Detailed Explanation to SGA Components in Oracle Database

What is the role & impact of different SGA components? 

The System Global Area (SGA) is a crucial memory area in Oracle databases, shared by all server processes and background processes.  It holds data and control information for a single database instance, significantly impacting performance.  Efficient management of the SGA is essential for optimal database operation. Here's a more detailed look at its components:

libnjni12.so(), but a runtime definition of the symbol was not found

/oracle/app/oracle/product/12.1.0/dbhome_1/lib/libnjni12.so(), but a runtime definition of the symbol was not found.

libnjni12.so(), but a runtime definition of the symbol was not found

Unable to connect to PDB | ORA-12154 ORA-12518 | Oracle 12c

ORA-12154: TNS:could not resolve the connect identifier specified | ORA-12518: TNS:listener could not hand off client connection

ORA-12154 and ORA-12154 generating when you are having issues with database connectivity whenever you try to login into your database. In my scenario, I was trying to install and configure Oracle Enterprise Manager 12c on my local system for pratice purposes and for that I had installed repository database named as EMCTLDB. This is a 12c database where EMCTLDB is the CDB name and EMCTLPDB is the PDB name. After the database was installed, I made the entries in the LISTENER.ORA and TNSNAMES.ORA like this,