Configuring Kernel Parameters For Oracle 10g Installation

This section documents the checks and modifications to the Linux kernel that should be made by the DBA to support Oracle Database 10g. Before detailing these individual kernel parameters, it is important to fully understand the key kernel components that are used to support the Oracle Database environment.

The kernel parameters and shell limits presented in this section are recommended values only as documented by Oracle. For production database systems, Oracle recommends that we tune these values to optimize the performance of the system.

Verify that the kernel parameters shown in this section are set to values greater than or equal to the recommended values.

Shared Memory  :  Shared memory allows processes to access common structures and data by placing them in a shared memory segment. This is the fastest form of  Inter-Process Communications (IPC) available - mainly due to the fact that no kernel involvement occurs when data is being passed between the processes. Data does not need to be copied between processes .

Oracle makes use of shared memory for its Shared Global Area (SGA) which is an area of memory that is shared by all Oracle backup and foreground processes. Adequate sizing of the SGA is critical to Oracle performance since it is responsible for holding the database buffer cache, shared SQL, access paths, and so much more.

To determine all current shared memory limits, use the following :

# ipcs  -lm

------ Shared Memory Limits --------

max number of segments = 4096

max seg size (kbytes) = 4194303

max total shared memory (kbytes) = 1073741824

min seg size (bytes) = 1 

The following list describes the kernel parameters that can be used to change the shared memory configuration for the server:

1.) shmmax  -   Defines the maximum size (in bytes) for a shared memory segment. The Oracle SGA is comprised of shared memory and it is possible that incorrectly setting shmmax  could limit the size of the SGA. When setting shmmax, keep in mind that the size of the SGA should fit within one shared memory segment. An inadequate shmmax setting could result in the following:

ORA-27123: unable to attach to shared memory segment

We can determine the value of shmmax by performing the following :

# cat /proc/sys/kernel/shmmax

4294967295

For most Linux systems, the default value for shmmax is 32MB. This size is often too small to configure the Oracle SGA. The default value for shmmax in CentOS 5 is 4GB which is more than enough for the Oracle configuration. Note that this value of 4GB is not the "normal" default value for shmmax in a Linux environment  inserts the following two entries in the file /etc/sysctl.conf:

# Controls the maximum shared segment size, in bytes

kernel.shmmax = 4294967295

2.) shmmni   :   This kernel parameter is used to set the maximum number of shared memory segments system wide. The default value for this parameter is 4096. This value is sufficient and typically does not need to be changed. We can determine the value of shmmni by performing the following:

# cat /proc/sys/kernel/shmmni 

4096

3.) shmall   :   This parameter controls the total amount of shared memory (in pages) that can be used at one time on the system. The value of this parameter should always be at least: We can determine the value of shmall by performing the following :

# cat /proc/sys/kernel/shmall 

268435456

For most Linux systems, the default value for shmall is 2097152 and is adequate for most configurations. The default value for shmall in CentOS 5 is 268435456 (see above) which is more than enough for the Oracle configuration described in this article. Note that this value of 268435456 is not the "normal" default value for shmall in a Linux environment , inserts the following two entries in the file /etc/sysctl.conf:

# Controls the maximum number of shared memory segments, in pages

kernel.shmall = 268435456

4.) shmmin :  This parameter controls the minimum size (in bytes) for a shared memory segment. The default value for shmmin is 1 and is adequate for the Oracle configuration described in this article.We  can determine the value of shmmin by performing the following:

# ipcs -lm | grep "min seg size"

min seg size (bytes) = 1

Semaphores : 

After the DBA has configured the shared memory settings, it is time to take care of configuring the semaphores. The best way to describe a semaphore is as a counter that is used to provide synchronization between processes (or threads within a process) for shared resources like shared memory. Semaphore sets are supported in System V where each one is a counting semaphore. When an application requests semaphores, it does so using "sets". To determine all current semaphore limits, use the following:

#  ipcs -ls

------ Semaphore Limits --------

max number of arrays = 128

max semaphores per array = 250

max semaphores system wide = 32000

max ops per semop call = 32

semaphore max value = 32767

We  can also use the following command:

# cat /proc/sys/kernel/sem

250     32000   32      128

The following list describes the kernel parameters that can be used to change the semaphore configuration for the server:

i.) semmsl - This kernel parameter is used to control the maximum number of semaphores per semaphore set. Oracle recommends setting semmsl to the largest PROCESS instance parameter setting in the init.ora file for all databases on the Linux system plus 10. Also, Oracle recommends setting the semmsl to a value of no less than 100.

