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18 Performing Application Tracing

This chapter contains the following sections:

18.1 End-to-End Application Tracing

End-to-End application tracing can identify the source of an excessive workload, such as a high load SQL statement, by client identifier, service, module, action, session, instance, or an entire database. This isolates the problem to a specific user, service, session, or application component.

This section contains the following topics:

See Also:

18.1.1 About End-to-End Application Tracing

In multitier environments, the middle tier routes a request from an end client to different database sessions, making it difficult to track a client across database sessions. End-to-End application tracing is an infrastructure that uses a client ID to uniquely trace a specific end-client through all tiers to the database.

18.1.1.1 Purpose of End-to-End Application Tracing

End-to-End application tracing simplifies diagnosing performance problems in multitier environments. For example, you can identify the source of an excessive workload, such as a high-load SQL statement, and contact the user responsible. Also, a user having problems can contact you. You can then identify what this user's session is doing at the database level.

End-to-End application tracing also simplifies management of application workloads by tracking specific modules and actions in a service. The module and action names are set by the application developer. For example, you would use the SET_MODULE and SET_ACTION procedures in the DBMS_APPLICATION_INFO package to set these values in a PL/SQL program.

End-to-End application tracing can identify workload problems for:

  • Client identifier - specifies an end user based on the logon ID, such as HR.HR

  • Service - specifies a group of applications with common attributes, service level thresholds, and priorities; or a single application, such as ACCTG for an accounting application

  • Module - specifies a functional block, such as Accounts Receivable or General Ledger, of an application

  • Action - specifies an action, such as an INSERT or UPDATE operation, in a module

  • Session - specifies a session based on a given database session identifier (SID), on the local instance

  • Instance - specifies a given instance based on the instance name

18.1.1.2 User Interfaces for End-to-End Application Tracing

The database provides the trcsess command-line utility that consolidates tracing information based on specific criteria. The SQL Trace facility and TKPROF are two basic performance diagnostic tools that can help you monitor applications running against the Oracle database. After tracing information is written to files, you can consolidate this data with the trcsess utility, and then diagnose it with TKPROF or SQL Trace.

The recommended interface for end-to-end application tracing is Oracle Enterprise Manager Cloud Control (Cloud Control). Using Cloud Control, you can view the top consumers for each consumer type, and enable or disable statistics gathering and SQL tracing for specific consumers. If Cloud Control is unavailable, then you can manage this feature using the DBMS_MONITOR APIs.

18.1.2 Enabling and Disabling Statistic Gathering for End-to-End Tracing

To gather the appropriate statistics using PL/SQL, you must enable statistics gathering for client identifier, service, module, or action using procedures in DBMS_MONITOR.

You can gather statistics by the following criteria:

The default level is the session-level statistics gathering. Statistics gathering is global for the database and continues after a database instance is restarted.

18.1.2.1 Enabling and Disabling Statistics Gathering for a Client ID

The procedure CLIENT_ID_STAT_ENABLE enables statistics gathering for a given client ID, whereas the procedure CLIENT_ID_STAT_DISABLE disables it. You can view client identifiers in the CLIENT_IDENTIFIER column in V$SESSION.

Assumptions

This tutorial assumes that you want to enable and then disable statistics gathering for the client with the ID oe.oe.

To enable and disable statistics gathering for a client identifier: 

  1. Start SQL*Plus, and then connect to the database with the appropriate privileges.

  2. Enable statistics gathering for oe.oe.

    For example, run the following command:

    EXECUTE DBMS_MONITOR.CLIENT_ID_STAT_ENABLE(client_id => 'OE.OE');
    
  3. Disable statistics gathering for oe.oe.

    For example, run the following command:

    EXECUTE DBMS_MONITOR.CLIENT_ID_STAT_DISABLE(client_id => 'OE.OE');
    

18.1.2.2 Enabling and Disabling Statistics Gathering for a Service, Module, and Action

The procedure SERV_MOD_ACT_STAT_ENABLE enables statistic gathering for a combination of service, module, and action, whereas the procedure SERV_MOD_ACT_STAT_DISABLE disables statistic gathering for a combination of service, module, and action.

