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Oracle   |   Archives
How to deconfigure/reconfigure Grid Infrastructure (12c)?
Last Modified: August 2019
In this article, we will see instructions to deconfigure/reconfigure or deinstall 12c Grid Infrastructure
Applying Oracle GI, Database and JVM PSU to RAC with DataGuard (12c) - July 2019
Last Modified: July 2019
In this article, I will be applying July 2019 PSU on the GI and Database Homes with Dataguard in place.
Remote ASM File Copy
Last Modified: March 2019
Copying file between mount points between different servers is straight forward and can be done using scp or ftp command. But transfering file between asm diskgroups of different servers will be a tricky one.
Restoring from RMAN to new ASM Diskgroups
Last Modified: January 2019
Recently I wanted to restore my Oracle database (2 nodes cluster database) on the same host but in a completely different ASM diskgroups. In most cases, you will be performing a similar operation rather on a different host.
Cloning A Standalone 12c GI Home (Oracle Restart)
Last Modified: August 2018
In this article I will attempt at copying or cloning the Non-Rac GRID Home path, for example from one partition to another using Oracle's cloning method.
Oracle Wallet (Secure External Password Store)
Last Modified: July 2018
It is often necessary to make connections to the database from shell scripts held on the filesystem. This can be a major security issue if these scripts contain the database connection details. One solution is to use OS Authentication, but Oracle 10g Release 2 gives us the option of using a secure external password store where the Oracle login credentials are stored in a client-side Oracle wallet. This allows scripts to contain connections using the /@>TNS_alias> syntax.
Recover Standby Using RMAN
Last Modified: June 2018
Sometimes if the standby database fails for any reason – then it can be necessary to recover the datafiles from full backup from primary. The recovery of the standby is relatively simple.
Recover Standby Using an Incremental Backup
Last Modified: June 2018
Sometimes if the standby database fails for any reason – then it can be necessary to recover the datafiles from full backup from primary. The recovery of the standby is relatively simple.
Applying Oracle GI, Database and JVM PSU to RAC with DataGuard (12c) - April 2018
Last Modified: April 2018
In this article, I will show you the way and methodology for installing GI, Database and Oracle Database JVM PSU to RAC database 12c (12.1.0.2) having Dataguard.
Applying Oracle Database and JVM PSU to Single Instance (12c)
Last Modified: April 2018
In this article, I will show you the way and methodology for installing DB PSU and OJVM PSU to a Single Instance 12c (12.1.0.2) Oracle Database.
Restore TABLE from RMAN backup (12c)
Last Modified: March 2018
One of the amazing features of Oracle Database 12c is that now you can do a logical restore from a physical backup. Before 12c it was not possible to restore a table from a RMAN backup. This feature is amazing speciall when you have a large database and needs to restore a small table. One of the pre-requisites is you must have a Full Backup of the database and also archivelogs after the fully backup must be available.
Restoring an Oracle Cluster Database (12c)
Last Modified: February 2018
Restoring a cluster database using RMAN backup.
Oracle Grid Infrastructure Upgrade from 12c R1 to 12c R2
Last Modified: January 2018
I recently did an upgrade of an Oracle Grid Infrastructure 12c Release 1 (12.1.0.2.0) hosted on a RAC Virtual Box environment on my Mac to the latest release 12c Release 2 12.2.0.1.0 version. Oracle Grid Infrastructure 12.2 software is now available as a single image file for direct download and quicker installation.
Data Guard - RAC Physical Standby (12c)
Last Modified: December 2017
This article explains the step by step process of building the 12c R1 (12.1.0.2) 2 node(s) RAC primary to 2 node(s) RAC Physical Standby.
ASM Disk Failure Scenario
Last Modified: August 2017
When a disk failure occurs for an ASM disk, behavior of ASM would be different, based on what kind of redundancy for the diskgroup is in use. If diskgroup has EXTERNAL REDUDANCY, diskgroup would keep working if you have redundancy at external RAID level. If there is no RAID at external level, the diskgroup would immediately get dismounted and disk would need a repair/replaced and then diskgroup might need to be dropped and re-created, and data on this diskgroup would require recovery.
Moving datafile from File System to ASM
Last Modified: August 2017
What if you had mistakenly created a datafile in local filesystem instead of ASM disk group in RAC database 11g? Below steps can resolve to move the datafile to ASM disk group. However, in 12c, it is straightforward (see at the bottom).
Create RAC physical standby database using RMAN Active Duplication - 12c
Last Modified: July 2017
From Oracle Database 11g onwards building a standby database has become a whole lot easier. With just one powerful RMAN command, the standby database can be created on another server without any backups. In this article, I will attempt to create RAC physical standby using RMAN's powerful Active Duplication.

