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//@file balance.h
/**
* 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/>.
*
* 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/util/background.h"
namespace mongo {
class BalancerPolicy;
struct MigrateInfo;
struct WriteConcernOptions;
/**
* The balancer is a background task that tries to keep the number of chunks across all
* servers of the cluster even. Although every mongos will have one balancer running, only one
* of them will be active at the any given point in time. The balancer uses a distributed lock
* for that coordination.
*
* The balancer does act continuously but in "rounds". At a given round, it would decide if
* there is an imbalance by checking the difference in chunks between the most and least
* loaded shards. It would issue a request for a chunk migration per round, if it found so.
*/
class Balancer : public BackgroundJob {
public:
Balancer();
virtual ~Balancer();
// BackgroundJob methods
virtual void run();
virtual std::string name() const {
return "Balancer";
}
private:
// hostname:port of my mongos
std::string _myid;
// time the Balancer started running
time_t _started;
// number of moved chunks in last round
int _balancedLastTime;
// decide which chunks to move; owned here.
std::unique_ptr<BalancerPolicy> _policy;
/**
* Checks that the balancer can connect to all servers it needs to do its job.
*
* @return true if balancing can be started
*
* This method throws on a network exception
*/
bool _init();
/**
* Gathers all the necessary information about shards and chunks, and decides whether there are
* candidate chunks to be moved.
*
* @param conn is the connection with the config server(s)
* @param candidateChunks (IN/OUT) filled with candidate chunks, one per collection, that could
* possibly be moved
*/
void _doBalanceRound(std::vector<std::shared_ptr<MigrateInfo>>* candidateChunks);
/**
* Issues chunk migration request, one at a time.
*
* @param candidateChunks possible chunks to move
* @param writeConcern detailed write concern. NULL means the default write concern.
* @param waitForDelete wait for deletes to complete after each chunk move
* @return number of chunks effectively moved
*/
int _moveChunks(const std::vector<std::shared_ptr<MigrateInfo>>& candidateChunks,
const WriteConcernOptions* writeConcern,
bool waitForDelete);
/**
* Marks this balancer as being live on the config server(s).
*/
void _ping(bool waiting = false);
/**
* @return true if all the servers listed in configdb as being shards are reachable and are
* distinct processes
*/
bool _checkOIDs();
};
extern Balancer balancer;
}
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