title: In PyMongo, The default value of MongoClient's maxPoolSize=100 has no effect?
body: <p>Below is a simple test snippet for PyMongo connections:</p>
  
  <pre><code>from pymongo import MongoClient
  
  clients = [] 
  for i in range(0,1000):
      con = MongoClient('mongodb://localhost:27017/')
      clients.append(con)
      print(i)
  </code></pre>
  
  <p>Here is the output:</p>
  
  <blockquote>
    <p>... 
    ...
    998
    999</p>
  </blockquote>
  
  <p>And here is the output in MongoDB Console:</p>
  
  <blockquote>
    <p>2018-03-24T20:00:55.746+0530 I NETWORK  [listener] connection
    accepted
        from 127.0.0.1:51272 #1500 (1000 connections now open)
        2018-03-24T20:00:55.747+0530 I NETWORK  [conn1500] received client
        metadata from 127.0.0.1:51272 conn: { driver: { name: "PyMongo",
        version: "3.6.1" }, os: { type: "Darwin", name: "Darwin",
        architecture: "x86_64", version: "10.10.1" }, platform: "CPython
        3.6.0.final.0" } 2018-03-24T20:00:55.773+0530 I NETWORK  [conn1486] end connection 127.0.0.1:51286 (999 connections now open)
        2018-03-24T20:00:55.773+0530 I NETWORK  [conn1485] end connection
        127.0.0.1:51285 (998 connections now open) 2018-03-24T20:00:55.773+0530 I NETWORK  [conn1484] end connection
        127.0.0.1:51284 (997 connections now open)
        . . .
        . . .</p>
  </blockquote>
  
  <p>I see MongoClient has a keyword argument <code>maxPoolSize</code>. This has the default value of only 100. </p>
  
  <p>But how the above code works?</p>