How to install Oracle RAC 11g on Linux

11.2.0.2  you can use  <= linux 6.3

VMWare settings

Create a VM with below configurations show below picture

Ram                 2GB

Processors       1          (if you are using dual core)

Hard Disk         35GB    (one disk is default, after install Linux we will add remaining disks)

Network adapter 2         (one card is default, after install Linux we will add remaining)

Prepare your host for cluster installation
-------------------------------------------
1.  Varify the os and kernel version
    visit the official documents at tahit.oracle.com
2.  Ensure all mandatory packages are installed
    rpm -q libaio-devel
3.  Ensure necessary users/ groups are created
    SOD
    Grid software : grid/oinstall (asmadmin, asmoper)
    Oracle software : oracle/oinstall (dba, oper)
4.  Ensure the mechines are time-synched. like NTP setup
    date && ssh rac2 date
    Or Ctssd will take care of it.
 (ctssd status ACTIVE OR OBSERVER)
5.  Establish SSH user equivalence
6.  Install ASMLib software on your host or rpms for ASM on every node.
     /etc/init.d/oracleasm configure -i
        ------------------- : grid
        ------------------- : asmadmin
        ------------------- : y
    Check /etc/sysconfig/oracleasm  file
7.  Provision of ASM disks
8.  Ensure the OS kernel parameters
    /etc/sysctl.conf
9.  Ensure the OS limits are configured.
    /etc/security/limits.conf
10. Ensure the mount points have suitable ownership and permissions.
11. Setup /etc/resolv.conf for DNS resolution
          /etc/hosts
         Check $ nslookup xxxxx
12.  Extract Oracle GI software
     Run cluster verification utility
     Invoke installer from one node
     Apply latest PSU bundle before running the root.sh script

-----------------------------------------------------------------------------------
 

Shared storage must be configured as ASM Disks.

1. Install linux in vmware

while installing change hostname

change these settings also (if you are using linux 6.3)

2. install all rpms

os related rpms form linux disk

asm related rpms from asm disk

grid realated rpms from grid disk

COPY ALL RPM FILES FROM LINUX CD
-------------------------------------------------------

copy all rpm files to local disk in folder "repo"

$cp /oracle/server/*.rpm   /u02/repo

CREATE A REPOSITORY FOR RPM

---------------------------------------------------

#cd /U02

#createrepo  -v repo

3.  change all shell parameters for linux

4.  change limits for oracle

Manual Setup

install required rpm:

---------------------

Goto ”repo” folder

#cd  /u02/repo

rpm -Uvh binutils-2.*

rpm -Uvh compat-libstdc++-33*

rpm -Uvh compat-libstdc++-33*.i386.rpm

rpm -Uvh elfutils-libelf*

rpm -Uvh gcc-4.*

rpm -Uvh gcc-c++-4.*

rpm -Uvh glibc-2.*

rpm -Uvh glibc-common-2.*

rpm -Uvh glibc-devel-2.*

rpm -Uvh glibc-headers-2.*

rpm -Uvh ksh*

rpm -Uvh libaio-0.*

rpm -Uvh libaio-devel-0.*

rpm -Uvh libgomp-4.*

rpm -Uvh libgcc-4.*

rpm -Uvh libstdc++-4.*

rpm -Uvh libstdc++-devel-4.*

rpm -Uvh make-3.*

rpm -Uvh sysstat-7.*

rpm -Uvh unixODBC-2.*

rpm -Uvh unixODBC-devel-2.*

rpm -Uvh numactl-devel-*

Oracle recommend the following minimum parameter settings.

#vi     /etc/sysctl.conf

fs.suid_dumpable = 1

fs.aio-max-nr = 1048576

fs.file-max = 6815744

kernel.shmall = 268435456

kernel.shmmax = 536870912

kernel.shmmni = 4096

kernel.sem = 250 32000 100 128

net.ipv4.ip_local_port_range = 9000 65500

net.core.rmem_default=262144

net.core.rmem_max=4194304

net.core.wmem_default=262144

net.core.wmem_max=1048586

Run the following command to change the current kernel parameters.

