Monday, June 26, 2023

Top 10 Db2 Performance Tips - No. 1: Analyze Query Execution Plans

Query execution plans play a crucial role in identifying performance bottlenecks within an IBM Db2 database. When a query is executed, the database optimizer determines the most efficient way to retrieve the requested data by generating a query execution plan. It does this by parsing SQL requests and turning them into actionable commands for accessing and modifying data. 

So the query execution plan outlines the steps and operations involved in executing the query, including accessing tables, applying filters, joining data, and performing sorting or aggregations.

Understanding query execution plans is important because they reveal the inner workings of how Db2 will process the query. And they also highlight areas where performance can be improved if you understand the various ways that data can be processed by Db2. By analyzing query execution plans, you can identify potential inefficiencies and take proactive steps to optimize queries for better performance.

For example, one high-level performance tuning step that you can identify using a query execution plan is to find table (space) scans that would be better off using an index instead.

Plan Tables

But how can you review and analyze query execution plans? Perhaps the first method used by most folks is to examine the Plan Tables. A lot of information is contained in the PLAN_TABLE. The PLAN_TABLE is simply a specific table used by the EXPLAIN command to populate information about the choices made by the Db2 Optimizer when it formulates a query execution plan. The information in the PLAN_TABLE provides detailed information about the access paths chosen, join strategies employed, and other relevant details that impact query performance. 

As long as EXPLAIN YES is specified when you bind your program, or you explicitly issue an EXPLAIN PLAN statement, information about the query execution plan will be placed in the PLAN_TABLE.

So, after the optimizer creates the access paths and populates the PLAN_TABLE with data representing those access paths, you will need to examine the results to determine if everything is satisfactory. Many questions can be answered by analyzing the results of EXPLAIN – questions like:

  • if we are joining what type of join is used (NLJ, MS, Hybrid),
  • was an index used, and if so how many columns matched,
  • are we doing a scan, and if so what type of scan (full or page range)
  • is prefetch being used, and if so what type (sequential, list)
  • was a hint used
  • was parallelism used, and if so what degree and type 
  • was a sort required, and if so why (Join, Unique, Group By, Order By)
  • what type of locking is required

And that just covers the main PLAN_TABLE. There are actually many other explain tables available that, if created, will be populated by EXPLAIN. But that is beyond the scope of this high-level tip, which is already becoming rather lengthy.

Other Tools

There are also several additional tools and techniques that can be used to analyze Db2 query execution plans. One commonly used tool is Visual Explain, which provides a graphical representation of the query execution plan. Many tuners prefer a visual approach to revieing and tuning access paths. Visual Explain allows users to visualize the flow of data, understand the order in which operations are performed, and identify potential performance bottlenecks.

Visual Explain is a feature of the free IBM Data Studio tool, as well as the new Db2 Administration Foundation offering. There are other tools, from other vendors, that also provide a visual Explain capability.

Speaking of which, another technique to analyze query execution plans is to use database monitoring tools. Such tools capture real-time performance data, including query execution plans, and provide useful performance metrics that can be reviewed and acted upon as needed. 

By monitoring the execution plans of frequently executed queries, it is possible to detect patterns, identify resource-intensive operations, and make informed decisions about query optimization.

A Bit of Guidance

It is wise to always Bind your production programs (that use static SQL) specifying EXPLAIN YES so that you can see the access paths chosen by Db2. This way, you can either check to make sure that no access paths have changed before proceeding to implement changes in production, or at least you have the information available should problems arise after you move code into production.

It can be difficult to determine if any access paths have changed, because you will need the old execution plans to compare to the new ones. For this reason, it is a good idea to keep several versions of access path information for each program. 

Additionally, sometimes the program has changed between running EXPLAIN, which can make it challenging to find the exact SQL statements to compare. But you are still better off with older versions  than without any historical data.

To optimize query execution plans for better performance, it is essential to focus on areas such as index usage, join strategies, and predicate selection. By strategically creating and maintaining appropriate indexes, rewriting complex queries, and refining predicate conditions, it is possible to influence the optimizer's decisions and improve query performance.

