The SGA is a shared memory region that stores data that is shared among Oracle processes, including cached data blocks, SQL execution plans, and other control information.
The PGA is a memory region that contains data and control information for a single process, not shared among processes, and is therefore not a part of the SGA.
Control files contain metadata about the database, such as the database name, the names and locations of datafiles, and the log history, which are essential for database recovery.
The Log Writer (LGWR) process is responsible for writing redo log entries from the Redo Log Buffer to the redo log files, ensuring that all changes to the database are logged.
The Oracle Instance consists of memory structures (such as the SGA) and background processes (such as DBWn and LGWR) that manage the database operations.