#/sbin/sysctl   -p

#vi    /etc/security/limits.conf

# refer orabug15971421 for more info.
oracle   soft   nproc    16384
# oracle-rdbms-server-11gR2-preinstall setting for nproc hard limit is 16384
oracle   hard   nproc    16384
# oracle-rdbms-server-11gR2-preinstall setting for stack soft limit is 10240KB
oracle   soft   stack    10240
# oracle-rdbms-server-11gR2-preinstall setting for stack hard limit is 32768KB
oracle   hard   stack    32768
# oracle-rdbms-server-11gR2-preinstall setting for memlock hard limit is maximum of {128GB (x86_64) / 3GB (x86) or 90 % of RAM}
oracle   hard   memlock    3145728
# oracle-rdbms-server-11gR2-preinstall setting for memlock soft limit is maximum of {128GB (x86_64) / 3GB (x86) or 90% of RAM}
oracle   soft   memlock    3145728

grid hard nproc 16384
grid soft nproc 2047
grid hard nofile 65536

5. Create the new groups and users.

#groupadd oinstall

#groupadd dba
#groupadd osoper

#groupadd asmadmin
#groupadd asmdba
#groupadd asmoper

#useradd -g oinstall –G dba, osoper  oracle
# useradd -g oinstall -G asmadmin, asmdba, asmoper  grid

#passwd oracle

#passwd grid

OR

 you can skip above 2,3,4 and 5, if you use below commands (need internet connection)

# yum install oracle-rdbms-server-11gR2-preinstall

# yum install oracleasm*

From ISO disk 

# yum install cuvqdisk-*.rpm

6. Set secure Linux  by editing

#vi   /etc/selinux/config

SELINUX=disable

[root@ora12a ~]# service iptables stop

iptables: Flushing firewall rules:                                  [  OK  ]
iptables: Setting chains to policy ACCEPT: filter          [  OK  ]
iptables: Unloading modules:                                      [  OK  ]

[root@ora12a ~]# chkconfig iptables off

7. Create the directories in which the Oracle software will be installed.

#mkdir -p /u01/app/oracle/product/11.2.0/db_1

mkdir -p /u01/app/11.2.0/grid

#chown -R grid:oinstall /u01

#chmod -R 775 /u01

#chmod -R 777 /u02

8. /etc/init.d/oracleasm configure
---------------------------------: oracle
---------------------------------:oinstall
---------------------------------: y
---------------------------------: y

8. install vmbox-configuramtion settings

     change time synch

9. change /etc/hosts

Change the /etc/hosts entries as below

# Do not remove the following line, or various programs

# that require network functionality will fail.

127.0.0.1               rac1.oracl.com rac1 localhost.localdomain localhost

::1             localhost6.localdomain6 localhost6

#Public

192.168.1.101           rac1.oracl.com             rac1

192.168.1.102           rac2.oracl.com             rac2

#Private

10.10.1.1               rac1-priv.oracl.com        rac1-priv

10.10.1.2               rac2-priv.oracl.com        rac2-priv

#Virtual

192.168.1.201           rac1-vip.oracl.com         rac1-vip

192.168.1.202           rac2-vip.oracl.com         rac2-vip

#SCAN

192.168.1.51            rac-scan.oracl.com           rac-scan

192.168.1.52            rac-scan.oracl.com           rac-scan

192.168.1.53            rac-scan.oracl.com           rac-scan8.

10. disable ntpd

# service ntpd stop

Shutting down ntpd: [ OK ]

# chkconfig ntpd off

# mv /etc/ntp.conf /etc/ntp.conf.orig

11. shut it down and clone vm.

12.  Add one or three 1GB hard-disks to any one VM machine as independent and allocate storage.

add the code to share disks in VM ware for both Machines.

disk.locking = "FALSE"

diskLib.dataCacheMaxSize = "0"

diskLib.dataCacheMaxReadAheadSize = "0"

diskLib.dataCacheMinReadAheadSize = "0"

diskLib.dataCachePageSize = "4096"

diskLib.maxUnsyncedWrites = "0"

scsi1.present = "TRUE"

scsi1.sharedBus = "VIRTUAL"

scsi1.virtualDev = "lsilogic"

scsi1:1.present = "TRUE"

scsi1:1.fileName = "D:\SharedDisks\Shared1.vmdk"

scsi1:1.writeThrough = "TRUE"

scsi1:1.mode = "independent-persistent"

scsi1:2.present = "TRUE"

scsi1:2.fileName = "D:\SharedDisks\Shared2.vmdk"

scsi1:2.writeThrough = "TRUE"

