How Oracle Manages Diagnostic Traces and Statistics?
Oracle traces various types of diagnostic and statistical information useful to the users and support groups.

01. For the Database Oracle maintains Alert Log File with an ability to the user to set which events are to be traced and which are not to. To identify critical errors and tracing the errors the user is enabled to define destinations for depositing the trace files by Oracle. They are generally called dump destinations.

Background dump destination
User dump destination
Core dump destination

02. Network diagnostic trace files are generated at the default destinations under ORACLE_HOME/network/log

Setting additional events to track the errors and diagnose the reasons user has the ability to set events at session, system and database level. Depending upon the nature of the event and the level of trace some events can be set at the session level, some at system level and some at database level.

The Initialization Parameters that impact the Oracle trace generation

(1) ORACLE_TRACE_COLLECTION_SIZE

ORACLE_TRACE_COLLECTION_SIZE specifies (in bytes) the maximum size of the Oracle Trace collection file (.dat). Once the collection file reaches this maximum, the collection is disabled. A value of 0 means that the file has no size limit.

(2) ORACLE_TRACE_COLLECTION_PATH

ORACLE_TRACE_COLLECTION_PATH specifies the directory pathname where the Oracle Trace collection definition (.cdf) and data collection (.dat) files are located. If you accept the default, the Oracle Trace .cdf and .dat files will be located in ORACLE_HOME/otrace/admin/cdf on UNIX Platforms and ORACLE_HOMEotraceadmincdf ON Windows platforms

(3) TRACEFILE_IDENTIFIER

TRACEFILE_IDENTIFIER specifies a custom identifier that becomes part of the Oracle Trace file name. Such a custom identifier is used to identify a trace file simply from its name and without having to open it or view its contents.

Each time this parameter is dynamically modified, the next trace dump will be written to a trace file which has the new parameter value embedded in its name. Trace file continuity information is automatically added to both the old and new trace files to indicate that these trace files belong to the same process.

This parameter can only be used to change the name of the foreground process’ trace file; the background processes continue to have their trace files named in the regular format. For foreground processes, the TRACEID column of the V$PROCESS view contains the current value of the TRACEFILE_IDENTIFIER parameter. When this parameter value is set, the trace file name has the following format:

sid_ora_pid_traceid.trc

In this example, sid is the oracle instance ID, pid is the process ID, and traceid is the value of the TRACEFILE_IDENTIFIER parameter.

(4) TIMED_OS_STATISTICS

TIMED_OS_STATISTICS specifies the interval (in seconds) at which Oracle collects operating system statistics when a request is made from the client to the server or when a request completes.

On dedicated servers, Oracle collects operating system statistics at user logon and after each subsequent client invocation through the OCI into the Oracle server as a remote procedure call message.

On shared servers, Oracle collects statistics when client calls to Oracle are processed.

A value of zero specifies that operating system statistics are not gathered. To collect statistics, set a value meaningful for your application and site needs.

Gathering operating system statistics is very expensive. Oracle Corporation recommends that you set this parameter in an ALTER SYSTEM statement rather than in the initialization parameter file, and that you reset the value to zero as soon as the needed statistics have been gathered.

(5) TRACE_ENABLED

TRACE_ENABLED controls tracing of the execution history, or code path, of Oracle. Oracle Support Services uses this information for debugging.

When TRACE_ENABLED is set to true, Oracle records information in specific files when errors occur. See Oracle9i Real Application Clusters Deployment and Performance for the types of files and the default destination directories in which Oracle records the execution history.

Oracle records this information for all instances, even if only one instance terminates. This allows Oracle to retain diagnostics for the entire cluster.

Although the overhead incurred from this processing is not excessive, you can improve performance by setting TRACE_ENABLED to false. You might do this, for example, to meet high-end benchmark requirements. However, if you leave this parameter set to false, you may lose valuable diagnostic information. Therefore, always set TRACE_ENABLED to true to trace system problems and to reduce diagnostic efforts in the event of unexplained instance failures.

(6) CORE_DUMP_DEST

This parameter was made dynamic via ALTER SYSTEM in Oracle 8.1.

CORE_DUMP_DEST should point to the directory where core dumps from the Oracle server will be placed. The above “Related” parameters determine the size of the core dumps. A core dump is a memory image of the Oracle shadow process produced when an unexpected , unrecoverable or invalid condition occurs.

Note that Oracle should always try to write a trace file before producing a core dump. Always check and locations for tracefiles first.

In some cases this parameter may not have been read when a core file is produced. In this case the core dump is typically written to the default location ($ORACLE_HOME/dbs).

CORE_DUMP_DEST should have WRITE permission for the Oracle user.

(7) USER_DUMP_DEST

USER_DUMP_DEST specifies the pathname for a directory where the server will write debugging trace files on behalf of a user process.

(8) BACKGROUND_DUMP_DEST

BACKGROUND_DUMP_DEST specifies the pathname (directory or disc) where debugging trace files for the background processes (LGWR, DBWn, and so on) are written during Oracle operations.

An alert file in the directory specified by BACKGROUND_DUMP_DEST logs significant database events and messages. Anything that affects the database instance or global database is recorded here. The alert file is a normal text file. Its filename is operating system-dependent. For platforms that support multiple instances, it takes the form alert_sid.log, where sid is the system identifier. This file grows slowly, but without limit, so you might want to delete it periodically. You can delete the file even when the database is running.

(9) DB_BLOCK_CHECKSUM

DB_BLOCK_CHECKSUM determines whether DBWn and the direct loader will calculate a checksum (a number calculated from all the bytes stored in the block) and store it in the cache header of every data block when writing it to disk. Checksums are verified when a block is read only if this parameter is true and the last write of the block stored a checksum. In addition, Oracle gives every log block a checksum before writing it to the current log.

If this parameter is set to false, DBWn calculates checksums only for the SYSTEM tablespace, but not for user tablespaces.

Checksums allow Oracle to detect corruption caused by underlying disks, storage systems, or I/O systems. Turning on this feature typically causes only an additional 1% to 2% overhead. Therefore, Oracle Corporation recommends that you set DB_BLOCK_CHECKSUM to true

(10) DB_BLOCK_CHECKING

DB_BLOCK_CHECKING controls whether Oracle performs block checking for data blocks. When this parameter is set to true, Oracle performs block checking for all data blocks. When it is set to false, Oracle does not perform block checking for blocks in the user tablespaces. However, block checking for the SYSTEM tablespace is always turned on.

Oracle checks a block by going through the data on the block, making sure it is self-consistent. Block checking can often prevent memory and data corruption. Block checking typically causes 1% to 10% overhead, depending on workload. The more updates or inserts in a workload, the more expensive it is to turn on block checking. You should set DB_BLOCK_CHECKING to true if the performance overhead is acceptable.

(11) EVENT

EVENT is a parameter used only to debug the system. Do not alter the value of this parameter except under the supervision of Oracle Corporation Worldwide Support staff.

There are events that can be set at session level, system level and Database level.

To set at the database level set the event in the init.ora file
To set at system level which is not persistent use ‘alter system’ command
To set at a session level which is limited to that session use ‘alter session’.

