Understanding Db2 Messages

Have you ever been confronted with a Db2 message and needed help deciphering what it is trying to tell you? 

I'm sure most of us have. But let's back up a moment and define what a Db2 message actually is. In Db2 for z/OS, a message refers to a notification from the Db2 subsystem that is conveying information about the status, events, errors, or other conditions within the Db2 environment. Db2 for z/OS generates messages to report various aspects of its operation, and these messages can be critical for monitoring, diagnosing, and resolving issues in the database system.

There is an entire manual devoted to describing Db2 Messages, titled, appropriately enough, Db2 for z/OS Messages. Db2 messages serve several purposes:

• Informational Messages: These messages provide general information about the status or activities of the Db2 subsystem. They might include details about ongoing processes, successful completion of operations, or other relevant information.
• Warning Messages: Warning messages indicate that an operation completed with a potential issue or that there's a condition that might require attention. While not necessarily errors, warnings prompt users to review and possibly take corrective actions.
• Error Messages: Error messages signify that a problem occurred during the execution of a Db2 operation. These messages provide details about the nature of the error and often include information to help identify the cause.
• Diagnostic Messages: Diagnostic messages provide additional details that can be useful for troubleshooting and debugging purposes. They offer insights into the internal workings of Db2 and can assist database administrators in identifying and resolving problems.

Where do you find Db2 messages? Well, the can be found in various places, including: system logs, job output, Db2 message files, and output from SQL queries or commands.

You can recognize a Db2 message because it will start with the three-letter indicator DSN. DSN is the product identifier used internally by IBM for Db2. Db2 for z/OS messages follow a specific format that includes important information about the message type, severity, and details about the message. 

Db2 messages are identified by unique message numbers, which are eight to ten characters long. Db2 for z/OS message identifiers have the following format:

      DSNSnnnnnI

The first three characters, as we have mentioned, is the three-character message identifier, which in Db2 for z/OS is DSN.

The next single character, shown by the S above, is the subcomponent identifier. This character identifies the subcomponent of Db2 that issued the message. Each subcomponent has an associated hexadecimal identifier (hex ID), which is the hexadecimal representation of the subcomponent identifier. These identifiers (as of Db2 13 for z/OS) are as follows:

A    Call attachment facility and some Db2 supplied stored procedures

B    Buffer manager

E    TSO attachment facility 

F    Message generator 

G    Database descriptor manager 

H    Precompiler, DSNH CLIST 

I    Data Manager

J    Recovery log manager

L    DDF

M    IMS Attachment Facility

P    Data space manager 

Q   MQListener

R    Recovery manager 

S    Storage manager 

T    Service controller, install 

U    Utilities U 

V    Agent services manager 

W    Instrumentation facility

X    Relational data system 

Y    Initialization procedures 

Z    System parameter manager

1    Service facilities

3    Subsystem support subcomponent

5    Db2 Accessories Suite for z/OS

7    Group manager 

8    Sample applications 

9    General command processor

The next three to five characters (beginning at the fifth character and indicated by nnnnn) is the numeric identifier of the message. This identifier is unique within each subcomponent.

The final character of the message identifier (indicated by I in the example above) is the type code. This is sometimes thought of a severity code, but most Db2 messages use I for the type code, regardless of the severity or whether an action is required. Some older Db2 messages use other type codes, but keep in mind that the type code does not necessarily reflect the severity of the message. 

What Does the Message Mean?

To understand the meaning of a message you will need to look up the message identifier in the Db2 Messages manual. The manual is broken down into chapters, with each chapter devoted to a subcomponent. So, what if you receive a DSNJ994I Db2 message?

Well, we know that the J means this is a recovery log manager error. If we look this up in the manual (Chapter 8 for Db2 13 for z/OS), we see the following explanation:

    VSAM OPEN failed with the indicated ACB error-code
    for the indicated dd-name.

This is a time to contact your system programmer because Db2 cannot open the underyling VSAM data set.

Summing Things Up

Understanding Db2 messages is a crucial aspect of being able to effectively program, manage, monitor, and resolve Db2 problems. Be sure to have the Db2 manuals and documentation available (either online or downloaded to your computer) to be able to retrieve detailed information about the various messages and their meanings when you need them.

The Db2 for z/OS Messages manual provides comprehensive information about Db2 messages and it is a valuable resource for troubleshooting and understanding system behavior.