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/**
* Copyright (C) 2014 MongoDB 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/>.
*
* 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 GNU Affero General 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/platform/basic.h"
#include "mongo/db/exec/multi_plan.h"
#include <algorithm>
#include <math.h>
#include "mongo/base/owned_pointer_vector.h"
#include "mongo/db/catalog/collection.h"
#include "mongo/db/catalog/database.h"
#include "mongo/db/client.h"
#include "mongo/db/exec/scoped_timer.h"
#include "mongo/db/exec/working_set_common.h"
#include "mongo/db/query/explain.h"
#include "mongo/db/query/plan_cache.h"
#include "mongo/db/query/plan_ranker.h"
#include "mongo/db/query/qlog.h"
#include "mongo/db/storage/record_fetcher.h"
#include "mongo/util/mongoutils/str.h"
#include "mongo/util/log.h"
namespace mongo {
// static
const char* MultiPlanStage::kStageType = "MULTI_PLAN";
MultiPlanStage::MultiPlanStage(OperationContext* txn,
const Collection* collection,
CanonicalQuery* cq)
: _txn(txn),
_collection(collection),
_query(cq),
_bestPlanIdx(kNoSuchPlan),
_backupPlanIdx(kNoSuchPlan),
_failure(false),
_failureCount(0),
_statusMemberId(WorkingSet::INVALID_ID),
_commonStats(kStageType) { }
MultiPlanStage::~MultiPlanStage() {
for (size_t ix = 0; ix < _candidates.size(); ++ix) {
delete _candidates[ix].solution;
delete _candidates[ix].root;
}
}
void MultiPlanStage::addPlan(QuerySolution* solution, PlanStage* root,
WorkingSet* ws) {
_candidates.push_back(CandidatePlan(solution, root, ws));
}
bool MultiPlanStage::isEOF() {
if (_failure) { return true; }
// If _bestPlanIdx hasn't been found, can't be at EOF
if (!bestPlanChosen()) { return false; }
// We must have returned all our cached results
// and there must be no more results from the best plan.
CandidatePlan& bestPlan = _candidates[_bestPlanIdx];
return bestPlan.results.empty() && bestPlan.root->isEOF();
}
PlanStage::StageState MultiPlanStage::work(WorkingSetID* out) {
// Adds the amount of time taken by work() to executionTimeMillis.
ScopedTimer timer(&_commonStats.executionTimeMillis);
if (_failure) {
*out = _statusMemberId;
return PlanStage::FAILURE;
}
CandidatePlan& bestPlan = _candidates[_bestPlanIdx];
// Look for an already produced result that provides the data the caller wants.
if (!bestPlan.results.empty()) {
*out = bestPlan.results.front();
bestPlan.results.pop_front();
_commonStats.advanced++;
return PlanStage::ADVANCED;
}
// best plan had no (or has no more) cached results
StageState state = bestPlan.root->work(out);
if (PlanStage::FAILURE == state && hasBackupPlan()) {
QLOG() << "Best plan errored out switching to backup\n";
// Uncache the bad solution if we fall back
// on the backup solution.
//
// XXX: Instead of uncaching we should find a way for the
// cached plan runner to fall back on a different solution
// if the best solution fails. Alternatively we could try to
// defer cache insertion to be after the first produced result.
_collection->infoCache()->getPlanCache()->remove(*_query);
_bestPlanIdx = _backupPlanIdx;
_backupPlanIdx = kNoSuchPlan;
return _candidates[_bestPlanIdx].root->work(out);
}
if (hasBackupPlan() && PlanStage::ADVANCED == state) {
QLOG() << "Best plan had a blocking stage, became unblocked\n";
_backupPlanIdx = kNoSuchPlan;
}
// Increment stats.
if (PlanStage::ADVANCED == state) {
_commonStats.advanced++;
}
else if (PlanStage::NEED_TIME == state) {
_commonStats.needTime++;
}
else if (PlanStage::NEED_FETCH == state) {
_commonStats.needFetch++;
}
return state;
}
Status MultiPlanStage::tryYield(PlanYieldPolicy* yieldPolicy) {
// There are two conditions which cause us to yield during plan selection if we have a
// YIELD_AUTO policy:
// 1) The yield policy's timer elapsed, or
// 2) some stage requested a yield due to a document fetch (NEED_FETCH).