Creating a RAC standby database is similar to single instance standby database creation:
  • first a single instance standby database is created by RMAN Active Duplication even if RMAN creates an SPFILE with some RAC parameters set like CLUSTER_DATABASE (this is because RMAN Active Duplication copies the primary database SPFILE for the new database)

  • remaining RAC standby database instance parameters must be configured manually by changing specific RAC parameters in the common SPFILE (INSTANCE_NUMBER, INSTANCE_NAME)

  • RAC standby database and its database instances must be added manually to Oracle Cluster Registry (OCR) as new resources with srvctl command at the end
Dataguard Failover in 12c
Last Modified: June 2017
Failover is a one way process where your primary database goes down due to some reasons and you convert your existing Physical Standby database to start behaving as Primary database.
Dataguard Switchover in 12c
Last Modified: June 2017
Switchover is a two way process in Oracle Dataguard and is a role reversal between the Primary database and one of its Standby databases. This way of role transition where the current Primary database starts behaving as a Physical Standby and on the other hand the current Physical Standby database starts behaving as a Primary database. Bystander standbys will receive redo from the new primary database.
Oracle Database 12c Release 2 (12.2) RAC On Oracle Linux 7
Last Modified: June 2017
This article describes the installation of Oracle Grid Infrastructure and Cluster Database 12c Release 2 (2 nodes) on Oracle Linux 7.3 using VirtualBox.
Oracle Database 12c Release 2 (12.2) Installation on Oracle Linux 7
Last Modified: May 2017
This article describes the installation of Oracle Database 12c Release 2 (12.2) 64-bit on Oracle Linux 7.2.
OEM Cloud Control 13c Release 2 Installation
Last Modified: May 2017
This article describes the installation of Oracle Enterprise Manager Cloud Control 13c Release 2 on Oracle Linux 7.3 (x86_64).
OEM Cloud Control 12c Release 5 Installation
Last Modified: May 2017
This article describes the installation of Oracle Enterprise Manager Cloud Control 12c Release 5 on Oracle Linux 6.6 (x86_64).
Removing/Deleting a Node from 12c RAC Cluster
Last Modified: April 2017
Deleting a node from a cluster does not remove a node’s configuration information from the cluster. The residual configuration information does not interfere with the operation of the cluster. Before starting, you can optionally delete the instance from the node to be c using 'dbca'.
Adding a New Node to 12c RAC Cluster
Last Modified: April 2017
This article doesn't cover the installation of 12c RAC, instead it only focuses on extending my two nodes cluster to three nodes cluster. If you care about installing 12c RAC, check this blog Grid Infrastructure and Database 12c R1 Installation (2 Node RAC).
Recovering a dropped tablespace
Last Modified: March 2017
To recover from a case of a dropped tablespace, the Tablespace Point In Time Recovery (TSPITR) method cannot be used. When we drop a tablespace, the controlfile will then no longer have any records of the tablespace which has been dropped. Attempts to use the RMAN RECOVER TABLESPACE would fail.
Rebuilding the database (12c) using RMAN backup
Last Modified: March 2017
This article demonstrates rebuilding the database using the rman backup into the same server. Let us imagine that accidentally someone removed all the datafiles in the ASM diskgroup including the controlfiles. And we have got a valid rman backup in the same server which we can use to restore. Also we have the recent archive logs (+FRA) generated after the last backup was taken.
UDEV SCSI Rules Configuration for ASM (Oracle Linux 7)
Last Modified: March 2017
In order for ASM to use disks, it needs to be able to identify the devices consistently and to have the correct ownership and permissions. In Linux we can use ASMLib, but is seen as an additional layer of complexity. Another alternative is Linux's native device manager 'udev' to perform these tasks. I will demonstrate it here in this article.
How to Add/Resize Datafiles in Logical Standby
Last Modified: March 2017
What if we have a Logical Standby Database and want to add/resize datafiles to the primary, while the Logical Standby DB uses an other directory structure than the Primary.
Refresh Physical Standby Using Incremental Backup
Last Modified: March 2017
Synchronizing the standby and primary databases can be done by copying and applying the archived logs from the primary database but this process is quite time consuming as it will first apply both the COMMITED and the NON COMMITED transactions followed by rolling back uncommitted transactions. Employing incremental backups of the primary database containing changes since the standby database was last refreshed is a faster alternative.
Refresh the Physical Standby - 12c (using RECOVER…FROM SERVICE)
Last Modified: March 2017
In 12c, refreshing the physical standby has been dramatically simplified. Now you can use the RECOVER … FROM SERVICE command to synchronize the physical standby database with the primary database.
Using a Physical Standby Database for Read/Write Testing
Last Modified: March 2017
Consider a scenario your application/QA team wants to test the DR application using the most recent production data. Let us assume your standby database is already running in the DR site and is constantly in sync with the primary database.
Steps to SHUTDOWN/START Standby Database for Maintenance Work
Last Modified: March 2017
There may be situations when you (DBAs) will be required to shutdown and startup the physical standby database in the remote site for various reasons. Mostly for maintenance activity.
Grid Infrastructure and Database 12c Installation (2 Node RAC) on Oracle Linux 7.3
