Any client application that uses a database must establish a connection to that database before any work can be done. The connection forms a channel through which all activity from the client application takes place. For example, your user ID determines permissions to perform actions on the database—and the database server has your user ID because it is part of the request to establish a connection.

When a user connects to a database, the database server assigns the connection a unique connection ID. For each new connection to the database server, the server increments the connection ID value by 1. These connection IDs are logged in the -z server output. The connection ID can be used to filter request logging information, identify which connection has a lock on the database, or track the total number of connections to a server since it started and the order in which those connections were made.

See Request logging and How locking works.

You can also obtain a user's connection-id using the CONNECTION_PROPERTY function to request the connection number. The following statement returns the connection ID of the current connection:

SELECT CONNECTION_PROPERTY( 'number' );

Connecting from SQL Anywhere APIs

To establish a connection, the client application calls functions in one of the SQL Anywhere interfaces. SQL Anywhere provides the following interfaces:

The interface uses connection information included in the call from the client application, perhaps together with information held in a data source, the SQLCONNECT environment variable, or the server address cache, to locate and connect to a server running the required database. The following figure is a simplified representation of the pieces involved.

What to read

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