scsi1:2.mode = "independent-persistent"

scsi1:3.present = "TRUE"

scsi1:3.fileName = "D:\SharedDisks\Shared3.vmdk"

scsi1:3.writeThrough = "TRUE"

scsi1:3.mode = "independent-persistent"

scsi1:4.present = "TRUE"

scsi1:4.fileName = "D:\SharedDisks\Shared4.vmdk"

scsi1:4.writeThrough = "TRUE"

scsi1:4.mode = "independent-persistent"

scsi1:5.present = "TRUE"

scsi1:5.fileName = "D:\SharedDisks\Shared5.vmdk"

scsi1:5.writeThrough = "TRUE"

scsi1:5.mode = "independent-persistent"

13. Start rac1 VM Machine  and configure ASM disks as below

# fdisk -l

# fdisk /dev/sdf

type n

type 1

enter 

enter 

type w

# /etc/init.d/oracleasm createdisk VOTE1  /dev/sdf1

-------------------------------------------------------------: [OK]

14.  Start second VM Machine and rename it's hostname as rac2

#vi /etc/sysconfig/network

hostname= rac2.oracle.com

:wq

15. Shutdown  the machine.

16.  add 2 nic cards, 

Start the VM ware 

change their ip addresses using neat command 

or  Administraton--> network configuration

as shown in /etc/hosts

Restart the Mechine.

17. copy Grid and Database Software in /u02 and change the permissions on both nodes

# chmod -R 775 /u02/grid
# chown -R grid:oinstall /u02/grid

18.  install Grid Software 

# su - grid

$ cd /u02/grid

. runInstaller

while setup it will configure ssh setup will be done 

After install grid will be installed.

to diconfigure rac

/u01/app/11.2/0/grid/crs/install/rootcrs.pl -deconfig -force -lastnode

Oracle Grid Infrastructure Groups and Users Example

• An Oracle central inventory group, or oraInventory group (oinstall), whose members that have this group as their primary group. Members of this group are granted the OINSTALL system privileges, which grants permissions to write to the oraInventory directory, and other associated install binary privileges.
• An OSASM group (asmadmin), associated with Oracle Grid Infrastructure during installation, whose members are granted the SYSASM privileges to administer Oracle ASM.
• An OSDBA for ASM group (asmdba), associated with Oracle Grid Infrastructure storage during installation. Its members include grid and any database installation owners, such as oracle1 and oracle2, who are granted access to Oracle ASM. Any additional installation owners that use Oracle ASM for storage must also be made members of this group.
• An OSOPER for ASM group for Oracle ASM (asmoper), associated with Oracle Grid Infrastructure during installation. Members of asmoper group are granted limited Oracle ASM administrator privileges, including the permissions to start and stop the Oracle ASM instance.
• An Oracle Grid Infrastructure installation owner (grid), with the oraInventory group (oinstall) as its primary group, and with the OSASM (asmadmin) group and the OSDBA for ASM (asmdba) group as secondary groups.
• /u01/app/oraInventory. The central inventory of Oracle installations on the cluster. This path remains owned by grid:oinstall, to enable other Oracle software owners to write to the central inventory.
• An OFA-compliant mount point /u01 owned by grid:oinstall before installation, so that Oracle Universal Installer can write to that path.
• An Oracle base for the grid installation owner /u01/app/grid owned by grid:oinstall with 775 permissions, and changed during the installation process to 755 permissions.
• A Grid home /u01/app/12.1.0/grid owned by grid:oinstall with 775 (drwxdrwxr-x) permissions. These permissions are required for installation, and are changed during the installation process to root:oinstall with 755 permissions (drwxr-xr-x).