ii.) semmni - This kernel parameter is used to control the maximum number of semaphore sets in the entire Linux system. Oracle recommends setting semmni to a value of no less than 100.

iii.) semmns - This kernel parameter is used to control the maximum number of semaphores (not semaphore sets) in the entire Linux system. Oracle recommends setting the semmns to the sum of the PROCESSES instance parameter setting for each database on the system, adding the largest PROCESSES twice, and then finally adding 10 for each Oracle database on the system. Use the following calculation to determine the maximum number of semaphores that can be allocated on a Linux system. It will be the lesser of:

SEMMNS  -or-  (SEMMSL * SEMMNI)

iv.) semopm - This kernel parameter is used to control the number of semaphore operations that can be performed per semop system call. The semop system call (function) provides the ability to do operations for multiple semaphores with one semop system call. A semaphore set can have the maximum number of semmslsemaphores per semaphore set and is therefore recommended to set semopm equal to semmsl in some situations. Oracle recommends setting the semopm to a value of no less than 100.

File Handles :

When configuring the Linux server, it is critical to ensure that the maximum number of file handles is large enough. The setting for file handles denotes the number of open files that you can have on the Linux system. Use the following command to determine the maximum number of file handles for the entire system:

# cat /proc/sys/fs/file-max 

102312

Oracle recommends that the file handles for the entire system be set to at least 65536.  We can query the current usage of file handles by using the following :

# cat /proc/sys/fs/file-nr

3072    0       102312

The file-nr file displays three parameters:

•        Total allocated file handles

•        Currently used file handles

•        Maximum file handles that can be allocated

If we need to increase the value in /proc/sys/fs/file-max, then make sure that the ulimit is set properly. Usually for Linux 2.4 and 2.6 it is set to unlimited. Verify theulimit setting my issuing the ulimit command : 

# ulimit

unlimited

IP Local Port Range  :

Oracle strongly recommends to set the local port range ip_local_port_range for outgoing messages to "1024 65000" which is needed for systems with high-usage. This kernel parameter defines the local port range for TCP and UDP traffic to choose from.

The default value for ip_local_port_range is ports 32768 through 61000 which is inadequate for a successful Oracle configuration. Use the following command to determine the value of ip_local_port_range:

# cat /proc/sys/net/ipv4/ip_local_port_range

32768   61000

Networking Settings  : 

With Oracle 9.2.0.1 and later, Oracle makes use of UDP as the default protocol on Linux for inter-process communication (IPC), such as Cache Fusion and Cluster Manager buffer transfers between instances within the RAC cluster.

Oracle strongly suggests to adjust the default and maximum receive buffer size (SO_RCVBUF socket option) to 1MB and the default and maximum send buffer size (SO_SNDBUF socket option) to 256KB.The receive buffers are used by TCP and UDP to hold received data until it is read by the application. The receive buffer cannot overflow because the peer is not allowed to send data beyond the buffer size window.

This means that datagrams will be discarded if they don't fit in the socket receive buffer, potentially causing the sender to overwhelm the receiver. Use the following commands to determine the current buffer size (in bytes) of each of the IPC networking parameters:

# cat /proc/sys/net/core/rmem_default

109568

# cat /proc/sys/net/core/rmem_max

131071

# cat /proc/sys/net/core/wmem_default

109568

# cat /proc/sys/net/core/wmem_max

131071

Setting Kernel Parameters for Oracle

If the value of any kernel parameter is different to the recommended value, they will need to be modified. For this article, I identified and provide the following values that will need to be added to the /etc/sysctl.conf file which is used during the boot process.

kernel.shmmax = 2147483648

kernel.shmmni = 4096

kernel.shmall = 2097152

kernel.sem = 250 32000 100 128

fs.file-max = 65536

net.ipv4.ip_local_port_range = 1024 65000

net.core.rmem_default = 1048576

net.core.rmem_max = 1048576

net.core.wmem_default = 262144

net.core.wmem_max = 262144

After adding the above lines to the /etc/sysctl.conf file, they persist each time the system reboots. If we would like to make these kernel parameter value changes to the current system without having to first reboot, enter the following command:

# /sbin/sysctl –p

Enjoy     :-) 

What is Oracle Streams ?