When you change the module or action using the preceding DBMS_MONITOR procedures, the change takes effect when the next user call is executed in the session. For example, if a module is set to module1 in a session, and if the module is reset to module2 in a user call in the session, then the module remains module1 during this user call. The module is changed to module2 in the next user call in the session.

Assumptions

This tutorial assumes that you want to gather statistics as follows:

  • For the ACCTG service

  • For all actions in the PAYROLL module

  • For the INSERT ITEM action within the GLEDGER module

To enable and disable statistics gathering for a service, module, and action: 

  1. Start SQL*Plus, and then connect to the database with the appropriate privileges.

  2. Enable statistics gathering for the desired service, module, and action.

    For example, run the following commands:

    EXECUTE DBMS_MONITOR.SERV_MOD_ACT_STAT_ENABLE(
            service_name => 'ACCTG' 
         ,  module_name  => 'PAYROLL');
    
    EXECUTE DBMS_MONITOR.SERV_MOD_ACT_STAT_ENABLE(
            service_name => 'ACCTG' 
         ,  module_name  => 'GLEDGER'
         ,  action_name  => 'INSERT ITEM');
    
  3. Disable statistic gathering for the previously specified combination of service, module, and action.

    For example, run the following command:

    EXECUTE DBMS_MONITOR.SERV_MOD_ACT_STAT_DISABLE(
            service_name => 'ACCTG' 
         ,  module_name  => 'GLEDGER'
         ,  action_name  => 'INSERT ITEM');
    

18.1.3 Viewing Gathered Statistics for End-to-End Application Tracing

You can display the statistics that have been gathered with the following V$ views:

  • The DBA_ENABLED_AGGREGATIONS view can display the accumulated global statistics for the currently enabled statistics.

  • The V$CLIENT_STATS view displays the accumulated statistics for a specified client identifier.

  • The V$SERVICE_STATS view displays accumulated statistics for a specified service.

  • The V$SERV_MOD_ACT_STATS view displays accumulated statistics for a combination of specified service, module, and action.

  • The V$SERVICEMETRIC view displays accumulated statistics for elapsed time of database calls and for CPU use.

18.1.4 Enabling and Disabling for End-to-End Tracing

To enable tracing for client identifier, service, module, action, session, instance or database, execute the appropriate procedures in the DBMS_MONITOR package. You can enable tracing for specific diagnosis and workload management by the following criteria:

With the criteria that you provide, specific trace information is captured in a set of trace files and combined into a single output trace file.

18.1.4.1 Enabling and Disabling Tracing for a Client Identifier

To enable tracing globally for the database for a specified client identifier, use the CLIENT_ID_TRACE_ENABLE procedure. The CLIENT_ID_TRACE_DISABLE procedure disables tracing globally for the database for a given client identifier.

Assumptions

This tutorial assumes the following:

  • OE.OE is the client identifier for which SQL tracing is to be enabled.

  • You want to include wait information in the trace.

  • You want to exclude bind information from the trace.

To enable and disable tracing for a client identifier: 

  1. Start SQL*Plus, and then connect to the database with the appropriate privileges.

  2. Enable tracing for the client.

    For example, execute the following program:

    BEGIN 
      DBMS_MONITOR.CLIENT_ID_TRACE_ENABLE(
           client_id => 'OE.OE' 
    ,      waits     => true
    ,      binds     => false
    );
    END;
    
  3. Disable tracing for the client.

    For example, execute the following command:

    EXECUTE DBMS_MONITOR.CLIENT_ID_TRACE_DISABLE(client_id => 'OE.OE');
    

18.1.4.2 Enabling and Disabling Tracing for a Service, Module, and Action

The SERV_MOD_ACT_TRACE_ENABLE procedure enables SQL tracing for a specified combination of service name, module, and action globally for a database, unless the procedure specifies a database instance name. The SERV_MOD_ACT_TRACE_DISABLE procedure disables the trace at all enabled instances for a given combination of service name, module, and action name globally.

