Happy Holidays 2023

Did you know that there are over two dozen holidays celebrated across the world between November 1st and January 15th? 

 

 

So in the spirit of the season, I want to wish all of my readers everywhere a Happy Holiday season.

 

This will be the last post I make here this year.

I hope that you will take some time to celebrate whichever holidays you observe... and that you enjoy this time of year with your family and friends. 

 

And let's meet back here next year to talk some more about our favorite DBMS... Db2!

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.

My Top Ten Db2 Performance Posts

Regular readers of this blog will notice that the past few months have been consumed by my posts outlining my Top Ten Db2 Performance tips.

So, it being December and the end of the year, I thought it would be a good idea to publish a post with links to each of the Top Ten tips... so here it is!

Number 1 - Analyze Query Execution Plans

Number 2 - Optimize Your Database Design

Number 3 - Efficient Indexing Strategies

Number 4 - Effective Memory Configuration

Number 5 - Workload Management and Query Optimization

Number 6 - Monitoring and Performance Metrics

Number 7 - Configuration Parameters and Tuning

Number 8 - I/O Optimization

Number 9 - Regular Maintenance and Housekeeping

Number 10 - Stay Up-to-Date

Of course, a list such as this will not be comprehensive in terms of listing everything that you may encounter on your path to efficient Db2 performance... but it can serve as a good place to start that journey.

Let me know your thoughts on anything in this list... or share your performance stories and headaches with us here on the blog!

Top Ten Db2 Performance Tips - No. 10 Stay Up to Date

Keeping Db2 up to date is of paramount importance for ensuring the security, stability, and optimal performance of your database environment. For Db2 for z/OS this means formulating a plan for applying PTFs (Program Temporary Fixes) and correlating your DB2 fixes with your system, ideally following IBM's RSU (Recommended Service Upgrade) preventive service philosophy. For Db2 for LUW it means keeping up with fix packs.

Why is it important to stay current with maintenance? And what are the benefits of doing so?

• Security: Cyber threats and vulnerabilities are ever-evolving, and database systems are potential targets for malicious activities. By staying up to date with the latest patches and fixes, you can ensure that your Db2 systems are protected with the latest security enhancements. Patching known vulnerabilities helps protect sensitive data, prevent unauthorized access, and reduce the risk of security breaches.
• Bug Fixes and Stability: Software systems, including Db2, are not immune to bugs and glitches. The release of patches and fixes addresses identified issues, improving the overall stability and reliability of the database system. Applying these updates helps mitigate performance issues, software crashes, or data inconsistencies that may arise from known bugs. Keeping your Db2 environment updated with the latest fixes contributes to a smoother and more reliable database experience.
• Performance: IBM regularly releases performance enhancements for Db2. Applying the latest patches and fixes ensures that you benefit from these improvements, allowing your database to operate at its optimal efficiency. The updates may include query optimization, resource management enhancements, or other performance-related optimizations, helping to maximize the speed and responsiveness of your Db2 systems and applications.

Another important aspect of staying up to date is tracking and upgrading the version and level of your Db2 systems. IBM clearly provides information on the product lifecycle for Db2 (and all of their products). Information for DB2 for z/OS is provided here. The first thing to be aware of is that you always want to be running supported software. 

If your software is not supported and you run into issues or problems, IBM will not provide support for unsupported software. When your software versions reach their EOS date and support is no longer available through standard Software S&S, you have the option to purchase Continuing Support (typically at a higher rate). It is usually more cost-effective and less risky to migrate to the new, supported version. Furthermore, documentation for unsupported versions of IBM software typically is not available in IBM Knowledge Center.

Therefore, it is wise to be watchful of the EOM and EOS announcements made for your current version of Db2. EOM is the End of Marketing date. When this date is reached you can no longer order that version of the software. IBM Db2 12 for a/OS reached its EOM date in June 2023. More important is the EOS, or End of Service, date. After this date is reached that version of the software is out of support. For Db2 12 for z/OS EOS is scheduled for 2023-12-31 (at the time this blog is being published). At times, EOS and EOM date may be revised due to customer and/or IBM needs.

I maintain links to the IBM product lifecycle pages on my web site at https://www.mullinsconsulting.com/db2.htm. 

Furthermore, as of Db2 12 for /OS, it is also important to keep up to date with the Function Level for your subsystems. Instead of requiring new versions or releases to provide new functionality, IBM is now using a continuous delivery model. So, instead of waiting years for a new version. This means that you should also be tracking function levels, applying maintenance when needed to support them, and activating new function levels on a continuous basis. Failing to do so means that you will be behind the curve when an eventual new version is released.

To access the latest patches and fixes for Db2, IBM provides resources and support channels that you can leverage:

• IBM Fix Central: IBM Fix Central is a centralized portal where you can search, download, and apply patches, fixes, and updates for various IBM software products, including Db2. It offers an intuitive interface to locate the required fixes based on specific product versions and platforms.
•  IBM Support Portal: The IBM Support Portal is a comprehensive resource for accessing product documentation, technical articles, and obtaining support for IBM software. It provides a wealth of information on Db2, including links to downloads, useful articles, and official product documentation.
•  IBM Passport Advantage: If you have a valid software maintenance subscription or license agreement with IBM, you can access the latest patches, fixes, and updates through the IBM Passport Advantage website. This platform enables authorized users to download software updates and manage their entitlements.

