archiver will maintain the Historical data from Master data
based on time.
this data will be used for planning and forecasting.

select sid from v$mystat where rownum=1;

select username,sid,serial# from v$session

show sga
It shows :
Total System Global Area  135338868 bytes
Fixed Size                   453492 bytes
Variable Size             109051904 bytes
Database Buffers           25165824 bytes
Redo Buffers                 667648 bytes

select * from v$sga;

Fixed Size       72536    bytes 
Variable Size    22900736 bytes 
Database Buffers 409600   bytes 
Redo Buffers     77824    bytes 


Total System Global Area : - Total in bytes of all the sub-
divisions that makes up the SGA. 

Total System Global Area 23460696 bytes

There are 2 basic memory structures on the Oracle Instance

1.	System Global Area (SGA)
2.	Program Global Area (PGA)

Free extents cannot be merged together in Ver 6.0.

Free extents are periodically coalesces with the neighboring
free extent in Ver 7.0

Database buffer is part of SGA, Which it is contain oracle
blocks copied from datafile and modification carried in this
area. In oracle 9i BUFFER CACHE is divided into three parts
buffer_cache, buffer_keep_cache,buffer_recycle_cahce.

THANKS

Database buffers store the most recently used blocks of 
database data. It can also contain modified data that has 
not yet been permanently written to disk.

OPTIMAL parameter is used to set the optimal length of a
rollback segment

Number  of  times processes repeatedly query the dictionary
table is called recursive  hints.  It  is due to the data
dictionary cache is too small. By increasing  the
SHARED_POOL_SIZE parameter we can optimize the size of Data
Dictionary Cache.

this can be monitored in DB_data_files

SQL>desc dba_data_files;
SQL>desc v$tablespace;
SQL>select bytes from dba_data_files where tablespace_name 
like 'TABLSPACE_NAME';

this contains the commited and uncommited data stored in
rollback table space prior to 9i. in 9i, it is called as
undo table space.

ROLLBACK SEGMENT OR UNDO SEGMENT IS THE AREA IN UNDO TABLE 
SPACE WHERE CHANGED OR NEW UNCOMMITTED DATA RESIDES.

WHEN WE COMMIT, UNDO SEGMENT DATA BECOME UNUSEABLE. BUT IT 
STILL RESIDES IN THE UNDO SEGMENT FOR 600 SECONDS.

TO REMOVE THE CONSITANCY ISSUE FROM ORACLE DB.

WHEN WE COMMIT, UNDO SEGMENT DATA BECOME UNUSEABLE. BUT IT 
STILL RESIDES IN THE UNDO SEGMENT FOR 900 SECONDS.

it is called undo retention period

TRANSACTION RECOVERY, READ CONSISTENCY

use of rollback segment is used  for if our transection is 
not complete than starat with initial level

A oracle block divided into three parts.
block header,pctfree,pctused.


block header :its contain the information datafiles.


pctfree: its a free space in a datablock for updation and 
insertion of a row.default is 10% of a block size.one more 
thing it's default value is depand of OS also.


pctused : its a space where data are store in a block.its 
default value is 40% of a block size.

pctfree is only used for future updation, not for inserts.

when ever the buffer cache is crashed, the transactions
present in the buffer cache is lost. this can be recovered
by the redo log buffer, which contains all the transactions
present in the buffer cache

SYSTEM - Data dictionary tables.
DATA  - Standard operational tables.
DATA2- Static tables used for standard operations
INDEXES - Indexes for Standard operational tables.
INDEXES1 - Indexes of static tables used for standard
operations.
TOOLS - Tools table.
TOOLS1 - Indexes for tools table.
RBS - Standard Operations Rollback Segments,
RBS1,RBS2 - Additional/Special Rollback segments.
TEMP - Temporary purpose tablespace
TEMP_USER - Temporary tablespace for users.
USERS - User tablespace.