(12) ORACLE_TRACE_COLLECTION_NAME

A collection is data collected for events that occurred while an instrumented product was running. ORACLE_TRACE_COLLECTION_NAME specifies the Oracle Trace collection name for this instance. Oracle also uses this parameter in the output file names (collection definition file .cdf and data collection file .dat). If you set ORACLE_TRACE_ENABLE to true, setting this value to a non-null string will start a default Oracle Trace collection that will run until this value is set to null again. Valid collection name up to 16 characters long (except for platforms that enforce 8-character file names)

(13) ORACLE_TRACE_FACILITY_PATH

ORACLE_TRACE_FACILITY_PATH specifies the directory pathname where Oracle Trace facility definition files are located. On Solaris, the default path is ORACLE_HOME/otrace/admin/fdf/. On Windows, the default path is ORACLE_HOMEotraceadminfdf

(14) ORACLE_TRACE_FACILITY_NAME

ORACLE_TRACE_FACILITY_NAME specifies the event set that Oracle Trace collects. The value of this parameter, followed by the .fdf extension, is the name of the Oracle Trace product definition file. That file must be located in the directory specified by the ORACLE_TRACE_FACILITY_PATH parameter. The product definition file contains definition information for all the events and data items that can be collected for products that use the Oracle Trace data collection API.

The Oracle server has multiple event sets and therefore multiple product definition files:

ORACLE is the ALL event set
ORACLED is the DEFAULT event set
ORACLEE is the EXPERT event set
ORACLESM is the SUMMARY event set
ORACLEC is the CACHEIO event set
Oracle Corporation recommends that you use the DEFAULT event set for Oracle server collections, ORACLED.

(15) ORACLE_TRACE_ENABLE

To enable Oracle Trace collections for the server, set ORACLE_TRACE_ENABLE to true. This setting alone does not start an Oracle Trace collection, but it allows Oracle Trace to be used for the server.

With ORACLE_TRACE_ENABLE set to true, you can perform Oracle Trace collection of server event data in any of the following ways:

By using Oracle Trace Manager, which is supplied with the Oracle Diagnostic Pack

By using the Oracle Trace command line interface, which is supplied with the server

By specifying a collection name in the ORACLE_TRACE_COLLECTION_NAME parameter

Tracing the execution paths for Performance Tuning

Explain Plan

Usage:

Explain plan for select * from emp;

Explain Plan is a great way to tune your queries.
As a bonus for using Explain Plan, you will learn more about how the DBMS works “behind the scenes”, enabling you to write efficient queries the first time around.

Explain Plan executes your query and records the “plan” that Oracle devises to execute your query. By examining this plan, you can find out if Oracle is picking the right indexes and joining your tables in the most efficient manner. There are a few different ways to utilize Explain Plan.

The first thing you will need to do is make sure you have a table called plan_table available in your schema.

If this table is not there run this script provided by oracle to create that table
ORACLE_HOME/rdbms/admin/utlxplan.sql .. for UNIX plat formas and
ORACLE_HOMErdbmsadminutlxplan.sql .. for WINDOWS platforms

When the plan table is populated then use this query to fetch the data formatted. So thatyou understand how oracle is planning data access paths

select *
from table(dbms_xplan.display);

Ex: on windows 2000 Oracle 10.1

SQL> @d:oracleora10rdbmsadminutlxplan.sql

Table created.

SQL> explain plan for select * from emp
2 ;

Explained.

SQL> select *
2 from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
————————————————————————————————-
Plan hash value: 4080710170

————————————————————————————————-
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
————————————————————————————————-
| 0 | SELECT STATEMENT | | 14 | 518 | 3 (0) | 00:00:01 |
| 1 | TABLE ACCESS FULL | EMP | 14 | 518 | 3 (0) | 00:00:01 |
————————————————————————————————–

8 rows selected.

Transient Kernel Profiling (TKProf)

From Oracle Docs

The SQL Trace Facility and TKPROF
The SQL trace facility and TKPROF are two basic performance diagnostic tools which can help you monitor and tune applications that run against the Oracle Server. This chapter covers:

Note: The output of the EXPLAIN PLAN command reflects the behavior of the Oracle optimizer. Because the optimizer is likely to evolve between releases of the Oracle Server, output from the EXPLAIN PLAN command will also evolve. Similarly, the SQL trace facility and TKPROF program are also subject to change in future releases of the Oracle Server. Such changes will be documented in future versions of Oracle manuals.

Introduction

The SQL trace facility and TKPROF enable you to accurately assess the efficiency of the SQL statements your application runs. For best results, use these tools together rather than using EXPLAIN PLAN alone. This section covers:

About the SQL Trace Facility
About TKPROF
How to Use the SQL Trace Facility and TKPROF
About the SQL Trace Facility
The SQL trace facility provides performance information on individual SQL statements. It generates the following statistics for each statement:

parse, execute, and fetch counts
CPU and elapsed times
physical reads and logical reads
number of rows processed
misses on the library cache
username under which each parse occurred
each commit and rollback
You can enable the SQL trace facility for a session or for an instance. When the SQL trace facility is enabled, performance statistics for all SQL statements executed in a user session or in an instance are placed into a trace file.

The additional overhead of running the SQL trace facility against an application with performance problems is normally insignificant, compared with the inherent overhead caused by the application’s inefficiency.

About TKPROF
You can run the TKPROF program to format the contents of the trace file and place the output into a readable output file. Optionally, TKPROF can also determine the execution plans of SQL statements create a SQL script that stores the statistics in the database

Since TKPROF reports each statement executed with the resources, which it has consumed, the number of times it was called, and the number of rows, which it processed, you can easily locate those statements, which are using the greatest resource. With experience or with baselines available, you can assess whether the resources used are reasonable given the work done.

How to Use the SQL Trace Facility and TKPROF

Follow these steps to use the SQL trace facility and TKPROF.

Set initialization parameters for trace file management.

Enable the SQL trace facility for the desired session and run your application. This step produces a trace file containing statistics for the SQL statements issued by the application.
Run TKPROF to translate the trace file created ins step 2 into a readable output file. This step can optionally create a SQL script that stores the statistics in the database.
Interpret the output file created in step 3.
Optionally, run the SQL script produced in step 3 to store the statistics in the database.
In the following sections each of these steps is discussed in depth.

Step 1:

Setting Initialization Parameters for Trace File Management

When the SQL trace facility is enabled for a session, Oracle generates a trace file containing statistics for traced SQL statements for that session. When the SQL trace facility is enabled for an instance, Oracle creates a separate trace file for each process.

Before enabling the SQL trace facility, you should:

Check settings of the TIMED_STATISTICS, USER_DUMP_DEST, and MAX_DUMP_FILE_SIZE parameters.

Parameter
TIMED_STATISTICS
Notes
This parameter enables and disables the collection of timed statistics, such as CPU and elapsed times, by the SQL trace facility, as well as the collection of certain statistics in the dynamic performance tables. The default value of FALSE disables timing. A value of TRUE enables timing. Enabling timing causes extra timing calls for low-level operations. This is a dynamic parameter.
Parameter
MAX_DUMP_FILE_SIZE
Notes
When the SQL trace facility is enabled at the instance level, every call to the server produces a text line in an operating system file. The maximum size of these files (in operating system blocks) is limited by the initialization parameter MAX_DUMP_FILE_SIZE. The default is 500. If you find that your trace output is truncated, increase the value of this parameter before generating another trace file.
Parameter
USER_DUMP_DEST

Notes
This parameter must fully specify the destination for the trace file according to the conventions of your operating system. The default value for this parameter is the default destination for system dumps on your operating system.This value can be modified with ALTER SYSTEM SET USER_DUMP_DEST=newdir.