Oracle Streams enables information sharing. Using Oracle Streams, each unit of shared information is called a message, and we can share these messages in a stream. The stream can propagate information within a database or from one database to another. The stream  routes specified information to specified destinations. The result is a feature that provides greater functionality and flexibility than traditional solutions for capturing and managing messages, and sharing the messages with other databases and applications. Streams provide the capabilities needed to build and operate distributed enterprises and applications, data warehouses, and high availability solutions.

Using Oracle Streams, we control what information is put into a stream, how the stream flows or is routed from database to database, what happens to messages in the stream as they flow into each database, and how the stream terminates. Based on our specifications, Streams can capture, stage, and manage messages in the database automatically, including, but not limited to, data manipulation language (DML) changes and data definition language (DDL) changes. we can also put user-defined messages into a stream, and Streams can propagate the information to other databases or applications automatically. When messages reach a destination, Streams can consume them based on our specifications.

.

                                        Oracle  Streams information flow

What Can Streams Do? 

The following sections provide an overview of what Streams can do.

1.) Capture Messages at a Database   :     A capture process can capture database events, such as changes made to tables, schemas, or an entire database. Such changes are recorded in the redo log for a database, and a capture process captures changes from the redo log and formats each captured change into a message called a logical change record (LCR). The rules used by a capture process determine which changes it captures, and these captured changes are called captured messages.

The database where changes are generated in the redo log is called the source database. A capture process can capture changes locally at the source database, or it can capture changes remotely at a downstream database. A capture process enqueues logical change records (LCRs) into a queue that is associated with it.

2.) Stage Messages in a Queue    :    Messages are stored (or staged) in a queue. These messages can be captured messages or user-enqueued messages. A capture process enqueues messages into a ANYDATA queue. An ANYDATA queue can stage messages of different types. Users and applications can enqueue messages into an ANYDATA queue or into a typed queue.

3.) Propagate Messages from One Queue to Another   :    Streams propagations can propagate messages from one queue to another. These queues can be in the same database or in different databases. Rules determine which messages are propagated by a propagation.

4.) Consume Messages    :    A message is consumed when it is dequeued from a queue. An apply process can dequeue messages from a queue implicitly. A user, application, or messaging client can dequeue messages explicitly. The database where messages are consumed is called the destination database.

Rules determine which messages are dequeued and processed by an apply process. An apply process can apply messages directly to database objects or pass messages to custom PL/SQL subprograms for processing.

Rules determine which messages are dequeued by a messaging client. A messaging client dequeues messages when it is invoked by an application or a user.

What Are the Uses of Streams?

The following sections briefly describe some of the reasons for using Streams. In some cases, Streams components provide infrastructure for various features of Oracle.

1.) Data Replication  :    Streams can capture DML and DDL changes made to database objects and replicate those changes to one or more other databases . A Streams capture process captures changes made to source database objects and formats them into LCRs, which can be propagated to destination databases and then applied by Streams apply processes.

The destination databases can allow DML and DDL changes to the same database objects, and these changes might or might not be propagated to the other databases in the environment. In other words, we can configure a Streams environment with one database that propagates changes, or we can configure an environment where changes are propagated between databases bidirectionally. Also, the tables for which data is shared do not need to be identical copies at all databases. Both the structure and the contents of these tables can differ at different databases, and the information.

2.) Event Management and Notification   :    Business events are valuable communications between applications or organizations. An application can enqueue messages that represent events into a queue explicitly, or a Streams capture process can capture database events and encapsulate them into messages called LCRs. These captured messages can be the results of DML or DDL changes. Propagations can propagate messages in a stream through multiple queues. Finally, a user application can dequeue messages explicitly, or a Streams apply process can dequeue messages implicitly. An apply process can reenqueue these messages explicitly into the same queue or a different queue if necessary. 

3.) Data Warehouse Loading  :  Data warehouse loading is a special case of data replication. Some of the most critical tasks in creating and maintaining a data warehouse include refreshing existing data, and adding new data from the operational databases. Streams components can capture changes made to a production system and send those changes to a staging database or directly to a data warehouse or operational data store. Streams capture of redo data avoids unnecessary overhead on the production systems. Support for data transformations and user-defined apply procedures enables the necessary flexibility to reformat data or update warehouse-specific data fields as data is loaded. 

4.)  Data Protection    :     One solution for data protection is to create a local or remote copy of a production database. In the event of human error or a catastrophe, the copy can be used to resume processing. we can use Streams to configure flexible high availability environments.

