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One property BookKeeper satisfies is persistence: if an entry e is added to a ledger and the client receives a confirmation, then the last entry of the ledger once it is closed is at least e.

The procedure we use to recover a ledger Ledger recovery alone does not prevent a violation of the persistence property. Consider the following scenario. We have an application with a ledger writer and a ledger reader waiting until the ledger writer closes the ledger to read. The leader reader, however, suspects incorrectly that the ledger writer has crashed and proceeds to open the ledger and recover it. The reader reads as many entries as it can and writes the identifier of the last confirmed entry to the metadata store. The ledger writer concurrently writes more entries to the ledger successfully, even though the ledger has been closed already.

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