Last Modified: January 2017
This article describes the installation of Oracle Grid Infrastructure and Cluster Database 12c Release 1 (2 nodes) on Oracle Linux 7.3 using VirtualBox.
Manual failover in 12c using DGMGRL Utility
Last Modified: December 2016
Role change of primary and standby databases using DGMGRL utility.
Dataguard Switchover in 12c using DGMGRL Utility
Last Modified: December 2016
Role change of primary and standby databases using DGMGRL utility.
Data Guard Broker - 12c
Last Modified: December 2016
The DG broker logically groups the primary and standby databases into a broker configuration that allows the broker to manage and monitor them together as an integrated unit. We can manage a broker configuration using either Oracle Enterprise Manager Cloud Control (Cloud Control) or the Oracle Data Guard command-line interface. But I will, throughout this article, be using the command-line interface.
Creating a Physical Standby Database using RMAN (ACTIVE DUPLICATE) (12c)
Last Modified: December 2016
From Oracle Database 11g onwards building a standby database has become a whole lot easier. With just one powerful RMAN command, the standby database can be created on another server without any backups.
Creating a Logical Standby (12c)
Last Modified: December 2016
We can easily convert a physical standby to a logical standby. The standby database will need to get the data dictionary from somewhere. The dictionary information should be put into the redo stream that comes from the primary. So, on the primary database, issue the following to build the LogMiner tables for dictionary.
Data Guard Protection Modes (Redo Transport Rules)
Last Modified: December 2016
A Data Guard configuration always runs in one of three data protection modes (also called as redo transport rules). a) Maximum Protection, b) Maximum Availability and c) Maximum Performance
CRS-4700: CTSS is in Observer mode
Last Modified: December 2016
This is very important to keep the time of cluster nodes synchronized across the cluster. Time difference among nodes can cause issues, and sometime it can cause the node(s) restart. If you plan to use ctss (Cluster Time Synchronized Service), you would need to disable OS level NTP on all RAC nodes and then restart all nodes, or alternatively restart cluster services to have ctss start working for RAC nodes time synchronization.
RAC Services
Last Modified: December 2016
The srvctl utility, dbca utility and DBMS_SERVICES package can all be used to create and modify services, but for this article we will restrict ourselves to looking at the srvctl utility. Let’s assume we have two applications that should run in the following way.
Why Standby Redo Logs (SRL)?
Last Modified: October 2016
If you configure your standby for Maximum Protection, then Standby Redo Logs (SRLs) are required. Most implementations are configured for Maximum Performance because they do not want the performance hit Max Protection may impart on their application. Even if you are using Max Performance, you still want to implement SRLs.
RMAN Restore/Recovery (RAC -> Single Instance)
Last Modified: September 2016
This article demonstrates the step by step procedure of restoring and recovering a RAC database to a different server (single instance).
DNS configuration for SCAN resolution
Last Modified: September 2016
This article provides the basic DNS configuration steps necessary to use the Single Client Access Name (SCAN) introduced in Oracle 11g Release 2 RAC.
Renaming or relocating Oracle Home
Last Modified: July 2016
Recently I encountered a space issue with the Oracle Home which was located under the root partition. Since this was a virtual box, I could easily add another disk and mount it. Then I had relocate the Oracle Home to the new added disk.
Installation of Oracle Restart 12c
Last Modified: June 2016
Step by step installation guide of Oracle Restart 12c (Oracle Grid Infrastructure for Standalone server).
Convert Single Instance to RAC - Using RMAN backup
Last Modified: May 2016
I will try to convert single instance stand alone database to RAC (3 nodes). My 3 nodes cluster is already installed and configured. I am demonstrating this in Grid Infrastructure 12c (12.1.0.2) version. There are several ways we can achieve this. But here I will try the traditional RMAN restore method.
Convert Single Instance to RAC - Using DBCA
Last Modified: May 2016
In this article, I will attempt to convert single instance stand alone database to RAC (3 nodes) using DBCA. My 3 nodes cluster is already installed and configured. I am demonstrating this in Grid Infrastructure 12c (12.1.0.2) version. The single instance database datafiles are currently on the normal filesystem and durin the RAC migration will be converted to ASM.
Oracle Cluster Registry (OCR)
Last Modified: April 2016
Physical standby database is an identical, block-for-block copy of the primary database and is kept in sync with the primary using media recovery. As redo gets generated on the primary database, it gets transferred to the standby database where an RFS process receives the primary redo and applies the change vectors directly to the standby database. A physical standby database is an excellent choice for disaster recovery..
Oracle Local Registry (OLR)
Last Modified: April 2016
In Oracle Clusterware 11g Release 2 and later an additional component related to the OCR called the Oracle Local Registry (OLR) is installed on each node in the cluster. The OLR is a local registry for node specific resources. The OLR is not shared by other nodes in the cluster. It is installed and configured when Oracle Clusterware is installed.
Relocating OCR or VOTEDISK to another ASM disks
Last Modified: April 2016
