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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.
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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.
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Every Oracle Database has a control file, which is a small binary file that records the physical structure of the database.
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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.
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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.
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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.
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February 2010
Listener log file 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.
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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.
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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.
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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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).
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February 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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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June 2013
How to move datafile from one diskgroup to another in few simple steps.
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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.
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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.
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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.
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June 2015
Step by step installation guide of Oracle Restart 12c (Oracle Grid Infrastructure for Standalone server).
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Step by step installation guide of Oracle Restart 12c (Oracle Grid Infrastructure for Standalone server) on Windows Server 2012 R2.
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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.
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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..
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August 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..
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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.
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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.
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September 2016
This article demonstrates the step by step procedure of restoring and recovering a RAC database to a different server (single instance).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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).
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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'.
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May 2017
This article describes the installation of Oracle Enterprise Manager Cloud Control 12c Release 5 on Oracle Linux 6.6 (x86_64).
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This article describes the installation of Oracle Enterprise Manager Cloud Control 13c Release 2 on Oracle Linux 7.3 (x86_64).
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This article describes the installation of Oracle Database 12c Release 2 (12.2) 64-bit on Oracle Linux 7.2.
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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.
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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.
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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.
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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.
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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.
Read more ...
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