Title Database-Programming-Complete-Note.pdf ✅

Database Instance A Database Instance is an interface between client applications (users) and the database. An Oracle instance consists of three main parts: System Global Area (SGA), Program Global Area (PGA), and background processes. The SGA is a shared memory structure allocated when the instance started up and released when it is shut down. The SGA is a group of shared memory structures that contain data and control information for one database instance. Different from the SGA, which is available to all processes, PGA is a private memory area allocated to each session when the session started and released when the session ends. Major Oracle Database’s background processes The following are the major background processes of an Oracle instance: • PMON is the process monitor that regulates all other processes. PMON cleans up abnormally connected database connections and automatically registers a database instance with the listener process. PMON is a process that must be alive in an Oracle database. • SMON isthe system monitor processthat performssystem-level clean-up operation. It has two primary responsibilities including automatically instance recovery in the event of a failed instance, e.g., power failure and cleaning up of temporary files. • DBWn is the database writer. Oracle performs every operation in memory instead of the disk because processing in memory is faster and more efficient than on disk. The DBWn process reads data from disk and writes it back to the disk. An Oracle instance has many database writers DBW0, DBW1, DBW2, and so on. • CKPT is the checkpoint process. In Oracle, data that is on disk is called block and the data which in memory is called buffer. When a block is written to the buffer and bcanepaltu.com