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// @file queryoptimizercursor.h
/**
* Copyright (C) 2011 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/>.
*/
namespace mongo {
/** Helper class for caching and counting matches during execution of a QueryPlan. */
class CachedMatchCounter {
public:
/**
* @param aggregateNscanned - shared count of nscanned for this and othe plans.
* @param cumulativeCount - starting point for accumulated count over a series of plans.
*/
CachedMatchCounter( long long &aggregateNscanned, int cumulativeCount ) : _aggregateNscanned( aggregateNscanned ), _nscanned(), _cumulativeCount( cumulativeCount ), _count(), _checkDups(), _match( Unknown ), _counted() {}
/** Set whether dup checking is enabled when counting. */
void setCheckDups( bool checkDups ) { _checkDups = checkDups; }
/**
* Usual sequence of events:
* 1) resetMatch() - reset stored match value to Unkonwn.
* 2) setMatch() - set match value to a definite true/false value.
* 3) knowMatch() - check if setMatch() has been called.
* 4) countMatch() - increment count if match is true.
*/
void resetMatch() {
_match = Unknown;
_counted = false;
}
void setMatch( bool match ) { _match = match ? True : False; }
bool knowMatch() const { return _match != Unknown; }
void countMatch( const DiskLoc &loc ) {
if ( !_counted && _match == True && !getsetdup( loc ) ) {
++_cumulativeCount;
++_count;
_counted = true;
}
}
bool enoughCumulativeMatchesToChooseAPlan() const {
// This is equivalent to the default condition for switching from
// a query to a getMore, which was the historical default match count for
// choosing a plan.
return _cumulativeCount >= 101;
}
bool enoughMatchesToRecordPlan() const {
// Recording after 50 matches is a historical default (101 default limit / 2).
return _count > 50;
}
int cumulativeCount() const { return _cumulativeCount; }
int count() const { return _count; }
/** Update local and aggregate nscanned counts. */
void updateNscanned( long long nscanned ) {
_aggregateNscanned += ( nscanned - _nscanned );
_nscanned = nscanned;
}
long long nscanned() const { return _nscanned; }
long long &aggregateNscanned() const { return _aggregateNscanned; }
private:
bool getsetdup( const DiskLoc &loc ) {
if ( !_checkDups ) {
return false;
}
pair<set<DiskLoc>::iterator, bool> p = _dups.insert( loc );
return !p.second;
}
long long &_aggregateNscanned;
long long _nscanned;
int _cumulativeCount;
int _count;
bool _checkDups;
enum MatchState { Unknown, False, True };
MatchState _match;
bool _counted;
set<DiskLoc> _dups;
};
/** Dup tracking class, optimizing one common case with small set and few initial reads. */
class SmallDupSet {
public:
SmallDupSet() : _accesses() {
_vec.reserve( 250 );
}
/** @return true if @param 'loc' already added to the set, false if adding to the set in this call. */
bool getsetdup( const DiskLoc &loc ) {
access();
return vec() ? getsetdupVec( loc ) : getsetdupSet( loc );
}
/** @return true when @param loc in the set. */
bool getdup( const DiskLoc &loc ) {
access();
return vec() ? getdupVec( loc ) : getdupSet( loc );
}
private:
void access() {
++_accesses;
mayUpgrade();
}
void mayUpgrade() {
if ( vec() && _accesses > 500 ) {
_set.insert( _vec.begin(), _vec.end() );
}
}
bool vec() const {
return _set.size() == 0;
}
bool getsetdupVec( const DiskLoc &loc ) {
if ( getdupVec( loc ) ) {
return true;
}
_vec.push_back( loc );
return false;
}
bool getdupVec( const DiskLoc &loc ) const {
for( vector<DiskLoc>::const_iterator i = _vec.begin(); i != _vec.end(); ++i ) {
if ( *i == loc ) {
return true;
}
}
return false;
}
bool getsetdupSet( const DiskLoc &loc ) {
pair<set<DiskLoc>::iterator, bool> p = _set.insert(loc);
return !p.second;
}
bool getdupSet( const DiskLoc &loc ) {
return _set.count( loc ) > 0;
}
vector<DiskLoc> _vec;
set<DiskLoc> _set;
long long _accesses;
};
} // namespace mongo
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