MongoDB-Middle-Level--大数据量下MapReduce取代GroupBy

MongoDB Middle Level (大数据量下MapReduce取代GroupBy)
MongoDB中的MapReduce其实更类似关系型数据库中的GroupBy 。

刚做了下这样试验，对于大数据量的GroupBy（MapReduce）还是比较理想的，生成100W条3
位随机字符串
for (var i=0; i<1000000; i++)
{
var x = "0123456789";
var tmp="";
for (var j=0; j<3; j++)
{
tmp += x.charAt(Math.ceil(Math.random()*100000000)%x.length);|
}
var u = {_id:i,v1:tmp};
db.RandomNum.insert(u);
}
然后进行对相同的随机数取Count数所以必须GroupBy
var m = function(){emit(this.v1,{count:1}); }; //map key类似关系型数据的group by 第二个是value 就var r = function (key,values) { var total = 0;for (var i=0; i<values.length; i++) { total += var res = db.RandomNum.mapReduce(m, r, {out:{replace:'Result'}});
db[res.result].find()
测试了下时间：
var startTime = new Date();
var m = function(){emit(this.v1,{count:1}); };
var r = function (key,values) { var total = 0;for (var i=0; i<values.length; i++) { total += var res = db.RandomNum.mapReduce(m, r, {out:{replace:'Result'}});
db[res.result].find()
(new Date().getTime()-startTime.getTime())/1000
结果如下：
> db[res.result].find()
{ "_id" : "000", "value" : { "count" : 1075 } }
{ "_id" : "001", "value" : { "count" : 1045 } }
{ "_id" : "002", "value" : { "count" : 1022 } }
{ "_id" : "003", "value" : { "count" : 968 } } { "_id" : "004", "value" : { "count" : 994 } } { "_id" : "005", "value" : { "count" : 1009 } } { "_id" : "006", "value" : { "count" : 948 } } { "_id" : "007", "value" : { "count" : 1003 } } { "_id" : "008", "value" : { "count" : 983 } } { "_id" : "009", "value" : { "count" : 993 } } { "_id" : "010", "value" : { "count" : 987 } } { "_id" : "011", "value" : { "count" : 982 } } { "_id" : "012", "value" : { "count" : 957 } } { "_id" : "013", "value" : { "count" : 1031 } } { "_id" : "014", "value" : { "count" : 971 } } { "_id" : "015", "value" : { "count" : 1053 } } { "_id" : "016", "value" : { "count" : 974 } } { "_id" : "017", "value" : { "count" : 975 } } { "_id" : "018", "value" : { "count" : 978 } } { "_id" : "019", "value" : { "count" : 1010 } } has more
>
> (new Date().getTime()-startTime.getTime())/1000 63.335s
> bye
测试机的性能：。