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  • When increasing the number of monReqServer queues (with the -q option) it is necessary to increase the number of buffers (with the -n option, defaults to 8) because this line shares the total number of buffers among all the queues: https://github.com/slac-lcls/lcls2/blob/5301f172c23b448dc8904f7eee20e508b4adc2e9/psalg/psalg/shmem/XtcMonitorServer.cc#L594.  So far we have been using twice the number of buffers as queues (i.e. 2 buffers per queue)

  • Some of the various "plumbing" message queues (that the users don't see) create queues with with the full number of buffers (set with the -n option).  This can easily exceed the default linux system limit (currently 10) set in /proc/sys/fs/mqueue/msg_max which .  This can create an mq_open error because the mq_maxmsg value of the mq_attr struct is too large.  That  The system limit needs to be set appropriately.  An example of the error:

    Code Block
    mq_open output: Invalid argument
name: '/PdsToMonitorEvQueue_tmo_6'
mq_attr:
        mq_flags 0x800
        mq_maxmsg 0xc
        mq_msgsize 0x10
        mq_curmsgs 0x0

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