4-32 IBM Informix OnLine Database Server Administrator’s Guide

Verify the Archive Level

Verify the Archive Level
As part of the archive request, you specify an archive level. Thetbtape
process compares the specified archive level with the information that was
obtained from thePAGE_ARCH reserved page.
Iftbtape 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.
(Alevel-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
problemsthis could create if a data restore were needed, avoid this situation.)
Check Free Space in the Logical Log
The tbtape process temporarily freezes the status of unreleased logical log
files and does not permit any log file to become free. Thetbtape process
checksthe 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.
Force a Checkpoint
Aftertbtape verifies that the archive can proceed, it forces a checkpoint.
Duringthe checkpoint, tbtape gathers reference information that serves as a
snapshot of all OnLine data at this time.
Thecheckpoint marks the beginning of the archive. OnLine shared memory
and disk pages are brought to a consistent state. (Refer topage 2-70 for
further information about checkpoints.)
Theaddress of the most-recently written record in the current logical log file
isnoted. This record becomes the last record from the log that will be copied
as part of this OnLine archive.
Ifthis archive is an online archive, all changes to OnLine data that occur after
thispoint are considered beyond the range of the archive and are retained as
part of the logical log file records.