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Diffstat (limited to 'src/mongo/s/balancer_policy.h')
| -rw-r--r-- | src/mongo/s/balancer_policy.h | 98 |
1 files changed, 98 insertions, 0 deletions
diff --git a/src/mongo/s/balancer_policy.h b/src/mongo/s/balancer_policy.h new file mode 100644 index 00000000000..cef5aa64afc --- /dev/null +++ b/src/mongo/s/balancer_policy.h @@ -0,0 +1,98 @@ +// @file balancer_policy.h + +/** +* Copyright (C) 2010 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/>. +*/ + +#ifndef S_BALANCER_POLICY_HEADER +#define S_BALANCER_POLICY_HEADER + +#include "../pch.h" + +namespace mongo { + + class BalancerPolicy { + public: + struct ChunkInfo; + + /** + * Returns a suggested chunk to move whithin a collection's shards, given information about + * space usage and number of chunks for that collection. If the policy doesn't recommend + * moving, it returns NULL. + * + * @param ns is the collections namepace. + * @param shardLimitMap is a map from shardId to an object that describes (for now) space + * cap and usage. E.g.: { "maxSize" : <size_in_MB> , "usedSize" : <size_in_MB> }. + * @param shardToChunksMap is a map from shardId to chunks that live there. A chunk's format + * is { }. + * @param balancedLastTime is the number of chunks effectively moved in the last round. + * @returns NULL or ChunkInfo of the best move to make towards balacing the collection. + */ + typedef map< string,BSONObj > ShardToLimitsMap; + typedef map< string,vector<BSONObj> > ShardToChunksMap; + static ChunkInfo* balance( const string& ns, const ShardToLimitsMap& shardToLimitsMap, + const ShardToChunksMap& shardToChunksMap, int balancedLastTime ); + + // below exposed for testing purposes only -- treat it as private -- + + static BSONObj pickChunk( const vector<BSONObj>& from, const vector<BSONObj>& to ); + + /** + * Returns true if a shard cannot receive any new chunks bacause it reache 'shardLimits'. + * Expects the optional fields "maxSize", can in size in MB, and "usedSize", currently used size + * in MB, on 'shardLimits'. + */ + static bool isSizeMaxed( BSONObj shardLimits ); + + /** + * Returns true if 'shardLimist' contains a field "draining". Expects the optional field + * "isDraining" on 'shrdLimits'. + */ + static bool isDraining( BSONObj shardLimits ); + + /** + * Returns true if a shard currently has operations in any of its writeback queues + */ + static bool hasOpsQueued( BSONObj shardLimits ); + + private: + // Convenience types + typedef ShardToChunksMap::const_iterator ShardToChunksIter; + typedef ShardToLimitsMap::const_iterator ShardToLimitsIter; + + }; + + struct BalancerPolicy::ChunkInfo { + const string ns; + const string to; + const string from; + const BSONObj chunk; + + ChunkInfo( const string& a_ns , const string& a_to , const string& a_from , const BSONObj& a_chunk ) + : ns( a_ns ) , to( a_to ) , from( a_from ), chunk( a_chunk ) {} + }; + + /** + * Field names used in the 'limits' map. + */ + struct LimitsFields { + // we use 'draining' and 'maxSize' from the 'shards' collection plus the following + static BSONField<long long> currSize; // currently used disk space in bytes + static BSONField<bool> hasOpsQueued; // writeback queue is not empty? + }; + +} // namespace mongo + +#endif // S_BALANCER_POLICY_HEADER |