Quick Beginnings

Overview

If your application programs have been pre-compiled with both the CONNECT 2 and SYNCPOINT TWOPHASE options, you can use DB2 Connect Enterprise Edition to update multiple DB2 for OS/390 Version 5.1 databases over TCP/IP connections using two-phase commit.
Note: For ODBC applications, use the ODBC Manager to set the DSN two-phase option ON for the database.

Any connection between your two-phase commit application and a DB2 for OS/390 Version 5.1 database can also participate with DB2 Universal Database Version 5 database servers in the same transaction.

Additionally, when using DB2 Connect Enterprise Edition Version 5, DB2 for OS/390 Version 5.1 can act as the TM_DATABASE for the entire two-phase commit transaction providing that all the databases participating in the unit of work are either:

DB2 Universal Database Version 5.0 (Workgroup Edition or Enterprise Edition only), or
DB2 for OS/390 Version 5.1.

You can set the TM_DATABASE database manager configuration parameter using the following CLP command:

   update dbm cfg using tm_database 1ST_CONN

What to Do

Follow these steps:

Choose your setting for TM_DATABASE. We recommend 1ST_CONN, especially if the first database connected to will be a DB2 for OS/390 Version 5.1 database. Set TM_DATABASE as indicated above.
Ensure that those databases to be updated by your DUOW transaction over TCP/IP connections will be accessible READ-WRITE if required. See "Limitations".
CLP users must turn off autocommit and use the following set client command prior issuing connect commands:
```
   set db2options=+c
   set client connect 2 syncpoint twophase
```

Limitations

The following limitations apply when using two-phase commit with DB2 Connect Enterprise Edition Version 5.0:

Any connection involved in a distributed unit of work can be over either TCP/IP or SNA. If these protocols are mixed, and the TM_DATABASE is at DB2 for OS/390, then databases connected via SNA will be READ_ONLY participants in the transaction. (If you want to use SNA, see Chapter 22. "Setting Up Two-phase Commit Using SNA").
If DB2 for OS/390 owns the TM_DATABASE, then the client initiating the transaction must specify 1ST_CONN for TM_DATABASE.
DB2 for OS/390 Version 5.1 cannot act as a TM_DATABASE if any of the databases participating in the transaction is either:
- DB2 Common Server Version 2.1 or earlier
- DB2 for MVS/ESA Version 3.1 or earlier.
When SNA connections are used, the LU 6.2 Syncpoint Manager (SPM) permits DB2 for MVS/ESA Version 3.1 databases to be participants in two-phase transactions, but not to act as the TM_DATABASE for such transactions.
You can mix connections to different database levels, including
- DB2 for OS/390 Version 5.1 over TCP/IP
- DB2 for MVS/ESA Version 3.1 over SNA (using SPM)
- DB2 Common Server Version 2.1
- DB2 Universal Database Version 5.0 databases
To do so, you must use a DB2 Universal Database Version 5 client, and DB2 Universal Database Version 5.0 must provide the TM_DATABASE for the transaction.

Migration

The diagram Figure 25 illustrates possible two-phase commit scenarios:

DB2 for OS/390 can function as the TM_DATABASE (we recommend setting TM_DATABASE=1ST_CONN in this case).
If you will mix DB2 CS V2.1 and DB2 Universal Database Version 5.0 databases in the same unit of work, then DB2 Connect Version 5.0 must own the TM_DATABASE locally.
If you will mix SNA and TCP/IP Wide Area Network (WAN) Connections to DB2 for MVS/ESA Version 3.1 as well as DB2 for OS/390 Version 5.1, then DB2 Connect Version 5.0 must run the SPM, and own the TM_DATABASE locally.
If you will connect to DB2 Universal Database Version 5.0 in these scenarios, then the DB2 Client also must be at Version 5.0.

Figure 25. Two-Phase Commit Migration Scenarios.

In the diagram, databases 3-A and 4-A are back-level (DB2 for MVS/ESA Version 3.1).
Systems 1 and 3 are back-level.
Only a DB2 Version 5.0 client can use DB2 Connect Version 5.0 functions, including TCP/IP connections to DB2 for OS/390 Version 5.1.
Connections from system 3 (DDCS Version 2.3 gateway) can use only SNA (lightly shaded arrows).
Connections from system 4 (DB2 Connect Version 5.1 gateway) can use SNA for any connection to DB2 for OS/390, DB2 for MVS, DB2 for AS/400, and DB2 for VM & VSE; or they can use TCP/IP to DB2 for OS/390 Version 5.1 only.

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