In addition, we can use Oracle Data Guard, a data protection feature that uses some of the same infrastructure as Streams, to create and maintain a logical standby database, which is a logically equivalent standby copy of a production database.

5.)  Database Availability During Upgrade and Maintenance Operations  :  we can use the features of Oracle Streams to achieve little or no database down time during database upgrade and maintenance operations. Maintenance operations include migrating a database to a different platform, migrating a database to a different character set, modifying database schema objects to support upgrades to user-created applications, and applying an Oracle software patch.

Below is an example of  Oracle Streams  Sharing Information Between Databases

Enjoy        J J J

ORACLE 10G INSTALLATION ON REDHAT 5.1 LINUX

This is a step by step Oracle Installation , which will helps in  installation of Oracle 10g on RHEL 5.1 (Red Hat Enterprise Linux 5.1)  32-bit architecture.

Step  1 :  The first thing we need to verify is  the hardware for an Oracle 10g Installation.

  Ø           Check Physical RAM.

                # grep  MemTotal   /proc/meminfo

                   MemTotal :      2075424 kB

 We need at least 1024 MB of physical RAM.  In my case I have 2048 MB.

Ø           Check Swap Space.

              # grep  SwapTotal    /proc/meminfo

                      SwapTotal:     3148732 kB
The following is Oracle's requirement for swap space:

Available RAM	Swap Space Required
Between 1 GB and 2 GB	1.5 or 2  times the size of RAM
Between 2 GB and 8 GB	Equal to the size of RAM
More than 8 GB	.75 times the size of RAM

Ø       Check space available in /tmp

           # df  -h  /tmp

              Filesystem            Size     Used         Avail     Use%     Mounted on

              /dev/sda5             1.5G     35M         1.4G      3% /        tmp

We need to have at least 400 MB of space in the /tmp directory.  Make sure we have 400MB in the column "Avail" in the above output.

  In my case I have 1.4G space available in /tmp.

Ø    Check space for Oracle Software and pre-configured database.

 I have created a separate partition "/u01" for Oracle Software  and database files.

             # df -h /u01

               Filesystem            Size        Used        Avail    Use%   Mounted on

               /dev/sda2              15G     166M         14G       2%        /u01

I  have 14G available space on the partition /u01.  Space requirement for Oracle Software:

     Enterprise Edition         2.5G

     Standard Edition           2.3G

     Custom (maximum)      3G

Once all hardware requirements are verified, we will proceed with further configuration.Make sure that there is an entry in /etc/hosts file for your machine like this:

[IP-address]   [fully-qualified-machine-name]   [machine-name]

Where "fully-qualified-machine-name" is your  "machine_name"."domain_name"

Step 2 :  Before start installing Oracle10g software, make sure that we have the below packages installed on our Linux box,  else we will get error(s) during the installation process.

glibc-2.3.4-2.13

glibc-common-2.3.4-2.13

gcc-3.4.4-2

gcc-c++-3.4.4-2

libstdc++-3.4.4-2

libstdc++-devel-3.4.4-2

libaio-0.3.103-3

binutils-2.15.92.0.2-15

make-3.80-5

compat-db-4.1.25-9

gnome-libs-1.4.1.2.90-44.1

pdksh-5.2.14-30.3

sysstat-5.0.5-1

Execute the below comand as root to make sure that we have this rpms installed. If not installed, then download them  from appropriate linux site. For example ,

# rpm -qa  | grep glib*

The above command will display all the installed packages, name starting with  glib,  similarly we can check for all others packages .

If any of the above packages are  not installed, run the following command:

# rpm -ivh </path/to/><version>.i386.rpm

we will find the  package from the Red Hat Enterprise Linux 5 DVD .

Step 3 : Create user for Installation  :

We need  OS  “oracle”  user account created which owns the Oracle software. Oracle Software installation needs to be proceeds by this account for installing and managing. We do not need oinstall group if we are not installing on the production server or we (or our team) are the only person responsible for future installations/upgrades of Oracle Software. Members of the dba group can administer Oracle databases, for example starting up and shutting down databases. The oinstall group is often needed for those organizations who have separate groups that maintain the software and the database. In this scenario, the group membership prevents unauthorized access to the database by personnel who maintain the software, and it prevents the database administrators from making changes to the software and the installations inventory directory.

