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schedule recoverability


Need to address the effect of transaction failures on concurrently running transactions.

Recoverable schedule — if a transaction Tj reads a data items previously written by a transaction Ti , the commit operation of Ti  appears before the commit operation of Tj.

The following schedule (Schedule 5) is not recoverable if T9 commits immediately after the read

Cascading rollback – a single transaction failure leads to a series of transaction rollbacks. Consider the following schedule where none of the transactions has yet committed (so the schedule is recoverable).

If T10 fails, T11 and T12 must also be rolled back.