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Oracle RDBMS Server Articles

Table Fragmentation

Mohammad taj's picture

When rows are not stored contiguously, or if rows are split onto more than one block, performance decreases because these rows require additional block accesses.

Note that table fragmentation is different from file fragmentation. When a lot of DML operations are applied on a table, the table will become fragmented because DML does not release free space from the table below the HWM.

Tuning a 'LIKE-clause' by using Oracle Text or Reverse Key Indexes

The LIKE-clause can ignore indexes, causing queries to run forever while doing full table scans. This document describes how to tune such SQL statements by making use of Oracle Text or reverse key indexes.

Materialized View Fast Refreshes are Slow

vjain's picture

A materialized view that is verified to be fast refresh should update relatively fast. But, what happens when there are few changes to the master table, no network issues, no aggregation in the snapshot query and the refresh still runs slow?

Sizing your undo tablespace

sethunathu's picture

It is always a puzzle for a DBA to look into the user's complaint of getting "ORA-01555 Snapshot too old : rollback segment number x with name "_SYSSMUx$" too small " error. You have looked into the database. If your UNDO_MANAGEMENT is set to AUTO, you can not do anything to size the rollback segments manually since it is being managed by oracle. All the associated tables and indexes have been analyzed and statistics are up to date. The undo tabelspace is almost full. You may advise the user that there should be frequent commits (if it is a data loading process) or if there is a long running query and other users change the data that is being selected by the query, this can happen and in that case, if possible, advise the user not to run these two at the same time.

Installing the April 2007 Critical Patch Update on Windows

Mohammad taj's picture

This article describes the procedure to install the April 2007 CPU patch on Oracle Database Release 10.1.0.5. The Patch Number is p5907304_10105_WINNT.zip

Upgrade the Oracle database from 10.1.0.2.0 to 10.1.0.5.0

Mohammad taj's picture

This article describes the process of upgrading the Oracle Database Server 10g Release 10.1.0.2 to Oracle Database 10g Release 10.1.0.5 on Windows XP SP2.

Simulating ASM with 10g Database by faking the hardware

Pankaj Chandiramani's picture

Caution: This method is for Testing & Learning purposes only.

Most of the Oracle 10g databases are using ASM for storage as it's very simple to maintain the storage w.r.t. to Disks, Datafiles etc.

Flashback Database: A Primer

saibal's picture

Introduction

Oracle 10g’s brilliant alternative to database point in time recovery is the the Flashback Database feature. With this feature in place you can do almost everything that you can with point in time recovery, without actually having to go through all the disruptions and hassle that a PITR necessarily entails.I recently had a first hand opportunity to see the power of this feature, when I ran a scriptfile to drop tables and unwittingly dropped one of the tables containing sensitive information belonging to my employer Creative Infotech. I later recovered the table and was amazed at seeing how easy it had become to get back dropped objects in Oracle 10g, especially Release 2. Below is a simplified version of what I did

Failover and Load balancing in Oracle

saibal's picture

Advanced features of Oracle Net include failover and load balancing. These features are actually interrelated in as much as you usually don’t have one without the other. While they are mostly used in a RAC environment, they can be set up in a single instance environment as well.

FAILOVER:
In the context of Oracle Net, failover refers to the mechanism of switching over to an alternate resource when connection to the primary resource gets terminated due to any reason. Connection failure may be broadly categorized as:

How to kill RAC using the db_files parameter?

Once upon a time Le Petit Chaperon Rouge (LPCR) decided to change db_files from 200 to 300 on a busy cluster of four nodes.

Soon after the change applications started to block each other, timeout and crash (enq: TX - contention, cursor: pin S wait on X, enq: HW - contention). Those applications which were actively inserting into LOB columns - suffered the most.

Many lock holders were waiting for "DFS lock handle". Thus LPCR learned that DFS stands for "Distributed File System".

As soon as she reversed the changes - everything went back to normal.

Moral: