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Best Practices - ReadMultipleItems vs SubscribeMultipleItems

13 May 2019 16:29 - 13 May 2019 16:29 #7356 by support
this is a good question.

For performance/efficiency reasons, in the OPC, it is recommended to use subscriptions, instead of periodically polling by Reads. The subscriptions allow the server to optimize the data collection, and the data transfer (only changes are sent).

So, this is a general rule, and I would normally follow it when designing a new solution. On the other hand, subscriptions have some disadvantages, too. Thet are more difficult to setup, and the code gets more complicated.

If you have actually positively determined that your solution works, and does not create too much load anywhere (the device, the communication to the device, the server, the network, the client etc.), there is nothing that prevents you from simply using what you have done, especially if that works reliably already. But your test must be with the full number of items, real amount of data, and in parallel with anything else that would run on these systems. If it works, then you are OK.

Last edit: 13 May 2019 16:29 by support.
The following user(s) said Thank You: davide

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13 May 2019 13:21 #7355 by davide
Dear OPC Labs team,
I'm a newbie and I want ask you the best practice to use a DA Client. I need to read tags (more or less 2k) and the ways to do it are:
  • by polling using ReadMultipleItems
  • by monitoring changes using SubscribeMultipleItems
At this moment I've implemented the "polling" way and it works great. If the tags changes frequently (more or less like to my polling interval) has sense to implement the other way (SubscribeMultipleItems)? Which are the main pros and cons?
Thanks in advance.

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