DB2 10.5 for Linux, UNIX, and Windows

Connecting to distributed relational databases

Distributed relational databases are built on formal requester-server protocols and functions.

An application requester supports the application end of a connection. It transforms a database request from the application into communication protocols suitable for use in the distributed database network. These requests are received and processed by a database server at the other end of the connection. Working together, the application requester and the database server handle communication and location considerations, so that the application can operate as if it were accessing a local database.

An application process must connect to a database manager's application server before SQL statements that reference tables or views can be executed. The CONNECT statement establishes a connection between an application process and its server.

There are two types of CONNECT statements:

CONNECT (Type 1) supports the single database per unit of work (Remote Unit of Work) semantics.
CONNECT (Type 2) supports the multiple databases per unit of work (Application-Directed Distributed Unit of Work) semantics.

The DB2® call level interface (CLI) and embedded SQL support a connection mode called concurrent transactions, which allows multiple connections, each of which is an independent transaction. An application can have multiple concurrent connections to the same database.

The application server can be local to or remote from the environment in which the process is initiated. An application server is present, even if the environment is not using distributed relational databases. This environment includes a local directory that describes the application servers that can be identified in a CONNECT statement.

The application server runs the bound form of a static SQL statement that references tables or views. The bound statement is taken from a package that the database manager has previously created through a bind operation.

For the most part, an application connected to an application server can use statements and clauses that are supported by the application server's database manager. This is true even if an application is running through the application requester of a database manager that does not support some of those statements and clauses.