Problem

When performing multiple transfers using pTCP, we sometimes encounter the below error:

25/02/25 07:21:50.00 CFTA03E SetupOtherConnectionsAsync(peer:NET0_PTCP_PTCP_CtoP, session:84): error in ptcp_socket_connect: errno: 24 strerror: Too many open
25/02/25 07:21:50.00 CFTA03E+files

The CNX and the associated values are set correctly following the Transfer CFT documentation.

Resolution

When we use pTCP, the file descriptor values are taken into account for parallel pTCP connections. By default, the file descriptor value is set to 1024 which limits the parallel pTCP connections to 100 if acceleration.ptcp.net0_ptcp.nb_connections UCONF is set to 10.

This was later enhanced in Transfer CFT 3.10 2309 and the file descriptor values are not taken into account for parallel pTCP connections.

Extract from the Transfer CFT 3.10 2309 Release Notes:
Enhancements:
Removed a previous pTCP connection limitation, increasing the number of pTCP accelerated transfers you can do in parallel.

Hence, to resolve the 'Too many open files' error, you can either update your Transfer CFT instance to 3.10 2309 and above or increase the file descriptor to a higher value to increase the parallel pTCP connections.