Assumptions

This tutorial assumes the following:

  • You want to enable tracing for the service ACCTG.

  • You want to enable tracing for all actions for the combination of the ACCTG service and the PAYROLL module.

  • You want to include wait information in the trace.

  • You want to exclude bind information from the trace.

  • You want to enable tracing only for the inst1 instance.

To enable and disable tracing for a service, module, and action: 

  1. Start SQL*Plus, and then connect to the database with the appropriate privileges.

  2. Enable tracing for the service, module, and actions.

    For example, execute the following command:

    EXECUTE DBMS_MONITOR.SERV_MOD_ACT_TRACE_ENABLE(
            service_name  => 'ACCTG'
         ,  module_name   => 'PAYROLL'
         ,  waits         =>  true
         ,  binds         =>  false
         ,  instance_name => 'inst1'
    );
    
  3. Disable tracing for the service, module, and actions.

    For example, execute the following command:

    EXECUTE DBMS_MONITOR.SERV_MOD_ACT_TRACE_DISABLE(
            service_name  => 'ACCTG'
         ,  module_name   => 'PAYROLL'
         ,  instance_name => 'inst1'
    );
    

18.1.4.3 Tracing for Session

The SESSION_TRACE_ENABLE procedure enables the trace for a given database session identifier (SID), on the local instance.

To enable tracing for a specific session ID and serial number, determine the values for the session to trace:

SELECT SID, SERIAL#, USERNAME FROM V$SESSION;

       SID    SERIAL# USERNAME
---------- ---------- ------------------------------
        27         60 OE
...

Use the appropriate values to enable tracing for a specific session:

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(session_id => 27, serial_num => 60,
        waits => true, binds => false);

The true argument includes wait information in the trace. The false argument excludes bind information from the trace.

The SESSION_TRACE_DISABLE procedure disables the trace for a given database session identifier (SID) and serial number. For example:

EXECUTE DBMS_MONITOR.SESSION_TRACE_DISABLE(session_id => 27, serial_num => 60);

While the DBMS_MONITOR package can only be invoked by a user with the DBA role, any user can also enable SQL tracing for their own session by using the DBMS_SESSION package. A user can invoke the SESSION_TRACE_ENABLE procedure to enable session-level SQL trace for the user's session. For example:

EXECUTE DBMS_SESSION.SESSION_TRACE_ENABLE(waits => true, binds => false);

The true argument includes wait information in the trace. The false argument excludes bind information from the trace.

The SESSION_TRACE_DISABLE procedure disables the trace for the invoking session. For example:

EXECUTE DBMS_SESSION.SESSION_TRACE_DISABLE();

18.1.4.4 Tracing for Entire Instance or Database

The DATABASE_TRACE_ENABLE procedure enables SQL tracing for a given instance or an entire database. Tracing is enabled for all current and future sessions. For example:

EXECUTE DBMS_MONITOR.DATABASE_TRACE_ENABLE(waits => true, binds => false, 
        instance_name => 'inst1');

In this example, the inst1 instance is specified to enable tracing for that instance. The true argument specifies that wait information is in the trace. The false argument specifies that no bind information is in the trace. This example results in SQL tracing of all SQL in the inst1 instance.

The DATABASE_TRACE_ENABLE procedure overrides all other session-level traces, but is complementary to the client identifier, service, module, and action traces. All new sessions inherit the wait and bind information specified by this procedure until the DATABASE_TRACE_DISABLE procedure is called. When you invoke this procedure with the instance_name parameter, the procedure resets the session-level SQL trace for the named instance. If you invoke this procedure without the instance_name parameter, then the procedure resets the session-level SQL trace for the entire database.

