MongoDB数据库的MapReduce简单操作(转)
MongoDB也简单的实现了MapReduce的功能来提供分布式的数据查询服务,MapReduce的分布是功能主要用在Shard上 db.runCommand( { mapreduce : <collection>, map : <mapfunction>, reduce : <reducefunction> [, query : <query filter object>] [, sort : <sort the query.useful for optimization>] [, limit : <number of objects to return from collection>] [, out : <output-collection name>] [, keeptemp: <true|false>] [, finalize : <finalizefunction>] [, scope : <object where fiel...