Federated cache for federated three-part names

The federated cache is a catalog cache that stores metadata and statistics for remote objects.

When you issue an SQL statement against a remote table or view that is referenced by a federated three-part name, the metadata and statistics for the remote object are stored in the federated cache on the first reference. Subsequent queries that reference the same three-part name, in the same session or in other sessions, will obtain metadata directly from the federated cache.

The metadata information in a cache entry is associated with an expiration duration. The expiration duration is the interval at which the metadata is considered valid and up-to-date since it was loaded from a remote server. The default value of the expiration duration is zero (0). A zero value means that metadata is always considered validated, unless you choose to explicitly invalidate the data.

You can change the interval value by setting the environment variable FEDCACHE_EXPIRE_INTERVAL. You specify this value in units of seconds.

Recommendation: Set the FEDCACHE_EXPIRE_INTERVAL variable in the db2dj.ini file.

Examples

You can flush the cache to keep cached entries up-to-date by issuing the following commands:

To invalidate specific three-part name metadata:
```
FLUSH FEDERATED CACHE FOR rudb.rschema.t1
```
To invalidate all three-part name metadata in a specific schema named rschema:
```
FLUSH FEDERATED CACHE FOR rudb.rschema.*
```
To invalidate all three-part name metadata in a specific server named rudb:
```
FLUSH FEDERATED CACHE FOR rudb.*.*
```
To flush a server named rudb:
```
FLUSH FEDERATED CACHE FOR SERVER rudb
```