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Category: Tuning Basics

Performance Tuning Basics 5 : Trace and TKPROF – Part 1: Trace

Tracing a SQL statement, generating TKPROF of the trace and understanding it carefully are some key steps that you will have to do when faced with a tough to break performance issue. This post will describe the methodology of this process.

Tkprof is very useful for diagnosing performance issues. It essentially formats a trace file into a more readable format for performance analysis. The DBA can then identify and resolve performance issues such as poor SQL, indexing, and wait events.

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Performance Tuning Basics 4 : Bind Variables

Bind variables are often known as one of the key feature for better SQL query performance. Bind variables as per Oracle documentation is a placeholder in a SQL statement that must be replaced with a valid value or value address for the statement to execute successfully. By using bind variables, you can write a SQL statement that accepts inputs or parameters at run time.

You can think of SQL query as a kind of “function” in any programming language and bind variables as “values” that you pass to the function.

Example:

Select * from EMP where EMP_ID=1;
Select * from EMP where EMP_ID=:a;

First statement uses a literal value (1) to run the query while the second SQL statement uses bind variable (:a) to run the SQL statement. The value of (:a) will be provide to Oracle at run time.

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Performance Tuning Basics 3 : Parent and Child Cursors

A “cursor” is a memory area in the library cache that is allocated to the SQL statement which users execute. This memory area stores key information about the SQL statement like SQL text, SQL execution plan, statistics etc.

Each SQL statement has one Parent cursor and one or more child cursors.Let us understand what a parent and child cursors are.
Please keep in mind Cursor = Memory Area

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Performance Tuning Basics 2 : Parsing

From performance tuning perspectives, it is very important to understand the concept of parsing. Parsing is primary phase in the SQL execution. It is followed by other stages: Execute and Fetch.

PARSING BASICS:

Whenever a SQL statement is executed, Oracle Engine performs below actions on it:

  1. Validate the Syntax
  2. Validate the objects being referenced in the statement
  3. Privileges assigned to user executing the Job
  4. Verifying if statement is already available in the shared pool. Oracle engine will calculate the hash value for the SQL statement and look in
  5. If statement is not already present then allocate shared memory and create a cursor in shared pool
  6. Generate the Execution Plan

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Key Reasons for Database Performance Issues

Some of the key reasons which attributes to database performance issues are mentioned below:

Below post is based on Oracle Documentation

1.Bad connection management

The application connects and disconnects for each database interaction. This problem is common with stateless middleware in application servers. It has over two orders of magnitude impact on performance, and is totally unscalable.

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