Devise a way of recognizing the resulting trace file.

Be sure you know how to distinguish the trace files by name. Oracle writes them to the user dump destination specified by USER_DUMP_DEST. However, this directory may soon contain many hundreds of files, usually with generated names. It may be difficult to match trace files back to the session or process which created them. You can tag trace files by including in your programs a statement like SELECT `program name’ FROM DUAL. You can then trace each file back to the process that created it.

If your operating system retains multiple versions of files, be sure your version limit is high enough to accommodate the number of trace files you expect the SQL trace facility to generate.

The generated trace files may be owned by an operating system user other than yourself. This user must make the trace files available to you before you can use TKPROF to format them.

Step 2:

Enabling the SQL Trace Facility
You can enable the SQL trace facility for a session or for the instance. This section covers:

Enabling the SQL Trace Facility for Your Current Session
Enabling the SQL Trace Facility for a Different User Session
Enabling the SQL Trace Facility for an Instance
Attention: Because running the SQL trace facility increases system overhead, you should enable it only when tuning your SQL statements, and disable it when you are finished.

Enabling the SQL Trace Facility for Your Current Session
To enable the SQL trace facility for your current session, enter:

ALTER SESSION SET SQL_TRACE = TRUE;

Alternatively, you can enable the SQL trace facility for your session by using the DBMS_SESSION.SET_SQL_TRACE procedure.

To disable the SQL trace facility for your session, enter:

ALTER SESSION SET SQL_TRACE = FALSE;

The SQL trace facility is automatically disabled for your session when your application disconnects from Oracle.

Note:

You may need to modify your application to contain the ALTER SESSION command. For example, to issue the ALTER SESSION command in Oracle Forms, invoke Oracle Forms using the -s option, or invoke Oracle Forms (Design) using the statistics option. For more information on Oracle Forms, see the Oracle Forms Reference manual.

Enabling the SQL Trace Facility for a Different User Session
To enable the SQL trace facility for a session other than your current session, you can call the procedure DBMS_SYSTEM.SET_SQL_TRACE_IN_SESSION. This can be useful for database administrators who are not located near their users, or who do not have access to the application code to set SQL trace from within an application.

This procedure requires the session ID and serial number of the user session in question, which you can obtain from the V$SESSION view. In the WHERE clause you can specify sessions by referencing the value of the OSUSER, USERNAME, or PROGRAM column in V$SESSION. For example, the following Server Manager line mode session obtains the session ID and serial number for the operating system user jausten and then enables SQL trace for that user’s session:

SVRMGR> SELECT sid, serial#, osuser
2> FROM v$session
3> WHERE osuser = ‘jausten’;

SID SERIAL# OSUSER
———- ———- —————
8 12 jausten
1 row selected.

SVRMGR> EXECUTE dbms_system.set_sql_trace_in_session(8,12,TRUE);
Statement processed.

To enable SQL trace in stored procedures, use this SQL statement:

DBMS_SESSION.SET_SQL_TRACE (TRUE);

Enabling the SQL Trace Facility for an Instance
To enable the SQL trace facility for your instance, set the value of the SQL_TRACE initialization parameter to TRUE. Statistics will be collected for all sessions.

Once the SQL trace facility has been enabled for the instance, you can disable it for an individual session by entering:

ALTER SESSION SET SQL_TRACE = FALSE;

Step 3:

Formatting Trace Files with TKPROF
This section covers:

Sample TKPROF Output
Syntax of TKPROF
TKPROF Statement Examples
TKPROF accepts as input a trace file produced by the SQL trace facility and produces a formatted output file. TKPROF can also be used to generate execution plans.

Once the SQL trace facility has generated a number of trace files, you can:

run TKPROF on each individual trace file, producing a number of formatted output files, one for each session
concatenate the trace files and then run TKPROF on the result to produce a formatted output file for the entire instance
TKPROF does not report COMMITs and ROLLBACKs that are recorded in the trace file.

Sample TKPROF Output

Sample output from TKPROF is as follows:

SELECT * FROM emp, dept WHERE emp.deptno = dept.deptno;

call count cpu elapsed disk query current rows
—- ——- ——- ——— ——– ——– ——- ——
Parse 1 0.16 0.29 3 13 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.03 0.26 2 2 4 14

Misses in library cache during parse: 1
Parsing user id: (8) SCOTT

Rows Execution Plan
——- —————————————————
14 MERGE JOIN
4 SORT JOIN
4 TABLE ACCESS (FULL) OF ‘DEPT’
14 SORT JOIN
14 TABLE ACCESS (FULL) OF ‘EMP’

For this statement, TKPROF output includes the following information:

the text of the SQL statement
the SQL trace statistics in tabular form
the number of library cache misses for the parsing and execution of the statement
the user initially parsing the statement
the execution plan generated by EXPLAIN PLAN
TKPROF also provides a summary of user level statements and recursive SQL calls for the trace file.

Syntax of TKPROF
Invoke TKPROF using this syntax:

If you invoke TKPROF with no arguments, online help is displayed.

Use the following arguments with TKPROF:

TKPROF Arguments

Argument Meaning
filename1 Specifies the input file, a trace file containing statistics produced by the SQL trace facility. This file can be either a trace file produced for a single session or a file produced by concatenating individual trace files from multiple sessions.

filename2 Specifies the file to which TKPROF writes its formatted output.

AGGREGATE If you specify AGGREGATE = NO, then TKPROF does not aggregate multiple users of the same SQL text.

EXPLAIN Determines the execution plan for each SQL statement in the trace file and writes these execution plans to the output file. TKPROF determines execution plans by issuing the EXPLAIN PLAN command after connecting to Oracle with the user and password specified in this parameter. The specified user must have CREATE SESSION system privileges. TKPROF will take longer to process a large trace file if the EXPLAIN option is used.

TABLE Specifies the schema and name of the table into which TKPROF temporarily places execution plans before writing them to the output file. If the specified table already exists, TKPROF deletes all rows in the table, uses it for the EXPLAIN PLAN command (which writes more rows into the table), and then deletes those rows. If this table does not exist, TKPROF creates it, uses it, and then drops it.

The specified user must be able to issue INSERT, SELECT, and DELETE statements against the table. If the table does not already exist, the user must also be able to issue CREATE TABLE and DROP TABLE statements. For the privileges to issue these statements, see the Oracle8 Server SQL Reference.

This option allows multiple individuals to run TKPROF concurrently with the same user in the EXPLAIN value. These individuals can specify different TABLE values and avoid destructively interfering with each other’s processing on the temporary plan table.

If you use the EXPLAIN parameter without the TABLE parameter, TKPROF uses the table PROF$PLAN_TABLE in the schema of the user specified by the EXPLAIN parameter. If you use the TABLE parameter without the EXPLAIN parameter, TKPROF ignores the TABLE parameter.

INSERT Creates a SQL script that stores the trace file statistics in the database. TKPROF creates this script with the name filename3. This script creates a table and inserts a row of statistics for each traced SQL statement into the table.

