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Subscription vs Read multiple items

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29 Jan 2021 08:22 #9375 by support
Hello.
You have posted under "OPC Alarms&Events". There are subscriptions in OPC A&E, but no Reads, therefore your question cannot be answered as posted.

Did you want to refer to OPC DA (Data Acccess) instead?

If so, then yes, it's CPU load, but mainly network load and speed that comes form that. Imagine that you have 1000 items, and on average, 5 of them change every second, and you want to get them all. Roughly speaking

- Doing a Read means that the request containing 1000 items must be issued at least twice a second, transferred over the network, and the server needs to process it and respond back with all 1000 items, shipping them back over the network.
- With subscribing to the items, after you have subscribed, the server will ship just the 5 items that have changed every second.

Regards

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28 Jan 2021 19:40 #9372 by Sacha
Why choose Event Subscription or Read multiple items ?
CPU load ?
Speed ?

Regards

Sacha

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