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DB2 Manager User Guide 15
StorageTek Proprietary
Rows which have a high likelihood of being updated after archival may
cause a significant amount of archival and re-archival processing. A
table containing rows which are likely to be updated in this manner are
not suitable for migration using DB2 Manager.
DB2 Manager does not impose limitations on the way in which rows are
referenced from a DB2 application program. Every possible means of
accessing a migrated row via SQL commands is supported, including joins
and unions.
Multiple migrated and un-migrated rows from one or more tables may be
accessed via a single SQL command from a DB2 application program.
However, if a large number of migrated rows is referenced by execution of
such a command, then it may take a substantial length of time for execution
of that command to be completed if migrated rows are not resident on
Archive Manager disk storage. Table migration via DB2 Manager may not
be appropriate if retrieval requests of this nature are likely to be performed on
a frequent basis.
Alternatively, in these circumstances replacement of a single SQL command
via a row-by-row operation using DB2 cursor processing will give a program
control over the number of retrievals of migrated rows which may be required
to complete an operation – in this case there will be a one-for-one
relationship between a single FETCH command and a single migrated row
retrieval operation.
DB2 management processing
Database backup and recovery
There is no change required to backup and recovery processing procedures
for tablespaces containing tables which have been enabled for DB2 Manager
migration. Image copies should be taken normally as for non-enabled
tables. However, as the size of the tablespaces used for storage of tables
may now have been substantially reduced, the length of time taken for image-
copy processing will be reduced by a corresponding amount.
Restore of a tablespace containing a migration-enabled table is performed in
an identical manner to that of a tablespace containing a non-enabled table.
DB2 will restore the 18-byte stubs containing information about migrated
rows, as well as restoring non-migrated rows, to the condition they were in at
the time the image-copy was taken. The stubs contain all the information
necessary to access migrated rows from Archive Manager.
Database reorganization
Tables which have been enabled for migration processing must be defined in
a partitioned tablespace. This tablespace will have one partition for