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AdministeringIn addition to administering the database server, you can tune performance, replicate data, and archive data.
System administrationThese topics contain concepts, procedures, and reference information for database and database server administrators to use for managing and tuning HCL OneDB™ database servers.
Performance GuideThe HCL OneDB™ Performance Guide describes how to configure and operate your HCL OneDB™ database server to improve overall system throughput and to improve the performance of SQL queries.
Effect of configuration on memory utilizationThe combination of operating-system and HCL OneDB™ configuration parameters can affect memory utilization.
Configure and monitor memory cachesThe database server uses caches to store information in memory instead of performing a disk read or another operation to obtain the information. These memory caches improve performance for multiple queries that access the same tables. You can set some configuration parameters to increase the effectiveness of each cache. You can view information about memory caches by running onstat commands.
Data-dictionary cacheThe first time that the database server accesses a table, it retrieves the information that it needs about the table (such as the column names and data types) from the system catalog tables on disk. After the database server has accessed the table, it places that information in the data-dictionary cache in shared memory.
Data-dictionary configurationThe database server uses a hashing algorithm to store and locate information within the data-dictionary cache. The DD_HASHSIZE and DD_HASHMAX configuration parameters control the size of the data-dictionary cache.

Data-dictionary configuration

The database server uses a hashing algorithm to store and locate information within the data-dictionary cache. The DD_HASHSIZE and DD_HASHMAX configuration parameters control the size of the data-dictionary cache.

To modify the number of buckets in the data-dictionary cache, use DD_HASHSIZE (must be a prime number). To modify the number of tables that can be stored in one bucket, use DD_HASHMAX.

For medium to large systems, you can start with the following values for these configuration parameters:

DD_HASHSIZE: 503
DD_HASHMAX: 4

With these values, you can potentially store information about 2012 tables in the data-dictionary cache, and each hash bucket can have a maximum of 4 tables.

If the bucket reaches the maximum size, the database server uses a least recently used mechanism to clear entries from the data dictionary.

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