6.1.11.2 Oracle Database DB1 Groups and Users Example

• An Oracle Database software owner (oracle1), which owns the Oracle Database binaries for DB1. The oracle1 user has the oraInventory group as its primary group, and the OSDBA group for its database (dba1) and the OSDBA for ASM group for Oracle Grid Infrastructure (asmdba) as secondary groups. In addition the oracle1 user is a member of asmoper, granting that user privileges to start up and shut down Oracle ASM.
• An OSDBA group (dba1). During installation, you identify the group dba1 as the OSDBA group for the database installed by the user oracle1. Members of dba1 are granted the SYSDBA privileges for the Oracle Database DB1. Users who connect as SYSDBA are identified as user SYS on DB1.
• An OSBACKUPDBA group (backupdba1). During installation, you identify the group backupdba1 as the OSDBA group for the database installed by the user oracle1. Members of backupdba1 are granted the SYSBACKUP privileges for the database installed by the useroracle1 to back up the database.
• An OSDGDBA group (dgdba1). During installation, you identify the group dgdba1 as the OSDGDBA group for the database installed by the useroracle1. Members of dgdba1 are granted the SYSDG privileges to administer Oracle Data Guard for the database installed by the useroracle1.
• An OSKMDBA group (kmdba1). During installation, you identify the group kmdba1 as the OSKMDBA group for the database installed by the useroracle1. Members of kmdba1 are granted the SYSKM privileges to administer encryption keys for the database installed by the user oracle1.
• An OSOPER group (oper1). During installation, you identify the group oper1 as the OSOPER group for the database installed by the useroracle1. Members of oper1 are granted the SYSOPER privileges (a limited set of the SYSDBA privileges), including the right to start up and shut down the DB1 database. Users who connect as OSOPER privileges are identified as user PUBLIC on DB1.
• An Oracle base /u01/app/oracle1 owned by oracle1:oinstall with 775 permissions. The user oracle1 has permissions to install software in this directory, but in no other directory in the /u01/app path.

6.1.11.3 Oracle Database DB2 Groups and Users Example

• An Oracle Database software owner (oracle2), which owns the Oracle Database binaries for DB2. The oracle2 user has the oraInventory group as its primary group, and the OSDBA group for its database (dba2) and the OSDBA for ASM group for Oracle Grid Infrastructure (asmdba) as secondary groups. However, the oracle2 user is not a member of the asmoper group, so oracle2 cannot shut down or start up Oracle ASM.
• An OSDBA group (dba2). During installation, you identify the group dba2 as the OSDBA group for the database installed by the user oracle2. Members of dba2 are granted the SYSDBA privileges for the Oracle Database DB2. Users who connect as SYSDBA are identified as user SYS on DB2.
• An OSBACKUPDBA group (backupdba2). During installation, you identify the group backupdba2 as the OSDBA group for the database installed by the user oracle2. Members of backupdba2 are granted the SYSBACKUP privileges for the database installed by the useroracle2 to back up the database.
• An OSDGDBA group (dgdba2). During installation, you identify the group dgdba2 as the OSDGDBA group for the database installed by the useroracle2. Members of dgdba2 are granted the SYSDG privileges to administer Oracle Data Guard for the database installed by the useroracle2.
• An OSKMDBA group (kmdba2). During installation, you identify the group kmdba2 as the OSKMDBA group for the database installed by the useroracle2. Members of kmdba2 are granted the SYSKM privileges to administer encryption keys for the database installed by the user oracle2.
• An OSOPER group (oper2). During installation, you identify the group oper2 as the OSOPER group for the database installed by the useroracle2. Members of oper2 are granted the SYSOPER privileges (a limited set of the SYSDBA privileges), including the right to start up and shut down the DB2 database. Users who connect as OSOPER privileges are identified as user PUBLIC on DB2.
• An Oracle base /u01/app/oracle2 owned by oracle1:oinstall with 775 permissions. The user oracle2 has permissions to install software in this directory, but in no other directory in the /u01/app path.

# useradd -u 54322 -g oinstall -G asmadmin,asmdba grid
# useradd -u 54321 -g oinstall -G dba1,backupdba1,dgdba1,kmdba1,asmdba,asmoper oracle1
# useradd -u 54331 -g oinstall -G dba2,backupdba2,dgdba2,kmdba2,asmdba oracle2

Creating Active Standby database (ASM To FileSystem) using RMAN

Database version must be 11g


Source database db_unique_name = orcl
Duplicate database db_unique_name = sb

In standby server:

1. Check standby server meats our requirements or not.
2. Check standby server has sufficient privileges.

3. Check whether database software is installed or not.

4.  Check mount point has enough space or not.

5.  Check Oracle net configured or not.

Creating Physical Standby Database:

For Primary :

1. Check Oracle Net must be configured
Start the listener

2. Database must be up and running.

3. Database must be in archivelog mode.
SQL>SELECT NAME, DB_UNIQUE_NAME, OPEN_MODE, LOG_MODE, FORCE_LOGGING, DATABASE_ROLE FROM V$DATABASE;