In Conclusion 

Analyzing query execution plans is a vital step in optimizing the performance of IBM Db2 applications. By using tools like EXPLAIN and Visual Explain, PLAN_TABLE data, and monitoring tools, it is possible to gain valuable insights into query execution, identify potential bottlenecks, and enhance overall performance. 

By proactively analyzing and optimizing query execution plans, organizations can achieve faster response times, improved scalability, and a more efficient database environment.

Be sure to check back here next week when we will address database design as a performance issue.

Wednesday, June 21, 2023

Top 10 Performance Tuning Tips for IBM Db2

Performance is a critical aspect of any database management system, and IBM Db2 is no exception. As organizations deal with ever-increasing data volumes and complex workloads, it is crucial that Db2 environments are fine-tuned to ensure optimal performance, responsiveness, and scalability. In this multi-part blog post, I will examine the top ten performance tuning tips for assuring optimal IBM Db2 applications and systems.

Whether you are an experienced database administrator or just starting your journey with Db2, these performance tuning tips will provide some practical strategies and techniques to enhance the efficiency and speed of your Db2 deployments. This series of posts will cover a range of topics, including query optimization, database design, indexing strategies, memory configuration, I/O optimization, and more. 

By following these Db2 performance tips, you can significantly improve query response times, optimize resource utilization, and ensure the smooth operation of your Db2 environment. Whether you are dealing with transactional workloads, analytical queries, or a combination of both, the tips presented here will equip you with the knowledge and techniques to tackle performance bottlenecks and fine-tune Db2 to meet your specific needs.

Whether you are looking to optimize existing Db2 deployments or planning for a new implementation, this blog post will serve as a valuable resource to guide your performance tuning efforts. So, let's dive into the top ten performance tuning tips for IBM Db2 and discover how you can unlock the full potential of your database system.

Here's an outline for the upcoming posts in this series on "Top 10 Performance Tuning Tips for IBM Db2":

  Tip 1: Analyze Query Execution Plans

  Tip 2: Optimize Database Design

  Tip 3: Efficient Indexing Strategies

  Tip 4: Effective Memory Configuration

  Tip 5: Workload Management and Query Optimization

  Tip 6: Monitoring and Performance Metrics

  Tip 7: Configuration Parameters and Tuning

  Tip 8: I/O Optimization

  Tip 9: Regular Maintenance and Housekeeping

  Tip 10: Stay Up to Date 

So be sure to keep tuning in to the Db2 Portal blog as we publish these Top 10 Performance Tips over the course of the next few weeks.

And be sure to share your own performance and tuning thoughts here... or on any of the subsequent posts in this series.

Thursday, June 01, 2023

Manage Your Test Data Before It Becomes a Bottleneck

Test data management is an important aspect of application development. Anybody who has ever been involved in software development knows that creating applications requires test data. Without the data to test your programs against, there is really no way to ensure that the programs are doing what you want them to do.

Image by Freepik

But test data management can quickly consume a lot of time and effort. Supporting multiple programmers, multiple database environments, and making sure you have sufficient test cases is easier said than done. And we are not just talking about developing new applications, but also modifying existing ones!

So, what can be done? Well, I'm going to point you to a couple of resources. First, I am delivering a webinar on this topic on June 8, 2023 titled Manage Your Test Data Before it Becomes a Bottleneck -- the same title as this blog post!

In this webinar, I discuss test data management and the trends impacting application development and testing. Some of the issues I examine include automation, shift-left testing, agile development, and DevOps. And I'll uncover the impact of these trends and how they drive up the speed and complexity of creating and testing applications. I will also define the components and requirements of test data management and examine the pitfalls that can lead test data management to become a bottleneck, slowing down your developers.

Another resource you can take a look at is the article I wrote for ELNION, titled The Test Data Management Struggles of Modern App Development.

In this article, I explore the issues impacting application developers regarding test data management, and look at how they can overcome these challenges to ensure a successful testing process.

So if test data management is a challenge for you and your organization, I urge you to take advantage of these resources by registering for and attending the webinar, and also reading the article.