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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.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kQuery
#include "mongo/db/exec/sort.h"
#include <algorithm>
#include "mongo/db/catalog/collection.h"
#include "mongo/db/exec/scoped_timer.h"
#include "mongo/db/exec/working_set_common.h"
#include "mongo/db/exec/working_set_computed_data.h"
#include "mongo/db/index/btree_key_generator.h"
#include "mongo/db/index_names.h"
#include "mongo/db/query/find_common.h"
#include "mongo/db/query/query_knobs_gen.h"
#include "mongo/db/query/query_planner.h"
#include "mongo/stdx/memory.h"
#include "mongo/util/log.h"
namespace mongo {
using std::endl;
using std::unique_ptr;
using std::vector;
using stdx::make_unique;
// static
const char* SortStage::kStageType = "SORT";
SortStage::WorkingSetComparator::WorkingSetComparator(BSONObj p) : pattern(p) {}
bool SortStage::WorkingSetComparator::operator()(const SortableDataItem& lhs,
const SortableDataItem& rhs) const {
// False means ignore field names.
int result = lhs.sortKey.woCompare(rhs.sortKey, pattern, false);
if (0 != result) {
return result < 0;
}
// Indices use RecordId as an additional sort key so we must as well.
return lhs.recordId < rhs.recordId;
}
SortStage::SortStage(OperationContext* opCtx,
const SortStageParams& params,
WorkingSet* ws,
PlanStage* child)
: PlanStage(kStageType, opCtx),
_ws(ws),
_pattern(params.pattern),
_limit(params.limit),
_sorted(false),
_resultIterator(_data.end()),
_memUsage(0) {
_children.emplace_back(child);
BSONObj sortComparator = FindCommon::transformSortSpec(_pattern);
_sortKeyComparator = stdx::make_unique<WorkingSetComparator>(sortComparator);
// If limit > 1, we need to initialize _dataSet here to maintain ordered set of data items while
// fetching from the child stage.
if (_limit > 1) {
const WorkingSetComparator& cmp = *_sortKeyComparator;
_dataSet.reset(new SortableDataItemSet(cmp));
}
}
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::doWork(WorkingSetID* out) {
const size_t maxBytes = static_cast<size_t>(internalQueryExecMaxBlockingSortBytes.load());
if (_memUsage > maxBytes) {
mongoutils::str::stream ss;
ss << "Sort operation used more than the maximum " << maxBytes
<< " bytes of RAM. Add an index, or specify a smaller limit.";
Status status(ErrorCodes::OperationFailed, ss);
*out = WorkingSetCommon::allocateStatusMember(_ws, status);
return PlanStage::FAILURE;
}
if (isEOF()) {
return PlanStage::IS_EOF;
}
// Still reading in results to sort.
if (!_sorted) {
WorkingSetID id = WorkingSet::INVALID_ID;
StageState code = child()->work(&id);
if (PlanStage::ADVANCED == code) {
WorkingSetMember* member = _ws->get(id);
// Planner must put a fetch before we get here.
verify(member->hasObj());
SortableDataItem item;
item.wsid = id;
// We extract the sort key from the WSM's computed data. This must have been generated
// by a SortKeyGeneratorStage descendent in the execution tree.
auto sortKeyComputedData =
static_cast<const SortKeyComputedData*>(member->getComputed(WSM_SORT_KEY));
item.sortKey = sortKeyComputedData->getSortKey();
if (member->hasRecordId()) {
// The RecordId breaks ties when sorting two WSMs with the same sort key.
item.recordId = member->recordId;
}
addToBuffer(item);
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(...)
sortBuffer();
_resultIterator = _data.begin();
_sorted = true;
return PlanStage::NEED_TIME;
} else if (PlanStage::FAILURE == code) {
// The stage which produces a failure is responsible for allocating a working set member
// with error details.
invariant(WorkingSet::INVALID_ID != id);
*out = id;
return code;
} else if (PlanStage::NEED_YIELD == code) {
*out = id;
}
return code;
}
// Returning results.