SYS Enables and disables the listing of SQL statements issued by the user SYS, or recursive SQL statements into the output file. The default value of YES causes TKPROF to list these statements. The value of NO causes TKPROF to omit them. Note that this parameter does not affect the optional SQL script. The SQL script always inserts statistics for all traced SQL statements, including recursive SQL statements.

SORT Sorts the traced SQL statements in descending order of the specified sort option before listing them into the output file. If more than one option is specified, the output is sorted in descending order by the sum of the values specified in the sort options. If you omit this parameter, TKPROF lists statements into the output file in order of first use.

The sort options are as follows:

PRSCNT number of times parsed
PRSCPU CPU time spent parsing
PRSELA elapsed time spent parsing
PRSDSK number of physical reads from disk during parse
PRSMIS number of consistent mode block reads during parse
PRSCU number of current mode block reads during parse
PRSMIS number of library cache misses during parse
EXECNT number of executes
EXECPU CPU time spent executing
EXEELA elapsed time spent executing
EXEDSK number of physical reads from disk during execute
EXEQRY number of consistent mode block reads during execute
EXECU number of current mode block reads during execute
EXEROW number of rows processed during execute
EXEMIS number of library cache misses during execute
FCHCNT number of fetches

FCHCPU CPU time spent fetching
FCHELA elapsed time spent fetching
FCHDSK number of physical reads from disk during fetch
FCHQRY number of consistent mode block reads during fetch
FCHCU number of current mode block reads during fetch
FCHROW number of rows fetched
PRINT Lists only the first integer sorted SQL statements into the output file. If you omit this parameter, TKPROF lists all traced SQL statements. Note that this parameter does not affect the optional SQL script. The SQL script always inserts statistics for all traced SQL statements.
RECORD Creates a SQL script with the specified filename with all of the non-recursive SQL in the trace file. This can be used to replay the user events from the trace file.

TKPROF Statement Examples

This section provides two brief examples of TKPROF usage. For an extensive example of TKPROF output, see “Sample TKPROF Output” on page 22-7.

Example 1
If you are processing a large trace file using a combination of SORT parameters and the PRINT parameter, you can produce a TKPROF output file containing only the highest resource-intensive statements. For example, the following statement will print the ten statements in the trace file that have generated the most physical I/O:

TKPROF ora53269.trc ora 53269.prf
SORT = (PRSDSK, EXEDSK, FCHDSK)
PRINT = 10

Example 2
This example runs TKPROF, accepts a trace file named dlsun12_jane_fg_svrmgr_007.trc, and writes a formatted output file named outputa.prf:

TKPROF DLSUN12_JANE_FG_SVRMGR_007.TRC OUTPUTA.PRF
EXPLAIN=SCOTT/TIGER TABLE=SCOTT.TEMP_PLAN_TABLE_A INSERT=STOREA.SQL
SYS=NO SORT=(EXECPU,FCHCPU)

This example is likely to be longer than a single line on your screen and you may have to use continuation characters, depending on your operating system.

Note the other parameters in this example:

The EXPLAIN value causes TKPROF to connect as the user SCOTT and use the EXPLAIN PLAN command to generate the execution plan for each traced SQL statement. You can use this to get access paths and row source counts.
The TABLE value causes TKPROF to use the table TEMP_PLAN_TABLE_A in the schema SCOTT as a temporary plan table.
The INSERT value causes TKPROF to generate a SQL script named STOREA.SQL that stores statistics for all traced SQL statements in the database.
The SYS parameter with the value of NO causes TKPROF to omit recursive SQL statements from the output file. In this way you can ignore internal Oracle statements such as temporary table operations.
The SORT value causes TKPROF to sort the SQL statements in order of the sum of the CPU time spent executing and the CPU time spent fetching rows before writing them to the output file. For greatest efficiency, always use SORT parameters.

Step 4:

Interpreting TKPROF Output
This section provides pointers for interpreting TKPROF output.

Tabular Statistics
Library Cache Misses
User Issuing the SQL Statement
Execution Plan
Deciding What Statements to Tune
While TKPROF provides a very useful analysis, the most accurate measure of efficiency is the actual performance of the application in question. Note that at the end of the TKPROF output is a summary of the work done in the database engine by the process during the period that the trace was running.

Tabular Statistics

TKPROF lists the statistics for a SQL statement returned by the SQL trace facility in rows and columns. Each row corresponds to one of three steps of SQL statement processing. The step for which each row contains statistics is identified by the value of the call column:

Parse
This step translates the SQL statement into an execution plan. This step includes checks for proper security authorization and checks for the existence of tables, columns, and other referenced objects.

Execute This step is the actual execution of the statement by Oracle. For INSERT, UPDATE, and DELETE statements, this step modifies the data. For SELECT statements, the step identifies the selected rows.

Fetch This step retrieves rows returned by a query. Fetches are only performed for SELECT
statements.

The other columns of the SQL trace facility output are combined statistics for all parses, all executes, and all fetches of a statement. These values are zero (0) if TIMED_STATISTICS is not turned on. The sum of query and current is the total number of buffers accessed.

count Number of times a statement was parsed, executed, or fetched.

cpu
Total CPU time in seconds for all parse, execute, or fetch calls for the statement.

elapsed
Total elapsed time in seconds for all parse, execute, or fetch calls for the statement.

disk
Total number of data blocks physically read from the datafiles on disk for all parse, execute, or fetch calls.

query
Total number of buffers retrieved in consistent mode for all parse, execute, or fetch calls. Buffers are usually retrieved in consistent mode for queries.

current
Total number of buffers retrieved in current mode. Buffers are retrieved in current mode for statements such as INSERT, UPDATE, and DELETE.

Rows
Statistics about the processed rows appear in the “rows” column.

rows
Total number of rows processed by the SQL statement. This total does not include rows processed by subqueries of the SQL statement.

For SELECT statements, the number of rows returned appears for the fetch step. For UPDATE, DELETE, and INSERT statements, the number of rows processed appears for the execute step.

Resolution of Statistics
Since timing statistics have a resolution of one hundredth of a second, any operation on a cursor that takes a hundredth of a second or less may not be timed accurately. Keep this in mind when interpreting statistics. In particular, be careful when interpreting the results from simple queries that execute very quickly.

Recursive Calls
Sometimes in order to execute a SQL statement issued by a user, Oracle must issue additional statements. Such statements are called recursive calls or recursive SQL statements. For example, if you insert a row into a table that does not have enough space to hold that row, Oracle makes recursive calls to allocate the space dynamically. Recursive calls are also generated when data dictionary information is not available in the data dictionary cache and must be retrieved from disk.

If recursive calls occur while the SQL trace facility is enabled, TKPROF produces statistics for the recursive SQL statements and clearly marks them as recursive SQL statements in the output file. Note that the statistics for a recursive SQL statement are included in the listing for that statement, not in the listing for the SQL statement that caused the recursive call. So when you are calculating the total resources required to process a SQL statement, you should consider the statistics for that statement as well as those for recursive calls caused by that statement. Note that setting the SYS command line parameter to NO suppresses the listing of recursive calls in the output file.

Library Cache Misses
TKPROF also lists the number of library cache misses resulting from parse and execute steps for each SQL statement. These statistics appear on separate lines following the tabular statistics. If the statement resulted in no library cache misses, TKPROF does not list the statistic. In the example, the statement resulted in one library cache miss for the parse step and no misses for the execute step.

