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/**
* Copyright (C) 2008 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/>.
*/
#pragma once
#include <boost/shared_ptr.hpp>
#include <memory>
#include "mongo/db/clientcursor.h"
#include "mongo/db/diskloc.h"
namespace mongo {
class QueryPlan;
class Cursor;
/** Implements an optimized procedure for finding the first op in the oplog. */
class FindingStartCursor {
public:
/**
* The cursor will attempt to find the first op in the oplog matching the
* 'ts' field of the qp's query.
*/
static FindingStartCursor *make( const QueryPlan &qp );
/** @return true if the first matching op in the oplog has been found. */
bool done() const { return !_findingStart; }
/** @return cursor pointing to the first matching op, if done(). */
shared_ptr<Cursor> cursor() { verify( done() ); return _c; }
/** Iterate the cursor, to continue trying to find matching op. */
void next();
/** Yield cursor, if not done(). */
bool prepareToYield() {
if ( _findingStartCursor ) {
return _findingStartCursor->prepareToYield( _yieldData );
}
return false;
}
/** Recover from cursor yield. */
void recoverFromYield() {
if ( _findingStartCursor ) {
if ( !ClientCursor::recoverFromYield( _yieldData ) ) {
_findingStartCursor.reset( 0 );
msgassertedNoTrace( 15889, "FindingStartCursor::recoverFromYield() failed to recover" );
}
}
}
/**
* @return a BasicCursor constructed using a FindingStartCursor with the provided query and
* order parameters.
* @yields the db lock.
* @asserts on yield recovery failure.
*/
static shared_ptr<Cursor> getCursor( const char *ns, const BSONObj &query, const BSONObj &order );
/**
* @return the first record of the first nonempty extent preceding the extent containing
* @param rec, or DiskLoc() if there is no such record or the beginning of the
* collection is reached.
* public for testing
*/
DiskLoc prevExtentFirstLoc( const DiskLoc& rec ) const;
/** For testing only. */
static int getInitialTimeout() { return _initialTimeout; }
static void setInitialTimeout( int timeout ) { _initialTimeout = timeout; }
private:
FindingStartCursor( const QueryPlan &qp );
void init();
enum FindingStartMode { Initial, FindExtent, InExtent };
const QueryPlan &_qp;
bool _findingStart;
FindingStartMode _findingStartMode;
auto_ptr< CoveredIndexMatcher > _matcher;
Timer _findingStartTimer;
ClientCursorHolder _findingStartCursor;
shared_ptr<Cursor> _c;
ClientCursor::YieldData _yieldData;
static int _initialTimeout;
/** @return the first record of the extent containing @param rec. */
DiskLoc extentFirstLoc( const DiskLoc &rec );
void createClientCursor( const DiskLoc &startLoc = DiskLoc() );
void destroyClientCursor() {
_findingStartCursor.reset( 0 );
}
bool firstDocMatchesOrEmpty() const;
};
}
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