Should I keep a database connection open to handle every request? And how to do that in the right way

Question

For example a database such as MongoDB. I doubt that it is unnecessary to open and close a connection for every request. So I try to keep a connection to handle every request like this.

public class MongoUtils {
private static final String connectionString = "mongodb://localhost:27017";
private static final MongoClient client;

static {
    client = MongoClients.create(connectionString);
}

public static MongoClient getConnection(){
    return client;
}

}

But maybe I'm doing this wrong somewhere. I don't know why it create the first connection and leave it there, then it create the second connection and use that to handle my db request. Here's the log

2018-10-25 11:37:36 INFO  AnnotationMBeanExporter:433 - Registering beans for JMX exposure on startup
2018-10-25 11:37:36 INFO  Http11NioProtocol:180 - Starting ProtocolHandler ["http-nio-8808"]
2018-10-25 11:37:36 INFO  NioSelectorPool:180 - Using a shared selector for servlet write/read
2018-10-25 11:37:36 INFO  TomcatWebServer:206 - Tomcat started on port(s): 8808 (http) with context path '/api'
2018-10-25 11:37:36 INFO  Backend:59 - Started Backend in 3.251 seconds (JVM running for 6.935)
2018-10-25 11:37:56 INFO  [/api]:180 - Initializing Spring FrameworkServlet 'dispatcherServlet'
2018-10-25 11:37:56 INFO  DispatcherServlet:494 - FrameworkServlet 'dispatcherServlet': initialization started
2018-10-25 11:37:56 INFO  DispatcherServlet:509 - FrameworkServlet 'dispatcherServlet': initialization completed in 39 ms
2018-10-25 11:37:56 INFO  cluster:71 - Cluster created with settings {hosts=[10.184.153.232:27017], mode=SINGLE, requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms', maxWaitQueueSize=500}
2018-10-25 11:37:56 INFO  cluster:71 - Cluster description not yet available. Waiting for 30000 ms before timing out
2018-10-25 11:37:56 INFO  connection:71 - Opened connection [connectionId{localValue:1, serverValue:27}] to 10.184.153.232:27017
2018-10-25 11:37:56 INFO  cluster:71 - Monitor thread successfully connected to server with description ServerDescription{address=10.184.153.232:27017, type=STANDALONE, state=CONNECTED, ok=true, version=ServerVersion{versionList=[4, 0, 3]}, minWireVersion=0, maxWireVersion=7, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=3393851}
2018-10-25 11:37:56 INFO  connection:71 - Opened connection [connectionId{localValue:2, serverValue:28}] to 10.184.153.232:27017

ernest_k ernest_k · Accepted Answer · 2018-10-25T05:07:04

To quote directly from the JavaDocs of com.mongodb.MongoClient:

A MongoDB client with internal connection pooling. For most applications, you should have one MongoClient instance for the entire JVM.

The client itself has internal connection pooling and is thread-safe. So you should use a single MongoClient instance for your application. This suggests that you're already using it as recommended.

Should I keep a database connection open to handle every request? And how to do that in the right way

2 Answers