The DATABASE_TRACE_DISABLE procedure disables the tracing for an entire instance or database. For example:

EXECUTE DBMS_MONITOR.DATABASE_TRACE_DISABLE(instance_name => 'inst1');

This preceding example disables all session-level SQL tracing for the inst1 instance. To disable the session-level SQL tracing for an entire database, invoke the DATABASE_TRACE_DISABLE procedure without specifying the instance_name parameter:

EXECUTE DBMS_MONITOR.DATABASE_TRACE_DISABLE();

18.1.5 Viewing Enabled Traces for End to End Tracing

A Cloud Control report or the DBA_ENABLED_TRACES view can display outstanding traces. In the DBA_ENABLED_TRACES view, you can determine detailed information about how a trace was enabled, including the trace type. The trace type specifies whether the trace is enabled for client identifier, session, service, database, or a combination of service, module, and action.

18.2 Using the trcsess Utility

The trcsess utility consolidates trace output from selected trace files based on several criteria:

  • Session ID

  • Client ID

  • Service name

  • Action name

  • Module name

After trcsess merges the trace information into a single output file, the output file could be processed by TKPROF.

trcsess is useful for consolidating the tracing of a particular session for performance or debugging purposes. Tracing a specific session is usually not a problem in the dedicated server model as a single dedicated process serves a session during its lifetime. You can see the trace information for the session from the trace file belonging to the dedicated server serving it. However, in a shared server configuration a user session is serviced by different processes over time. The trace pertaining to the user session is scattered across different trace files belonging to different processes. This makes it difficult to get a complete picture of the life cycle of a session.

18.2.1 Syntax for trcsess

The syntax for the trcsess utility is:

trcsess  [output=output_file_name]
         [session=session_id]
         [clientid=client_id]
         [service=service_name]
         [action=action_name]
         [module=module_name]
         [trace_files]

where

  • output specifies the file where the output is generated. If this option is not specified, then the utility writes to standard output.

  • session consolidates the trace information for the session specified. The session identifier is a combination of session index and session serial number, such as 21.2371. You can locate these values in the V$SESSION view.

  • clientid consolidates the trace information given client ID.

  • service consolidates the trace information for the given service name.

  • action consolidates the trace information for the given action name.

  • module consolidates the trace information for the given module name.

  • trace_files is a list of all the trace file names, separated by spaces, in which trcsess should look for trace information. You can use the wildcard character (*) to specify the trace file names. If you do not specify trace files, then trcsess takes all the files in the current directory as input.

You must specify one of the session, clientid, service, action, or module options. If more then one of the session, clientid, service, action, or module options is specified, then the trace files which satisfies all the criteria specified are consolidated into the output file.

18.2.2 Sample Output of trcsess

This sample output of trcsess shows the container of traces for a particular session. In this example, the session index and serial number equals 21.2371.

You can invoke trcsess with various options. In the following case, all files in current directory are taken as input:

trcsess session=21.2371

In this case, several trace files are specified:

trcsess session=21.2371 main_12359.trc main_12995.trc 

The sample output is similar to the following:

[PROCESS ID = 12359] 
*** 2012-04-02 09:48:28.376 
PARSING IN CURSOR #1 len=17 dep=0 uid=27 oct=3 lid=27 tim=868373970961 hv=887450622 ad='22683fb4' 
select * from cat 
END OF STMT 
PARSE #1:c=0,e=339,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=868373970944 
EXEC #1:c=0,e=221,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=868373971411 
FETCH #1:c=0,e=791,p=0,cr=7,cu=0,mis=0,r=1,dep=0,og=4,tim=868373972435 
FETCH #1:c=0,e=1486,p=0,cr=20,cu=0,mis=0,r=6,dep=0,og=4,tim=868373986238 
*** 2012-04-02 10:03:58.058 
XCTEND rlbk=0, rd_only=1 
STAT #1 id=1 cnt=7 pid=0 pos=1 obj=0 op='FILTER  ' 
STAT #1 id=2 cnt=7 pid=1 pos=1 obj=18 op='TABLE ACCESS BY INDEX ROWID OBJ$ ' 
STAT #1 id=3 cnt=7 pid=2 pos=1 obj=37 op='INDEX RANGE SCAN I_OBJ2 ' 
STAT #1 id=4 cnt=0 pid=1 pos=2 obj=4 op='TABLE ACCESS CLUSTER TAB$J2 ' 
STAT #1 id=5 cnt=6 pid=4 pos=1 obj=3 op='INDEX UNIQUE SCAN I_OBJ# ' 
[PROCESS ID=12995] 
*** 2012-04-02 10:04:32.738 
Archiving is disabled  

