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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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 <boost/optional.hpp>
#include <vector>
#include "mongo/db/s/balancer/balancer_policy.h"
#include "mongo/s/catalog/type_chunk.h"
#include "mongo/s/chunk_version.h"
namespace mongo {
class ChunkType;
class NamespaceString;
class OperationContext;
template <typename T>
class StatusWith;
/**
* Interface used by the balancer for selecting chunks, which need to be moved around in order for
* the sharded cluster to be balanced. It is up to the implementation to decide what exactly
* 'balanced' means.
*/
class BalancerChunkSelectionPolicy {
BalancerChunkSelectionPolicy(const BalancerChunkSelectionPolicy&) = delete;
BalancerChunkSelectionPolicy& operator=(const BalancerChunkSelectionPolicy&) = delete;
public:
virtual ~BalancerChunkSelectionPolicy();
/**
* Potentially blocking method, which gives out a set of chunks, which need to be split because
* they violate the policy for some reason. The reason is decided by the policy and may include
* chunk is too big or chunk straddles a tag range.
*/
virtual StatusWith<SplitInfoVector> selectChunksToSplit(OperationContext* opCtx) = 0;
/**
* Given a valid namespace returns all the splits the balancer would need to perform
* with the current state
*/
virtual StatusWith<SplitInfoVector> selectChunksToSplit(OperationContext* opCtx,
const NamespaceString& nss) = 0;
/**
* Potentially blocking method, which gives out a set of chunks to be moved.
*/
virtual StatusWith<MigrateInfoVector> selectChunksToMove(
OperationContext* opCtx,
const std::vector<ClusterStatistics::ShardStatistics>& shardStats,
stdx::unordered_set<ShardId>* availableShards) = 0;
/**
* Given a valid namespace returns all the Migrations the balancer would need to perform
* with the current state
*/
virtual StatusWith<MigrateInfosWithReason> selectChunksToMove(OperationContext* opCtx,
const NamespaceString& nss) = 0;
/**
* Requests a single chunk to be relocated to a different shard, if possible. If some error
* occurs while trying to determine the best location for the chunk, a failed status is
* returned. If the chunk is already at the best shard that it can be, returns boost::none.
* Otherwise returns migration information for where the chunk should be moved.
*/
virtual StatusWith<boost::optional<MigrateInfo>> selectSpecificChunkToMove(
OperationContext* opCtx, const NamespaceString& nss, const ChunkType& chunk) = 0;
/**
* Asks the chunk selection policy to validate that the specified chunk migration is allowed
* given the current rules. Returns OK if the migration won't violate any rules or any other
* failed status otherwise.
*/
virtual Status checkMoveAllowed(OperationContext* opCtx,
const ChunkType& chunk,
const ShardId& newShardId) = 0;
protected:
BalancerChunkSelectionPolicy();
};
} // namespace mongo
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