Oracle Server monitoring

Oracle server has two componnets : 1) Database 2) Instance

Database - Set of datafiles (data+redologs+controlfiles)

Instance - Memory structures allocated at startup+ background processes associated to database

Database files : 

1) data files : Tables and indexes

2) Control files - Record the physical structure of database

3) Redo logs - Contains redo entries

Memory strcture = System global area(SGA)  + Process global area (PGA)

SGA-  Contains seperately for each instance , it is shared memory region contains data and control information for one oracle instance.Allocated at instance startup and deallocate at instance shutdown

PGA - It is a private sql area ,creates when server process is started .Memory buffer that contains data and control information for a server process.


SGA = buffer cacche+shared pool+redo log buffer

buffer cache :   stores the most recent blocks of data and improves the performance by reducing disk i/o activity.

shared pool :  shared sql area (parse tree and execution plan for sql statements) , dictionary cache,library cache

redolog buffer : strores redo log entries (log of changes made to DB) written to the online redo log(used during db recovery)