A fix is available
APAR status
Closed as program error.
Error description
A race condition exists between IBM MQ clients and queue manager when closing down a TCP/IP network connection. The network resource at the end which issues the close first enters a TIME_WAIT state for a period of time in which delayed TCP packets will be discarded. If the queue manager side is the first to close the network resource across many connections within a short period of time, this state could eventually lead to a shortage of available ephemeral ports to accept new connections. This is equivalent APAR to distributed APAR IT27924.
Local fix
Clients using SHARECNV(0) have a greater chance of the client closing the network connection first and so a TIME_WAIT on the server is usually avoided, but can't be guaranteed.
Problem summary
**************************************************************** * USERS AFFECTED: All users of IBM MQ for z/OS Version 8 * * Release 0 Modification 0. * **************************************************************** * PROBLEM DESCRIPTION: A large number of channel connections * * to a queue manager are left in a * * TIME_WAIT state when disconnecting, * * resulting in a potential shortage of * * ephemeral ports. * **************************************************************** A race condition exists when sending and receiving the final MQ protocol flows to indicate the end of a TCP/IP connection. The first side of a channel that closes the network connection will cause the ephemeral port that was used for the connection to enter a TIME_WAIT state for a short period of time to prevent its reuse. The duration of the TIME_WAIT state is relative to the maximum segment lifetime, this is to prevent delayed TCP packets from interfering with a new conversation reusing the same destination port. As a port in the TIME_WAIT state may be unavailable for reuse for a few minutes, it is desirable for MQ clients to be the side of the connection to close the network resources, this is so that the the range of ephemeral ports available for new connections is not diminished on the network interface being used by the queue manager.
Problem conclusion
Responding message channel agents (MCAs) have been modified to wait briefly for the connection to be closed by the other end of the channel when it is deemed appropriate to do so. Under normal circumstances these changes cause TCP/IP TIME_WAIT state to occur on the initiating end of the channel. The changed behaviour will only be seen if the fix (or the distributed equivalent IT27924) is applied at both the sending and receiving end of a channel.
Temporary fix
Comments
APAR Information
APAR number
PH21216
Reported component name
IBM MQ Z/OS V8
Reported component ID
5655W9700
Reported release
000
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2020-01-21
Closed date
2020-09-16
Last modified date
2020-11-02
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
PH27932 UI71584
Modules/Macros
CSQIRECP CSQMSTRT CSQXCCAX CSQXCCCX CSQXCCIT CSQXCCXD CSQXRMSS
Fix information
Fixed component name
IBM MQ Z/OS V8
Fixed component ID
5655W9700
Applicable component levels
R000 PSY UI71584
UP20/10/13 P F010
Fix is available
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Document Information
Modified date:
03 November 2020