Server Connection Issues

1. Check Port Status

   Use tools like telnet, ssh, and nc to test port connectivity. For example, to test if port 8911 is open on a server with the IP address 192.168.1.206, execute the following command in the Command Prompt (for Windows) or Terminal (for Linux):

   telnet 192.168.1.206 8911
   //telnet <ip> <port>

   Note: You can replace ip and port with the server's IP address and port number.

   If the connection is established, the Command Prompt goes to a blank screen (in Windows) or Connected to 192.168.1.206 8911 is displayed in the Terminal (in Linux).

2. Check Packet Transmission Rate

   Use the pingcommand to send data packets to the server and measure how long they take to return.

   For Windows users, use:

   ping -l 16534 ip

   For Linux users, use:

   ping -s 16534 ip

   For example,to ping the destination 192.168.1.206:

   # ping -s 16534 192.168.1.206
   PING 192.168.1.206 (192.168.1.206) 16534(16562) bytes of data.
   16542 bytes from 192.168.1.206: icmp_seq=1 ttl=61 time=18.9 ms
   16542 bytes from 192.168.1.206: icmp_seq=2 ttl=61 time=15.8 ms
   16542 bytes from 192.168.1.206: icmp_seq=3 ttl=61 time=16.0 ms

   Assuming the network is stable, examine connection capacity as a possible cause of the issue.

When the number of connections reaches the limit specified bymaxConnections (default: 64 for Windows, 512 for Linux), new connections cannot be established and the following error message is thrown.

"Maximum connections {num} reached. Close unused connections or increase maxConnections limit. RefId:S00006"

You can check for connection leaks by getSessionMemoryStat(), which provides the status of all connection sessions. Each session consumes one connection.

select * from getSessionMemoryStat() where sessionId is not null

If connections fail due to limited maxConnections, you can resort to the following methods:

1. Set a higher maxConnections: Use the setMaxConnections function to modify the maximum number of connections to the current node online.

   Temporarily increase the connection limit by setMaxConnections:

   pnodeRun(setMaxConnections{5000})

2. Close Inactive Connections: Use lastActiveTime to identify inactive sessions and close these connections by closeSessions. Alternatively, you can use the ops module:

   use ops
   closeInactiveSessions(hours=12)

   where the closeInactiveSessions function clears connections idle for the specified period (default value is 12 hours). The duration can be adjusted as needed.

   Note: This approach carries more risk than increasing the connection limit.

If the issue persists after following these steps, try restarting the affected DolphinDB node.