18.3 Understanding SQL Trace and TKPROF

The SQL Trace facility and TKPROF enable you to accurately assess the efficiency of the SQL statements an application runs. For best results, use these tools with EXPLAIN PLAN rather than using EXPLAIN PLAN alone.

18.3.1 Understanding 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

  • User name under which each parse occurred

  • Each commit and rollback

  • Wait event data for each SQL statement, and a summary for each trace file

If the cursor for the SQL statement is closed, then SQL Trace also provides row source information that includes:

  • Row operations showing the actual execution plan of each SQL statement

  • Number of rows, number of consistent reads, number of physical reads, number of physical writes, and time elapsed for each operation on a row

Although it is possible to enable the SQL Trace facility for a session or for an instance, it is recommended that you use the DBMS_SESSION or DBMS_MONITOR packages instead. When the SQL Trace facility is enabled for a session or for an instance, performance statistics for all SQL statements executed in a user session or in the instance are placed into trace files. Using the SQL Trace facility can have a severe performance impact and may result in increased system overhead, excessive CPU usage, and inadequate disk space.

Oracle Database provides the trcsess command-line utility that consolidates tracing information from several trace files based on specific criteria, such as session or client ID. See "Using the trcsess Utility".

See Also:

"Enabling and Disabling for End-to-End Tracing" to learn how to use the DBMS_SESSION or DBMS_MONITOR packages to enable SQL tracing for a session or an instance

18.3.2 Understanding TKPROF

You can run the TKPROF program to format the contents of the trace file and place the output into a readable output file. TKPROF can also:

  • Create a SQL script that stores the statistics in the database

  • Determine the execution plans of SQL statements

    Note:

    If the cursor for a SQL statement is not closed, then TKPROF output does not automatically include the actual execution plan of the SQL statement. In this situation, use the EXPLAIN option with TKPROF to generate an execution plan.

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

18.4 Using the SQL Trace Facility and TKPROF

This section explains the basic procedure for using SQL Trace and TKPROF.

To use the SQL Trace facility and TKPROF: 

  1. Set initialization parameters for trace file management.

    See "Step 1: Setting Initialization Parameters for Trace File Management".

  2. Enable the SQL Trace facility for the desired session, and run the application. This step produces a trace file containing statistics for the SQL statements issued by the application.

    See "Step 2: Enabling the SQL Trace Facility".

  3. Run TKPROF to translate the trace file created in Step 2 into a readable output file. This step can optionally create a SQL script that you can use to store the statistics in a database.

    See "Step 3: Formatting Trace Files with TKPROF".

  4. Interpret the output file created in Step 3.

    See "Step 4: Interpreting TKPROF Output".

  5. Optionally, run the SQL script produced in Step 3 to store the statistics in the database.

    See "Step 5: Storing SQL Trace Facility Statistics".

18.4.1 Step 1: Setting Initialization Parameters for Trace File Management

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

To set initialization parameters for trace file management: 

  1. Check the settings of the TIMED_STATISTICS, MAX_DUMP_FILE_SIZE, and DIAGNOSTIC_DEST initialization parameters, as indicated in Table 18-1.

