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Clear old data out of subscription buffers
November 1, 2016
14:28, EET
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MichaelBraveDigital
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March 10, 2016
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Hi,

I’m using two subscriptions to pull data in realtime from numerous OPC servers. Normally there is a once-per-minute update of each OPC server’s data to the app, which is done via a low speed subscription.

When the user requests real time data from a specific OPC server, another subscription, a high-speed once-per-second subscription is resumed and starts to stream realtime data to the app.

Both subscriptions are created on startup of the system, and the high-speed subscription is immediately paused.

My problem is that when the user requests the realtime data and the high-speed subscription is unpaused, it seems to send through a small burst of old data from the last time it was resumed, resulting in the realtime data showing a flash of incorrect data for the first second of activation.

Is there some way I can tell the subscription to clear it’s buffers or not to transmit old data? I’m using subscription.setPublishingEnabled() to perform the pausing and resuming.

November 1, 2016
14:49, EET
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Jouni Aro
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Are you using buffers in the monitored items (QueueSize > 1)? If you take this down to 1, the server should reset the buffer.

Another, perhaps better alternative would be to set the MonitoringMode of the MonitoredItems to Sampling, instead of disabling the subscription. In this case, the server should sample data, but not send any notifications until it is changed back to Reporting.

I think the latter is designed exactly for the case that you have. The only problem is that you need to set this separately for each item.

November 3, 2016
12:00, EET
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MichaelBraveDigital
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Ah okay thanks, I’ll try that.

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