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For ERP LN feature pack upgrade, what method of install are you using?
Installation Wizard into existing VRC
41%
Installation Wizard into new VRC
29%
Manual into existing VRC
6%
Manual into new VRC
24%
Total votes: 17

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Redo & Rollback: Checkpoint not complete misguided solutions
By patvdv at 23 Feb 2008 - 23:23

A common problem for people with very active systems who use filesystems to store their datafiles is the error, Thread cannot allocate new log, sequence ; Checkpoint not complete. The most commonly recommended remedies for this situation are either to use larger or more online redologs.

 

Unfortunately, if checkpoint not complete is a chronic problem, neither of these solutions will eliminate the problem. They may forestall, or even reduce the frequency of the error, but the problem will not be solved.


Redo & Rollback: Big batch jobs should use a dedicated rollback segment
By patvdv at 23 Feb 2008 - 23:15

A common habit among DBAs is to assign large batch jobs that make many changes, or have very large transactions, to a dedicated rollback segment, using the set transaction use rollback segment; command. Many databases have a rollback segment called rbs_large or something similar for this purpose.

 


Redo & Rollback: Snapshot too old can be avoided by using set transaction use rollback segment
By patvdv at 23 Feb 2008 - 23:12

It is often asserted that if you get the ubiquitous ORA-01555: Snapshot too old: Rollback segment with name too small, you are running out of rollback segment. This misconception is partially the fault of the misleading error text. The rollback segment mentioned is not necessarily too small. This error is actually a failure to obtain read consistency.

 


Redo & Rollback: Shutdown abort is bad
By patvdv at 23 Feb 2008 - 23:04

The best way to shut down a database is to force a checkpoint and then use the

 

shutdown abort

 

command. In the few situations such as cold backups and version upgrades where consistent datafiles are required, the shutdown abort can be followed by a

 

startup restrict

 

and a

 

shutdown immediate


Backup & Recovery: Export is a good way to backup up the database
By patvdv at 23 Feb 2008 - 23:00

Many guides to backup and recovery give the Export and Import utilities billing equal to physical backup methods. As a method, Export and Import provide uniformly inferior reliability on backups, as well as recoveries. In addition to being failure prone, mean time to recovery with Import is much longer than comparative recoveries using physical backups. Export creates dump files that contain the DDL for all objects and the table data in the database.

 


Backup & Recovery: Cold backup once a week as a baseline
By patvdv at 23 Feb 2008 - 22:55

A number of books and manuals suggest a backup schedule for Oracle databases in archivelog mode something like, daily hot (online) backups and weekly cold backups. What is strange about this recommendation is that the weekly cold backups serve no apparent purpose, other than to needlessly remove the instance or instances from service for some period of time. Shutting the database down for a cold backup also has the side effect of requiring the buffer cache be reloaded all over again after startup, which degrades performance while all reads are initially physical for a period of time.


Backup & Recovery: Always switch logfile before/after online backups
By patvdv at 23 Feb 2008 - 22:53

In order to be sure that all changes generated during a hot backup are available for a recovery, Oracle recommends that the current online log be archived after the last tablespace in a hot backup is taken out of backup mode. A similar recommendation stands for after a recovery manager online database backup is taken. A wide variety of literature on backup and recovery, including the oracle documentation, suggests using the

 


Backup & Recovery: Media recovery will be required in the case of instance failure during backup mode
By patvdv at 23 Feb 2008 - 22:50

If an instance crashes or is aborted while one of the tablespaces is in backup mode, the tablespace(s) will appear to need media recovery upon startup. In normal instance failure situations, automatic crash recovery using the online redologs will be automatically performed, with no intervention required.

 


Backup & Recovery: Hot backup mode stops writing to the datafiles
By patvdv at 23 Feb 2008 - 22:25

During an Oracle tablespace hot backup, a script or program puts a tablespace into backup mode, then copies the datafiles to disk or tape, then takes the tablespace out of backup mode. Although these steps are widely understood, the idea that datafiles are not written during backup mode is probably the most alarming and widely held misconception about Oracle. So many people think this is true, that it is actually asserted as fact in the backup/recovery sections of a number of major published books on Oracle.


General Practices: Count (1) is better than count (*)
By patvdv at 23 Feb 2008 - 22:18

The idea that you get faster results by selecting count(1) or count('x') or some similar literal value rather than count(*) has been poplar ever since I began working with Oracle in 1994. The truth is that Oracle8's cost-based optimizer will do an index fast full scan on the first unique index on a not-null column (usually the primary key) if it is available. If no such index is available, a full table scan will be performed. This behavior is the same under the cost-based and rule-based optimizers no matter what you put in the parentheses of the count function.



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