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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/exec/fetch.h"
#include <memory>
#include "mongo/db/catalog/collection.h"
#include "mongo/db/concurrency/write_conflict_exception.h"
#include "mongo/db/exec/filter.h"
#include "mongo/db/exec/scoped_timer.h"
#include "mongo/db/exec/working_set_common.h"
#include "mongo/util/fail_point.h"
#include "mongo/util/str.h"
namespace mongo {
using std::unique_ptr;
using std::vector;
// static
const char* FetchStage::kStageType = "FETCH";
FetchStage::FetchStage(ExpressionContext* expCtx,
WorkingSet* ws,
std::unique_ptr<PlanStage> child,
const MatchExpression* filter,
const Collection* collection)
: RequiresCollectionStage(kStageType, expCtx, collection),
_ws(ws),
_filter((filter && !filter->isTriviallyTrue()) ? filter : nullptr),
_idRetrying(WorkingSet::INVALID_ID) {
_children.emplace_back(std::move(child));
}
FetchStage::~FetchStage() {}
bool FetchStage::isEOF() {
if (WorkingSet::INVALID_ID != _idRetrying) {
// We have a working set member that we need to retry.
return false;
}
return child()->isEOF();
}
PlanStage::StageState FetchStage::doWork(WorkingSetID* out) {
if (isEOF()) {
return PlanStage::IS_EOF;
}
// Either retry the last WSM we worked on or get a new one from our child.
WorkingSetID id;
StageState status;
if (_idRetrying == WorkingSet::INVALID_ID) {
status = child()->work(&id);
} else {
status = ADVANCED;
id = _idRetrying;
_idRetrying = WorkingSet::INVALID_ID;
}
if (PlanStage::ADVANCED == status) {
WorkingSetMember* member = _ws->get(id);
// If there's an obj there, there is no fetching to perform.
if (member->hasObj()) {
++_specificStats.alreadyHasObj;
} else {
// We need a valid RecordId to fetch from and this is the only state that has one.
verify(WorkingSetMember::RID_AND_IDX == member->getState());
verify(member->hasRecordId());
try {
if (!_cursor)
_cursor = collection()->getCursor(opCtx());
if (!WorkingSetCommon::fetch(opCtx(), _ws, id, _cursor, collection()->ns())) {
_ws->free(id);
return NEED_TIME;
}
} catch (const WriteConflictException&) {
// Ensure that the BSONObj underlying the WorkingSetMember is owned because it may
// be freed when we yield.
member->makeObjOwnedIfNeeded();
_idRetrying = id;
*out = WorkingSet::INVALID_ID;
return NEED_YIELD;
}
}
return returnIfMatches(member, id, out);
} else if (PlanStage::NEED_YIELD == status) {
*out = id;
}
return status;
}
void FetchStage::doSaveStateRequiresCollection() {
if (_cursor) {
_cursor->saveUnpositioned();
}
}
void FetchStage::doRestoreStateRequiresCollection() {
if (_cursor) {
const bool couldRestore = _cursor->restore();
uassert(50982, "could not restore cursor for FETCH stage", couldRestore);
}
}
void FetchStage::doDetachFromOperationContext() {
if (_cursor)
_cursor->detachFromOperationContext();
}
void FetchStage::doReattachToOperationContext() {
if (_cursor)
_cursor->reattachToOperationContext(opCtx());
}
PlanStage::StageState FetchStage::returnIfMatches(WorkingSetMember* member,
WorkingSetID memberID,
WorkingSetID* out) {
// We consider "examining a document" to be every time that we pass a document through
// a filter by calling Filter::passes(...) below. Therefore, the 'docsExamined' metric
// is not always equal to the number of documents that were fetched from the collection.
// In particular, we can sometimes generate plans which have two fetch stages. The first
// one actually grabs the document from the collection, and the second passes the
// document through a second filter.
//
// One common example of this is geoNear. Suppose that a geoNear plan is searching an
// annulus to find 2dsphere-indexed documents near some point (x, y) on the globe.
// After fetching documents within geo hashes that intersect this annulus, the docs are
// fetched and filtered to make sure that they really do fall into this annulus. However,
// the user might also want to find only those documents for which accommodationType==
// "restaurant". The planner will add a second fetch stage to filter by this non-geo
// predicate.
++_specificStats.docsExamined;
if (Filter::passes(member, _filter)) {
*out = memberID;
return PlanStage::ADVANCED;
} else {
_ws->free(memberID);
return PlanStage::NEED_TIME;
}
}
unique_ptr<PlanStageStats> FetchStage::getStats() {
_commonStats.isEOF = isEOF();
// Add a BSON representation of the filter to the stats tree, if there is one.
if (nullptr != _filter) {
BSONObjBuilder bob;
_filter->serialize(&bob);
_commonStats.filter = bob.obj();
}
unique_ptr<PlanStageStats> ret = std::make_unique<PlanStageStats>(_commonStats, STAGE_FETCH);
ret->specific = std::make_unique<FetchStats>(_specificStats);
ret->children.emplace_back(child()->getStats());
return ret;
}
const SpecificStats* FetchStage::getSpecificStats() const {
return &_specificStats;
}
} // namespace mongo
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