User Issuing the SQL Statement
TKPROF also lists the user ID of the user issuing each SQL statement. If the SQL trace input file contained statistics from multiple users and the statement was issued by more than one user, TKPROF lists the ID of the last user to parse the statement. The user ID of all database users appears in the data dictionary in the column ALL_USERS.USER_ID.

Execution Plan
If you specify the EXPLAIN parameter on the TKPROF command line, TKPROF uses the EXPLAIN PLAN command to generate the execution plan of each SQL statement traced. TKPROF also displays the number of rows processed by each step of the execution plan.

Note:
Trace files generated immediately after instance startup contain data that reflects the activity of the startup process. In particular, they reflect a disproportionate amount of I/O activity as caches in the System Global Area (SGA) are filled. For the purposes of tuning, ignore such trace files.

Deciding What Statements to Tune
The following listing shows TKPROF output for one SQL statement as it appears in the output file:

SELECT * FROM emp, dept WHERE emp.deptno = dept.deptno;

call count cpu elapsed disk query current rows
—- ——- ——- ——— ——– ——– ——- ——
Parse 11 0.08 0.18 0 0 0 0
Execute 11 0.23 0.66 0 3 6 2
Fetch 35 6.70 6.83 100 12326 2 824
——————————————————————
total 57 7.01 7.67 100 12329 8 826

Misses in library cache during parse: 0

10 user SQL statements in session.
0 internal SQL statements in session.
10 SQL statements in session.

If it is acceptable to expend 7.01 CPU seconds to insert, update or delete 2 rows and to retrieve 824 rows, then you need not look any further at this trace output. In fact, a major use of TKPROF reports in a tuning exercise is to eliminate processes from the detailed tuning phase.

You can also see from this summary that 1 unnecessary parse call was made (because there were more parse calls than SQL statements) and that array fetch operations were performed. (You know this because more rows were fetched than there were fetches performed.)

Finally, you can see that very little physical I/O was performed; this is suspicious and probably means that the same database blocks were being continually re-visited.

Having established that the process has used excessive resource, the next step is to discover which SQL statements are the culprits. Normally only a small percentage of the SQL statements in any process need to be tuned, and these are the ones which use the greatest resource.

The examples which follow were all produced with TIMED_STATISTICS=TRUE. However, with the exception of locking problems and inefficient PL/SQL loops, neither the CPU nor the elapsed time are necessary to find the problem statements. The key is the number of block visits both query (that is, subject to read consistency) and current (not subject to read consistency). Segment headers and blocks which are going to be updated are always acquired in current mode, but all query and sub-query processing requests the data in query mode. These are precisely the same measures as the instance statistics consistent gets and db block gets.

The SQL parsed as SYS is recursive SQL used to maintain the dictionary cache, and is not normally of great benefit; if the number of internal SQL statements looks high it may be worth checking to see what has been going on. (There may be excessive space management overhead.)

Step 5:

Storing SQL Trace Facility Statistics
This section covers:

Generating the TKPROF Output SQL Script
Editing the TKPROF Output SQL Script
Querying the Output Table
You may want to keep a history of the statistics generated by the SQL trace facility for your application and compare them over time. TKPROF can generate a SQL script that creates a table and inserts rows of statistics into it. This script contains

a CREATE TABLE statement that creates an output table named TKPROF_TABLE
INSERT statements that add rows of statistics, one for each traced SQL statement, to the TKPROF_TABLE
After running TKPROF, you can run this script to store the statistics in the database.

Generating the TKPROF Output SQL Script
When you run TKPROF, use the INSERT parameter to specify the name of the generated SQL script. If you omit this parameter, TKPROF does not generate a script.

Editing the TKPROF Output SQL Script
After TKPROF has created the SQL script, you may want to edit the script before running it.

If you have already created an output table for previously collected statistics and you want to add new statistics to the existing table, remove the CREATE TABLE statement from the script. The script will then insert the new rows into the existing table.

If you have created multiple output tables, perhaps to store statistics from different databases in different tables, edit the CREATE TABLE and INSERT statements to change the name of the output table.

Querying the Output Table
The following CREATE TABLE statement creates the TKPROF_TABLE:

CREATE TABLE tkprof_table
(date_of_insert DATE,
cursor_num NUMBER,
depth NUMBER,
user_id NUMBER,
parse_cnt NUMBER,
parse_cpu NUMBER,
parse_elap NUMBER,
parse_disk NUMBER,
parse_query NUMBER,
parse_current NUMBER,
parse_miss NUMBER,
exe_count NUMBER,
exe_cpu NUMBER,
exe_elap NUMBER,
exe_disk NUMBER,
exe_query NUMBER,
exe_current NUMBER,
exe_miss NUMBER,
exe_rows NUMBER,
fetch_count NUMBER,
fetch_cpu NUMBER,
fetch_elap NUMBER,
fetch_disk NUMBER,
fetch_query NUMBER,
fetch_current NUMBER,
fetch_rows NUMBER,
clock_ticks NUMBER,
sql_statement LONG)

These columns help you identify a row of statistics:

SQL_STATEMENT
The column value is the SQL statement for which the SQL trace facility collected the row of statistics. Note that because this column has datatype LONG, you cannot use it in expressions or WHERE clause conditions.

DATE_OF_INSERT
The column value is the date and time when the row was inserted into the table. Note that this value is not exactly the same as the time the statistics were collected by the SQL trace facility. Most output table columns correspond directly to the statistics that appear in the formatted output file. For example, the PARSE_CNT column value corresponds to the count statistic for the parse step in the output file.

DEPTH
This column value indicates the level of recursion at which the SQL statement was issued. For example, a value of 1 indicates that a user issued the statement. A value of 2 indicates Oracle generated the statement as a recursive call to process a statement with a value of 1 (a statement issued by a user). A value of n indicates Oracle generated the statement as a recursive call to process a statement with a value of n-1.

USER_ID
This column value identifies the user issuing the statement. This value also appears in the formatted output file.

CURSOR_NUM
This column value is used by Oracle to keep track of the cursor to which each SQL statement was assigned. Note that the output table does not store the statement’s execution plan.

The following query returns the statistics from the output table. These statistics correspond to the formatted output shown in the section “Step 4: Interpreting TKPROF Output”

SELECT * FROM tkprof_table;
DATE_OF_INSERT CURSOR_NUM DEPTH USER_ID PARSE_CNT PARSE_CPU PARSE_ELAP
————– ———- —– ——- ——— ——— ———-
27-OCT-1993 1 0 8 1 16 29

PARSE_DISK PARSE_QUERY PARSE_CURRENT PARSE_MISS EXE_COUNT EXE_CPU
———- ———– ————- ———- ——— ——-
3 13 0 1 1 0

EXE_ELAP EXE_DISK EXE_QUERY EXE_CURRENT EXE_MISS EXE_ROWS FETCH_COUNT
——– ——– ——— ———– ——– ——– ———–
0 0 0 0 0 0 1

FETCH_CPU FETCH_ELAP FETCH_DISK FETCH_QUERY FETCH_CURRENT FETCH_ROWS
——— ———- ———- ———– ————- ———-
3 26 2 2 4 14

SQL_STATEMENT
———————————————————————
SELECT * FROM EMP, DEPT WHERE EMP.DEPTNO = DEPT.DEPTNO

Avoiding Pitfalls in TKPROF Interpretation
This section describes some fine points of TKPROF interpretation:

Finding the Statements Which Constitute the Bulk of the Load
The Argument Trap
The Read Consistency Trap
The Schema Trap
The Time Trap
The Trigger Trap
The “Correct” Version
See Also: “EXPLAIN PLAN Restrictions” on page 21-16 for information about TKPROF and bind variables.

