SQL Reference

Options that Govern Distributed Unit of Work Semantics

The semantics of type 2 connection management are determined by a set of precompiler options. These are summarized briefly below with the defaults indicated by bold and underlined text. For details refer to the Command Reference or Administrative API Reference manuals.

• CONNECT (1 | 2)

  Specifies whether CONNECT statements are to be processed as type 1 or type 2.

• SQLRULES (DB2 | STD)

  Specifies whether type 2 CONNECTs should be processed according to the DB2 rules which allow CONNECT to switch to a dormant connection, or the SQL92 Standard (STD) rules which do not allow this.

• DISCONNECT (EXPLICIT | CONDITIONAL | AUTOMATIC)

  Specifies what database connections are disconnected when a commit operation occurs. They are either:

  • those which had been explicitly marked for release by the SQL RELEASE statement (EXPLICIT), or
  • those that have no open WITH HOLD cursors as well as those marked for release (CONDITIONAL) ¹¹ , or
  • all connections (AUTOMATIC).
• SYNCPOINT (ONEPHASE | TWOPHASE | NONE)

  Specifies how commits or rollbacks are to be coordinated among multiple database connections.

  ONEPHASE

  Updates can only occur on one database in the unit of work, all other databases are read-only. Any update attempts to other databases raise an error (SQLSTATE 25000).

  TWOPHASE

  A Transaction Manager (TM) will be used at run time to coordinate two phase commits among those databases that support this protocol.

  NONE

  Does not use any TM to perform two phase commit and does not enforce single updater, multiple reader. When a COMMIT or ROLLBACK statement is executed, individual COMMITs or ROLLBACKs are posted to all databases. If one or more rollbacks fails an error (SQLSTATE 58005) is raised. If one or more commits fails an error (SQLSTATE 40003) is raised.

Any of the above options can be overridden at run time using a special SET CLIENT application programming interface (API). Their current settings can be obtained using the special QUERY CLIENT API. Note that these are not SQL statements; they are APIs defined in the various host languages and in the Command Line Processor. These are defined in the Command Reference and Administrative API Reference manuals.

Data Representation Considerations

Different systems represent data in different ways. When data is moved from one system to another, data conversion sometimes must be performed. Products supporting DRDA will automatically perform any necessary conversions at the receiving system.

With numeric data, the information needed to perform the conversion is the data type of the data and how that data type is represented by the sending system. With character data, additional information is needed to convert character strings. String conversion depends on both the code page of the data and the operation that is to be performed with that data. Character conversions are performed in accordance with the IBM Character Data Representation Architecture (CDRA). For more information on character conversion, refer to Character Data Representation Architecture Reference SC09-1390.

¹¹

The CONDITIONAL option will not work properly with downlevel servers prior to Version 2. A disconnection will occur in these cases regardless of the presence of WITH HOLD cursors