Does open database really open?

Ra ra ra, the database has been created, then the tables were created, and even data was entered into the table. Ok, so now I want to shut this thing
down and see if it starts again.

OK, so I shutdown the database, then was about to issue a startup when I thought wait a minute does this thing really open any files when I say open
database.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.


SQL> startup mount;
ORACLE instance started.

Total System Global Area 2.6991E+10 bytes
Fixed Size                  2213976 bytes
Variable Size            1.7448E+10 bytes
Database Buffers         9395240960 bytes
Redo Buffers              145174528 bytes
Database mounted.

I then found out the process id (PID's) of the Database Writer process.

[root@isvx3 ~]#  ps -ef | grep dbw
oracle    9433     1  0 Dec22 ?        00:00:00 asm_dbw0_+ASM
oracle   32005     1  0 15:43 ?        00:00:00 ora_dbw0_abc
oracle   32007     1  0 15:43 ?        00:00:00 ora_dbw1_abc
oracle   32009     1  0 15:43 ?        00:00:00 ora_dbw2_abc
root     32039 31716  0 15:44 pts/3    00:00:00 grep dbw

Then straced one of the database writed process and collected the output in file.

[root@isvx3 ~]# strace -o /tmp/dbw.txt -p 32005 &

Then I issued the database open command at the sql prompt

SQL> alter database open;

Database altered.

SQL>

Now the moment of truth, Ta-Da....

-bash-3.2$ cat /tmp/dbw.txt | grep open
open("/proc/31987/stat", O_RDONLY)      = 18
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_system_6kt8jg4q_.dbf", O_RDONLY) = 18
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_system_6kt8jg4q_.dbf", O_RDONLY) = 18
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_system_6kt8jg4q_.dbf", O_RDWR|O_SYNC) = 18
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_sysaux_6kt8jg6r_.dbf", O_RDONLY) = 19
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_sysaux_6kt8jg6r_.dbf", O_RDONLY) = 19
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_sysaux_6kt8jg6r_.dbf", O_RDWR|O_SYNC) = 19
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_undotbs1_6kt8jg8b_.dbf", O_RDONLY) = 20
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_undotbs1_6kt8jg8b_.dbf", O_RDONLY) = 20
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_undotbs1_6kt8jg8b_.dbf", O_RDWR|O_SYNC) = 20
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_users_6kt8jgbw_.dbf", O_RDONLY) = 21
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_users_6kt8jgbw_.dbf", O_RDONLY) = 21
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_users_6kt8jgbw_.dbf", O_RDWR|O_SYNC) = 21
open("/u02/app/oracle/oradata/ABC/datafile/foo1.dbf", O_RDONLY) = 22
open("/u02/app/oracle/oradata/ABC/datafile/foo1.dbf", O_RDONLY) = 22
open("/u02/app/oracle/oradata/ABC/datafile/foo1.dbf", O_RDWR|O_SYNC) = 22
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_temp_6kt8lr7z_.tmp", O_RDONLY) = 23
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_temp_6kt8lr7z_.tmp", O_RDONLY) = 23
open("/u02/app/oracle/oradata/ABC/datafile/o1_mf_temp_6kt8lr7z_.tmp", O_RDWR|O_SYNC) = 23
open("/u02/app/oracle/product/11.2.0/dbhome_1/rdbms/mesg/oraus.msb", O_RDONLY) = 24
-bash-3.2$

We can see a list of all the files that were opened after open database was called at the sqlplus prompt.