High Level Db2 Indexing Advice for Large and Small Tables

In general, creating indexes to support your most frequent and important Db2 SQL queries is a good idea. But the size of the table will be a factor in decided whether to index at all and/or how many indexes to create.

For tables more than 100 (or so) pages, it usually is best to define at least one index. This gives Db2 guiidance on how to cluster the data. And, for the most part, you should follow the general advice of having a primary key for every table... and that means at least one unique index to support the primary key.

If the table is large (more than 20,000 pages or so), you need to perform a balancing act to limit the indexes to those absolutely necessary for performance. When a large table has multiple indexes, data modification performance can suffer. When large tables lack indexes, however, access efficiency will suffer. This fragile balance must be monitored closely. In most situations, more indexes are better than fewer indexes because most applications are query-intensive rather than update-intensive. However, each table and application will have its own characteristics and requirements.

For tables containing a small number of pages (up to 100 or so pages) consider limiting indexes to those required for uniqueness and perhaps to support common join criterion. This is a reasonable approach because such a small number of pages can be scanned as, or more, efficiently than using an index.

For small tables you can add indexes when the performance of queries that access the table suffers. Test the performance of the query after the index is created, though, to ensure that the index helps. When you index a small table, increased I/O (due to index accesses) may cause performance to suffer when compared to a complete scan of all the data in the table.

A Guide to Db2 Application Performance for Developers: A Holiday Discount!

Regular readers of my blog know that I have written a couple of Db2 books, including DB2 Developer's Guide, which has been in print for over 20 years across 6 different editions. But you may not be aware that I recently wrote a new Db2 book, this time focusing on the things that application programmers and developers need to do to write programs that perform well from the very start. This new book is called A Guide to Db2 Application Performance for Developers.

You see, in my current role as an independent consultant that focuses on data management issues and involves a lot of work with Db2, I get to visit a lot of different organizations... and I get to see a lot of poorly performing programs and applications. So I thought: "Wouldn't it be great if there was a book I could recommend that would advise coders on how to ensure optimal performance in their code as they write their Db2 programs?" Well, now there is... A Guide to Db2 Application Performance for Developers.

This book is written for all Db2 professionals, covering both Db2 for LUW and Db2 for z/OS. When there are pertinent differences between the two it will be pointed out in the text. The book’s focus is on develop­ing applications, not database and system administration. So it doesn’t cover the things you don’t do on a daily basis as an application coder.  Instead, the book offers guidance on application devel­opment procedures, techniques, and philosophies for producing optimal code. The goal is to educate developers on how to write good appli­cation code that lends itself to optimal performance. 

By following the principles in this book you should be able to write code that does not require significant remedial, after-the-fact modifications by performance ana­lysts. If you follow the guidelines in this book your DBAs and performance analysts will love you!

The book does not rehash material that is freely available in Db2 manuals that can be downloaded or read online. It is assumed that the reader has access to the Db2 manuals for their environment (Linux, Unix, Windows, z/OS).

The book is not a tutorial on SQL; it assumes that you have knowledge of how to code SQL statements and embed them in your applications. Instead, it offers advice on how to code your programs and SQL statements for performance.

What you will get from reading this book is a well-grounded basis for designing and developing efficient Db2 applications that perform well. 

OK, you may be saying, but what about that "Holiday Discount" you mention in the title? Well, I am offering a discount for anyone who buys the book before the end of the year (2019). There are different discounts and codes for the print and ebook versions of the book:

• To receive a 5% discount on the print version of the book, use code 5poff when you order at this link.
• To receive $5.00 off on the ebook version of the book, user code 5off when you order at this link.

These codes only work on the Bookbaby site. You can, of course, buy the book at other book stores, such as Amazon, at whatever price they are currently charging!

Happy holidays... and why not treat the programmer in your life to a copy of A Guide to Db2 Application Performance for Developers?  They'll surely thank you for it.

