4-44 IBM Informix OnLine Database Server Administrator’s Guide
Step 4: Roll Back Incomplete Transactions
Step 4: Roll Back Incomplete TransactionsThe final step in fast recovery is to roll back all logical log records that are
associated with transactions that were not committed (or were rolled back).
This rollback procedure ensures that all databases are left in a consistent
state.
Sinceit is possible that one or more transactions have spanned several check-
points without being committed, this rollback procedure might read
backwardthrough the logical log past the most-recent checkpoint record. All
logical log files that contain records for open transactions are available to
OnLinebecause a log is not freed until all transactions contained within it are
closed.Figure 4-7 illustrates the roll-back procedure. When fast recovery is
complete, OnLine goes to quiescent or online mode.
Figure4-7
Fast recovery,
step4
Fast Recovery: Step 4
OnLine rolls back all incomplete transactions, ensuring that all databases are
left in a consistent state. Records written earlier than the checkpoint might be
rolled back.
Disk A
Logical log
Uncommittedchanges
rolled back