Configuration parameters that affect the Db2 pureScale Feature
In a Db2 pureScale environment, database configuration parameters are designated as either global database configuration parameters or per-member database configuration parameters. This distinction allows a Db2 pureScale instance to benefit from global database configuration consistency while accommodating for differences between members.
Global database configuration parameters
Global database configuration parameters share a single, consistent value for all members in a Db2 instance. An update to a value of a global parameter applies globally across all members, regardless of which member issues the update. Global database configuration consistency ensures all members in a Db2 instance access and manipulate the same set of data homogeneously.
Per-member database configuration parameters
Per-member database configuration parameters can have different values between each member in a Db2 instance. By default, an update to a value of a per-member parameter applies globally across all members, unless that update is specified for a specific member only. Any member in the Db2 instance can issue an update. Per-member database configuration parameters in the Db2 pureScale Feature are intended for use when a non-homogenous environment is wanted.
For a database, where the available resources on each member are different, customizing database configurations on each member can optimize database performance. For example, differences in the available memory on each member can benefit from unique database configurations on each member.
A database where members are mapped to applications of differing function can benefit from customized database configurations on each member.
Updating database configuration parameters in a Db2 pureScale environment
You can update database configuration parameters in a Db2 pureScale instance using the Db2 command line processor (CLP) or using Db2 configuration APIs. The use of the MEMBER clause is optional and is only intended for use with per-member database configuration parameters.
- Updating global database configuration parameters
Global database configuration parameters are stored in a single database configuration file. The updating member is responsible for updating the database configuration file. Updates to global parameters fail only if the updating member is unable to write to the global configuration file.Note: No rollback is required when a member fails to write to the configuration file because all members within the Db2 pureScale instance are in a consistent state.
If you attempt to update a global database configuration parameter using the MEMBER clause you receive an error (SQL5125N).
- Updating per-member database configuration parameters
Members within a Db2 pureScale instance can be configured with different values for the same configuration parameter. Use the MEMBER clause to specify an update to a single member within an instance. If you omit the MEMBER clause the change is applied across all members in the instance.The following command updates the util_heap_sz parameter for MEMBER 2 to a value of 5000:
UPDATE DATABASE CONFIGURATION FOR WSDB MEMBER 2 USING UTIL_HEAP_SZ 5000
Only MEMBER 2 is updated with a value of 5000 for util_heap_sz. If you omit the MEMBER clause then util_heap_sz is updated to the value 5000 for all members across the Db2 pureScale instance.
This command can be issued by any member within the Db2 pureScale instance. In the event MEMBER 2 goes down or becomes inactive, the configuration update might fail. Every member in a Db2 pureScale instance can write to the configuration file of another member, so the update fails only if the updating member is unable to successfully write to the configuration file of MEMBER 2.Note: If the MEMBER clause is not specified and the updating member attempts and fails to update the configuration file for MEMBER 2 then the update is rolled back across the entire Db2 pureScale instance. If the rollback fails as well, the configuration files might be in an inconsistent state.
For database configuration parameters that can be updated when the database is online, no additional measures are taken to ensure that cached and in-memory values are consistent across a Db2 pureScale instance.