 # su -

#  groupadd dba

# groupadd oinstall

# useradd -g oinstall -G dba oracle

# passwd oracle

<<Enter password>>

Step 4:    Setting System parameters

Kernel Parameters : Oracle recommends that we set shared memory segment attributes as well as semaphores to the following values. If not set, database instance creation will fail.. Every OS process needs semaphore where It waits on for the resources. I added the following lines to /etc/sysctl.conf file. For more about the kernel parameter click here

Add/change the appropriate variables value in the   /etc/sysctl.conf  file as shown below.

kernel.shmall = 2097152

kernel.shmmax = 2147483648

kernel.shmmni = 4096

kernel.sem = 250 32000 100 128

fs.file-max = 65536

net.ipv4.ip_local_port_range = 1024 65000

net.core.rmem_default = 262144

net.core.rmem_max = 262144

net.core.wmem_default = 262144

net.core.wmem_max = 262144

After adding these lines to /etc/sysctl.conf, run the below command as root to make them enabled.

 #  sysctl  -p

Step 4: Edit the /etc/pam.d/login file and add following line

session required pam_limits.so

Step 5:   Edit the /etc/security/limits.conf file

To improve the performance of the software on Linux systems, we must increase the following shell limits  for the oracle user .Add the following lines to the /etc/security/limits.conf file:

oracle    soft  nproc  2047

oracle    hard  nproc  16384

oracle    soft  nofile  1024

oracle    hard  nofile  65536

Where "nproc" is the maximum number of processes available to the user and "nofiles" is the number of open file descriptors.

Step 6 : Creating oracle directories

As per OFA, oracle base directory has the path  : /mount_point/app/oracle_sw_owner where mount_point  is the mount point directory for the file system that will contain the Oracle software . I have used  /u01 for the mount point directory. However, we could choose another mount point directory,  such as /oracle or /opt/soft.

# mkdir  -p /u01/app/oracle

# chown  -R  oracle:oinstall  /u01/app/oracle

#mkdir  -p   /u02/oradata/db102

# chown  -R  oracle:oinstall /u02/oradata/db102

# chmod  -R  775  /u01/app/oracle

# chmod  -R  775  /u02/oradata/db102

Step  7:   Setting Oracle Enviroment

Edit the /home/oracle/.bash_profile  file and add following lines:

TMP=/tmp; export TMP

TMPDIR=$TMP; export TMPDIR

# If /tmp doesn't have 400mb space free then you can workaround it

# by pointing the variables TMP AND TMPDIR to a location where you

# have sufficient space. Oracle will then use this directory for

# temporary files.

ORACLE_BASE=/u01/app/oracle; export ORACLE_BASE

ORACLE_HOME=$ORACLE_BASE/product/10.2.0/db_1; export ORACLE_HOME

ORACLE_SID=orcl; export ORACLE_SID

ORACLE_TERM=xterm; export ORACLE_TERM

PATH=/usr/sbin:$PATH; export PATH

PATH=$ORACLE_HOME/bin:$PATH; export PATH

LD_LIBRARY_PATH=$ORACLE_HOME/lib:/lib:/usr/lib;

export LD_LIBRARY_PATH

CLASSPATH=$ORACLE_HOME/JRE:$ORACLE_HOME/jlib:$ORACLE_HOME/rdbms/jlib;

export CLASSPATH

if [ $USER = "oracle" ]; then

      if [ $SHELL = "/bin/ksh" ]; then

                ulimit -p 16384

                ulimit -n 65536

      else

                ulimit -u 16384 -n 65536

      fi

fi

Step 8:   Release specification 

Oracle 10g is not certified to be installed on RHEL 5, therefore, it runs a check on the operating system when the installer starts and will bounce back with an error if the redhat release is not redhat-4 or redhat-3 etc. Open /etc/redhat-release, remove whatever release is specified over there and put this:  redhat-4.

Step 9:   Installation Process of Oracle 10g Software

#  xhost +     (access control disabled, clients can connect from any host)

# mount  /media/cdrom    (--- if u have your s/w in cd else no need of this steps ) 

# su - oracle

$ echo $ORACLE_BASE

/u01/app/oracle

$ echo $ORACLE_SID

orcl

$ ./media/cdrom/runInstaller

The OUI (Oracle Universal Installer) should start and we should see graphical screens and install as per requirements.

Note:  Disable secure linux by editing the /etc/selinux/config file, making sure the SELINUX flag is set as follows:  SELINUX=disabled . If we  leave SELINUX=enforcing then we may get an error later while starting sqlplus:

Enjoy         : -)