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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.
*/
#pragma once
#include "mongo/client/syncclusterconnection.h"
#include "mongo/s/client/multi_host_query.h"
namespace mongo {
/**
* Query handler that plugs in to a SyncClusterConnection and allows query on fastest host
* (if enabled).
*
* Glue code which shields the MultiHostQuery and server parameters from the separate client
* module which knows about neither.
*
* There is a *single* SCCFastQueryHandler for every SCC. Each SCCFastQueryHandler contains
* its own thread pool (lazily initialized) so that at maximum there is a thread-per-SCC-host
* and this thread may have an open connection to the host until it times out.
* If using the "fastestConfigReads" options, clients must be ready for the additional thread
* and connection load when configs are slow.
*/
class SCCFastQueryHandler : public SyncClusterConnection::QueryHandler {
public:
SCCFastQueryHandler();
virtual ~SCCFastQueryHandler() {}
virtual bool canHandleQuery(const std::string& ns, Query query);
virtual std::unique_ptr<DBClientCursor> handleQuery(const std::vector<std::string>& hostStrings,
const std::string& ns,
Query query,
int nToReturn,
int nToSkip,
const BSONObj* fieldsToReturn,
int queryOptions,
int batchSize);
private:
// The thread pool itself is scoped to the handler and SCC, and lazily creates threads
// per-host as needed. This ensures query starvation cannot occur due to other active
// client threads - though a thread must be created for every client.
HostThreadPools _queryThreads;
};
}
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