    Table 18-1 Initialization Parameters to Check Before Enabling SQL Trace

    Parameter Description

    DIAGNOSTIC_DEST

    Specifies the location of the Automatic Diagnostic Repository (ADR) Home. The diagnostic files for each database instance are located in this dedicated directory. Oracle Database Reference for information about the DIAGNOSTIC_DEST initialization parameter.

    MAX_DUMP_FILE_SIZE

    When the SQL Trace facility is enabled at the database instance level, every call to the database writes a text line in a file in the operating system's file format. The maximum size of these files in operating system blocks is limited by this initialization parameter. The default is UNLIMITED. See Oracle Database Administrator's Guide to learn how to control the trace file size.

    TIMED_STATISTICS

    Enables and disables the collection of timed statistics, such as CPU and elapsed times, by the SQL Trace facility, and the collection of various statistics in the V$ views.

    If STATISTICS_LEVEL is set to TYPICAL or ALL, then the default value of TIMED_STATISTICS is true. If STATISTICS_LEVEL is set to BASIC, then the default value of TIMED_STATISTICS is false. See Oracle Database Reference for information about the STATISTICS_LEVEL initialization parameter.

    Enabling timing causes extra timing calls for low-level operations. This is a dynamic parameter. It is also a session parameter. See Oracle Database Reference for information about the TIMED_STATISTICS initialization parameter.


  2. Devise a way of recognizing the resulting trace file.

    Be sure you know how to distinguish the trace files by name. You can tag trace files by including in your programs a statement such as SELECT 'program_name' FROM DUAL. You can then trace each file back to the process that created it.

    You can also set the TRACEFILE_IDENTIFIER initialization parameter to specify a custom identifier that becomes part of the trace file name (see Oracle Database Reference for information about the TRACEFILE_IDENTIFIER initialization parameter). For example, you can add my_trace_id to subsequent trace file names for easy identification with the following:

    ALTER SESSION SET TRACEFILE_IDENTIFIER = 'my_trace_id';
    
  3. If the operating system retains multiple versions of files, then ensure that the version limit is high enough to accommodate the number of trace files you expect the SQL Trace facility to generate.

  4. If the generated trace files can be owned by an operating system user other than yourself, then ensure that you have the necessary permissions to use TKPROF to format them.

18.4.2 Step 2: Enabling the SQL Trace Facility

Enable the SQL Trace facility at either of the following levels:

  • Database instance

    Use DBMS_MONITOR.DATABASE_TRACE_ENABLE procedure to enable tracing, and DBMS_MONITOR.DATABASE_TRACE_DISABLE procedure to disable tracing.

  • Database session

    Use DBMS_SESSION.SET_SQL_TRACE procedure to enable tracing (true) or disable tracing (false).

    Caution:

    Because running the SQL Trace facility increases system overhead, enable it only when tuning SQL statements, and disable it when you are finished.

To enable and disable tracing at the database instance level: 

  1. Start SQL*Plus, and connect to the database with administrator privileges.

  2. Enable tracing at the database instance level.

    The following example enables tracing for the orcl instance:

    EXEC DBMS_MONITOR.DATABASE_TRACE_ENABLE(INSTANCE_NAME => 'orcl');
    
  3. Execute the statements to be traced.

  4. Disable tracing for the database instance.

    The following example disables tracing for the orcl instance:

    EXEC DBMS_MONITOR.DATABASE_TRACE_DISABLE(INSTANCE_NAME => 'orcl');
    

To enable and disable tracing at the session level: 

  1. Start SQL*Plus, and connect to the database with the desired credentials.

  2. Enable tracing for the current session.

    The following example enables tracing for the current session:

    EXEC DBMS_SESSION.SET_SQL_TRACE(sql_trace => true);
    
  3. Execute the statements to be traced.

  4. Disable tracing for the current session.

    The following example disables tracing for the current session:

    EXEC DBMS_SESSION.SET_SQL_TRACE(sql_trace => false);
    

See Also:

Oracle Database PL/SQL Packages and Types Reference to learn about DBMS_MONITOR.DATABASE_TRACE_ENABLE

18.4.3 Step 3: Formatting Trace Files with TKPROF

TKPROF accepts as input a trace file produced by the SQL Trace facility, and it produces a formatted output file. TKPROF can also be used to generate execution plans.

