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为什么建议不要在Node.js代码中的任何地方关闭MongoDB连接?

分类: 技术问答 • 2022-07-15 09:53:17
问题描述：

考虑以下是Node.js代码:

Consider following is the Node.js code:

function My_function1(_params) {
    db.once('open', function (err){
     //Do some task 1
});
}

function My_function2(_params) {
    db.once('open', function (err){
     //Do some task 2
});
}

请参阅最佳做法链接，该链接指出不要关闭任何连接

See the link for best practice, which says not to close any connections

https://groups.google.com/forum/#!topic/node -mongodb-native/5cPt84TUsVg

我已经看到日志文件包含以下数据:

I have seen log file contains following data:

Fri Jan 18 11:00:03 Trying to start Windows service 'MongoDB'
Fri Jan 18 11:00:03 Service running
Fri Jan 18 11:00:03 [initandlisten] MongoDB starting : pid=1592 port=27017 dbpath=\data\db\ 64-bit host=AMOL-KULKARNI
Fri Jan 18 11:00:03 [initandlisten] db version v2.2.1, pdfile version 4.5
Fri Jan 18 11:00:03 [initandlisten] git version: d6...e0685521b8bc7b98fd1fab8cfeb5ae
Fri Jan 18 11:00:03 [initandlisten] build info: windows sys.getwindowsversion(major=6, minor=1, build=7601, platform=2, service_pack='Service Pack 1') BOOST_LIB_VERSION=1_49
Fri Jan 18 11:00:03 [initandlisten] options: { config: "c:\mongodb\mongod.cfg", logpath: "c:\mongodb\log\mongo.log", service: true }
Fri Jan 18 11:00:03 [initandlisten] journal dir=/data/db/journal
Fri Jan 18 11:00:03 [initandlisten] recover begin
Fri Jan 18 11:00:04 [initandlisten] recover lsn: 6624179
Fri Jan 18 11:00:04 [initandlisten] recover /data/db/journal/j._0
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:59343 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:118828 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:238138 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:835658 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:955218 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:3467218 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:3526418 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:3646154 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section seq:3705844 < lsn:6624179
Fri Jan 18 11:00:04 [initandlisten] recover skipping application of section more...
Fri Jan 18 11:00:05 [initandlisten] recover cleaning up
Fri Jan 18 11:00:05 [initandlisten] removeJournalFiles
Fri Jan 18 11:00:05 [initandlisten] recover done
Fri Jan 18 11:00:10 [initandlisten] query MYDB.system.namespaces query: { options.temp: { $in: [ true, 1 ] } } ntoreturn:0 ntoskip:0 nscanned:5 keyUpdates:0  nreturned:0 reslen:20 577ms
Fri Jan 18 11:00:10 [initandlisten] waiting for connections on port 27017
Fri Jan 18 11:00:10 [websvr] admin web console waiting for connections on port 28017
Fri Jan 18 11:01:10 [PeriodicTask::Runner] task: WriteBackManager::cleaner took: 32ms
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50076 #1 (1 connection now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50077 #2 (2 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50078 #3 (3 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50079 #4 (4 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50080 #5 (5 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50081 #6 (6 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50082 #7 (7 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50083 #8 (8 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50084 #9 (9 connections now open)
Fri Jan 18 13:36:27 [initandlisten] connection accepted from 192.168.0.1:50085 #10 (10 connections now open)
...........................................
Fri Jan 18 13:36:48 [initandlisten] connection accepted from 192.168.0.1:50092 #97 (97 connections now open)

这不是通过打开多个连接而不是关闭多个连接而在服务器上造成的开销，它是否在内部处理连接池?

Doesn't this create a overhead on server by opening multiple connection and not closing it, Does it handles connection pooling internally?

但是在 MongoDB文档a>提到对于不使用请求池的应用程序，这是正常行为"

But in MongoDB Docs it is mentioned "This is normal behavior for applications that do not use request pooling"

有人可以帮助我理解这一点吗?

Can somebody help me understanding this.

答

您一次使用MongoClient打开一个Db连接，然后在您的应用程序中重复使用它.如果需要使用多个数据库，则可以在Db对象上使用.db函数，以使用相同的基础连接池在不同的数据库上工作.保留一个池以确保单个阻止操作不会冻结您的node.js应用程序.如果一个池中有5个连接，则为默认大小.

You open a Db connection once with MongoClient and reuse it across your application. If you need to use multiple db's you use the .db function on the Db object to work on a different db using the same underlying pool of connections. A pool is kept to ensure a single blocking operation cannot freeze up your node.js application. Default size if 5 connections in a pool.

http://mongodb.github.com/node- mongodb-native/driver-articles/mongoclient.html

我也忘记添加.正如另一个答案指出的那样，建立新的TCP连接在时间和内存上都是昂贵的，这就是您重新使用连接的原因.另外，新的连接也会导致使用Db上的内存在MongoDB上创建新的线程.

I also forgot to add. As the other answer pointed out setting up a new TCP connection is EXPENSIVE timewise and memory wise that's why you reuse connections. Also a new connection will cause a new Thread to be created on MongoDB using memory on the Db as well.

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