order to achieve optimal performance, the placement of database objects should 

be carefully planned. 

...

insert 

update

delete

commit

insert

...

Buffer pool

Log buffer

Data and indexes

Logical log files

Figure 9 6   Explaining logical log

As shown in Figure 9 6, all data modifications are not only written to table space 

containers, but are also logged to ensure recoverability. Because every 

INSERT

, 

UPDATE

, or 

DELETE

 is replicated in the transactional log, the flushing speed of the 

logical log buffer can be crucial for the entire database performance. To 

understand the importance of logical log placement, you should keep in mind that 

the time necessary to write data to disk depends on the physical data distribution 

on disk. The more random reads or writes are performed, the more disk head 

movements are required, and therefore, the slowest is the writing speed. 

Flushing logical log buffer to disk by its nature is sequential and should not be 

interfered by other operations. Locating logical log files on separate devices 

isolates them from other processes, and ensures uninterrupted sequential writes.

To change logical log files to a new location you need to modify the 

NEWLOGPATH

database parameter as shown in Example 9 30. The logs will be relocated to the 

new path on the next database activation (this can take some time to create the 

files).

Example 9 30   Relocation of logical logs

db2 update db cfg for sample using NEWLOGPATH /db2/logs

 Chapter 9. Testing and tuning 

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