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wait_timeout is the number of seconds the server waits for activity on a noninteractive non interactive connection before closing it.
Unfortunately, the server doesn't tell the client wether whether the connection is closed so that the client will use a closed connection which throws an error
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You can increase the value of wait_timeout to avoid the problem but then you can get problems with the max. numbers number of connections.
A workaround in the JobScheduler is to configure a job with a repeat interval in its schedule which is shorter than the wait_timeout value.
For example you can use the scheduler_dequeue_mail job in ./config/live/sos/housekeeping/scheduler_dequeue_mail.job.xml.
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