11gR1 database file path

ORACLE_BASE
$Oracle base = /u01/app/oracle.
ORACLE_BASE specifies the directory at the top of the Oracle software and administrative file structure.
The value recommended for an OFAconfiguration is software_mount_point/app/oracle.
For example: /u01/app/oracle.
If you are not using an OFA-compliant system, you do not have to set
ORACLE_BASE, but it is highly recommended that you do set it.
 ORACLE_HOME

$ORACLE_HOME = /u01/app/oracle/product/11.1.0/db_1
 ORACLE_HOME specifies the directory containing the Oracle software for a given release.
The Optimal Flexible Architecture recommended value is:
$ORACLE_BASE/product/release. For example:
/u01/app/oracle/product/11.1.0.

ORACLE_BASE – ORACLE_BASE is the root of the Oracle Database directory tree.
If you install an OFA-compliant database using Oracle Universal Installer defaults, then ORACLE_BASE is X:\oracle\product\11.1.0 where X is any hard drive.
ORACLE_HOME – ORACLE_HOME corresponds to the environment in which Oracle Database products run.
This environment includes the location of installed product files, the PATH variable pointing to the binary files of installed products, registry entries, net service names, and program groups.
If you install an OFA-compliant database, using Oracle Universal Installer defaults, then Oracle home (known as ORACLE_HOME in this guide) is located beneath ORACLE_BASE. It contains subdirectories for Oracle Database software executables and network files.

What Is a Control File?

Every Oracle Database has a control file, which is a small binary file that records the physical structure of the database. The control file includes:

• The database name
• Names and locations of associated datafiles and redo log files
• The timestamp of the database creation
• The current log sequence number
• Checkpoint information

The control file must be available for writing by the Oracle Database server whenever the database is open. Without the control file, the database cannot be mounted and recovery is difficult.
The control file of an Oracle Database is created at the same time as the database. By default, at least one copy of the control file is created during database creation. On some operating systems the default is to create multiple copies. You should create two or more copies of the control file during database creation. You can also create control files later, if you lose control files or want to change particular settings in the control files.

Path :- /u01/app/oracle/oradata/orcl
C = control file <.ctl>
control01.ctl  control03.ctl     
control02.ctl 

What Is the Redo Log?

The most crucial structure for recovery operations is the redo log, which consists of two or more preallocated files that store all changes made to the database as they occur. Every instance of an Oracle Database has an associated redo log to protect the database in case of an instance failure.
Path :- /u01/app/oracle/oradata/orcl
R = redo file <.log>
redo01.log redo02.log  redo03.log
 Database datafiles

Database datafiles are physical files stored on disk. These files are used to store data on disk. Database datafiles are only written to by the DBWR processes that we introduced you to earlier (there is an exception or two to this statement, but for now, assume that this point this true).

These database datafiles are associated with Oracle “tablespaces”, which are “logical” containers for tables and indexes.  

Path :- /u01/app/oracle/oradata/orcl 

D = data file <.dbf>
example01.dbf    sysaux01.dbf  temp01.dbf    users01.dbf system01.dbf  undotbs01.dbf

Parameter file Concepts

The parameter file (sometimes called init.ora) contains configuration information for the database to use at startup time. The parameter file you configure how much RAM the database is going to use, where to find the control files, where to write trace files, and a whole host of other information. In most cases the database will not start without a parameter file. Oracle allows you to have a manual parameter file (called a PFILE) or a server-side parameter file (called a SPFILE).

P_file = /11g/oracle/admin/orcl/pfile  <init.ora.5212012161047>
            /11g/oracle/product/11.1.0/db_1/dbs/init.ora

Sp_file = /11g/oracle/product/11.1.0/db_1/dbs  <spfileorcl.ora>
 Trace Files 
Created by Oracle in a number of different situations. These can be created as a result of a database crash, a session failure, an unexpected but non-fatal database failure, or based on specific user operational commands.

Tace file location :-

/11g/oracle/diag/rdbms/orcl/orcl/trace
 Alert log 

This is the general log file for each Oracle database.

Alert file location :-

/11g/oracle/diag/rdbms/orcl/orcl/alert

Audit_file_dest(adump) = /11g/oracle/admin/orcl/adump <ora_17508.aud>

Datapump_dump(dpdump) = /11g/oracle/admin/orcl/dpdump <dp.log>

diagnostic_dest= /11g/oracle

db_recovery_file_dest= /11g/oracle/flash_recovery_area

Bin = /11g/oracle/product/11.1.0/db_1/bin
  Networking configuration files 
These files are used to configure the different network components of the Oracle database. These include files such as tnsnames.ora and listener.ora.
Network Configuration File<tnsnames.ora> = /11g/oracle/product/11.1.0/db_1/network/admin/

Online redo logs concepts

Think of the online redo logs like a tape recorder that records every change in the Oracle database. As changes occur, they are regularly recorded in the online redo logs, just like you might record a movie on your VCR.

In the event that a disk crashes, you may have to replace the disk and restore the disk data from a backup tape.  If this backup tape was several days ago, you have lost a lot of data.

Fortunately, Oracle can “replay” the saved transactions in the online redo logs, and re-apply lost transactions back into the database. Many times, this means that Oracle can recover from a crash without the DBA having to do anything other than just telling the database to startup. We will cover the topic of online redo log files and how they relate to database recovery in later chapters of this book.

At a minimum, Oracle requires that you have two online redo logs assigned to the database. Oracle will write redo to the first log, and when the first log is full, Oracle will switch to the second log and write the same redo. Each of these individual online redo logs is known as an online redo log group.

The reason we call them groups is that there can be mirrored copies of the online redo log files in each group. Like control files, it’s a good idea to have multiplexed copies of the Online redo logs. Oracle allows you to define multiple copies of these files. Each copy is called a member. Each redo log group can have one or more members. We will discuss the online redo log files in more detail in later chapters.