Subject:            INIT.ORA Parameters and SGA Size
Last Revision Date: 11 September 1994
Author: Ramana Gourinani



                     INIT.ORA Parameters and SGA Size
                        ( For Unix Based Machines)

P.S. Appendix D of Database Administrator's Guide (V6) has
     all the information about init{sid}.ora parameters
     refered here.

    The description of SGA is in Chapter 8 of DBA (V6) Guide.

Terms
=====

   init{sid}.ora   -- Startup file which has all the
                      tunable parameters for V6 database.

   sid             -- Oracle system identifier
                       ( every instance is identfied by an sid )

   SGA             -- System Global Area
   DBA             -- Database Administrator

Purpose of this Bulletin
========================

  To get an idea of the list of init{sid}.ora parameters
  that would affect the SGA size which normally resides in
  memory/virtual memory.

Description
===========

  The SGA is  displayed as having four comoponents

        - Fixed size
        - Variable size
        - Database buffers
        - Log buffers

  All the components of the SGA are tunable except the Fixed size
  component.

  Under each component of SGA the list of init{sid}.ora parameters
  that would mainly effect that particular component would be
  listed. The init{sid}.ora parametrs are listed in upper case
  letters. But they could be listed in lower case letters on
  unix based machines.

   *  Fixed size
      ----------

                This is the fixed portion of the SGA.

                The init{sid}.ora parameter values do no effect
                this portion of the SGA.

                The size may vary between versions because of
                additional init{sid}.ora parameters in new versions.
                The size could also vary between different unix
                platforms due to different alignment Procedures.

                So this component of SGA is not tunable.

  *  Variable size
     -------------

           The variable portion of the SGA consists of arrays
           of variables that are allocated based upon the
           init{sid}.ora parameters.

                . DB_FILES
                    Lower the value of this parameters, the less
                    space needed. If this is set to 10 the gain
                    in the space would be approximately 6240 Bytes.

                . DB_FILE_MULTIBLOCK_READ_COUNTS
                    Higher the value for this parameter, the less
                    space needed.

                . All Dictionary cache parameters
                     ( i.e. all DC_XXX Paratamers )

                    Space needed for additional  values of
                    these parameters is not too high.

                . DDL_LOCKS
                    Space needed for additional value of 100
                    for this parameter would be ~ 5.0k.

                . DML_LOCKS
                    Space needed for additional value of 100
                    for this parameter would be ~ 9.76K.

                . ENQUEUE_RESOURSES
                    Space needed for additional value of 10
                    for this parameter would be ~ 0.7k.

                . PROCESSES
                    Space needed for additional value of 10
                    for this parameter would be ~ 19.5k.

                . ROW_CACHE_ENQUEUES
                    Space needed for addtional value of 100
                    for this parameter would be ~ 3.5K

                . SEQUENCE_CACHE_ENTRIES
                    Space needed for additional value of 10
                    for this parameter would be ~ 1.17k

                . SEQUENCE_CACHE_HASH_BUCKETS
                    Space needed for additional value of 10 for
                    this parameter would be ~ 0.08k

                . SESSIONS
                    Space need for additional value of 10 for
                    this parameter would be ~ 5.3K

                . TRANSACTIONS
                    Space needed for additional value of 10 for
                    this parameter would be ~ 0.85K.

                . TRANSACTIONS_PER_ROLLBACK_SEGMENTS
                    More space is needed for lower values of
                    this parameter.

  *  Database buffers
     ----------------

                . DB_BLOCK_SIZE
                . DB_BLOCK_BUFFERS

           The total space occupied by database buffers would
           be equal to DB_BLOCK_SIZE * DB_BLOCK_BUFFERS.

  *  Log Buffers
     -----------

                . LOG_BUFFERS

           The LOG_BUFFERS parameter is specifed in bytes.
           so the total space occupied  by Log Buffers would be
           equal to the value specified for LOG_BUFFERS.

Manuals to Refer
===============

         -  DBA Guide ( V6)
         -  Performance Tuning Guide
         -  Installtion Guide for a Unix Based machine