After the SQL Trace facility has generated trace files, you can:

  • Run TKPROF on each individual trace file, producing several 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.

  • Run the trcsess command-line utility to consolidate tracing information from several trace files, then run TKPROF on the result. See "Using the trcsess Utility".

TKPROF does not report COMMITs and ROLLBACKs that are recorded in the trace file.

18.4.3.1 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.

18.4.3.2 Syntax of TKPROF

TKPROF is run from the operating system prompt. The syntax is:

tkprof filename1 filename2 [waits=yes|no] [sort=option] [print=n]
    [aggregate=yes|no] [insert=filename3] [sys=yes|no] [table=schema.table]
    [explain=user/password] [record=filename4] [width=n]

The input and output files are the only required arguments. If you invoke TKPROF without arguments, then the tool displays online help. Use the arguments in Table 18-2 with TKPROF.

Table 18-2 TKPROF Arguments

Argument Description

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.

WAITS

Specifies whether to record summary for any wait events found in the trace file. Valid values are YES (default) and NO.

SORT

Sorts traced SQL statements in descending order of specified sort option before listing them in the output file. If multiple options are specified, then the output is sorted in descending order by the sum of the values specified in the sort options. If you omit this parameter, then TKPROF lists statements into the output file in order of first use. Sort options are listed 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

  • PRSQRY - 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 executions

  • 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

  • USERID - Userid of user that parsed the cursor

PRINT

Lists only the first integer sorted SQL statements from the output file. If you omit this parameter, then TKPROF lists all traced SQL statements. This parameter does not affect the optional SQL script. The SQL script always generates insert data for all traced SQL statements.

AGGREGATE

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

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. This parameter does not affect the optional SQL script. The SQL script always inserts statistics for all traced SQL statements, including recursive SQL statements.

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 exists, then TKPROF deletes all rows in the table, uses it for the EXPLAIN PLAN statement (which writes more rows into the table), and then deletes those rows. If this table does not exist, then 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 exist, then the user must also be able to issue CREATE TABLE and DROP TABLE statements. For the privileges to issue these statements, see Oracle Database SQL Language Reference.

This option enables 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.

TKPROF supports the following combinations:

  • 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

  • The TABLE parameter without the EXPLAIN parameter

    TKPROF ignores the TABLE parameter.

If no plan table exists, then TKPROF creates the table PROF$PLAN_TABLE and then drops it at the end.

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 statement after connecting to Oracle Database with the user and password specified in this parameter. The specified user must have CREATE SESSION system privileges. TKPROF takes longer to process a large trace file if the EXPLAIN option is used.

RECORD

Creates a SQL script with the specified filename with all of the nonrecursive SQL in the trace file. You can use this script to replay the user events from the trace file.

WIDTH

An integer that controls the output line width of some TKPROF output, such as the explain plan. This parameter is useful for post-processing of TKPROF output.


18.4.3.3 Examples of TKPROF Statement

This section provides two brief examples of TKPROF usage. For an complete example of TKPROF output, see "Sample TKPROF Output".

18.4.3.3.1 TKPROF Example 1

If you are processing a large trace file using a combination of SORT parameters and the PRINT parameter, then you can produce a TKPROF output file containing only the highest resource-intensive statements. For example, the following statement prints the 10 statements in the trace file that have generated the most physical I/O:

TKPROF ora53269.trc ora53269.prf SORT = (PRSDSK, EXEDSK, FCHDSK) PRINT = 10
18.4.3.3.2 TKPROF Example 2

This example runs TKPROF, accepts a trace file named examp12_jane_fg_sqlplus_007.trc, and writes a formatted output file named outputa.prf:

TKPROF examp12_jane_fg_sqlplus_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 the screen, and you might need to use continuation characters, depending on the 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 statement to generate the execution plan for each traced SQL statement. You can use this to get access paths and row source counts.

