IBM 000-8697 Determine Archive Criteria

Data Consistency, Recovery, and Migration 4-37
Determine Archive Criteria
Determine Archive Criteria
Astbtape 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 thesecriteria:
■The page has been allocated.
■The page isnot 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.
Beforetbtape 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 topage 2-103.)
Astbtape 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
contiguousblock 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 reading a blobspace chunk, it queries the blobspace free-
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-
mationis still current. (Refer to page 2-148 for further information about the
blobspace free-map page.)
The tbtape process checks the snapshot of reference information to identify
eachdbspace page that was part of a logical log file or part of the physical log
atthe time that the archive began. While tbtape reads each dbspace chunk, it
recognizes the address of the first page in the contiguous block that was the
physicallog or was a logical log file at the time the archive began. When this
occurs,tbtape skips to the page that was, at the time, the end of the block.
Thearchive level affects the archive criteria. A level-0 archive requires tbtape
to archive all used disk pages containing a timestamp less than the begin-
archive checkpoint timestamp.