You ever needed to migrate the OCR (Cluster Registry files) and Voting Disks from one asm diskgroup to another? Let's take a look of the step-by-step instructions on how to move these files to a different diskgroup.
How to recover OCR from loss and recreate Votedisk?
Last Modified: April 2016
What if we lost the diskgroup +OCRDG where our OCR, Voting Disk, ASM spfile, mgmtDB and its spfile exist due to the underlying ASM disk failure.
Data Guard - Physical Standby 12c
Last Modified: March 2016
A physical standby database is an identical, block-for-block copy of the primary database and is kept in sync with the primary using media recovery. As redo gets generated on the primary database, it gets transferred to the standby database where an RFS process receives the primary redo and applies the change vectors directly to the standby database. A physical standby database is an excellent choice for disaster recovery.
Changing AWR Snapshot Retention and Interval
Last Modified: February 2016
By default AWR snapshot interval is set to 60 minutes and retention of snapshots is set to 8 days. For better and precise investigation of problems, it is recommended to use an interval of 15 minutes and retention of 31 days.
Enabling DDL logging (12c)
Last Modified: February 2016
DDL logging is enabled by setting init parameter enable_ddl_logging, which is same in previous Oracle releases.
Dataguard - Creating Standby Database using Active Database Duplication
Last Modified: September 2015
Physical standby database is an identical, block-for-block copy of the primary database and is kept in sync with the primary using media recovery. As redo gets generated on the primary database, it gets transferred to the standby database where an RFS process receives the primary redo and applies the change vectors directly to the standby database. A physical standby database is an excellent choice for disaster recovery..
Oracle Database Server 11g R2 Installation
Last Modified: August 2015
This articles demonstrates the step-by-step installation procedure of Oracle 11g Release 2 on Oracle Enterprise Linux 6.6 (x64) operating system.
How to find Oracle DBID
Last Modified: August 2015
DBID stands for database identifier, which is a unique identifier for each oracle database running. It is found in control files as well as datafile header. If the database is open you can directly querying with the v$database and find the DBID. You can find it without access to the datafiles too.
Installation of Oracle Restart 12c (Windows)
Last Modified: June 2015
Step by step installation guide of Oracle Restart 12c (Oracle Grid Infrastructure for Standalone server) on Windows Server 2012 R2.
Cleanup Grid Infrastructure after installation failure
Last Modified: April 2015
Let's assume due to some unkown reasons, the Grid Infrastructure installation got stuck in the middle, especially when running the root.sh script. Failures can be due to tons of reasons. Once our investigation to conclude the failure is confirmed, we decide to repeat the installation after properly cleaning up everything. In this article, let us try to clean up everything as if a brand new environment for a fresh installation is made available again.
Why Automatic Storage Management (ASM)?
Last Modified: February 2015
Compared to standard volume managers and filesystems (either clustered or single system), ASM has a number of advantages. I can hardly think of any disadvatanges, maybe a couple.
Installing and Configuring Oracle ASMLib
Last Modified: February 2015
Installing and configuring the Oracle Automatic Storage Management library driver software manually
Resolving Gaps in Data Guard Redo-Apply
Last Modified: August 2014
We know that the standby database is expected to be lagging behind the primary database (assuming this is an asynchronous non-real time apply). But what if the gap is significantly wide in terms of hours or days
Grid Infrastructure and Database 11g R2 Installation (2 Node RAC) on RHEL 5.4
Last Modified: April 2014
In this article, I would demonstrate how to build a 11g R2 Real Application Cluster with 2 nodes on Red Hat 5.4 using VirtualBox.
Table Partitioning
Last Modified: December 2013
Divide and conquer is what Oracle was thinking with this one. Table partitioning is about optimizing “medium selectivity queries”. The Oracle database has optimization techniques for high selectivity queries, with the use of indexes. If we need to process all data in a big table, we have to live with the fact it will take a while, but the engine will process the data as fast as possible. However, a medium selectivity query needs just a portion of the data, for instance a tenth. This is to much data for indexes, to little data for full table scans so the processing time might become rather long regarding the outcome.
DBNAME vs DB_UNIQUE_NAME
Last Modified: July 2013
The DB_UNIQUE_NAME parameter defaults to the value of the DB_NAME parameter. This is useful when you are creating a new database; fewer parameters to specify; but is not so efficient if that database will become part of a standby configuration.
Moving datafile between diskgroups in ASM
Last Modified: June 2013
How to move datafile from one diskgroup to another in few simple steps.
Materialized View (Snapshot)
Last Modified: March 2013
Unlike an ordinary view which is only a stored select statement that runs whenever we use the view, a Materialized View (also known as snapshots) stores the resultset of the select statement in a typical table object in the local or remote database. Which means, materialized view will always hold the data in a table segment as would any other segment.Because Oracle treats materialized view internally as a table segment and is created in the same name as materialized view name. We can query USER_TABLES to list this objects which we will see in a moment after creating a simple materialized view.

