Database 1

Tablespace

Table1

Table2

Table3

/dev1/dbase1

/dev3/dbase1

container 0

container 2

/dev2/dbase1

/dev4/dbase1

container 1

container 3

Figure 1 9   Relationship between table space and containers

Buffer pools

A buffer pool is the amount of memory allocated to cache table and index data 

pages. The purpose of the buffer pool is to improve system performance. 

Data can be accessed much faster from memory than from disk; therefore, 

the fewer times the database manager needs to read from or write to a disk 

(I/O) synchronously, the better the performance of the application. The size of 

the buffer pool is the single most important performance tuning area, because 

you can reduce the delay caused by synchronous I/O.

DB2 directory structure

On Linux systems the default installation path for DB2UD V8.1 is 

/opt/IBM/db2/V8.1. $DB2DIR is the environment variable for the DB2 installation 

directory. Figure 1 10 shows the default directory structure for a simple 

CREATE 

DATABASE

 command with no table space options specified. By default DB2 

creates SMS table space containers in the specified database directory. The 

three default table spaces created are system catalog, system temporary, and 

user table space. For the log files, DB2 creates a directory called 

sqllogdir

. On a 

Linux system a 

sqllib

 directory will be created under the instance home directory, 

which has a symbolic link to the DB2 installation directory.

 Chapter 1. Introduction 

17