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106 lines
3.5 KiB
C++
106 lines
3.5 KiB
C++
//@file balance.h
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/**
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* Copyright (C) 2008 10gen Inc.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License, version 3,
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include "../pch.h"
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#include "../util/background.h"
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#include "../client/dbclient.h"
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#include "balancer_policy.h"
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namespace mongo {
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/**
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* The balancer is a background task that tries to keep the number of chunks across all servers of the cluster even. Although
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* every mongos will have one balancer running, only one of them will be active at the any given point in time. The balancer
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* uses a 'DistributedLock' for that coordination.
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*
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* The balancer does act continuously but in "rounds". At a given round, it would decide if there is an imbalance by
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* checking the difference in chunks between the most and least loaded shards. It would issue a request for a chunk
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* migration per round, if it found so.
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*/
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class Balancer : public BackgroundJob {
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public:
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Balancer();
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virtual ~Balancer();
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// BackgroundJob methods
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virtual void run();
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virtual string name() const { return "Balancer"; }
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private:
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typedef BalancerPolicy::ChunkInfo CandidateChunk;
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typedef shared_ptr<CandidateChunk> CandidateChunkPtr;
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// hostname:port of my mongos
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string _myid;
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// time the Balancer started running
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time_t _started;
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// number of moved chunks in last round
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int _balancedLastTime;
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// decide which chunks to move; owned here.
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scoped_ptr<BalancerPolicy> _policy;
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/**
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* Checks that the balancer can connect to all servers it needs to do its job.
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*
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* @return true if balancing can be started
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*
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* This method throws on a network exception
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*/
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bool _init();
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/**
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* Gathers all the necessary information about shards and chunks, and decides whether there are candidate chunks to
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* be moved.
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*
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* @param conn is the connection with the config server(s)
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* @param candidateChunks (IN/OUT) filled with candidate chunks, one per collection, that could possibly be moved
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*/
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void _doBalanceRound( DBClientBase& conn, vector<CandidateChunkPtr>* candidateChunks );
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/**
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* Issues chunk migration request, one at a time.
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*
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* @param candidateChunks possible chunks to move
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* @return number of chunks effectively moved
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*/
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int _moveChunks( const vector<CandidateChunkPtr>* candidateChunks );
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/**
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* Marks this balancer as being live on the config server(s).
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*
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* @param conn is the connection with the config server(s)
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*/
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void _ping( DBClientBase& conn );
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/**
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* @return true if all the servers listed in configdb as being shards are reachable and are distinct processes
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*/
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bool _checkOIDs();
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};
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extern Balancer balancer;
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}
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