Conditional restart
A conditional restart is a Db2 restart that is directed by a user-defined conditional restart control record (CRCR).
If you want to skip some portion of the log processing during Db2 restart, you can use a conditional restart. However, if a conditional restart skips any database change log records, data in the associated objects becomes inconsistent, and any attempt to process them for normal operations might cause unpredictable results. The only operations that can safely be performed on the objects are recovery to a prior point of consistency, total replacement, or dropping.
In unusual cases, you might choose to make inconsistent objects available for use without recovering them. For example, the only inconsistent object might be a table space that is dropped as soon as Db2 is restarted, or the Db2 subsystem might be used only for testing application programs that are still under development. In cases like those, where data consistency is not critical, normal recovery operations can be partially or fully bypassed by using conditional restart control records in the BSDS.
Restart considerations for identity columns
Cold starts and conditional restarts that skip forward recovery can cause additional data inconsistency within identity columns and sequence objects. After such restarts, Db2 might assign duplicate identity column values and create gaps in identity column sequences.
Restart considerations when subsystem parameter CDDS_MODE is set to SOURCE_ONLY
Setting subsystem parameter CDDS_MODE to SOURCE_ONLY causes the compression dictionary data set (CDDS) to be used to store the expansion dictionary for compressed log records that are read using IFI calls for IFCID 0306.
When subsystem parameter CDDS_MODE is set to SOURCE_ONLY, during a conditional restart for which ENDLRSN, ENDRBA, SYSPITRT, or SYSPITR is specified as a log truncation point for a prior point in time, and the ENDLRSN, ENDRBA, SYSPITRT, or SYSPITR value is not X'FFFFFFFFFFFFFFFFFFFF', Db2 sets the CDDS to an empty state and issues message DSNJ396I. Db2 takes this action because the entries in the CDDS might no longer match the entries in the expansion dictionary that is in a compressed table space that contains a table with the DATA CAPTURE CHANGES attribute. After you restart Db2 on a stand-alone subsystem or all members of a data sharing group, you need to run REORG TABLESPACE with the INITCDDS option on all compressed table spaces with tables that have the DATA CAPTURE CHANGES attribute. This action repopulates the expansion dictionary entries in the CDDS.
