You can now use the group attach facility of DB2® with CICS®.
Instead of a specific DB2 subsystem, you can specify a DB2 group
ID on the DB2CONN resource definition. With a DB2GROUPID specified,
the group attach facility chooses any member of the group that is
active on the local MVS™ image for the connection to CICS (members
that are active on other MVS images are not eligible for selection).
There are some restrictions regarding the use of the DB2ID and
DB2GROUPID attributes:
- You cannot specify both DB2ID and DB2GROUPID in the same DB2CONN
resource definition:
- If you attempt to set both on the same CEDA panel, the DB2ID takes
precedence and the DB2GROUPID is ignored.
- If you attempt to set both attributes on a CEDA, or DFHCSDUP,
DEFINE command line, an error message is issued and the last-named
attribute is accepted.
- If you attempt to set both on an EXEC CICS CREATE
or SET command, the command fails with an INVREQ response.
If an installed DB2CONN definition specifies a DB2ID, and you
want to override this and switch to the group attach facility:
- Specify a DB2GROUPID using the CEMT, or EXEC CICS, SET
DB2CONN command
- Specify a DB2GROUPID using the CEDA command to alter the CSD resource
definition, and reinstall the DB2CONN.
If an installed DB2CONN definition specifies a DB2GROUPID, and
you want to override this and switch off the group attach facility,
you can:
- Specify a DB2ID on the DSNC STRT command.
- Specify a DB2ID (or blank-out the DB2GROUPID) using the CEMT,
or EXEC CICS, SET DB2CONN command
- Specify a DB2ID (or blank-out the DB2GROUPID) using the CEDA command
to alter the CSD resource definition, and reinstall the DB2CONN
The INITPARM system initialization parameter method of specifying a DB2ID (INITPARM=(DFHD2INI=db2id))
continues to be supported, but is effective only if both the DB2GROUPID
and DB2ID attributes are blank in the DB2CONN resource definition.
If a DB2CONN specifies a DB2ID or a DB2GROUPID, INITPARM is ignored.
Note that if you issue an INQUIRE DB2CONN command, or look at the
statistics output, you might sometimes see both a DB2GROUPID and a
DB2ID. This happens under the following circumstances:
- You are using group attach, and CICS is
connected to the DB2 shown in the DB2ID field at the
time of the inquiry, or at the time the statistics were taken.
- You are using group attach and CICS is
waiting to reconnect to a specific DB2 subsystem,
because RESYNCMEMBER(YES) is specified and the DB2 subsystem
for which CICS is holding outstanding units of work is unavailable.
In this case, the DB2ID of the DB2 for
which CICS is waiting is shown, with the status CONNECTING.
You need to consider the resolution of indoubt units of work when
you are using the group attach facility. CICS maintains
a history of the last DB2 data sharing group member to which
it connected, which is cataloged and maintained across warm, emergency
and cold starts (but not initial starts). During connection to DB2,
the CICS DB2 attachment facility checks this
history to see if any outstanding UOW information is being held for
the last DB2 data sharing group member to which it connected.
If no outstanding UOW information is being held, the group attach
facility operates normally and can choose any active member of the
data sharing group for the connection. However, if there are outstanding
units-of-work involving a specific DB2 member,
the connection process depends on the value specified for the new
RESYNCMEMBER attribute of the DB2CONN resource definition. The new
RESYNCMEMBER attribute on the DB2CONN resource definition gives you
some control over a connection when there are outstanding UOWs, and
operates as follows:
- If RESYNCMEMBER(YES), CICS ignores the group attach facility
and waits until it can reconnect to the DB2 data
sharing group member it needs to resolve the indoubt units of work.
- If RESYNCMEMBER(NO), CICS makes one attempt to reconnect
to the last recorded DB2 data sharing group member. If
this attempt is successful, the indoubt units of work can be resolved.
If it is unsuccessful, CICS uses group attach to connect
to any active member of the DB2 data sharing group, and issues
the warning message DFHDB2064 stating that there may be unresolved
indoubt units of work with the last recorded member. If you specify
RESYNCMEMBER(NO) when you are using group attach, CICS could
connect to a DB2 data sharing group member that is not the one
for which it had outstanding units of work. In this case, any outstanding
UOWs remain unresolved until CICS can
connect to the original DB2 subsystem to which the UOWs relate.
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