Which SQL command should a database administrator use to change the VECTOR MEMORY SIZE parameter for a pluggable database (PDB)?

The command to change the VECTOR MEMORY SIZE parameter for a pluggable database (PDB) is correctly identified as needing to use the ALTER SYSTEM command. This command is intended to modify system-level parameters that affect the performance and behavior of the Oracle Database.

Choosing to specify the parameter with the correct syntax is essential: "ALTER SYSTEM SET vector memory size=1G SCOPE=BOTH" signifies that the administrator is setting the vector memory size to 1 gigabyte, which will apply both to the current session and will be retained in the configuration for future sessions. The "SCOPE=BOTH" clause indicates that the change is immediate and should also be persistent, meaning it will remain even after the database instance is restarted, effectively ensuring that system performance can be maintained in the context of vector searches.

By using this command, the administrator is directly addressing the parameters that influence vector searches effectively within the pluggable database context, which is particularly crucial for managing resources in a multi-tenant environment that a PDB represents.

Thus, this choice is the most fitting in terms of properly addressing the task of adjusting the VECTOR MEMORY SIZE parameter in a way that guarantees both immediate and persistent application of the changes made.