To calculate the percentage of the buffer cache used by an individual object

 To calculate the percentage of the buffer cache used by an individual object:

Find the Oracle Database internal object number of the segment by querying the DBA_OBJECTS view:

SELECT data_object_id, object_type

FROM DBA_OBJECTS 

WHERE object_name = UPPER('segment_name'); 

Because two objects can have the same name (if they are different types of objects), use the OBJECT_TYPE column to identify the object of interest.

Find the number of buffers in the buffer cache for SEGMENT_NAME:

SELECT COUNT(*) buffers

FROM V$BH

WHERE objd = data_object_id_value;

For data_object_id_value, use the value of DATA_OBJECT_ID from the previous step.

Find the number of buffers in the database instance:

SELECT name, block_size, SUM(buffers)

FROM V$BUFFER_POOL

GROUP BY name, block_size

HAVING SUM(buffers) > 0;

Calculate the ratio of buffers to total buffers to obtain the percentage of the cache currently used by SEGMENT_NAME:

% cache used by segment_name = [buffers(Step2)/total buffers(Step3)]