Finding the Statements Which Constitute the Bulk of the Load
Look at the totals and try to identify the statements, which constitute the bulk of the load.

Do not attempt to perform many different jobs within a single query. It is more effective to separate out the different queries which should be used when certain optional parameters are present, and when the parameters provided contain wild cards.

If certain parameters are not specified by the report user, the query uses bind variables which have been set to “%” to cause the LIKE clauses in the query to operate as if they were not there. It would be more efficient to run a query in which these clauses are not present.

Note:
TKPROF cannot tell the TYPE of the bind variables simply by looking at the text of the SQL statement. It assumes that TYPE is CHARACTER; if this is not the case, you should put appropriate type conversions in the SQL statement.

The Argument Trap
Especially where the LIKE operator is used, the query may be markedly less efficient for certain values, or types of value, in a bind variable. This is because the optimizer must make an assumption about the probable selectivity without knowing the value. If you are not aware of the values being bound at run time then it is possible to fall into the “argument trap”.

The Read Consistency Trap
The next example illustrates the read consistency trap. Without knowing that an uncommitted transaction had made a series of updates to the NAME column it is very difficult to see why so many block visits would be incurred.

Cases like this are not normally repeatable: if the process were run again, it is unlikely that another transaction would interact with it in the same way.

select NAME_ID
from CQ_NAMES where NAME = ‘FLOOR’
call count cpu elapsed disk query current rows
—- —– — ——- —- —– ——- —-
Parse 1 0.11 0.21 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.15 0.24 4 150 0 1
Misses in library cache during parse: 1
Parsing user id: 13 (DJONES)
Rows Execution Plan
—- ——— —-
0 SELECT STATEMENT
1 TABLE ACCESS (BY ROWID) OF ‘CQ_NAMES’
2 INDEX (RANGE SCAN) OF ‘CQ_NAMES_NAME’ (NON_UNIQUE)

The Schema Trap
This example shows an extreme and thus easily detected example of the schema trap. At first it is difficult to see why such an apparently straightforward indexed query needs to look at so many database blocks, or why it should access any blocks at all in current mode.

select NAME_ID
from CQ_NAMES where NAME = ‘FLOOR’

call count cpu elapsed disk query current rows
——– ——- ——– ——— ——- —— ——- —-
Parse 1 0.04 0.12 0 0 0 0
Execute 1 0.01 0.01 0 0 0 0
Fetch 1 0.32 0.32 38 44 3 1

Misses in library cache during parse: 0
Parsing user id: 13 (JAUSTEN

Rows Execution Plan
——- —————————————————
0 SELECTSTATEMENT
3519 TABLE ACCESS (BY ROWID) OF ‘CQ_NAMES’
0 INDEX (RANGE SCAN) OF ‘CQ_NAMES_NAME’ (NON-UNIQUE)

Two statistics suggest that the query may have been executed via a full table scan. These statistics are the current mode block visits, plus the number of rows originating from the Table Access row source in the execution plan. The explanation is that the required index was built after the trace file had been produced, but before TKPROF had been run.

The Time Trap
Sometimes, as in the following example, you may wonder why a particular query has taken so long.

update CQ_NAMES set ATTRIBUTES = lower(ATTRIBUTES)
where ATTRIBUTES = :att

call count cpu elapsed disk query current rows
——– ——- ——– ——— ——– ——– ——- ——
—-
Parse 1 0.08 0.24 0 0 0 0
Execute 1 0.63 19.63 33 526 13 7
Fetch 0 0.00 0.00 0 0 0 0

Misses in library cache during parse: 1
Parsing user id: 13 (JAUSTEN)

Rows Execution Plan
——- —————————————————
0 UPDATE STATEMENT
3519 TABLE ACCESS (FULL) OF ‘CQ_NAMES’
Again, the answer is interference from another transaction. In this case another
transaction held a shared lock on the table CQ_NAMES for several seconds
before and after the update was issued. It takes a fair amount of experience to
diagnose that interference effects are occurring. Comparative data is essential
when the interference is only contributing a short delay (or a small increase in
block visits in the previous example). On the other hand, if the interference is
only contributing a modest overhead, and the statement is essentially efficient,
its statistics may never have to be subjected to analysis.

The Trigger Trap
The resources reported for a statement include those for all of the SQL issued while the statement was being processed. They therefore include any resources used within a trigger, along with the resources used by any other recursive SQL (such as that used in space allocation). With the SQL trace facility enabled, TKPROF will report these resources twice. Avoid trying to tune the DML statement, if the resource is actually being consumed at a lower level of recursion.

You may need to inspect the raw trace file to see exactly where the resource is being expended. The entries for recursive SQL follow the PARSING IN CURSOR entry for the user’s statement. Within the trace file, the order is less easily defined.

The “Correct” Version
For comparison with the output which results from one of these traps having sprung, here is the TKPROF output for the indexed query with the index in place and without any contention effects.

select NAME_ID
from CQ_NAMES where NAME = ‘FLOOR’

call count cpu elapsed disk query current rows
—– —— —— ——– —– —— ——- —–
Parse 1 0.01 0.01 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 0 4 0 1

Misses in library cache during parse: 0
Parsing user id: 13 (JAUSTEN)

Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT
1 TABLE ACCESS (BY ROWID) OF ‘CQ_NAMES’
2 INDEX (RANGE SCAN) OF ‘CQ_NAMES_NAME’ (NON-UNIQUE)

One of the marked features of this correct version is that the parse call took 10 milliseconds of both elapsed and CPU time, but the query apparently took no time at all to execute and no time at all to perform the fetch. In fact, no parse took place because the query was already available in parsed form within the shared SQL area. These anomalies are due to the clock tick of 10 msec being too long to reliably record simple and efficient queries.

TKPROF Sample Output
This section provides an extensive example of TKPROF output. Note that portions have been edited out for the sake of brevity.