The materialized view can be a select statement based on tables, views or even another materialized view.
Deadlocks Explained
Last Modified: March 2013
The most common cause of deadlocks is the normal row-level locking, which is relatively easy to find. But that's not the only reason. ITL shortage, Bitmap index locking, lack of FK index, Direct Path load, PK overlaps are some of the potential causes.
Data Guard - Snapshot Standby (11g)
Last Modified: March 2013
Physical standby database can be temporarily converted into an updateable one called Snapshot Standby Database. In that mode, we can run our appplication — which may modify a lot of tables — and gauge its impact. Once the impact is assessed, we can easily convert the database back into a standby undergoing the normal recovery. This is accomplished by creating a restore point in the database, using the Flashback database feature to flashback to that point and undo all the changes.

Prior to 11g, we could open a Physical Standby in Read Write mode (something similar as explained here) for testing purpose, for example and flashback afterwards.

The difference is, in 11g Snapshot Standby together with the possibility of putting Physical Standby in Read Write mode, it can continue to receive Redo from the Primary. In 10g, that was just not possible. In 11g, while in Snapshot Standby mode, Redo gets written into Standby Logs and archived as usual. Only the Redo Apply is stopped.
Recovery Scenarios
Last Modified: November 2012
This article is the first in a series to introduce various database recovery techniques using user managed hot backups and RMAN hot backups.
Running tuning Advisor from SQL Plus
Last Modified: November 2012
In your environment if you are using Oracle Enterprise Manager (OEM), then running the tuning Advisor is pretty straightforward. If you do not have the OEM installed in your setup, nothing to worry. We could still run the SQL Tuning Advisor in few steps from the SQL Plus itself.
Top Wait Events (ranked by Top Wait Time)
Last Modified: September 2012
Oracle continues to add new wait events as they add new functionality to the Oracle kernel. In this article, we will take a look at the Top Wait Events ranked by Total Wait Time which represent over 90% of all wait events in production databases in multiple industries.
Data Guard - Physical Standby Maintenance
Last Modified: August 2012
A physical standby database is an identical, block-for-block copy of the primary database and is kept in sync with the primary using media recovery. As redo gets generated on the primary database, it gets transferred to the standby database where an RFS process receives the primary redo and applies the change vectors directly to the standby database. A physical standby database is an excellent choice for disaster recovery.

