How to Improve Performance 5-15
How Is Tuning Done?
How Is Tuning Done?
You can increase the number of shared-memory resources by increasing the
valueof TBLSPACES,LOCKS,orUSERSin the configuration file. If you increase
thevalue of USERS, you might need to also increase the value of TBLSPACES,
LOCKS,and BUFFERS, since the minimum values for all three of these param-
etersare based on the value of USERS. For further information about how to
change the value of these parameters, refer to the following pages:
TBLSPACES,page3-113; LOCKS,page 3-112; and USERS,page3-114.
Log Buffer Size
The optimal size for the physical and logical log buffers depends on your
environment.In general, the log buffers should be large enough to minimize
physicalI/O writing to the logs on disk. However, the buffers should not be
so large that you have allocated shared-memory space that could be used
more efficiently for some other purpose.
Asecond consideration is the amount of data that is held in volatile memory.
This is a concern only if you are using buffered logging. The larger the log
buffer, the more log data that can be lost in the event of operating system
failure.Log data that is lost cannot be used during fast recovery. Therefore,if
severalCOMMIT records are left in the logical log buffer (database uses
buffered logging) and lost, you cannot recover these transactions after a
failure. Thus, if any of your OnLine databases use buffered logging, you
shouldweigh the benefits of increased buffer size against the disadvantages
of possible data loss in the event of operating system failure.
(The following paragraphs rely on information presented onpage 5-11 that
explainsthe Bufsize and Pages/IO fields and how to interpret their values.)

Logging Status

Anadditional consideration in the decision to resize the logical log buffer is
the complication of the database logging status. The logging status of the
database affects the logical logPages/IO value. If a database uses unbuf-
fered logging, thePages/IO value is close to 1. If a database uses buffered
logging, thePages/IO value should be very close to the value of Bufsize.