It is an essential part of the SGA memory, and without it, the instance will not work. Control over it is achieved through the variable SHARED_POOL_SIZE, but of course, there is a limit to the value that this variable can take.

If you configure this part of the memory so that the size of the Shared Pool is significantly reduced, the instance will not operate.

ALTER SYSTEM SET SHARED_POOL_SIZE=4M SCOPE=SPFILE;

Notice that I have changed the size of the Shared Pool to 4MB, but the instance did not operate because the size of the Shared Pool is insufficient. The minimum size required to operate the instance is approximately 60MB.

The solution in such cases to get the instance running again is to create a PFILE from the SPFILE because the PFILE is a text file that allows you to modify the SHARED_POOL variable through the operating system. Then, create the SPFILE from the PFILE, and from there, start the database.

The Shared Pool contains other smaller parts of memory, but they are managed automatically by Oracle, and the database administrator has no control over the size of the Shared Pool.

You can identify these parts through querying the view V$SGASTAT.

Of course, each of these parts has a specific function that it performs, but as mentioned earlier, the database administrator does not control these parts; rather, they are managed by Oracle.

Among these important parts are the SQL AREA and also the LIBRARY CACHE, where SQL statements are executed and the validity of executed expressions is verified. There are also other important components such as the ROW CACHE and the ASH BUFFER, among others, which can be queried through the following inquiry:

SELECT * FROM V$SGASTAT WHERE POOL='SHARED POOL'; 

A small size of the Shared Pool definitely affects performance, but increasing the size of the Shared Pool beyond what is necessary will also reflect on performance.

To determine the optimal size, use the Shared Pool Advisor.

To enable this advisor, configure the STATISTICS_LEVEL variable to take the value TYPICAL, which is indeed the default value for this variable. After that, you can query the advisor through the view V$SHARED_POOL_ADVICE, and you can also interact with the advisor through Database Control.