Header

Copyright (c) Oracle Corporation 1979, 1997. All rights reserved.
Trace file: v80_ora_2758.trc
Sort options: default
********************************************************************************
count = number of times OCI procedure was executed
cpu = cpu time in seconds executing
elapsed = elapsed time in seconds executing
disk = number of physical reads of buffers from disk
query = number of buffers gotten for consistent read
current = number of buffers gotten in current mode (usually for update)
rows = number of rows processed by the fetch or execute call
********************************************************************************
The following statement encountered a error during parse:
select deptno, avg(sal) from emp e group by deptno
having exists (select deptno from dept
where dept.deptno = e.deptno
and dept.budget > avg(e.sal)) order by 1
Error encountered: ORA-00904
********************************************************************************

Body

alter session set sql_trace = true
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 0 0.00 0.00 0 0 0 0
Execute 1 0.00 0.15 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
——- —— ——– ———- ———- ———- ———- ———-
total 1 0.00 0.15 0 0 0 0
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
.
.
.
********************************************************************************
select emp.ename, dept.dname from emp, dept
where emp.deptno = dept.deptno
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.12 0.14 2 0 2 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 2 2 4 14
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.12 0.14 4 2 6 14
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
14 MERGE JOIN
4 SORT (JOIN)
4 TABLE ACCESS (FULL) OF ‘DEPT’
14 SORT (JOIN)
14 TABLE ACCESS (FULL) OF ‘EMP’
********************************************************************************
select a.ename name, b.ename manager from emp a, emp b
where a.mgr = b.empno(+)
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.01 0.01 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.01 0.01 1 54 2 14
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.02 0.02 1 54 2 14
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
13 NESTED LOOPS (OUTER)
14 TABLE ACCESS (FULL) OF ‘EMP’
13 TABLE ACCESS (BY ROWID) OF ‘EMP’
26 INDEX (RANGE SCAN) OF ‘EMP_IND’ (NON-UNIQUE)
.
.
.
********************************************************************************
select ename,job,sal
from emp
where sal =
(select max(sal)
from emp)
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 0 16 4 1
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.00 0.00 0 16 4 1
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
14 FILTER
14 TABLE ACCESS (FULL) OF ‘EMP’
14 SORT (AGGREGATE)
14 TABLE ACCESS (FULL) OF ‘EMP’
********************************************************************************
select deptno
from emp
where job = ‘clerk’
group by deptno
having count(*) >= 2
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 0 1 2 0
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.00 0.00 0 1 2 0
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
0 FILTER
0 SORT (GROUP BY)
14 TABLE ACCESS (FULL) OF ‘EMP’
********************************************************************************
select dept.deptno,dname,job,ename
from dept,emp
where dept.deptno = emp.deptno(+)
order by dept.deptno
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 0 2 4 15
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.00 0.00 0 2 4 15
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
14 MERGE JOIN (OUTER)
4 SORT (JOIN)
4 TABLE ACCESS (FULL) OF ‘DEPT’
14 SORT (JOIN)
14 TABLE ACCESS (FULL) OF ‘EMP’
********************************************************************************
select grade,job,ename,sal
from emp,salgrade
where sal between losal and hisal
order by grade,job
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.06 0.08 2 18 1 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.01 0.01 1 11 12 14
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.07 0.09 3 29 13 14
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
14 SORT (ORDER BY)
14 NESTED LOOPS
5 TABLE ACCESS (FULL) OF ‘SALGRADE’
70 TABLE ACCESS (FULL) OF ‘EMP’
********************************************************************************
select lpad(‘ ‘,level*2)||ename org_chart,level,empno,mgr,job,deptno
from emp
connect by prior empno = mgr
start with ename = ‘clark’
or ename = ‘blake’
order by deptno
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.01 0.01 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.01 0.01 0 1 2 0
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.02 0.02 0 1 2 0
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
0 SORT (ORDER BY)
0 CONNECT BY
14 TABLE ACCESS (FULL) OF ‘EMP’
0 TABLE ACCESS (BY ROWID) OF ‘EMP’
0 TABLE ACCESS (FULL) OF ‘EMP’
********************************************************************************
create table tkoptkp (a number, b number)
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.01 0.01 1 0 1 0
Fetch 0 0.00 0.00 0 0 0 0
——- —— ——– ———- ———- ———- ———- ———-
total 2 0.01 0.01 1 0 1 0
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 CREATE TABLE STATEMENT GOAL: CHOOSE
.
.
.
********************************************************************************
insert into tkoptkp
values
(1,1)
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.07 0.09 0 0 0 0
Execute 1 0.01 0.20 2 2 3 1
Fetch 0 0.00 0.00 0 0 0 0
——- —— ——– ———- ———- ———- ———- ———-
total 2 0.08 0.29 2 2 3 1
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 INSERT STATEMENT GOAL: CHOOSE
.
.
.
********************************************************************************
insert into tkoptkp select * from tkoptkp
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.02 0.04 0 2 3 12
Fetch 0 0.00 0.00 0 0 0 0
——- —— ——– ———- ———- ———- ———- ———-
total 2 0.02 0.04 0 2 3 12
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 INSERT STATEMENT GOAL: CHOOSE
12 TABLE ACCESS (FULL) OF ‘TKOPTKP’
********************************************************************************
select *
from
tkoptkp where a > 2
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.01 0.01 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 0 1 2 12
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.01 0.01 0 1 2 12
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 8 (SCOTT)
Rows Execution Plan
——- —————————————————
0 SELECT STATEMENT GOAL: CHOOSE
24 TABLE ACCESS (FULL) OF ‘TKOPTKP’
********************************************************************************

Summary

OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 18 0.40 0.53 30 182 3 0
Execute 19 0.05 0.41 3 7 10 16
Fetch 12 0.05 0.06 4 105 66 78
——- —— ——– ———- ———- ———- ———- ———-
total 49 0.50 1.00 37 294 79 94
Misses in library cache during parse: 18
Misses in library cache during execute: 1
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 69 0.49 0.60 9 12 8 0
Execute 103 0.13 0.54 0 0 0 0
Fetch 213 0.12 0.27 40 435 0 162
——- —— ——– ———- ———- ———- ———- ———-
total 385 0.74 1.41 49 447 8 162
Misses in library cache during parse: 13
19 user SQL statements in session.
69 internal SQL statements in session.
88 SQL statements in session.
17 statements EXPLAINed in this session.
********************************************************************************
Trace file: v80_ora_2758.trc
Trace file compatibility: 7.03.02
Sort options: default
1 session in tracefile.
19 user SQL statements in trace file.
69 internal SQL statements in trace file.
88 SQL statements in trace file.
41 unique SQL statements in trace file.
17 SQL statements EXPLAINed using schema:
SCOTT.prof$plan_table
Default table was used.
Table was created.
Table was dropped.
1017 lines in trace file.

Tracking the Explain Plan and Stats without doing anything but setting the parameters at SQL*Plus

SET AUTOTRACE OFF No AUTOTRACE report is generated. This is the default
SET AUTOTRACE ON The AUTOTRACE report includes both the optimizer execution path and the SQL statement execution statistics
SET AUTOTRACE ON EXPLAIN The AUTOTRACE report shows only the optimizer execution path
SET AUTOTRACE ON STATISTICS The AUTOTRACE report shows only the SQL statement execution statistics.
SET AUTOTRACE TRACEONLY Like SET AUTOTRACE ON, but suppresses the printing of the user’s query output, if any.

Utilities to gather Stats for the tables/indexes/schemas/database

DBMS_STATS

DBMS_STATS provides a mechanism for you to view and modify optimizer statistics gathered for database objects.The statistics can reside in two different locations:

The dictionary.

A table created in the user’s schema for this purpose.

Only statistics stored in the dictionary itself have an impact on the cost-based optimizer.

Example

Scenario

There has been a lot of modification against the emp table since the last time statistics were gathered. To ensure that the cost-based optimizer is still picking the best plan, statistics should be gathered once again; however, the user is concerned that new statistics will cause the optimizer to choose bad plans when the current ones are acceptable. The user can do the following:

BEGIN
DBMS_STATS.CREATE_STAT_TABLE (‘scott’, ‘savestats’);
DBMS_STATS.GATHER_TABLE_STATS (‘scott’, ’emp’, 5, stattab => ‘savestats’);
END;

This operation gathers new statistics on emp, but first saves the original statistics in a user stat table: emp.savestats.

