Progress/400
Product Guide
General Connection Considerations
When connecting to databases, there are three issues to consider:
Logical Database Names
A logical database name is a database reference representing the name of a connected physical database. The logical database name is used to resolve database references. When a procedure is compiled against a database, Progress stores the logical database name in the procedure’s object code. When you execute a procedure, the databases referenced by the procedure must match the logical name of a connected database.
When you connect to a database, it is automatically assigned a default logical name for the session. The default logical name is the physical database name, which is the OS/400 library name.
A database connection fails if the logical database name of the database that you are connecting to is the same as the logical name of an already connected database. If you try to connect a database with a logical database name that matches the logical database name of an existing, connected database of the same database type (Progress, DB2/400, ORACLE, and so forth), Progress assumes that the database is connected and ignores that request.
You can change a database’s logical name from a Progress procedure either with the CREATE ALIAS statement or by using the Edit Connection Information utility in the Data Administration tool. See "Remote Client DB2/400 Utilities," for more information.
Connection Modes
You can make the connection to the schema holder in single-user or multi-user mode. You are always connected to DB2/400 databases in multi-user mode. Single-user mode does not prevent others from accessing the DB2/400 database:
Using the Message Buffer Size (-Mm) Startup Parameter
This section provides some special usage notes on the Message Buffer Size startup parameter. This parameter instructs the Progress Client and the Progress/400 DataServer to create a buffer of a specified number of bytes. When a NO-LOCK query requests records, the DataServer packs records into this buffer until it contains all of the records that it can hold. At this point, the DataServer sends it to the Client in one transfer. Note that the -Mm startup parameter affects only Progress, it does not influence the hardware packet sizes.
Suppose, for example, that the hardware packet size on your network is 1500 bytes and the -Mm startup parameter is set to 4000 bytes. The DataServer sends a packet of 4000 bytes to the hardware. The hardware breaks the packet and sends 1500 bytes at a time over the communications line. On the other side of the line, the hardware reassembles these packets into the actual Progress buffer.
Because the hardware handles breaking and reassembling the buffer so rapidly, you should use the largest value possible for the -Mm startup parameter. The maximum size for the message buffer is 4094 on SNA. Using these larger message buffer sizes typically improves the overall performance of your Progress/400 queries in a networked environment.
One particular Progress error message might occur during connection to the Progress/400 DataServer. The following message might be returned when the AS/400 dictionary library name cannot be found (for example, if it is misspelled or does not exist):
Check your connect parameters to make sure that they are not the cause of this message.
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