QUESTION :What are the major Components in an RDBMS ?

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ANSWER : This describes the three major Components which make up the run-time processes.

1) The Database Server.
   This takes the SQL, decides how to execute it, with a
   sub-Component called the Query Optimiser, and produces a
   Query Execution Plan.
   It is possible to have many Database Server processes running
   simultaneously, with each one tailored to a particular
   kind of "SQL Query". I used to work as a DBA for Salomon, Smith Barney
   supporting databases for Florida,England and Germany running on the
   same UNIX box. I always had three Servers running, one for each location,
   so that I could provide high-priority,high-CPU percentage,high-memory allocation
   for the very demanding real-time applications,and lower-priority
   for background batch jobs. It also allowed me to handle each database
   independently, and bring down the server for England without affecting the
   Servers and the Databases for Florida and Germany.

2) An Archive Process.
   This writes completed Transactions onto a Journal or History File and
   deletes them from the Log File. This is done to avoid the Log File getting
   filled up because then everything fails and the Servers have to be brought
   down to recover. This is an embarrassing process. The worst part is that
   as the DBA, you often do not know that the Archive process is not running
   until the Log File fills up, no more transactions can start, everybody's program
   hangs and the phone rings off the hook. I also worked as a DBA at J.P.Morgan
   where the user were just as demanding as Salomon, Smith Barney, so I created
   some UNIX daemons which ran all the time and would notify me automatically
   if the Archive process was not running. This was in the situation where the
   normal messages from starting up the Database Server would not make it clear
   whether the Archive process had started correctly.

3) A Recovery Process.
   The Recovery Process handles the situations where is there is a Database crash
   and it recovers to the last known point at which the Database was running OK and
   had 'integrity'. In other words, all the data representing a consistent set of
   related records had been written to the Database at the end of a committed Transaction,
   with no open Transactions.