By setting dir_cache to "yes" the database, node and DCS directory files will be cached in memory. The use of the directory cache reduces connect costs by eliminating directory file I/O and minimizing the directory searches required to retrieve directory information. There are two types of directory caches:
| Note: | Only the private cache is applicable to Windows, Windows 95, Windows 98, and Windows NT environments. |
For private caches, when an application issues its first connect, each directory file is read and the information is cached in private memory for this application. The cache is used by the application process on subsequent connect requests and is maintained for the life of the application process. If a database is not found in the private cache, the directory files are searched for the information, but the cache is not updated. If the application modifies a directory entry, the next connect within that application will cause the cache for this application to be refreshed. The private cache for other applications will not be refreshed. When the application process terminates, the cache is freed. (To refresh the directory cache used by a command line processor session, issue a db2 terminate command.)
For shared caches, when a database manager instance is started (db2start), each directory file is read and the information is cached in shared memory. This cache is used by some of the database manager processes and is maintained until the instance is stopped (db2stop). If a directory entry is not found in this cache, the directory files are searched for the information. This shared cache is never refreshed during the time the instance is running.
Recommendation: Use directory caching if your directory files do not change frequently and performance is critical.
In addition, on remote clients, directory caching can be beneficial if your applications issue several different connection requests. In this case, caching reduces the number of times a single application must read the directory files.
Directory caching can also improve the performance of taking database system monitor snapshots. In addition, you should explicitly reference the database name on the snapshot call, instead of using database aliases.
| Note: | Errors may occur when performing snapshot calls if directory caching is turned on and if databases are cataloged, uncataloged, created, or dropped after the database manager is started. |