Performance Tuning for Content Manager

Chapter 7. Tuning operating systems for Content Manager 157

7.3.1 Configure appropriate ulimit

This specifies several maximums allowed per user, but changes affect all users

on the system. Of particular importance are open files, stack size, and number of

processes. If any of these numbers is set too low, errors might appear in the DB2

databases, Resource Manager, Web server, or operating system error logs.

These values are all maximums, so they can be set arbitrarily large or to

unlimited. However, this might remove some safeguards against runaway

processes or system attacks.

To display the current value and list the available flags, use the ulimit –a

command.

To change to a different value, use the command, with -1 for unlimited.

For a database application, we recommend setting the ulimit to at least 8000.

ulimit –n <new_value>

ulimit –n -1

You may also change the settings in the /etc/security/limits file.

7.3.2 Configure shared memory

Under a large workload, the DB2 database tuning for ASLHEAPSZ might require

a large value for the DB2 registry variable DB2_FMP_COMM_HEAPSZ. This in

turn might require a greater amount of shared memory allowed by the operating

system. To accomplish this, change the value of /proc/sys/kernel/shmmax.

echo 268435456 > /proc/sys/kernel/shmmax

This value takes effect immediately, but the command must be added to a boot

script such as rc.local to make it permanent. You will know if any of these values

are too small because errors will appear in db2diag.log, the database instance

will not start, or database connections after a certain point will be dropped.

Fortunately, DB2 UDB Version 8.2 has a new feature that checks the values of

the kernel.semmni, kernel.msgmni, and kernel.shmmax parameters when you

enter the db2start command, and changes them for you if the current values are

not optimal. This new feature makes these changes:

 The semmni kernel parameter is changed to 1024.

 The msgmni kernel parameter is changed to 1024.

 The shmmax kernel parameter is changed to 268435456 (32-bit) or

1073741824 (64-bit).