Otherwise enable the archive log mode when the database in mount start
SQL> ALTER DATABASE ARCHIVELOG;

4. Enable FORCE LOGGING and SUPPLIMENTARY LOGGING.
SQL> ALTER DATBASE FORCE LOGGING;

5. Create a standby redo log files more than Online redo logfiles.

SQL> ALTER DATABASE ADD STANDBY LOGFILE THREAD 5
('/...../standby_redo01.rdo',  '/...../standby_redo01.rdo', '/...../standby_redo01.rdo','/...../standby_redo01.rdo');

SQL> SELECT GROUP#,THREAD#,SEQUENCE#,ARCHIVED,STATUS FROM V$STANDBY_LOG;

6. Create a password file.

7. Check whether database using spfile.
SQL>show parameter spfile

8. Change the parameters of the database which is running using spfile.

SQL>ALTER SYSTEM SET PARAMETER= value SCOPE=BOTH;

Add below parameter

*.DB_UNIQUE_NAME='ORCL' (Must be configured at the time of db creation means already there)
*.FAL_CLIENT='ORCL'
*.FAL_SERVER='sb' #standby database name
*.STANDBY_FILE_MANAGEMENT='AUTO'
*.LOG_ARCHIVE_CONFIG='DG_CONFIG=(ORCL,sb)'

*.log_archive_dest_1='LOCATION=use_db_recovery_file_dest

VALID_FOR=(ALL_LOGFILES,ALL_ROLES) DB_UNIQUE_NAME=ORCL'

*.log_archive_dest_2='SERVICE=rac2 LGWR async

VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=sb'

*.LOG_ARCHIVE_DEST_STATE_1='ENABLE'
*.LOG_ARCHIVE_DEST_STATE_2='ENABLE'

*.DB_FILE_NAME_CONVERT='/u01/app/oracle/oradata/ORCL/',

'/u01/app/oracle/oradata/sb/'
*.log_file_name_convert='/u01/app/oracle/oradata/ORCL/',

'/u01/app/oracle/oradata/sb/'

Note: No need to restart the database because all the above parameters are dynamic parameters.

9. create a pfile.
SQL:> CREATE PFILE FROM SPFILE;

10. SCP your pfile to standby server location


For Standby :

1. Configure Oracle Net at standby server.
2. copy the initORCL.ora and orapwORCL into ORACLE_HOME/dbs/ location
3. make sure password file exist in ORALCLE_HOME/dbs location

4. Rename pfile and edit the pfile.

change the below parameter for standby

vi initsb.ora
control_files='/u01/app/oracle/oradata/sb/control_standby.ctl' # change
DB_UNIQUE_NAME='sb' #change
FAL_CLIENT='sb' #change
FAL_SERVER='ORCL' #change

log_archive_dest_1='LOCATION=use_db_recovery_file_dest
VALID_FOR=(ALL_LOGFILES,ALL_ROLES) DB_UNIQUE_NAME=sb' #change

log_archive_dest_2='SERVICE=rac1 LGWR async
VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=ORCL'#change

db_create_file_dest='/u01/app/oracle/oradata/test'
db_file_name_convert='+data','/u01/app/oracle/oradata/test'
:wq


5. start the database using pfile in nomount
$export ORACLE_SID=sb

$sqlplus / as sysdba
SQL> startup nomount

6. create a spfile
create spfile from pfile.

7. shut the database

8. start the database in nomount state
$export ORACLE_SID=sb
$sqlplus / as sysdba
SQL> startup nomount

9. Connect to RMAN
$rman target=system/system@tnsorcl catalog=rman/rman@catalog auxiliary system/system@tnssb

connected to recovery catalog database
connected to auxiliary database: sb(DBID=99469477)

RMAN> run{

allocate channel ch1 device type disk;
allocate channel ch2 device type disk;
allocate auxiliary channel aux1 device type disk;
allocate auxiliary channel aux2 device type disk;

set newname for datafile 1 to "/u02/oradata/sb/system01.dbf";
set newname for datafile 2 to "/u02/oradata/sb/sysaux01.dbf";
set newname for datafile 3 to "/u02/oradata/sb/undotbs01.dbf";
set newname for datafile 4 to "/u02/oradata/sb/users01.dbf";

