Various parameters in the database manager configuration file can be used to tune DB2 Connect. For information about changing these parameters, refer to the Administration Guide.
The RQRIOBLK parameter sets the maximum size of network I/O blocks. A larger block size may improve the performance of large requests. The block size does not usually affect the response time for small requests, such as a request for a single row of data.
A larger block size usually requires more memory on the DB2 Connect workstation. This increases the size of the working set and may cause large amounts of paging on small workstations.
Use the default DRDA block size (32767) if it does not cause too much paging on executing your application. Otherwise, reduce the I/O block size until there is no paging. Once paging begins, a noticeable degradation of performance will occur. Use performance monitor tools (such as the vmstat tool for UNIX-based systems or SPM/2 for OS/2) to determine whether paging is occurring on your system. For other tools, refer to Performance Tools.
The DIR_CACHE parameter determines whether directory information is cached. With caching (DIR_CACHE=YES), directory files are read and cached in memory to minimize the overhead of creating the internal directory structure and reading the directory files every time a connection is established.
Without caching (DIR_CACHE=NO), whenever you connect to a database the appropriate directory is read from a disk and then the search is performed. After the requested entries are found, all memory related to directory searches is freed.
With caching, a shared directory cache is built during db2start processing and freed when DB2 stops. This cache is used by all DB2 server processes (db2agent). Also, a private application directory cache is built when an application issues its first connect to a database and freed when the application ends.
Each cache provides an image of the system database directory, the database connection services directory and the node directory. The cache reduces connect costs by eliminating directory file I/O and minimizing directory searches.
If a cached directory is updated, the changes are not immediately propagated to the caches. If a directory entry is not found in a cache, the original directory is searched.
Caching increases the private memory that is needed for the life of an application. Without caching, this memory is needed only when a directory lookup is processed. Overall use of shared memory by DB2 increases slightly because directory information that is shared among database agents is moved to shared memory. The size of the memory required for a cache depends on the number of entries defined in each directory.
MAXDARI and NUMDB should be set to their minimum values if there is no local database on the DB2 Connect workstation. These settings will minimize resource consumption.
AGENTPRI applies only with remote clients. AGENTPRI controls the priority given by the operating system scheduler to agents of a DB2 Connect instance. The DB2 Connect instance is granted more CPU cycles if it has a higher priority (lower number). This reduces the number of CPU cycles left for other processes executing on the DB2 Connect workstation. For example, you could have a high-priority DB2 Connect instance and a low-priority DB2 Connect instance running on the same workstation with different AGENTPRI values.
Every connection from a client machine to a host or AS/400 database server through DB2 Connect requires an agent running on the DB2 Connect workstation. Set MAXAGENTS to a value greater than or equal to the peak number of remote client connections accessing a host or AS/400 database server through the DB2 Connect workstation.
If you decide to use accounting strings, using the sqlesact() API has performance advantages over the DB2ACCOUNT environment variable method. For more information, see Implementing Charge-Back Accounting on DB2 Universal Database for OS/390.
If you do not need a tailored SQLCODE mapping file, you can improve performance by using the default SQLCODE mapping or turning off SQLCODE mapping. (The default mapping file is imbedded in the DB2 Connect library; a tailored mapping file must be read from disk, which affects performance.) For more information about SQLCODE mapping, see SQLCODE Mapping.