This section covers Starting up and shutting down a physical standby and role transitions including Switchover and Failover.
Data Guard - Physical Standby (11g)
Last Modified: August 2012
A physical standby database is an identical, block-for-block copy of the primary database and is kept in sync with the primary using media recovery. As redo gets generated on the primary database, it gets transferred to the standby database where an RFS process receives the primary redo and applies the change vectors directly to the standby database. A physical standby database is an excellent choice for disaster recovery.
Voting Disks
Last Modified: July 2012
Voting disks are important component of Oracle Clusterware. Clusterware uses voting disk to determine which nodes are members of the cluster. After ASM is introduced to store these files, these are called as VOTING FILES. Primary function of voting disks is to manage node membership and prevent SPLITBRAIN Syndrome in which 2 or more instances attempt to control the RAC database.
Backup / Restore of Optimizer Statistics
Last Modified: April 2012
We gather statistics to ensure that the optimizer chooses the optimal execution plans, but gathering statistics invalidates the parsed representation of the SQL statement and reparsing the statement post gather stats can make the optimizer choose an execution plan which is different (and less optimised) than the original plan
How index can be efficient even in relatively smaller tables?
Last Modified: November 2012
How index can be efficient even in a relatively smaller table having a handful rows that can fit in one data block as against a FULL TABLE SCAN which requires just one consistent get operation to read data from the table via a full table scan. Well, not necessarily.
Performing RMAN Tablespace Point-in-Time Recovery(TSPITR)
Last Modified: December 2011
A table called BEST_USER.CO_PROVIDER was truncated mistakenly by a user at around 10:40 on 13/12/2011. After little analyzing, we decided to perform a Tablespace Point-In-Time Recovery. The below steps were performed to restore the tablespace (TS_BEST_D & TS_BEST_X) until the timestamp 09:30 AM (until archivelog 636).
How to resize redo logfile in Oracle?
Last Modified: August 2011
If your database is having a smaller redo logfile, then your instance may experience frequent log switches - conversely when having larger redo logfile, you run the risk of losing the data in the event an instance crash. Ideally, there shouldn't be more than five switches in an hour. But it all depends.
Managing Tablespaces and Datafiles
Last Modified: August 2011
This article explains how to manage the Talespaces and Datafiles.
DBNEWID Utility
Last Modified: July 2011
DBNEWID is a database utility that can change the internal database identifier (DBID) and the database name (DBNAME) for an operational database. Changing the DBID of a database is a serious procedure.
Hot backup using RMAN
Last Modified: July 2011
This guide will prepare you to run a simple RMAN shell script to perform a hot backup of the full database. In addition, you will learn few useful commands on how to list the RMAN binary backup files and on how to crosscheck if the backed up files are physically present on disk.
Performing disaster recovery using RMAN backup
Last Modified: March 2011
This article will demonstrate to rebuild a database using the rman backup into another server in a disaster recovery. Let us imagine that we have completely lost our server which was running the instance for some reason. And we have got a valid rman backup in a remote/safe location and a spare server which is already installed with the Oracle server software (10g).
How to duplicate database using RMAN DUPLICATE?
Last Modified: January 2011
DBNEWID is a database utility that can change the internal database identifier (DBID) and the database name (DBNAME) for an operational database. Changing the DBID of a database is a serious procedure.
Creating Oracle 11g Database manually in 5 easy steps
Last Modified: November 2010
Creating 11g database in 5 easy steps with bare minimum parameters and simple directory structure. In my opinion, it should take no more than 15 min.
Oracle Database Server 11g R2 Installation (RHEL 5.4 x86_64)
Last Modified: September 2010
This articles describes the step-by-step installation procedure of Oracle 11g Database Server Release 2 (10.2.0.4) on RHEL 5.4 (X86_64) operating system.
Oracle Database Server 11g R2 (CentOS 6.0 x86_64)
Last Modified: September 2010
This articles describes the step-by-step installation procedure of Oracle 11g Database Server Release 2 (10.2.0.4) on CentOS 6.0 x64 operating system.
Oracle Database Server 10g R2 Installation (RHEL 5.4 x86_64)
Last Modified: September 2010
This articles describes the step-by-step installation procedure of Oracle 10g Database Server Release 2 (10.2.0.4) on RHEL 5.4 (X86_64) operating system.
How to flush listener log (without stopping listener service)?
Last Modified: February 2010
Listener log file ($OH/network/log/listener.log) audits trail information which enables us to analyze network statistics, client connection requests, service registratione events and other useful information during troubleshooting of network related problems. The file is usually small and easy to diagnose. But in cases of very active databases (e.g. very active OLTP databases), it can grow very fast to several GBs.

