RE: OPC UA Device Support - Limit in the number of PVs [SEC=OFFICIAL]

["STARRITT, Andrew via Tech-talk" <tech-talk at aps.anl.gov>]

Hi, Eusebio,

When I ran into this situation with a new server (can’t recall which model), I just created two sessions
and two associated subscriptions. It was fairly easy to arrange an approx 50-50 split in the associated
substitution file. Might not have been the “best” solution but did solve the problem.
Cheers
Andrew

OFFICIAL

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of eusebio_naif AL-SOLIMAN FUENTES via Tech-talk
Sent: Saturday, 21 March 2026 1:17 AM
To: Ralph Lange <ralph.lange at gmx.de>
Cc: EPICS Tech Talk <tech-talk at aps.anl.gov>
Subject: Re: OPC UA Device Support - Limit in the number of PVs

 

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Hello Ralph.

 

Thanks for your response. In that case, I will check the configuration of my OPC UA server.

 

Best regards, Eusebio.

 

 

El mié, 18 mar 2026 a las 14:29, Ralph Lange via Tech-talk (<tech-talk at aps.anl.gov>) escribió:

What is your server?

 

That looks like a limitation on the server side, either on the total number of items per session or per subscription (I know a few servers doing that) or on the number of items per OPC UA service call (e.g., Siemens S7 has a limit of 1000) or on the number of registered items (I know a few servers doing that).

Getting BadConnectionClosed means that your server probably closed the connection after it found you were going over its limits. Brutal but not unheard of. (It's a simple way to avoid DoS-type attacks.)

 

If the item is not connected, any processing that leads to a conversion of a value to an unknown OPC UA type will fail - these are follow-up errors.

 

If you think the error message should be improved, please open an issue in the GitHub project.

 

Cheers,
~Ralph

 

--

Eusebio N. Al-Soliman

PhD Student

Departamento de Ingeniería de Computadores, Automática y Robótica

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University of Granada

18008, Granada, Spain | eunaif at go.ugr.es