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Understanding Explain Plan

Benjamin Disraeli, circa 1870 wrote:
Never complain and never explain.

Disraeli was a lot of things, but Oracle Programmer was not amongst them. To be fair, perhaps he wasn't talking about Explain Plan?

SQL is a goal-oriented language. Unlike procedural languages, we tell the database what we want rather than how to get it. Oracle's Cost Based Optimizer comes up with an execution plan that is hopefully the most efficient way to resolve the query, but for many reasons it will often choose a sub-optimal plan.

Getting information about previously run commands with statspack

cbruhn2's picture

Information


When you setup statspack with level 6 you can have information on the sql_plan associated with a sql. (statpack on oracle db version >=9i)

"Fixing" SYS for hacking purposes

How does one change Oracle's SYS password without having to login into the database? Is it possible?
The answer is, YES! All you need is a binary fiile editor and some knowledge of Oracle's internals.

This document is to be used only for testing purposes and should not be used in a production environment. The purpose is to show the audience how hackers can gain access to your system without knowing it - and how to prevent it.

Timing an ALL_ROWS query

The Problem

A common complaint in SQL is that "it runs in 5 seconds in SQL*Plus, but takes hours in Production. Why?"

The reason is because SQL*Plus and most GUI SQL tools display rows as soon as they are fetched. In this way, you can SELECT * FROM big_big_table and it will display the first 20 or so rows in the table in a fraction of a second, then go back for more. The SQL is not really finishing in seconds; if you timed how long it took to retrieve every row, you'd see that it takes just as long as in Production.

How to avoid primary key collision on multiple sites?

This article provides several comparative methods to avoid primary key conflicts across multiple sites.

Enabling plan_sql from statspack

cbruhn2's picture

Information


When you setup statspack with level 6 you can have information on the sql_plan associated with a sql.

Understanding Indexes

Of iPods and Indexes


I'm not really an "early-adopter" of technology. Don't get me wrong; I love it, I just don't want to feed the addiction. When I do get a new piece of technology though, it's like a fever; I can't concentrate on anything until I've read the manual from cover to cover and found out everything it can do, every built-in gizmo, and every trashy piece of after-market merchandise that can be plugged into it.

And I don't think I'm alone here.

PL/SQL Tuning for Batch Systems

A History Lesson

Where were you in 1990? Nelson Mandela was being freed from Victor Verster Prison after 26 years behind bars, Saddam Hussein was starting the Gulf War by invading Kuwait, and Tim Berners-Lee was inventing the World-Wide-Web at CERN in Geneva. Me? In 1990, I was writing an insurance system in Oracle SQL*Forms v2.3.

Impact of US Daylight saving changes on Oracle

Well, just for a briefing, since 1966, most of the United States has observed Daylight Saving Time from at 2:00 a.m. on the first Sunday of April to 2:00 a.m. on the last Sunday of October. But in 2007, most of the U.S. will begin Daylight Saving Time at 2:00 a.m. on the second Sunday in March and revert to standard time on the first Sunday in November.

So, Oracle has released patches to adapt these Daylight saving time changes. The databases that are using the following will be impacted…

1. Databases using TIMESTAMP WITH TIME ZONE and TIMESTAMP WITH LOCAL TIME ZONE data types and TZ_OFFSET function as they take their time zone information from Oracle's time zone files.

Oracle 10gR2 RAC on Windows Server x64 and Comparison with RHEL

Anu Chawla's picture

Recently Performance Tuning compared Oracle 10gR2 RAC on Windows Server 2003 x64 vs. RHEL. You can download the paper from microsoft-oracle.com

The following behavior was observed during testing of the Oracle RAC databases on Red
Hat Enterprise Linux x86_64 and Microsoft Windows Server 2003 Enter:
Oracle RAC Stress Test
o Transactions Per Minute were roughly equivalent for 2 - 150 user sessions.
o Transactions Per Minute were up to 16% higher for MS Windows for 150
- 250 users.
o CPU usage was above 90% for all of these tests for both Linux and MS
Windows Server.
o The response times for the “New Company Registration” test component