IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

As part of the archive request, you specify an archive level. The tbtape
process compares the specified archive level with the information that was
obtained from the

PAGE_ARCH

 reserved page.

If tbtape cannot find a record of a previous archive on the reserved page, the
only valid archive level is a level-0 archive. Otherwise, any archive level is
valid.

(A level-0 archive to /dev/null registers as a valid archive. Therefore, OnLine
permits you to create a level-1 archive on a tape device if your only level-0
archive was created when the archive device was /dev/null. Because of the
problems this could create if a data restore were needed, avoid this situation.)

The tbtape process temporarily freezes the status of unreleased logical log
files and does not permit any log file to become free. The tbtape process
checks the total amount of free log space. If free space is less than half of one
log file, OnLine refuses the archive request and recommends that you back
up the logical logs.

After tbtape verifies that the archive can proceed, it forces a checkpoint.
During the checkpoint, tbtape gathers reference information that serves as a
snapshot of all OnLine data at this time.

The checkpoint marks the beginning of the archive. OnLine shared memory
and disk pages are brought to a consistent state. (Refer to

further information about checkpoints.)

The address of the most-recently written record in the current logical log file
is noted. This record becomes the last record from the log that will be copied
as part of this OnLine archive.

If this archive is an online archive, all changes to OnLine data that occur after
this point are considered beyond the range of the archive and are retained as
part of the logical log file records.