Happy Thanksgiving 2019

Just a quick post today to wish all of my readers in the US (and everywhere, really) a very Happy Thanksgiving.

Thanksgiving is a day we celebrate in the USA by spending time with family, eating well (traditionally turkey), and giving thanks for all that we have and hold dear.

Oh... and also for watching football!

May all of you reading this have a warm and happy Thanksgiving holiday surrounded by your family and loved one.

Happy Thanksgiving!

Db2 12 for z/OS Function Level 506

Late last month, October 2019, IBM introduced a new function level, FL506, for Db2 12 for z/OS.  There are two significant impacts of this new function level:

• Alternative function names support
• Support for implicitly dropping explicitly created table spaces

The first impact, support for additional, alternative names for some existing Db2 built-in functions, was added is to improve compatibility across the Db2 product line. It is basically just a new way to refer to existing functionality, an alternative syntax, if you will. The following chart outlines the existing and new FL506 alternative syntax.

Table 1. Alternative Syntax for Function Names in FL506        

Existing Function Name	New Alternative Syntax Name
CHARACTER_LENGTH	CHAR_LENGTH
COVARIANCE or COVAR	COVAR_POP
HASH_MD5 or HASH-SHA1 or HASH_SHA256	HASH
POWER	POW
RAND	RANDOM
LEFT	STRLEFT
POSSTR	STRPOS
RIGHT	STRRIGHT
CLOB	TO_CLOB
TIMESTAMP_FORMAT	TO_TIMESTAMP

Support for these alternative spelling of built-in function names should make it easier to support applications across multiple members of the Db2 family where support already exists for these spellings. Of course, you may run into issues if you used any of the new spellings in your existing applications, for example as variable names.

The other significant feature of FL506 is support for implicitly dropping explicitly created universal table spaces when a DROP TABLE statement is executed. Prior to FL506 dropping a table that resides in an explicitly created table space does not drop the table space.

If you use vendor tools that manage and generate scripts for DDL changes, they need to be modified to support FL506. If not, they could produce -204 SQL codes when the generated DDL is executed if the DDL contains a DROP TABLESPACE statement. The table space will have already been implicitly dropped and trying to drop a table space that does not exist will throw an error. Be sure to discuss this with your tools vendor before migrating to FL506 to understand the cendor’s support timeline or if they have a workaround.

Summary

IBM is using function levels to deliver significant new capabilities for Db2 12 for z/OS. It is important for you and your organization to keep up-to-date on this new functionality and to determine where and when it makes sense to introduce it into your Db2 databases and applications.

Also, be aware that if you are not currently running at FL505, moving to FL506 activates all earlier function levels. You can find a list of all the current function levels here.

Have You Considered Speaking at the IDUG Db2 Technical Conference? You should!

The 2020 North American Db2 Technical Conference is being held in Dallas, TX the week of June 7th. And the call for papers is still open and IDUG is looking for Db2 folks who want to share their experiences with Db2. You can talk about a project you worked on, an experience you had tuning or optimizing your Db2 databases and applications, your experience implementing a new version or funtion level, how your team uses any Db2 feature or capability, or really, anything related to your experience with Db2.

Speaking at a user group is a good way to expand your contacts and develop additional personal interaction skills. And I have also found it to be a good way to increase my technical knowledge and skills. Sure, as the presenter you are sharing your knowledge with the audience, but it always seems like I expand my knowledge and way of thinking about things when I deliver a presentation. Either because of questions I receive, or because putting the presentation together made me stop and think about things in different ways.

And if you are accepted to speak your attendance at the conference is complimentary!

Putting together an abstract is not that difficult at all. You just need to complete a bit of biographical information about yourself, select a category for your presentation, provide an overview of your topic, and offer up a bulleted list of 5 objectives. The site guides you through submitting all of these things at this link.

Speaking at a conference can be a very rewarding experience... and once you start doing it, you'll want to do it again and again. So go ahead. Click here and submit your abstract and I hope I'll see you in Dallas in June 2020!