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• Enable Rolling History Buffer
  • Enable the Rolling History Buffer to store data in a rolling buffer to cover data loss in a keep alive timeout scenario
• Rolling History Prune Interval
  • Interval at which to attempt to prune the rolling history buffer in seconds
• Rolling History Max Age
  • The maximum age allowed of the data in the rolling history buffer in seconds
• Rolling History Prune Quantity
  • Removed in release 4.0.19
  • All data older than the Max Age will be pruned at The quantity of the oldest data over the Max Age to prune on each prune interval.

The ideal settings for your Rolling Buffer configuration will be dependent on the rate that your tags are changing. For example, consider these settings:

• Rolling history max age - 60s (2x the 30s keep alive timeout)

• Rolling history prune interval - 60s

• Rolling history prune quantity - 10

The rolling history prune interval is how frequently it checks to see if there is any data that’s older than the max age (60s). If there is, in this example, the prune quantity (10 metrics) will be pruned from the buffer for every prune interval (60s). If there’s 100 metrics in the buffer that are older than 60s, after pruning once, only the oldest 10 will be dropped and there will still be 90 old metrics there.

On a reconnect, these older metrics will be published since they’re still in the buffer. Having a lot of old tags in the buffer will increase the number of duplicates that you get. Keeping a proper balance between the tag change rate and these settings can be important for minimizing duplicates.

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