考虑以下是 Node.js 代码：
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
});
}
请参阅链接以获取最佳实践，该链接表示不要关闭任何连接
https://groups.google.com/forum/#!topic/node-mongodb-native/5cPt84TUsVg
我看到日志文件包含以下数据：
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)
通过打开多个连接而不是关闭它，这不会在服务器上产生开销吗？它是否在内部处理连接池？
但在 MongoDB Docs 中提到“这是不使用请求池的应用程序的正常行为”
有人可以帮助我理解这一点。
您使用 MongoClient 打开一次 Db 连接并在您的应用程序中重用它。如果您需要使用多个数据库，您可以使用 Db 对象上的 .db 函数来使用相同的底层连接池处理不同的数据库。保留一个池以确保单个阻塞操作不会冻结您的 node.js 应用程序。如果池中有 5 个连接，则默认大小。
http://mongodb.github.io/node-mongodb-native/driver-articles/mongoclient.html
我也忘了补充。正如另一个答案指出的那样，建立一个新的 TCP 连接在时间和内存方面都是昂贵的，这就是你重用连接的原因。此外，一个新连接也会导致在 MongoDB 上使用 Db 上的内存创建一个新线程。
MongoDB 将数据库连接池化以提高效率，因此在 mongodb.log 中打开许多连接并不罕见
但是，当您的应用程序完全关闭时关闭所有连接很有用。此代码最适合执行此操作。
process.on('SIGINT', function() {
mongoose.connection.close(function () {
console.log('Mongoose disconnected on app termination');
process.exit(0);
});
});
我不是 node.js 专家，但我认为大多数语言之间的原因是相对相同的。
建立连接是：
司机做的最重量级的事情之一。正确建立连接可能需要数百毫秒，即使在快速网络上也是如此。
(http://php.net/manual/en/mongo.connecting.pools.php)
如果那是针对 PHP 的，并且文档有点过时，那部分即使现在仍然适用，并且适用于大多数（如果不是全部）驱动程序。
每个连接也可以使用单独的线程，这会导致明显的开销。
似乎来自：
该 node.js 仍然使用连接池来尝试停止建立连接的开销。当然，这不再适用于其他驱动程序，例如 PHP 驱动程序。
它打开到您的数据库服务器的 x 个连接（默认为 5），并在需要数据时将工作转移到一个空闲连接，因此重用旧连接避免了这个可能导致这些日志的讨厌过程：
如果您想确保 mongo 在程序终止时断开连接，并且在程序运行期间只建立一个连接，我建议编写以下单例（不幸的是，这在 python 中不是节点，但同样的概念适用） .
import atexit
class MongoDB:
'''define class attributes'''
__instance = None
@staticmethod
def getInstance():
""" Static access method. """
# if the instance doesnt exist envoke the constructor
if MongoDB.__instance == None:
MongoDB()
# return instance
return MongoDB.__instance
def __init__(self) -> None:
""" Virtually private constructor. """
if MongoDB.__instance != None:
raise Exception("Singleton cannot be instantiated more than once")
else:
print("Creating MongoDB connection")
# set instance and instance attributes
self.client = MongoClient(config.CONNECTION_STRING)
MongoDB.__instance = self
@staticmethod
@atexit.register
def closeConnection():
'''
Python '__del__' aka destructor dunder doesnt always get called
mainly when program is terminated by ctrl-c so this method is decorated
by 'atexit' which ensures this method is called upon program termination
'''
if MongoDB.__instance != None:
MongoDB.__instance.client.close()
print("Closing Connections")
我认为这是一个很好的设计模式，可以确保在程序结束时所有连接都断开连接，并且共享相同的连接实例并且只建立一次，因为有人之前说过连接到数据库是最昂贵的任务应该避免
