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/**
* Copyright (C) 2013 10gen 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/>.
*/
#include "mongo/db/exec/sort.h"
#include <algorithm>
#include "mongo/db/exec/working_set.h"
#include "mongo/db/exec/working_set_common.h"
namespace mongo {
// Used in STL sort.
struct WorkingSetComparison {
WorkingSetComparison(WorkingSet* ws, BSONObj pattern) : _ws(ws), _pattern(pattern) { }
bool operator()(const WorkingSetID& lhs, const WorkingSetID& rhs) const {
WorkingSetMember* lhsMember = _ws->get(lhs);
WorkingSetMember* rhsMember = _ws->get(rhs);
BSONObjIterator it(_pattern);
while (it.more()) {
BSONElement patternElt = it.next();
string fn = patternElt.fieldName();
BSONElement lhsElt;
verify(lhsMember->getFieldDotted(fn, &lhsElt));
BSONElement rhsElt;
verify(rhsMember->getFieldDotted(fn, &rhsElt));
// false means don't compare field name.
int x = lhsElt.woCompare(rhsElt, false);
if (-1 == patternElt.number()) { x = -x; }
if (x != 0) { return x < 0; }
}
// A comparator for use with sort is required to model a strict weak ordering, so
// to satisfy irreflexivity we must return 'false' for elements that we consider
// equivalent under the pattern.
return false;
}
WorkingSet* _ws;
BSONObj _pattern;
};
SortStage::SortStage(const SortStageParams& params, WorkingSet* ws, PlanStage* child)
: _ws(ws), _child(child), _pattern(params.pattern), _sorted(false),
_resultIterator(_data.end()) { }
SortStage::~SortStage() { }
bool SortStage::isEOF() {
// We're done when our child has no more results, we've sorted the child's results, and
// we've returned all sorted results.
return _child->isEOF() && _sorted && (_data.end() == _resultIterator);
}
PlanStage::StageState SortStage::work(WorkingSetID* out) {
++_commonStats.works;
if (isEOF()) { return PlanStage::IS_EOF; }
// Still reading in results to sort.
if (!_sorted) {
WorkingSetID id;
StageState code = _child->work(&id);
if (PlanStage::ADVANCED == code) {
// We let the data stay in the WorkingSet and sort using the IDs.
_data.push_back(id);
// Add it into the map for quick invalidation if it has a valid DiskLoc.
// A DiskLoc may be invalidated at any time (during a yield). We need to get into
// the WorkingSet as quickly as possible to handle it.
WorkingSetMember* member = _ws->get(id);
if (member->hasLoc()) {
_wsidByDiskLoc[member->loc] = id;
}
++_commonStats.needTime;
return PlanStage::NEED_TIME;
}
else if (PlanStage::IS_EOF == code) {
// TODO: We don't need the lock for this. We could ask for a yield and do this work
// unlocked. Also, this is performing a lot of work for one call to work(...)
std::sort(_data.begin(), _data.end(), WorkingSetComparison(_ws, _pattern));
_resultIterator = _data.begin();
_sorted = true;
++_commonStats.needTime;
return PlanStage::NEED_TIME;
}
else {
if (PlanStage::NEED_FETCH == code) {
++_commonStats.needFetch;
}
else if (PlanStage::NEED_TIME == code) {
++_commonStats.needTime;
}
return code;
}
}
// Returning results.
verify(_resultIterator != _data.end());
verify(_sorted);
*out = *_resultIterator++;
++_commonStats.advanced;
return PlanStage::ADVANCED;
}
void SortStage::prepareToYield() {
++_commonStats.yields;
_child->prepareToYield();
}
void SortStage::recoverFromYield() {
++_commonStats.unyields;
_child->recoverFromYield();
}
void SortStage::invalidate(const DiskLoc& dl) {
++_commonStats.invalidates;
_child->invalidate(dl);
// _data contains indices into the WorkingSet, not actual data. If a WorkingSetMember in
// the WorkingSet needs to change state as a result of a DiskLoc invalidation, it will still
// be at the same spot in the WorkingSet. As such, we don't need to modify _data.
DataMap::iterator it = _wsidByDiskLoc.find(dl);
// If we're holding on to data that's got the DiskLoc we're invalidating...
if (_wsidByDiskLoc.end() != it) {
WorkingSetMember* member = _ws->get(it->second);
WorkingSetCommon::fetchAndInvalidateLoc(member);
_wsidByDiskLoc.erase(it);
++_specificStats.forcedFetches;
}
}
PlanStageStats* SortStage::getStats() {
_commonStats.isEOF = isEOF();
auto_ptr<PlanStageStats> ret(new PlanStageStats(_commonStats));
ret->setSpecific<SortStats>(_specificStats);
ret->children.push_back(_child->getStats());
return ret.release();
}
} // namespace mongo
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