This parameter specifies the number of local databases that can be concurrently active (that is, have applications connected to them). In a partitioned database environment, it limits the number of active database partitions on a database partition server, whether that server is the coordinator node for the application or not.
Since each database takes up storage and an active database uses a new shared memory segment, you can reduce system resource usage by limiting the number of separate databases on your machine. However, arbitrarily reducing the number of databases is not the answer. That is, putting all data, no matter how unrelated, in one database will reduce disk space, but may not be a good idea. It is generally a good practice to only keep functionally related information in the same database.
Recommendation: It is generally best to set this value to the actual number of databases that are already defined to the database manager and to add a reasonable increment to account for future growth in the number of databases over the short term (for example, 6 months to 1 year). The actual increment should not be excessively large, but it should allow you to add new databases without having to frequently update this parameter.
Changing the numdb parameter may impact the total amount of memory allocated. As a result, frequent updates to this parameter are not recommended. When updating this parameter, you should consider the other configuration parameters that can allocate memory for a database or an application connected to that database, including: