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Category: Tuning Basics

Performance Tuning Basics 6 : Trace and TKPROF – Part 2: Generating TKPROF

TKPROF output can be generated from a raw SQL Trace. It formats and summarizes the diagnostic information from the raw SQL Trace.TKPROF allows you to analyse a trace file in easy way to determine where time is being spent and what query plans are being used on SQL statements.

This post is part 2 of the below posts on trace and tkprof. Please refer other posts to read related information.

Part 1: Trace and the methods to generate trace
Part 2: Generating TKPROF from trace file
Part 3: Analyzing TKPROF files
Part 4: Using Trace Analyzer (TRCANLZR) Tool

This post will cover Part 2: Generating a tkprof file from trace file.


WHAT DOES A TKPROF FILE CONTAINS:

  • SQL Text that were executed
  • Timing information: The execution count, elapsed time, CPU time, physical reads (disk), logical reads (query/current) and the number of rows returned for each SQL. This is further broken down into Parse, Execute and Fetch stages.
  • Wait information: The times waited, maximum wait and total waited for each database wait event, both for each SQL and for the whole period of the trace. It only does this if the level is 8 (with waits) or 12 (with waits and binds). At least level 8 is recommend because it gives this extra information.
  • Execution Plan: The runtime execution plan for each SQL with the actual row source operation counts for each execution plan line. It only does this if the cursor has been closed for the SQL (in 10g and before) or the row source statistics for the SQL have been written to the trace. The execution plan will also contain the actual tables accessed if the SQL uses views or synonyms.

It also contains information like Library cache misses (hard parse) and total SQL and wait statistics for Recursive and Non-recursive SQL Statements

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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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