Db2 changes for the GDPS Continuous Availability with zero data loss solution

To support the GDPS Continuous Availability with zero data loss (GDPS Continuous Availability with zero data loss) solution, Db2 12 introduces subsystem parameters, commands, use of a new data set to support compressed log records, a new REORG TABLESPACE option, enhanced DISPLAY LOG command output, and new IFI qualification field values.

GDPS Continuous Availability with zero data loss solution terminology: A GDPS Continuous Availability with zero data loss solution that includes Db2 requires three data sharing environments. The solution includes a source Db2 data sharing group, a proxy Db2 data sharing group, and a target Db2 data sharing group. The proxy group uses a capture program to capture changes to tables on the source group. The proxy group then uses a replication program to replicate the changes to the target group. A VSAM key-sequenced data set, called the compression dictionary data set (CDDS), must be defined in the source group. It holds the following items for use in capture and replication:

The expansion dictionaries for Db2 tables whose changes are captured
Currently, the CDDS contains a maximum of three versions of the expansion dictionaries.
System status information that the proxy group uses to find the log data sets and to determine the status of the source group members

Subsystem parameters

The following subsystem parameters are added to support this configuration. These subsystem parameters cannot be changed online.

CDDS_MODE: Specifies whether a member of a Db2 data sharing group is part of a source data sharing group, a proxy data sharing group, or neither. Possible values are SOURCE, PROXY, and NONE.
CDDS_PREFIX: Specifies a prefix of up to 39 bytes for the CDDS name. The full CDDS name is this prefix, appended with '.CDDS'.

CDDS creation and population

You need to define the CDDS on the source data sharing group. You run the REORG TABLESPACE utility with the INITCDDS and SEARCHTIME options to populate the CDDS.

Commands for starting and stopping the CDDS

Before a CDDS can be recovered, it must be closed and deallocated. The -STOP CDDS command lets you close and deallocate a CDDS without stopping all members of a data sharing group. You can then recover the CDDS, and issue the -START CDDS command to allocate and open the CDDS on all members of the data sharing group. You can issue the -START CDDS and -STOP CDDS commands from the source or proxy data sharing group.

DISPLAY LOG command output changes

When a data sharing group is enabled as a source or proxy group, the DISPLAY LOG command includes message DSNJ375I, which shows the name of the CDDS, and whether it is enabled in source or proxy mode.

DSNJU008 (print CDDS) utility

The DSNJU008 stand-alone utility prints the CDDS. You can filter the output by DBID, PSID, table space partition, or expansion dictionary version.

IFI qualification changes

Begin program-specific programming interface information.

The IFI READS command for IFCID 0306 supports capture of log records. The following values are added to the WQALLCRI field to indicate that log records are being collected by the proxy data sharing group for the source data sharing group.

X'01' (WQALLCR1): Only log records for changed data capture and unit of recovery control from the proxy data sharing group in a GDPS Continuous Availability with zero data loss environment. Records are returned until the end-of-scope log point is reached.
X'02' (WQALLCR2): All types of log records from the proxy data sharing group in a GDPS Continuous Availability with zero data loss environment. Records are returned until the end-of-scope log point is reached.
X'03' (WQALLCR3): Only log records for changed data capture and unit of recovery control from the proxy data sharing group in a GDPS Continuous Availability with zero data loss environment. Records are returned until the end-of-log point is reached for all members of the data sharing group.
X'04' (WQALLCR4): All types of log records from the proxy data sharing group in a GDPS Continuous Availability with zero data loss environment. Records are returned until the end-of-log point is reached for all members of the data sharing group.

End program-specific programming interface information.