Go Back

User login

Frontpage Sponsor


How big is your Baan-DB (just Data AND Indexes)
0 - 200 GB
200 - 500 GB
500 - 800 GB
800 - 1200 GB
1200 - 1500 GB
1500 - 2000 GB
> 2000 GB
Total votes: 69

Baanboard at LinkedIn

Reference Content

Items for 'English' (by date)
By Date  
Alphabetically By Date  


You are browsing all items of this content category sorted by date (most recent first). Note that forum posts/threads are not included here.


If you would like to search through the content then please refer to the Site Search page.


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.

By patvdv at 23 Feb 2008 - 22:01

The halls of the companies and institutions using Oracle's database echo with the slightly raised voices of DBAs arguing over the finer points of Oracle administration. Disputes arise because there are two kinds of DBAs. Some DBAs base their methods on recommendations they read or heard somewhere, without completely understanding the reasons why. Other DBAs will do nothing without hard facts to support their methods. These latter DBAs believe that absent proof positive, even Oracle's own documentation is not to be entirely trusted.

Common DBA Misconceptions
By patvdv at 23 Feb 2008 - 22:00

Common DBA Misconceptions

by Jeremiah Wilton


These articles are from the Common Oracle Misconceptions series by Jeremiah Wilton at

Copyright (c) 2001 Jeremiah Wilton


All times are GMT +2. The time now is 12:51.

©2001-2018 - -