You should also keep up to date by following useful online forums and user groups. IDUG offers a good central site for such groups, and useful DB2 information is also offered by SHARE. Both of these organizations offer vibrant community forums and discussion boards that can provide valuable insights into the latest information about Db2. Furthermore, community members often share their experiences, recommendations, and helpful tips for staying up to date with Db2 updates.

Finally, I have to promote my web site Mullins Consulting, Inc. where I frequently post new information about Db2 as well as my articles and books on Db2.

Summing It All Up

In conclusion, staying up to date with the latest patches and fixes for Db2 is essential for maintaining a secure, stable, and high-performing database environment. By applying the latest updates, you benefit from enhanced security, bug fixes, stability improvements, and performance optimizations. Leveraging the resources available to you (such as those discussed above), and engaging with the Db2 community forums ensures that you have access to the most recent updates and support to keep your Db2 environment current and reliable.

Top Ten Db2 Performance Tips – No. 9 Regular Maintenance and Housekeeping

When thinking about the performance characteristics of your Db2 databases and applications keep in mind the routine maintenance that can help or hinder your performance. Regular maintenance and housekeeping tasks are essential for ensuring the optimal performance and stability of your Db2 environment. 

By performing routine maintenance activities, database administrators can proactively address performance degradation, optimize query execution, and maintain a healthy database environment. In today’s post, we will highlight the importance of regular maintenance tasks and discuss key activities that contribute to database performance.

Index Maintenance

Indexes play a crucial role in query performance, as they facilitate quick data retrieval. Over time, indexes can become fragmented, leading to increased disk I/O and decreased query performance. Regularly reorganizing indexes helps eliminate fragmentation and enhances query execution efficiency. By scheduling index reorganization tasks based on the fragmentation level and database activity, administrators can maintain optimal index performance and minimize the impact of fragmentation on query response times.

You should also monitor index usage and consider removing any unused indexes. You can identify unused indexes relatively easily using the LASTUSED information in the RTS SYSINDEXSPACESTATS table in the Db2 Catalog.

Tablespace Reorganization

As your database grows and data is modified or deleted, storage space can become fragmented, leading to suboptimal performance. Regularly reorganizing database structures helps to consolidate data, reclaim unused space, and optimize storage allocation. Reorganizing your tablespaces can improve I/O performance, reduce disk fragmentation, and enhance overall system efficiency. By performing regular database reorganizations based on data growth patterns and workload characteristics, administrators can maintain a well-organized and performant database environment.

Up-to-Date Statistics

Accurate and up-to-date statistics are essential for the Db2 optimizer to make informed decisions on query execution plans. As data in the database changes, statistics need to be updated to reflect the current distribution of data. Regularly updating statistics (using the RUNSTATS utility) ensures that the optimizer has the most accurate information to generate optimal execution plans. By analyzing data distribution patterns and scheduling statistics updates accordingly, administrators can improve query performance and avoid suboptimal query plans caused by outdated statistics.

For packages using static SQL, taking advantage of updated statistics requires rebinding. However, you may not want to rebind every time you run RUNSTATS unless application performance is suffering.

Routine Backups

Regular backups are vital for data protection and disaster recovery. Performing routine database backups not only safeguards the integrity of the database but also contributes to performance optimization. In the event of a failure or data loss, having a recent backup minimizes the recovery time and ensures business continuity. DBAs should establish a backup schedule based on the criticality of the data, recovery time objectives (RTOs), and workload requirements. 

And do not forget to regularly test your recovery plans and capabilities. Too often DBAs focus on backups at the expense of recovery… and backups are needed primarily to enable recovery, right?

Transaction Log Management

And let’s not forget the transaction logs! Logs play a critical role in ensuring data consistency and recoverability. Regularly monitoring and managing the transaction log space helps prevent log-related performance issues and ensures uninterrupted database operations. Activities such as transaction log backups, log file sizing, optimizing log offloading, and log file utilization monitoring are crucial for maintaining optimal transaction log performance and managing log space efficiently.

Buffer Pool Review

Regularly monitoring the efficiency of your Db2 buffer pools is important to ensure that you are achieving expected hit ratios and performance. As new applications are added, your amount of data increases, and access patterns change it will be necessary to adjust buffer pool sizes and parameters to optimize performance.

System Maintenance

Be sure to keep your Db2 subsystem updated with recent maintenance. You can use the -DIS GROUP command, even if you are not running data sharing, to display the current status of your Db2 software.

This command returns the message DSN7100I which is documented at https://www.ibm.com/docs/en/db2-for-zos/13?topic=messages-dsn7100i. It will show you the current version and function level, the current code level, and also the highest possible function level you can activate for your Db2 environment.

Be sure too to follow the IBM recommended preventive maintenance strategy to apply the appropriate maintenance using the IBM supplied RSU (Recommended Service Upgrade).

Summary

By incorporating these regular maintenance tasks into your database administration and management routine, DBAs and systems programmers can optimize performance, prevent performance degradation, and mitigate potential issues. Automation tools and scripts can streamline these maintenance activities and ensure consistency and timeliness in execution.