If the user believes that the new statistics are causing the optimizer to generate poor plans, then the original stats can be restored as follows:

BEGIN
DBMS_STATS.DELETE_TABLE_STATS (‘scott’, ’emp’);
DBMS_STATS.IMPORT_TABLE_STATS (‘scott’, ’emp’, stattab => ‘savestats’);
END;

DBMS_UTILITY

This package provides various utility subprograms.

DBMS_UTILITY submits a job for each partition. It is the users responsibility to control the number of concurrent jobs by setting the INIT.ORA parameter JOB_QUEUE_PROCESSES correctly. There is minimal error checking for correct syntax. Any error is reported in SNP trace files.

DBMS_UTILITY runs with the privileges of the calling user for the NAME_RESOLVE, COMPILE_SCHEMA, and ANALYZE_SCHEMA procedures. This is necessary so that the SQL works correctly.

This does not run as SYS. The privileges are checked using DBMS_DDL.

DBMS_SYSTEM

This package enables you to gather information about events set in the current session and manipulate other user’s sessions to set events and change the values of certain init.ora parameters. It provides some of the capability of DBMS_SESSION but with the ability to affect any session.

Oracle version 9.2 introduced a procedure to reset the IO counters in dynamic performance views (KCFRMS) and a suite of procedures that allow privileged users to write messages to the session trace file and instance alert log.

Note:

I should add that this package has been left undocumented for good reason and since Oracle8, it has been wrapped and moved into prvtutil.plb “for obscurity”.

Requirements

This package is owned by SYS and is not generally available. I recommend that you only use this when logged on as SYS or connected as SYSDBA

Privileges

Before using this package, you must run the DBMSUTIL.SQL and PRVTUTIL.PLB scripts to create the DBMS_SYSTEM package.

DIST_TXN_SYNC Procedure

There is no public information available for this procedure, but it somehow sounds like distributed transaction synchronisation. According to Tom Kyte it is used in XA interfaces and is nothing you would ever need to call directly.

Syntax

DBMS_SYSTEM.DIST_TXN_SYNC (inst_num IN NUMBER);

KCFRMS Procedure

This procedure resets the timers displayed by MAX_WAIT in V$SESSION_EVENT and MAXIORTM, MAXIOWTM in V$FILESTAT (X$KCFIO) views.

Syntax

DBMS_SYSTEM.KCFRMS ;

Example

To check for the current timer values:

SQL> select MAX_WAIT from V$SESSION_EVENT;
SQL> select MAXIORTM, MAXIOWTM from V$FILESTAT;

KSDDDT Procedure

This procedure prints the timestamp to the trace file. It can’t be used for the alert log.

Syntax

DBMS_SYSTEM.KSDDDT ;

Example

SQL> exec dbms_system.ksdddt ;

Output in tracefile looks like:

*** 2003-03-10 21:23:17.000

KSDFLS Procedure

This procedure flushes any pending output to the target file (alert log and/or trace file).

Syntax

DBMS_SYSTEM.KSDFLS ;

KSDIND Procedure

This procedure does an ‘indent’ before the next write (ksdwrt) by printing that many colons (:) before the next write.

Syntax

DBMS_SYSTEM.KSDIND (lvl IN BINARY_INTEGER);

Example

Write in the same line 5 ‘:’ and the text ‘Test Alert Msg’ to the tracefile and the alertlog:

SQL> exec dbms_system.ksdind (5);
SQL> exec dbms_system.ksdwrt (3, ‘Test Alert Msg’);

Output in tracefile/alertlog looks like:

:::::Test Alert Msg

KSDWRT Procedure

This procedure prints the message to the target file (alert log and/or trace file).

Syntax

DBMS_SYSTEM.KSDWRT (
dest IN BINARY_INTEGER,
tst IN VARCHAR2);

Example

Write the text ‘Test Alert Msg’ to the tracefile and the alertlog:

SQL> exec dbms_system.ksdwrt (3, ‘ ‘);
SQL> exec dbms_system.ksdwrt (3, ‘— Start —‘);
SQL> exec dbms_system.ksdddt;
SQL> exec dbms_system.ksdwrt (3, ‘ Test Alert Msg’);
SQL> exec dbms_system.ksdwrt (3, ‘— End —‘);
SQL> exec dbms_system.ksdwrt (3, ‘ ‘);

The output in the aleret log file is as under
(This is the output from Oracle 10.1)

Wed Aug 04 22:13:47 2004
ARC1: Evaluating archive log 2 thread 1 sequence 138
Committing creation of archivelog ‘D:ORACLEFLASH_RECOVERY_AREAORA10GARCHIVELOG2004_08_04O1_MF_1_138_0K39HD5M_.ARC’
Created Oracle managed file D:ORACLEFLASH_RECOVERY_AREAORA10GARCHIVELOG2004_08_04O1_MF_1_138_0K39HD5M_.ARC
Wed Aug 04 22:15:54 2004

— Start —
Test Alert Msg
— End —
ORADEBUG
ORADEBUG is an undocumented debugging utility supplied with Oracle

The ORADEBUG HELP command lists the commands available within ORADEBUG
These vary by release and platform. Commands appearing in this help do not necessarily work for the release/platform on which the database is running
For example in Oracle 10.1.0.2.0 (Windows 2000) the command
ORADEBUG HELP
Returns the following
HELP [command] Describe one or all commands
SETMYPID Debug current process
SETOSPID Set OS pid of process to debug
SETORAPID [‘force’] Set Oracle pid of process to debug
DUMP [addr] Invoke named dump
DUMPSGA [bytes] Dump fixed SGA
DUMPLIST Print a list of available dumps
EVENT Set trace event in process
SESSION_EVENT Set trace event in session
DUMPVAR [level] Print/dump a fixed PGA/SGA/UGA variable
SETVAR Modify a fixed PGA/SGA/UGA variable
PEEK [level] Print/Dump memory
POKE Modify memory
WAKEUP Wake up Oracle process
SUSPEND Suspend execution
RESUME Resume execution
FLUSH Flush pending writes to trace file
CLOSE_TRACE Close trace file
TRACEFILE_NAME Get name of trace file
LKDEBUG Invoke global enqueue service debugger
NSDBX Invoke CGS name-service debugger
-G Parallel oradebug command prefix
-R Parallel oradebug prefix (return output
SETINST Set instance list in double quotes
SGATOFILE Dump SGA to file; dirname in double quotes
DMPCOWSGA Dump & map SGA as COW; dirname in double quotes
MAPCOWSGA Map SGA as COW; dirname in double quotes
HANGANALYZE [level] [syslevel] Analyze system hang
FFBEGIN Flash Freeze the Instance
FFDEREGISTER FF deregister instance from cluster
FFTERMINST Call exit and terminate instance
FFRESUMEINST Resume the flash frozen instance
FFSTATUS Flash freeze status of instance
SKDSTTPCS Helps translate PCs to names
WATCH

Watch a region of memory
DELETE watchpoint Delete a watchpoint
SHOW watchpoints Show watchpoints
CORE Dump core without crashing process
UNLIMIT Unlimit the size of the trace file
PROCSTAT Dump process statistics
CALL [arg1] … [argn] Invoke function with arguments

This will be discussed in another lesson later as this lesson has already touched 30 pages