// In both cases, the actual yielding happens here.
if (NULL != yieldPolicy && (yieldPolicy->shouldYield() || NULL != _fetcher.get())) {
// Here's where we yield.
bool alive = yieldPolicy->yield(_fetcher.get());
if (!alive) {
_failure = true;
Status failStat(ErrorCodes::OperationFailed,
"PlanExecutor killed during plan selection");
_statusMemberId = WorkingSetCommon::allocateStatusMember(_candidates[0].ws,
failStat);
return failStat;
}
}
// We're done using the fetcher, so it should be freed. We don't want to
// use the same RecordFetcher twice.
_fetcher.reset();
return Status::OK();
}
Status MultiPlanStage::pickBestPlan(PlanYieldPolicy* yieldPolicy) {
// Adds the amount of time taken by pickBestPlan() to executionTimeMillis. There's lots of
// execution work that happens here, so this is needed for the time accounting to
// make sense.
ScopedTimer timer(&_commonStats.executionTimeMillis);
// Run each plan some number of times. This number is at least as great as
// 'internalQueryPlanEvaluationWorks', but may be larger for big collections.
size_t numWorks = internalQueryPlanEvaluationWorks;
if (NULL != _collection) {
// For large collections, the number of works is set to be this
// fraction of the collection size.
double fraction = internalQueryPlanEvaluationCollFraction;
numWorks = std::max(size_t(internalQueryPlanEvaluationWorks),
size_t(fraction * _collection->numRecords(_txn)));
}
// We treat ntoreturn as though it is a limit during plan ranking.
// This means that ranking might not be great for sort + batchSize.
// But it also means that we don't buffer too much data for sort + limit.
// See SERVER-14174 for details.
size_t numToReturn = _query->getParsed().getNumToReturn();
// Determine the number of results which we will produce during the plan
// ranking phase before stopping.
size_t numResults = (size_t)internalQueryPlanEvaluationMaxResults;
if (numToReturn > 0) {
numResults = std::min(numToReturn, numResults);
}
// Work the plans, stopping when a plan hits EOF or returns some
// fixed number of results.
for (size_t ix = 0; ix < numWorks; ++ix) {
bool moreToDo = workAllPlans(numResults, yieldPolicy);
if (!moreToDo) { break; }
}
if (_failure) {
invariant(WorkingSet::INVALID_ID != _statusMemberId);
WorkingSetMember* member = _candidates[0].ws->get(_statusMemberId);
return WorkingSetCommon::getMemberStatus(*member);
}
// After picking best plan, ranking will own plan stats from
// candidate solutions (winner and losers).
std::auto_ptr<PlanRankingDecision> ranking(new PlanRankingDecision);
_bestPlanIdx = PlanRanker::pickBestPlan(_candidates, ranking.get());
verify(_bestPlanIdx >= 0 && _bestPlanIdx < static_cast<int>(_candidates.size()));
// Copy candidate order. We will need this to sort candidate stats for explain
// after transferring ownership of 'ranking' to plan cache.
std::vector<size_t> candidateOrder = ranking->candidateOrder;
CandidatePlan& bestCandidate = _candidates[_bestPlanIdx];
std::list<WorkingSetID>& alreadyProduced = bestCandidate.results;
QuerySolution* bestSolution = bestCandidate.solution;
QLOG() << "Winning solution:\n" << bestSolution->toString() << endl;
LOG(2) << "Winning plan: " << Explain::getPlanSummary(bestCandidate.root);
_backupPlanIdx = kNoSuchPlan;
if (bestSolution->hasBlockingStage && (0 == alreadyProduced.size())) {
QLOG() << "Winner has blocking stage, looking for backup plan...\n";
for (size_t ix = 0; ix < _candidates.size(); ++ix) {
if (!_candidates[ix].solution->hasBlockingStage) {
QLOG() << "Candidate " << ix << " is backup child\n";
_backupPlanIdx = ix;
break;
}
}
}
// Logging for tied plans.
if (ranking->tieForBest && NULL != _collection) {
// These arrays having two or more entries is implied by 'tieForBest'.
invariant(ranking->scores.size() > 1);
invariant(ranking->candidateOrder.size() > 1);
size_t winnerIdx = ranking->candidateOrder[0];
size_t runnerUpIdx = ranking->candidateOrder[1];
LOG(1) << "Winning plan tied with runner-up."
