IBM 000-8697 Manuel d'utilisateur télécharger pdf (Page 409)

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Data Consistency, Recovery, and Migration 4-37

Determine Archive Criteria

As tbtape reads each disk page, it applies a set of criteria that determines

which disk pages should be archived.

The tbtape process only archives pages that meet these criteria:

■ The page has been allocated.

■ The page is not part of a logical log ﬁle or the physical log.

■ The page is needed for this archive level.

OnLine streamlines the archive procedure by ignoring disk pages that are

dedicated to OnLine but which were not yet allocated at the time of the

begin-archive checkpoint.

Before tbtape begins to read a chunk, it consults the snapshot of OnLine

activity to identify unallocated pages. (This information is contained in

entries on the dbspace chunk free-list pages. Refer to page 2-103.)

As tbtape reads a dbspace chunk, it recognizes the address of any unallo-

cated page that was, at the time that the archive began, the ﬁrst page of a

contiguous block of free space. If a block of free space is found, tbtape skips

to the page that was, at the time, the end of that block of space.

Whentbtape begins readinga blobspace chunk, itqueriestheblobspacefree-

map page and skips over any blobpage marked as free. Since blobspace

blobpage allocation was frozen at the time that the archive began, this infor-

mation is still current. (Referto page 2-148 for further information about the

blobspace free-map page.)

The tbtape process checks the snapshot of reference information to identify

eachdbspacepagethatwaspartofalogicallogﬁleorpartofthephysicallog

atthe timethat the archivebegan. While tbtapereadseachdbspace chunk, it

recognizes the address of the ﬁrst page in the contiguous block that was the

physical logor wasa logical log ﬁle at the timethe archive began. When this

occurs, tbtape skips to the page that was, at the time, the end of the block.

Thearchivelevel affectsthearchivecriteria.Alevel-0archiverequirestbtape

to archive all used disk pages containing a timestamp less than the begin-

archive checkpoint timestamp.

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IBM 000-8697 Manuel d'utilisateur Page 409

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