Installing Db2 connection definitions

This section describes the guidelines for installing and discarding DB2CONN definitions and the implications of interruptions in partial activity.

About this task

Only one DB2CONN can be installed in a CICS® system at any one time. An install of a second DB2CONN can implicitly DISCARD the existing DB2CONN and its associated DB2ENTRYs and DB2TRANs (unless reinstalling a DB2CONN of the same name) before proceeding with the installation.
A DB2CONN must be installed before any DB2ENTRY or DB2TRAN definitions. DB2ENTRY and DB2TRAN definitions cannot exist on their own, and can only be associated with a DB2CONN that is already installed. Also, if you discard a DB2CONN, the associated DB2ENTRY and DB2TRAN resource definitions are also discarded. Note that there is no attribute on a DB2ENTRY or DB2TRAN that explicitly specifies the DB2CONN to which they belong. This allows DB2ENTRY and DB2TRAN definitions to be shared by DB2CONN definitions without alteration.
Note: When DB2CONN, DB2ENTRYs, and DB2TRANs are defined in the same group, CICS automatically installs the DB2CONN first. If you install Db2® definitions from multiple groups (by means of a list or multiple INSTALL GROUP commands), the first group you install must contain the DB2CONN definition. Successive groups should not have any DB2CONN definitions. CICS issues an error message when installing a DB2ENTRY or DB2TRAN when no DB2CONN is installed. If multiple DB2CONN definitions are installed, all Db2 definitions installed before the final DB2CONN definition are discarded. CICS issues messages for all discards.
A DB2CONN must be installed before the CICS Db2 connection can be started. Because it contains information regarding pool threads and command threads, as well as global type information, a DB2CONN represents the minimum required to start the CICS Db2 connection. There are no entry threads, and all transactions use the pool. You can add DB2ENTRYs and DB2TRANs after the CICS Db2 connection is active.
A DB2CONN can be re-installed only if the CICS Db2 attachment facility is not connected to Db2, and therefore inactive.
A DB2CONN can be discarded only when the CICS Db2 attachment facility is not connected to Db2.
The discard of a DB2CONN implicitly discards all installed DB2ENTRYs and DB2TRANs.
Note: There is no group commit or group discard of DB2CONNs, DB2ENTRYs, and DB2TRANs. However when a DB2CONN is discarded, the underlying control block is marked stating that a discard is in progress. The DB2ENTRYs and DB2TRANs are discarded before the DB2CONN. If the discard fails when half completed, a DB2CONN control block results, and a message is issued that a discard is in progress. When using a partially discarded Db2 resource definition, a start of the CICS Db2 attachment facility fails with the following message:
```
DFHDB2074 CICS DB2 ATTACHMENT FACILITY STARTUP
          CANNOT PROCEED AS THE CURRENTLY
          INSTALLED DB2CONN IS NOT USABLE
```
You must re-issue the discard. When a CICS system restarts after a failure when discarding, it knows that a discard took place. CICS does not recover the blocks from the catalog, and this effectively completes the discard. (Note that the definitions are removed from the catalog as well.)
When you are installing, parts of any group or list install can fail, but messages are displayed that identify which resources have failed. You can proceed with a start of the CICS Db2 attachment facility when this happens.