<< " ns: " << _collection->ns()
<< " " << _query->toStringShort()
<< " winner score: " << ranking->scores[0]
<< " winner summary: "
<< Explain::getPlanSummary(_candidates[winnerIdx].root)
<< " runner-up score: " << ranking->scores[1]
<< " runner-up summary: "
<< Explain::getPlanSummary(_candidates[runnerUpIdx].root);
// There could be more than a 2-way tie, so log the stats for the remaining plans
// involved in the tie.
static const double epsilon = 1e-10;
for (size_t i = 2; i < ranking->scores.size(); i++) {
if (fabs(ranking->scores[i] - ranking->scores[0]) >= epsilon) {
break;
}
size_t planIdx = ranking->candidateOrder[i];
LOG(1) << "Plan " << i << " involved in multi-way tie."
<< " ns: " << _collection->ns()
<< " " << _query->toStringShort()
<< " score: " << ranking->scores[i]
<< " summary: "
<< Explain::getPlanSummary(_candidates[planIdx].root);
}
}
// Store the choice we just made in the cache. In order to do so,
// 1) the query must be of a type that is safe to cache, and
// 2) two or more plans cannot have tied for the win. Caching in the
// case of ties can cause successive queries of the same shape to
// use a bad index.
if (PlanCache::shouldCacheQuery(*_query) && !ranking->tieForBest) {
// Create list of candidate solutions for the cache with
// the best solution at the front.
std::vector<QuerySolution*> solutions;
// Generate solutions and ranking decisions sorted by score.
for (size_t orderingIndex = 0;
orderingIndex < candidateOrder.size(); ++orderingIndex) {
// index into candidates/ranking
size_t ix = candidateOrder[orderingIndex];
solutions.push_back(_candidates[ix].solution);
}
// Check solution cache data. Do not add to cache if
// we have any invalid SolutionCacheData data.
// XXX: One known example is 2D queries
bool validSolutions = true;
for (size_t ix = 0; ix < solutions.size(); ++ix) {
if (NULL == solutions[ix]->cacheData.get()) {
QLOG() << "Not caching query because this solution has no cache data: "
<< solutions[ix]->toString();
validSolutions = false;
break;
}
}
if (validSolutions) {
_collection->infoCache()->getPlanCache()->add(*_query, solutions, ranking.release());
}
}
return Status::OK();
}
vector<PlanStageStats*> MultiPlanStage::generateCandidateStats() {
OwnedPointerVector<PlanStageStats> candidateStats;
for (size_t ix = 0; ix < _candidates.size(); ix++) {
if (ix == (size_t)_bestPlanIdx) { continue; }
if (ix == (size_t)_backupPlanIdx) { continue; }
PlanStageStats* stats = _candidates[ix].root->getStats();
if (stats) {
candidateStats.push_back(stats);
}
}
return candidateStats.release();
}
bool MultiPlanStage::workAllPlans(size_t numResults, PlanYieldPolicy* yieldPolicy) {
bool doneWorking = false;
for (size_t ix = 0; ix < _candidates.size(); ++ix) {
CandidatePlan& candidate = _candidates[ix];
if (candidate.failed) { continue; }
// Might need to yield between calls to work due to the timer elapsing.
if (!(tryYield(yieldPolicy)).isOK()) {
return false;
}
WorkingSetID id = WorkingSet::INVALID_ID;
PlanStage::StageState state = candidate.root->work(&id);
if (PlanStage::ADVANCED == state) {
// Save result for later.
candidate.results.push_back(id);
// Once a plan returns enough results, stop working.
if (candidate.results.size() >= numResults) {
doneWorking = true;
}
}
else if (PlanStage::IS_EOF == state) {
// First plan to hit EOF wins automatically. Stop evaluating other plans.
// Assumes that the ranking will pick this plan.
doneWorking = true;
}
else if (PlanStage::NEED_FETCH == state) {
// Yielding for a NEED_FETCH is handled above. Here we just make sure that the
// WSM is fetchable as a sanity check.
