In utxo we store only the hash of the datum, so whenever you work with the Cardano cli to run a transaction - you should provide datum or its hash via tx-out-datum-embed-file, tx-in-datum-file, etc.
What about the PAB?
Did I understand correctly that original datum is stored in chainindex? At what step is original Datum sent from PAB to the chainindex?
If the datum is stored in chaindex - does it mean that all PAB apps should be connected to the same chainindex in order to share datum with each other? Are we going to have a global chainindex available for all PABs? What if two PABs are connected to different chainindex servers, does it mean that the datum will not be shared between them?