
System Architecture 2-71
OnLine Checkpoints
Onereasonanadministrator might wanttoinitiate a checkpointwould be to
forcea newcheckpoint recordin thelogical log. Forcing a checkpointwould
be a step in freeing a logical log file with status U-L. (Refer to page 3-41.)
Fast Recovery
Acheckpointiscritical to the operation of thefast-recoveryprocess.(Referto
page 4-39.) As fast recovery begins, OnLine data is brought to physical
consistency as ofthelast checkpointbyrestoringthe contents ofthe physical
log.
During fast recovery, OnLine reprocesses the transactions contained in the
logical logs, beginning at the point of the last checkpoint record and
continuingthroughalltherecordscontainedinthesubsequentlogicallog(s).
After fast recovery completes, the OnLine data is consistent up through the
last completed transaction. That is, all committed transactions recorded in
thelogicallogsondiskareretained;allincompletetransactions(transactions
with no
COMMIT WORK entry in the logical logs on disk) are rolled back.
Archive Checkpoints
Checkpoints that occur during an online archive may require slightly more
time to complete. The reason is that the archiving procedure forces pages to
remaininthephysicalloguntilthetbtapeprocess(thatperformsthearchive)
has had a chance to write the “before-image” pages to the archive tape. This
mustbe done to ensurethatthearchivehasall timestamped pages neededto
complete the archive. (Refer to page 4-30 for more information about what
happens during online archiving.)
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