Recently, I happened to notice the listener log of one of the production databases where I work stopped growing. Its size exceeded 4GB and stopped from further increasing. After some googling, I assumed, is less likely that Oracle set any upper limit for the listener log size. Largely it depends the limits enforced by the OS that hosts the database. In this case, the OS didn't allow the text file to grow beyond 4GB.

In such situations, it's not wise to empty out the active log whilst the listener service is up and running, which may render the log unusable. I followed these steps to resolve the problem. It needs a simple technique to rotate active log before it can either be safely backed up (if required) or emptied out.
Undo vs Redo
Last Modified: January 2010
Have you ever wondered how Oracle handles Undo and Redo information in the event of failures. We know that Undo data is stored in undo tablespaces or undo segments. But the point here is, the undo information is also protected by Redo. In other words, Oracle treats undo data just like a normal table segment data or index segment data. Which means, changes to undo information also causes redo generation.
Heterogeous Connection
Last Modified: November 2008
This document will guide you to establish a database link from Oracle Database server to SQL Server so as to fetch data from SQL Server into Oracle Database server.
Managing Control File
Last Modified: November 2008
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

It is strongly recommended that you multiplex control files i.e. Have at least two control files one in one hard disk and another one located in another disk, in a database. In this way if control file becomes corrupt in one disk the another copy will be available and you don’t have to do recovery of control file.

You can multiplex control file at the time of creating a database and later on also. If you have not multiplexed control file at the time of creating a database you can do it now by following given procedure.
Managing Redo
Last Modified: November 2008
Every Oracle database must have at least 2 redo logfile groups. Oracle writes all statements except, SELECT statement, to the logfiles. This is done because Oracle performs deferred batch writes i.e. it does write changes to disk per statement instead it performs write in batches. So in this case if a user updates a row, Oracle will change the row in db_buffer_cache and records the statement in the logfile and give the message to the user that row is updated. Actually the row is not yet written back to the datafile but still it give the message to the user that row is updated. After 3 seconds the row is actually written to the datafile. This is known as deferred batch writes.

Since Oracle defers writing to the datafile there is chance of power failure or system crash before the row is written to the disk. That’s why Oracle writes the statement in redo logfile so that in case of power failure or system crash oracle can re-execute the statements next time when you open the database.
Undo Tablespace Management
Last Modified: November 2008
Every Oracle Database must have a method of maintaining information that is used to roll back, or undo, changes to the database. Such information consists of records of the actions of transactions, primarily before they are committed. These records are collectively referred to as undo.

Undo records are used to:
  • Roll back transactions when a ROLLBACK statement is issued

  • Recover the database

  • Provide read consistency

  • Analyze data as of an earlier point in time by using Flashback Query

  • Recover from logical corruptions using Flashback features

Earlier releases of Oracle Database used rollback segments to store undo. Oracle9i introduced automatic undo management, which simplifies undo space management by eliminating the complexities associated with rollback segment management. Oracle strongly recommends that you use undo tablespace to manage undo rather than rollback segments.
Oracle Database Server Architecture (Concise)
Last Modified: November 2008
Oracle Database is widely regarded as the industry standard RDBMS (Relational Database Management System) and is available on many platforms including Windows, Unix. This concise article briefs the Instance and Database and its various components.