Architecture Overview - Expert Oracle Database Architecture - page 57

SQL> !ipcs -a

------ Shared Memory Segments --------
key shmid owner perms bytes nattch status

------ Semaphore Arrays --------
key semid owner perms nsems

------ Message Queues --------
key msqid owner perms used-bytes messages

■ On windows, Oracle executes as a single process with threads; you won't see separate processes as on
uNiX/Linux. Moreover, the windows threads will not have the same names as the processes just shown. i am using
uNiX/Linux specifically here so we can differentiate the individual processes and “see” them clearly.

Note

One interesting thing to note from this ps output is the process named oracleora12c . No matter how hard you
look on your system, you will not find an executable by that name. The Oracle binary that is executing is really the
binary file $ORACLE_HOME/bin/oracle .

■ it is assumed that the environment variable (on uNiX/Linux) or registry setting (on windows) named
ORACLE_HOME has been set and represents the fully qualified path to where the Oracle software is installed.

Note

The Oracle developers simply rename the process as it is loaded into memory. The name of the single Oracle
process that is running right now (our dedicated server process ; more on this later) is oracle$ORACLE_SID . That naming
convention makes it very easy to see what processes are associated with which instances and so on. So, let's try to start
the instance now:

SQL> startup
ORA-01078: failure in processing system parameters
LRM-00109: could not open parameter file '/home/ora12cr1/app/ora12cr1/product/12.1.0/dbhome_1/dbs/
initora12c.ora'

Notice the error about a missing file named initora12c.ora . That file, referred to colloquially as an init.ora file ,
or more properly as a parameter file , is the sole file that must exist to start up an instance—we need either a parameter
file (a simple flat file that I'll describe in more detail shortly) or a stored parameter file.
We'll create the parameter file now and put into it the minimal information we need to actually start a database
instance. (Normally, we'd specify many more parameters, such as the database block size, control file locations, and
so on). By default, this file is located in the $ORACLE_HOME/dbs directory and has the name init${ORACLE_SID}.ora :

[ora12cr1@dellpe dbs]$ cd $ORACLE_HOME/dbs
[ora12cr1@dellpe dbs]$ echo db_name=ora12c > initora12c.ora
[ora12cr1@dellpe dbs]$ cat initora12c.ora
db_name=ora12c