verify(_resultIterator != _data.end());
verify(_sorted);
*out = _resultIterator->wsid;
_resultIterator++;
return PlanStage::ADVANCED;
}
unique_ptr<PlanStageStats> SortStage::getStats() {
_commonStats.isEOF = isEOF();
const size_t maxBytes = static_cast<size_t>(internalQueryExecMaxBlockingSortBytes.load());
_specificStats.memLimit = maxBytes;
_specificStats.memUsage = _memUsage;
_specificStats.limit = _limit;
_specificStats.sortPattern = _pattern.getOwned();
unique_ptr<PlanStageStats> ret = make_unique<PlanStageStats>(_commonStats, STAGE_SORT);
ret->specific = make_unique<SortStats>(_specificStats);
ret->children.emplace_back(child()->getStats());
return ret;
}
const SpecificStats* SortStage::getSpecificStats() const {
return &_specificStats;
}
/**
* addToBuffer() and sortBuffer() work differently based on the
* configured limit. addToBuffer() is also responsible for
* performing some accounting on the overall memory usage to
* make sure we're not using too much memory.
*
* limit == 0:
* addToBuffer() - Adds item to vector.
* sortBuffer() - Sorts vector.
* limit == 1:
* addToBuffer() - Replaces first item in vector with max of
* current and new item.
* Updates memory usage if item was replaced.
* sortBuffer() - Does nothing.
* limit > 1:
* addToBuffer() - Does not update vector. Adds item to set.
* If size of set exceeds limit, remove item from set
* with lowest key. Updates memory usage accordingly.
* sortBuffer() - Copies items from set to vectors.
*/
void SortStage::addToBuffer(const SortableDataItem& item) {
// Holds ID of working set member to be freed at end of this function.
WorkingSetID wsidToFree = WorkingSet::INVALID_ID;
WorkingSetMember* member = _ws->get(item.wsid);
if (_limit == 0) {
// Ensure that the BSONObj underlying the WorkingSetMember is owned in case we yield.
member->makeObjOwnedIfNeeded();
_data.push_back(item);
_memUsage += member->getMemUsage();
} else if (_limit == 1) {
if (_data.empty()) {
member->makeObjOwnedIfNeeded();
_data.push_back(item);
_memUsage = member->getMemUsage();
return;
}
wsidToFree = item.wsid;
const WorkingSetComparator& cmp = *_sortKeyComparator;
// Compare new item with existing item in vector.
if (cmp(item, _data[0])) {
wsidToFree = _data[0].wsid;
member->makeObjOwnedIfNeeded();
_data[0] = item;
_memUsage = member->getMemUsage();
}
} else {
// Update data item set instead of vector
// Limit not reached - insert and return
vector<SortableDataItem>::size_type limit(_limit);
if (_dataSet->size() < limit) {
member->makeObjOwnedIfNeeded();
_dataSet->insert(item);
_memUsage += member->getMemUsage();
return;
}
// Limit will be exceeded - compare with item with lowest key
// If new item does not have a lower key value than last item,
// do nothing.
wsidToFree = item.wsid;
SortableDataItemSet::const_iterator lastItemIt = --(_dataSet->end());
const SortableDataItem& lastItem = *lastItemIt;
const WorkingSetComparator& cmp = *_sortKeyComparator;
if (cmp(item, lastItem)) {
_memUsage -= _ws->get(lastItem.wsid)->getMemUsage();
_memUsage += member->getMemUsage();
wsidToFree = lastItem.wsid;
// According to std::set iterator validity rules,
// it does not matter which of erase()/insert() happens first.
// Here, we choose to erase first to release potential resources
// used by the last item and to keep the scope of the iterator to a minimum.
_dataSet->erase(lastItemIt);
member->makeObjOwnedIfNeeded();
_dataSet->insert(item);
}
}
// There was a buffered result which we can throw out because we are executing a sort with a
// limit, and the result is now known not to be in the top k set. Free the working set member
// associated with 'wsidToFree'.
if (wsidToFree != WorkingSet::INVALID_ID) {
_ws->free(wsidToFree);
}
}
void SortStage::sortBuffer() {
if (_limit == 0) {
const WorkingSetComparator& cmp = *_sortKeyComparator;
std::sort(_data.begin(), _data.end(), cmp);
} else if (_limit == 1) {
// Buffer contains either 0 or 1 item so it is already in a sorted state.
return;
} else {
// Set already contains items in sorted order, so we simply copy the items
// from the set to the vector.
// Release the memory for the set after the copy.
vector<SortableDataItem> newData(_dataSet->begin(), _dataSet->end());
_data.swap(newData);
_dataSet.reset();
}
}
} // namespace mongo
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