The percentage of open databases from the number configured.
The metadata caches reside in the kernel and server structures portion of Adaptive Server memory.
When Adaptive Server opens a database, it needs to read information about it in the corresponding system tables: sysdatabases, sysindexes, and sysobjects.
The metadata cache for databases lets Adaptive Server access the information that describes it in the sysdatabases, sysindexes, or sysobjects row found in the in-memory structure. This improves performance because Adaptive Server bypasses calls that require a large amount of disk access. It also reduces synchronization and spinlock contention when Adaptive Server has to retrieve database information at runtime.
You configure the number of open databases using sp_configure "number of open databases".