I would like to use apache iotdb to store and retrieve Ignition history data.
Creating a module could be an option but I don't find any example as starting point with the current SDK.
I don't kown if the current 8.1 is a good choice for building this kind of module or if it is better to wait for 8.3 and som api change ?
Whether to target 8.1 or wait until 8.3 and a (hypothetical) API change is probably up to whether you can wait that long for business reasons.
Kymera has implemented a third-party historian (InfluxDB) on top of Ignition's historian, so it's certainly possible: Kymera Systems Inc – IIoT Solutions - InfluxDB Module
The 'starting point' is probably going to be the com.inductiveautomation.ignition.gateway.sqltags.config.TagHistoryProviderType extension point. That will be used to create a com.inductiveautomation.ignition.gateway.sqltags.history.TagHistoryProvider, which is the entry point to the various methods.
@jpark I think was also experimenting in this area, at least at one point; he may have insight he can offer?