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Tracing Parallel Execution

Mark Rittman's picture

If you're looking to tune an SQL statement or a batch job, a common way to find out what happened during the execution of the SQL is to run an extended SQL trace and examine the wait events. But what happens if you are using parallel execution, and all your trace file contains is the parallel execution wait events that are generally considered idle events? Your trace file shows how long your query took to run, and the work involved in controlling the PQ slaves, but the real details of what took up all the execution time are actually to be found in the corresponding PQ slave trace files in the BDUMP directory.

UNDO behavior in Oracle 9i and 10g under microscope

Shouvik Basu's picture

This article is the result of observations of the UNDO tablespace of Oracle 9i and Oracle 10g in various situations. We start with a simple query showing how to monitor the amount of undo generated in a session for a specific time. We investigate the creation, expansion, and resize of UNDO tablespace, and the issues that guide the reuse of UNDO segments. The impact of parameters like UNDO_RETENTION in Oracle 9i and UNDO_RETENTION and the GUARANTEE clause in CREATE UNDO statements is discussed using simple reproducible examples.

Tapping into Oracle's Metadata - Part 2

James Koopmann's picture

In this article James continues to explore the Oracle's Metadata API and provides a powerful function to compare objects and schemas and print the DDL required to bring them in sync.

Connecting Oracle with MS-Access

This article shows how Oracle's Heterogeneous Services can be configured to allow a database to connect to a Microsoft Access database using standard databases links. The method described can be used to connect to MS-Access from about any platform - Unix/ Linux or Windows.

Tapping into Oracle's Metadata - Part I

James Koopmann's picture

In this article James explores the Oracle's Metadata API (DBMS_METADATA) and shows how database users can extract object definitions (DDL statements) from an Oracle database without having to go through a stack of dictionary views.

Protect Your Passwords

Jared Still's picture

Jared explains how Oracle manages passwords and how "thinking like a hacker" can help you to better protect your databases from potential password theft.

Enhanced Aggregation, Cube, Grouping and Rollup

Shouvik Basu's picture

(OLAP reporting embedded in SQL)

Much of the OLAP reporting feature embedded in Oracle SQL is ignored. People turn to expensive OLAP reporting tools in the market - even for simple reporting needs. This article outlines some of the common OLAP reporting needs and shows how to meet them by using the enhanced aggregation features of Oracle SQL.

The article is divided in two sections. The first introduces the GROUP BY extensions of SQL, and the second uses them to generate some typical reports. A section at the end introduces the common OLAP terminologies.

AWR and SQL Tuning

Donald K. Burleson's picture

The AWR tables contain super-useful information about the time-series execution plans for SQL statements and this repository can be used to display details about the frequency of usage for table and indexes. This article will expore these AWR tables and expose their secrets.

Can you have too much cache?

Donald K. Burleson's picture

There is a great debate about the rapidly-falling costs of RAM and the performance benefits of full caching of Oracle databases. Let's take a closer look at the issues over large RAM data buffers, tuning by adjusting system parameters and using fast hardware to correct sub-optimal Oracle code:

Analytic functions by Example

Shouvik Basu's picture

This article provides a clear, thorough concept of analytic functions and its various options by a series of simple yet concept building examples. The article is intended for SQL coders, who for might be not be using analytic functions due to unfamiliarity with its cryptic syntax or uncertainty about its logic of operation. Often I see that people tend to reinvent the feature provided by analytic functions by native join and sub-query SQL. This article assumes familiarity with basic Oracle SQL, sub-query, join and group function from the reader. Based on that familiarity, it builds the concept of analytic functions through a series of examples.