I have temperature charts that change frequently, and other items that change very infrequently, such as AC status, and set values.
Is there a requirement on value persistence intervals or cron, in order to get a continuous graph in the sitemap?
The answer is, yes.
From the docs:
When using rrd4j persistence, the strategy
everyMinute(60 seconds) has to be used. Otherwise no data will be persisted (stored) and the chart will not be drawn projavay (see rrd4j Persistence).
Although I have no idea what that last word means, in effect you get diagonal lines between adjacent values, where a staircase line would be expected.
I’d guess it’s supposed to read “properly”.
The requirement goes beyond that. The way rrd4j works, all items require an everyMinute strategy or else it doesn’t work. The way it maintains a fixed size requires there to be a record every minute whether or not that record represents a change.
Filed a PR to fix the typo here: Fixed typo by rkoshak · Pull Request #1999 · openhab/openhab-docs · GitHub
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To the best of my knowledge this isn’t true anymore. The change of the rrd4j persistence to openHAB2 and above caused that change.
The quote sentence from the sitemap documentation was probably just missed.