on this topic @rob_outterson explains the difference very well between various provising typologies.
As far as I’m concerned I dont like the optimistic provisioning because it can cause a misperception of the data.
For example, IIQ send the update to the target system and update the data on itself without a confirmation. Until the next aggregation, the data that are stored in IIQ could be wrong; also, depending of the configuration, the update can launch triggers, workflow etc…and always until the next aggregation you dont know if those data are correct or not.
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