Cannot open more than 10 sessions for Linux XCOM port

Products

XCOM Data Transport XCOM Data Transport - Windows XCOM Data Transport - Linux PC XCOM Data Transport - z/OS

Issue/Introduction

Cannot open more than 10 sessions for a Linux XCOM port. How can the number of sessions for a port be increased?

Environment

Release: 11.6 , 12.0
Component: XCOM Data Transport for Linux

Resolution

In the $XCOM_HOME/txpi directory review the 4 txpi* files.
NOTE: At install time XCOM also creates symbolic links to those 4 files in the /etc/xinetd.d directory because xinetd is used to run the XCOM for Linux listener (XCOM Data Transport for UNIX/Linux 11.6.1 > Reference > Operating Environment > Remote Session Control Parameters)

Each of the 4 txpi* files refers to a protocol/port used:
txpi file corresponds to XCOM IPv4
txpis file corresponds to XCOM IPv4 SSL
txpi6 file corresponds to XCOM IPv6
txpi6s file corresponds to XCOM IPv6 SSL

In all files there are 2 lines for parameters per_source and instances that are commented as shown below:

# per_source = 10
# instances = 50

As the parameters are commented, their default values, stored in the file /etc/xinetd.conf, would be currently used. If the defaults in /etc/xinetd.conf are 10 & 50 respectively then uncommenting the 2 parameters alone won't change anything and the values also need to be increased to meet throughput requirements.
The per_source parameter needs to be increased because it "Defines the maximum number of instances for a service per source IP address" i.e. the number of simultaneous connections per remote partner.
The instances parameter "Specifies the maximum number of simultaneous requests that xinetd can process" and should also to be increased at the same time to ensure its value is large enough to handle the total simultaneous connection requirements from all remote partners.
Red Hat Enterprise Linux > 6 > Security Guide > 2.6.4. xinetd Configuration Files
Red Hat Enterprise Linux > 6 > Security Guide> 2.6.4.3.4. Resource Management Options

NOTES:
- To avoid impacting all xinetd service configurations it is not normally recommended to increase the default values of instances and per_source in the /etc/xinetd.conf file. However if that approach is preferred its impact should be noted.
- If just performing IPV4 transfers then only need to change the txpi file (non-secure transfer port 8044) and the txpis file (secure transfer port 8045).
- After making any changes to the txpi files please restart the xinetd service and also the xcomd service.
- Errors on a remote XCOM partner initiating a transfer to XCOM for Linux might indicate that the default per_resource limit of 10 has been reached e.g. on a XCOM for z/OS partner:
XCOMM0780E Txpi 227: Socket received 0 bytes: partner closed socket. Last error: 167

Additional Information

One needs to be careful when setting/tuning session values/parameters and requires a detailed understanding of the system resources and workload when doing such changes.
Currently, XCOM doesn't have an internal feature for workload/session balancing capabilities and relies on other network applications for this task. But you can set/limit the number of local and remote concurrent session/transfers at one time by
- Local transfers: via the xcom.sess. Please review the XCOM manual for details.
- Remote transfers: via the system /etc/xinetd.conf file.
Unfortunately each environment is unique and there are too many factors and unknowns such as disk I/O, network, CPU, memory, workload, as well as transfers themselves.
All can affect the XCOM workload and performance on a system, but once you have the above information you can begin to adjust the TXPI and session parameters based on that information.
We would recommend starting with lower values and monitor as the values are increased to reach a satisfactory goal.

NOTE: For UNIX platforms that use inetd rather than xinetd e.g. AIX and Solaris, there are no equivalent parameters for per_source and instances because inetd works differently from xinetd.

IMPORTANT NOTE: XCOM Data Transport for Linux r12.0 has been certified to run on RHEL 9 or SLES 15 SP03.

In order to run XCOM on these levels of the Operating System you need to install the latest XCOM solution LU11905 that installs XCOM listener services in SYSTEMD format since the XINETD system service has been deprecated on these latest Operating Systems. Also, solutions are cumulative and include all published fixes for XCOM Linux r12.0.