[rrd4j] Correctly identify Number items with dimensions and persist them in the defined unit

[kaikreuzer]

The persistence service will now use the defined unit of Number items with dimensions (which is derived from the unit given in its state description or - if not set - from the defaults of the used measurement system) for both writing and reading values from the database.

Fixes #8809
Fixes #8856

Signed-off-by: Kai Kreuzer kai@openhab.org

[lolodomo]

LGTM

[wborn]

Thanks a lot! 👍

[ghys]

FYI, either this or a related rrd4j PR had a significant impact on performance with retrieving data from /rest/persistence.
On my RPi3-equivalent, requests that used to be instant now take seconds.

Also some things in the UI, like the analyzer, don't work anymore because the unit comes with the number.

[kaikreuzer]

FYI, either this or a related rrd4j PR had a significant impact on performance with retrieving data from /rest/persistence.

No idea what could cause this - I don't see any performance degradation on my system so far.

Also some things in the UI, like the analyzer, don't work anymore because the unit comes with the number.

I just noticed the same after upgrading and @lolodomo reported openhab/openhab-core#1781.

[ghys]

(Copied from openhab/openhab-core#1781 (comment))

I have now downgraded to the M1 version of the rrd4j bundle and I'm back to acceptable perf levels again:
(see ~60ms vs 3.5s)

I would suspect there's something way heavier than before being done for each data point.

[openhab-bot]

This pull request has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/persistence-sitemap-charts-blank/153654/1