在nodejs中动态创建和重用多个mongodb连接的有效方法是什么？

Question

我使用的是mongodb 2.2.3和nodejs 0.10.5。 我正在创建一个应用程序，用于连接不同主机上的不同mongodb实例。 什么是动态创建和重用不同连接的最有效方式？

例如我有一个数组hostArray中的几个主机，我想获取它中的所有集合。

function getCollectionNames(hostsArray) {   
    async.map(hostsArray,function(item,callback){ 
     uri = "mongodb://" + item['user'] + ":" + item['passw'] + "@" + item['host'] + "/" + item['dbname']; 
     var mongoClient = new MongoClient.connect(uri,function(err,db){ 
      if(!err) { 
       db.collectionNames(function(error,collections){ 
        if(!err){ 
         callback(null,collections); 
        }else{ 
         callback(err,null); 
        } 
       }); 
      } else { 
       callback(error,null);  
      } 
     }); 
    },function(err,results){ 
     res.send(results); 
    }); 
} 

有太多打开的连接，我可以看到当的MongoDB服务器的控制台看上去，并且在到达更高的数字，它得到坠毁。

Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44311 #167 (87 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44312 #168 (88 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44313 #169 (89 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44314 #170 (90 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44315 #171 (91 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44316 #172 (92 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44317 #173 (93 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44318 #174 (94 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44319 #175 (95 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44320 #176 (96 connections now open) 
Mon Oct 21 16:34:20 [conn167] end connection 127.0.0.1:44311 (95 connections now open) 
Mon Oct 21 16:34:20 [conn169] end connection 127.0.0.1:44313 (94 connections now open) 
Mon Oct 21 16:34:20 [conn171] end connection 127.0.0.1:44315 (94 connections now open) 
Mon Oct 21 16:34:20 [conn173] end connection 127.0.0.1:44317 (92 connections now open) 
Mon Oct 21 16:34:20 [conn175] end connection 127.0.0.1:44319 (92 connections now open) 
Mon Oct 21 16:34:20 [conn168] end connection 127.0.0.1:44312 (90 connections now open) 
Mon Oct 21 16:34:20 [conn170] end connection 127.0.0.1:44314 (89 connections now open) 
Mon Oct 21 16:34:20 [conn172] end connection 127.0.0.1:44316 (88 connections now open) 
Mon Oct 21 16:34:20 [conn174] end connection 127.0.0.1:44318 (87 connections now open) 
Mon Oct 21 16:34:20 [conn176] end connection 127.0.0.1:44320 (86 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44321 #177 (87 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44322 #178 (88 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44323 #179 (89 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44324 #180 (90 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44325 #181 (91 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44326 #182 (92 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44327 #183 (93 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44328 #184 (94 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44329 #185 (95 connections now open) 
Mon Oct 21 16:34:20 [initandlisten] connection accepted from 127.0.0.1:44330 #186 (96 connections now open) 

Answer 1

您可以使用async.mapLimit来限制并行请求/连接的数量。

但是你当你与他们所做的，这可能（也）是为什么你正在运行出连接的原因也正在不关闭你的连接：

var mongoClient = new MongoClient.connect(uri,function(err,db){ 
    if (!err) { 
    db.collectionNames(function(error,collections){ 
     // done, close connection 
     db.close(); 

     // call back with results or error 
     if (!error){ 
     callback(null, collections); 
     } else { 
     callback(error, null); 
     } 
    }); 
    } else { 
    callback(err, null); 
    } 
}); 

（上面的代码应该也修复你的混合err和error变量）