IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 13. Databases 421

13.3.5 MIDAWs

MIDAWs, as described in 10.7.1, “MIDAWs” on page 368, helps improve performance when

accessing large chains of small blocks of data. In order to get this benefit the dataset must be

accessed by Media Manager. The bigger benefit is realized for the following datasets:

򐂰 Extended Format (EF) datasets

򐂰 Has small block sizes (4K)

Examples of DB2 applications that will benefit from MIDAWs are DB2 prefetch and DB2

utilities.

13.3.6 Monitoring the DS6000 performance

RMF can be used to monitor the performance of the DS6000. For a detailed discussion, see

10.9, “DS6000 performance monitoring tools” on page 371.

13.4 DS6000 DB2 UDB - open systems environment

This section discusses the performance considerations when using the DB2 Universal

Database™ (DB2 UDB) with the DS6000 in an open systems environment.

The information presented in this section is further discussed in detail in (and liberally

borrowed from) the redbook, IBM ESS and IBM DB2 UDB Working Together, SG24-6262.

Many of the concepts presented are applicable to the DS6000. We highly recommend this

redbook. However, based on customer solution experiences using SG24-6262, there are two

corrections we want to point out:

򐂰 In IBM ESS and IBM DB2 UDB Working Together, SG24-6262, Section 3.2.2, “Balance

workload across ESS resources”, suggests that a data layout policy should be established

that allows partitions and containers within partitions to be spread evenly across ESS

resources. It further suggests that you can choose either a horizontal mapping, in which

every partition has containers on every available ESS Rank, or a vertical mapping in which

DB2 partitions are isolated to specific arrays, with containers spread evenly across those

Ranks. We now recommend the vertical mapping approach.

򐂰 Another data placement consideration, suggests that it is important to manage where data

is placed on the disk, outer edge or middle. We no longer believe this is an important

consideration.

13.4.1 DB2 UDB storage concepts

DB2 Universal Database (DB2 UDB) is IBM’s object-relational database for UNIX, Linux,

OS/2, and Windows operating environments.

The database object that maps the physical storage is the

tablespace. Figure 13-1 on

page 422 illustrates how DB2 UDB is logically structured and how the tablespace maps the

physical object.

Note: Based on experience, we now recommend a vertical data mapping approach

(shared nothing) as well as not micro-managing data placement on storage.

422 IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Figure 13-1 DB2 UDB logical structure

Instances

An instance is a logical database manager environment where databases are cataloged and

configuration parameters are set. An instance is similar to an image of the actual database

manager environment. You can have several instances of the database manager product on

the same database server. You can use these instances to separate the development

environment from the production environment, tune the database manager to a particular

environment, and protect sensitive information from a particular group of users.

For database partitioning features (DPF) of the DB2 Enterprise Server Edition (ESE), all data

partitions reside within a single instance.

Databases

A relational database structures data as a collection of database objects. The primary

database object is the table (a defined number of columns and any number of rows). Each

database includes a set of system catalog tables that describe the logical and physical

structure of the data, configuration files containing the parameter values allocated for the

database, and recovery logs.

DB2 UDB allows multiple databases to be defined within a single database instance.

Configuration parameters can also be set at the database level, thus allowing you to tune, for

example, memory usage and logging.

Database partitions

A partition number in DB2 UDB terminology is equivalent to a data partition. Databases with

multiple data partitions residing on an SMP system are also called multiple logical partition

(MLN) databases.

Instance(s)

System

Database(s)

Tablespace(s)

Tables

Indexes

long data

SMS

Each container

is a directory

in the file space

of the operating

system.

DMS

Each container

is a fixed,

pre-allocated

file or physical

device such as

a disk.

Logical Database Objects

Equivalent Physical Object

Tablespaces is where tables are stored:

or

/fs.rb.T1.DA3a1

/fs.rb.T1.DA3b1