return _child.get();
}
private:
OperationContext* _opCtx = nullptr;
std::unique_ptr<RouterExecStage> _child;
};
} // namespace mongo
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