Figure 24 shows the prefetch quantity as a function of the page size and the buffer pool size. For certain utilities (REORG, RECOVER), the prefetch quantity can be twice as much.

Table 24. Number of Pages Read Asynchronously in One Prefetch Request

Page Size

Bufferpool Size

Prefetch Quantity

 

(buffers)

(pages/request)

 

 

 

4K

<224

8

 

 

 

 

224-999

16

 

 

 

 

>=1000

32

 

 

 

8K

<113

4

 

 

 

 

113-499

8

 

 

 

 

>=500

16

 

 

 

16K

<57

2

 

 

 

 

57-249

4

 

 

 

 

>=250

8

 

 

 

32K

<100

2

 

 

 

 

>=100

4

 

 

 

From the DB2 PM accounting trace, the average number of pages read in prefetch operations by an application program can be calculated. The average number of pages read is the total number of pages read in prefetch operations (E in Figure 33 on page 109) divided by the sum of prefetch operations (B, C, D in Figure 33), that is:

Average pages read by one prefetch operation = E / (B+C+D).

The DB2 PM statistics report calculates these values for every type of prefetch operation. Figure 34 on page 110 shows the average pages read by sequential prefetch (K), by list prefetch (L) and by dynamic prefetch (M). These numbers apply to the whole DB2 subsystem, while the accounting report numbers normally refer to one plan.

10.2.6 Data Management Threshold

The data management threshold (DMTH) is set by DB2 at 95% of each virtual buffer pool. The DMTH is maintained and checked independently for each individual virtual buffer pool.

This threshold is checked before a page is read or updated. If the threshold has not been exceeded, DB2 accesses the page in the virtual buffer pool once for each page, no matter how many rows are retrieved or updated in that page. If the threshold has been exceeded, DB2 accesses the page in the virtual buffer pool once for each row that is retrieved or updated in that page. Reaching this threshold has a significant effect on processor usage and performance.

106Storage Management with DB2 for OS/390

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IBM 5655-DB2, 5695-DF1 manual Data Management Threshold

5695-DF1, 5655-DB2 specifications

IBM 5655-DB2 and 5695-DF1 are significant components within the IBM software ecosystem, predominantly focusing on data management and integration solutions. These offerings cater primarily to enterprise environments that require robust database management systems and associated frameworks to maintain and manipulate data efficiently.

IBM 5655-DB2 is a well-known relational database management system (RDBMS) that excels in managing large volumes of structured data. Its architecture is designed to support high availability, scalability, and performance, crucial for businesses operating in today’s data-driven world. Some of its main features include advanced indexing capabilities, support for complex queries, and dynamic workload management. Additionally, it provides strong concurrency controls, which enable multiple users to access and manipulate data simultaneously without compromising data integrity.

One of the key characteristics of DB2 is its support for various data types, including JSON and XML, making it versatile for modern applications that generate data in diverse formats. It also features robust security mechanisms to protect sensitive data, aligning with compliance standards across industries. Integration with analytics tools further allows businesses to derive insights from their data, enhancing decision-making processes.

On the other hand, IBM 5695-DF1, also known as the InfoSphere DataStage, is a powerful data integration tool that facilitates the extraction, transformation, and loading (ETL) of data from various sources to target systems. It empowers organizations to streamline their data flows, ensuring that clean, consistent information is available for analysis and operational use. Key features of 5695-DF1 include a user-friendly graphical interface that enhances developer productivity and a rich set of connectors for numerous data sources, enabling seamless data integration.

DataStage also supports real-time data integration, allowing businesses to keep their data synchronized across multiple platforms. Its parallel processing capabilities dedicatedly optimize performance, enabling organizations to handle vast datasets efficiently. It incorporates data quality tools that help in validating and cleansing data before it is used for decision-making processes.

Both IBM 5655-DB2 and 5695-DF1 are part of a broader strategy to accommodate the evolving landscape of data management. Businesses leverage these technologies to enhance their data architectures, fostering agility and competitive advantage in their respective markets. Their integration capabilities, along with a focus on security and scalability, position them as vital assets in modern enterprise environments. Whether managing critical data within a database or ensuring seamless data flow across systems, these IBM offerings provide a comprehensive approach to handling complex data challenges.