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In the following diagram the lease refresh discovers that the lease is no longer valid, and the transaction is aborted.

Leases can must be refreshed periodically by TxnCoordinator, depending on the lease duration. Successful refreshing of a lease extends transaction deadline up to a lease upper bound.

The more frequent refreshing reduces the probability of txn abort due to reaching the deadline.The reasonable refresh rate can be calculated as a fraction of the lease duration D, for example  D/3is D/2, where D is a lease duration interval.

Commit reordering for dependent transactions

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