WorkingSetMember* member = candidate.ws->get(id);
invariant(member->hasFetcher());
// Transfer ownership of the fetcher and yield.
_fetcher.reset(member->releaseFetcher());
if (!(tryYield(yieldPolicy)).isOK()) {
return false;
}
}
else if (PlanStage::NEED_TIME != state) {
// FAILURE or DEAD. Do we want to just tank that plan and try the rest? We
// probably want to fail globally as this shouldn't happen anyway.
candidate.failed = true;
++_failureCount;
// Propagate most recent seen failure to parent.
if (PlanStage::FAILURE == state) {
_statusMemberId = id;
}
if (_failureCount == _candidates.size()) {
_failure = true;
return false;
}
}
}
return !doneWorking;
}
void MultiPlanStage::saveState() {
_txn = NULL;
for (size_t i = 0; i < _candidates.size(); ++i) {
_candidates[i].root->saveState();
}
}
void MultiPlanStage::restoreState(OperationContext* opCtx) {
invariant(_txn == NULL);
_txn = opCtx;
for (size_t i = 0; i < _candidates.size(); ++i) {
_candidates[i].root->restoreState(opCtx);
}
}
namespace {
void invalidateHelper(OperationContext* txn,
WorkingSet* ws, // may flag for review
const RecordId& dl,
list<WorkingSetID>* idsToInvalidate,
const Collection* collection) {
for (list<WorkingSetID>::iterator it = idsToInvalidate->begin();
it != idsToInvalidate->end();) {
WorkingSetMember* member = ws->get(*it);
if (member->hasLoc() && member->loc == dl) {
list<WorkingSetID>::iterator next = it;
next++;
WorkingSetCommon::fetchAndInvalidateLoc(txn, member, collection);
ws->flagForReview(*it);
idsToInvalidate->erase(it);
it = next;
}
else {
it++;
}
}
}
}
void MultiPlanStage::invalidate(OperationContext* txn,
const RecordId& dl,
InvalidationType type) {
if (_failure) { return; }
if (bestPlanChosen()) {
CandidatePlan& bestPlan = _candidates[_bestPlanIdx];
bestPlan.root->invalidate(txn, dl, type);
invalidateHelper(txn, bestPlan.ws, dl, &bestPlan.results, _collection);
if (hasBackupPlan()) {
CandidatePlan& backupPlan = _candidates[_backupPlanIdx];
backupPlan.root->invalidate(txn, dl, type);
invalidateHelper(txn, backupPlan.ws, dl, &backupPlan.results, _collection);
}
}
else {
for (size_t ix = 0; ix < _candidates.size(); ++ix) {
_candidates[ix].root->invalidate(txn, dl, type);
invalidateHelper(txn, _candidates[ix].ws, dl, &_candidates[ix].results, _collection);
}
}
}
bool MultiPlanStage::hasBackupPlan() const {
return kNoSuchPlan != _backupPlanIdx;
}
bool MultiPlanStage::bestPlanChosen() const {
return kNoSuchPlan != _bestPlanIdx;
}
int MultiPlanStage::bestPlanIdx() const {
return _bestPlanIdx;
}
QuerySolution* MultiPlanStage::bestSolution() {
if (_bestPlanIdx == kNoSuchPlan)
return NULL;
return _candidates[_bestPlanIdx].solution;
}
vector<PlanStage*> MultiPlanStage::getChildren() const {
vector<PlanStage*> children;
if (bestPlanChosen()) {
children.push_back(_candidates[_bestPlanIdx].root);
}
else {
for (size_t i = 0; i < _candidates.size(); i++) {
children.push_back(_candidates[i].root);
}
}
return children;
}
PlanStageStats* MultiPlanStage::getStats() {
if (bestPlanChosen()) {
return _candidates[_bestPlanIdx].root->getStats();
}
if (hasBackupPlan()) {
return _candidates[_backupPlanIdx].root->getStats();
}
_commonStats.isEOF = isEOF();
auto_ptr<PlanStageStats> ret(new PlanStageStats(_commonStats, STAGE_MULTI_PLAN));
return ret.release();
}
const CommonStats* MultiPlanStage::getCommonStats() {
return &_commonStats;
}
const SpecificStats* MultiPlanStage::getSpecificStats() {
return &_specificStats;
}
} // namespace mongo
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