DUPLICATE TARGET DATABASE
FOR STANDBY
FROM ACTIVE DATABASE
DORECOVER
NOFILENAMECHECK;

release channel ch2;
release channel aux1;
release channel aux2;

}

OUTPUT


allocated channel: aux1
channel aux1: sid=156 devtype=DISK
Starting Duplicate Db at 01-JAN-10
contents of Memory Script:
.......................................................
........................................................
....................................................
contents of Memory Script:
{
Alter clone database open resetlogs;
}

executing Memory Script
database opened
Finished Duplicate Db


10. Start the MRP process:
sql> recover managed standby database using current logfile disconnect from session;







log_file_name_convert='+data','/u01/app/oracle/oradata/test'






connected to target database: ORCL (DBID=231273269)


set newname for tempfile 1 to "/u02/oradata/sb/temp01.dbf";





release channel ch1;

Migrating the Database from Non-ASM FileSystem to ASM FileSystem

1. Create a ASM groups say "DATA1".

2.  connect to database which is in READ_WRITE mode.

3. 

sql> show parameter spfile;

sql> show parameter control_file;

sql> select name from v$datafile;

4. 

sql> alter system set db_create_file_dest='+DATA1' scope=spfile;

sql> alter system set control_files='+DATA1' scope=spfile;

5. shut immediate

6. startup nomount

7. connect to RMAN

rman> restore controlfile from  '/../../control01.ctl';

rman> sql 'alter database mount'

rman> backup as copy database format '+DATA1';

rman> switch database to copy;

rman> sql 'alter database open''

8. 

sql> show parameter spfile;
sql> show parameter control_file;
sql> select name from v$datafile;

9. 
sql> create pfile from spfile;
sql> create spfile='+DATA1/spfile/spfileDB.ora' from pfile;

10. goto ORACLE_HOME/dbs location

$> vi initDB.ora
spfile='+DATA1/spfile/spfileDB.ora'
:wq

11.  bounce database (restart database)

note:
online redolog files and temporary datafiles are not in ASM. So we need to move them manually.

12. create default temporary tablespace
sql> alter database default temporary tablespace temp001;

13. drop previous default temporary tablespace

sql> select name from v$tempfile;

sql> drop tablespace <defaultTSName>;

14. bounce database

SQL Query Execution in Oracle (For DBA)

SQL Statement Execution Phases:
-----------------------------------------

When Application queries a request, it creates a user process and gives to server process through dispatcher.

server process places sql query in shared pool - sql area

Insert Statement:
In shared pool it goes to 3 stages Parsing, Execution and Fetching.

Parsing:

it performs syntactical, semantic checks
if success it will generate sql_id and hash value for the sql query and will be stored in ShardPool --> Library Cache.
if same hash value already exists in Library Cache then
it try to get the data from Database Buffer Cache is called Soft Parsing is also called Cache Hit.
otherwise it is called Cache Miss then it goes for Hard Parsing.


Execution:

     Optimization:
In hard parsing it performs shared pool check.
Here optimizer evaluates multiple plans depending on
Optimizer statistics, Access paths, Optimizer hints
expressions, conditions and constraints.

Fetching:

Chooses lowest cost execution plan will be executed by server process and gets the data from datafile and places it in the database buffer cache.
finally the result set will be displayed in cursor area.

Update Statement:

If it is update command then copy of a result set will be stored into the undo segments for roll-back and copy of a database buffer cache will be modified and marked as dirty buffers.

Server process writes all redos to redo log buffers.

When commit is issued all the redo entries to that transaction will be written to online redo logfiles by LGWR.

When checkpoint  (log switch) occurs (CKPT) will signals the db writer (DBWr). db writer writes all related dirty blocks to the datafiles using logfiles and checkpoint will update the latest scn to datafile header and controlfile.

finally result will be displayed to cursor area.

Insert Statement:

If it is insert command then values are stored in database buffer cache and the pointer for the table is stored in the undo tablespace.

When commit is issued  log writer writes redo entries to redo logfiles 

when checkpoint occurs (CKPT) will signals the db writer (DBWr). db writer writes all related blocks to the datafile
and checkpoint will update the latest scn to datafile header and controlfile.

For DDL:

issue a COMMIT before executing Create statement.
Verify privileges
Verify which tablespace
Verify tablespace quotas is not exceed.
Verify same object not exist same schema.
Create a table into the data dictionary.
issue a commit or roll-back.