    Note:

    If the cursor for a SQL statement is not closed, then TKPROF output does not automatically include the actual execution plan of the SQL statement. In this situation, you can use the EXPLAIN option with TKPROF to generate an execution plan.
  • 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 Database 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.

18.4.4 Step 4: Interpreting TKPROF Output

This section provides guidelines for interpreting TKPROF output.

While TKPROF provides a useful analysis, the most accurate measure of efficiency is the performance of the application. At the end of the TKPROF output is a summary of the work that the process performed during the period that the trace was running.

18.4.4.1 Tabular Statistics in TKPROF

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. Statistics are identified by the value of the CALL column. See Table 18-3.

Table 18-3 CALL Column Values

CALL Value Meaning

PARSE

Translates the SQL statement into an execution plan, including checks for proper security authorization and checks for the existence of tables, columns, and other referenced objects.

EXECUTE

Actual execution of the statement by Oracle Database. For INSERT, UPDATE, and DELETE statements, this modifies the data. For SELECT statements, this identifies the selected rows.

FETCH

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, executions, and fetches of a statement. The sum of query and current is the total number of buffers accessed, also called Logical I/Os (LIOs). See Table 18-4.

Table 18-4 SQL Trace Statistics for Parses, Executes, and Fetches.

SQL Trace Statistic Meaning

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. This value is zero (0) if TIMED_STATISTICS is not enabled.

ELAPSED

Total elapsed time in seconds for all parse, execute, or fetch calls for the statement. This value is zero (0) if TIMED_STATISTICS is not enabled.

DISK

Total number of data blocks physically read from the data files 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. Usually, buffers are 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.


Statistics about the processed rows appear in the ROWS column. The column shows the 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.

Note:

The row source counts are displayed when a cursor is closed. In SQL*Plus, there is only one user cursor, so each statement executed causes the previous cursor to be closed; therefore, the row source counts are displayed. PL/SQL has its own cursor handling and does not close child cursors when the parent cursor is closed. Exiting (or reconnecting) causes the counts to be displayed.

18.4.4.2 Row Source Operations

Row source operations provide the number of rows processed for each operation executed on the rows and additional row source information, such as physical reads and writes. The following is a sample:

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  DELETE  (cr=43141 r=266947 w=25854 time=60235565 us)
  28144   HASH JOIN ANTI (cr=43057 r=262332 w=25854 time=48830056 us)
  51427    TABLE ACCESS FULL STATS$SQLTEXT (cr=3465 r=3463 w=0 time=865083 us)
 647529    INDEX FAST FULL SCAN STATS$SQL_SUMMARY_PK 
                      (cr=39592 r=39325 w=0 time=10522877 us) (object id 7409)

In this sample TKPROF output, note the following under the Row Source Operation column:

  • cr specifies consistent reads performed by the row source

  • r specifies physical reads performed by the row source

  • w specifies physical writes performed by the row source

  • time specifies time in microseconds

18.4.4.3 Wait Event Information

If wait event information exists, then the TKPROF output includes a section similar to the following:

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file sequential read                      8084        0.12          5.34
  direct path write                             834        0.00          0.00
  direct path write temp                        834        0.00          0.05
  db file parallel read                           8        1.53          5.51
  db file scattered read                       4180        0.07          1.45
  direct path read                             7082        0.00          0.05
  direct path read temp                        7082        0.00          0.44
  rdbms ipc reply                                20        0.00          0.01
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1        0.00          0.00

In addition, wait events are summed for the entire trace file at the end of the file.

To ensure that wait events information is written to the trace file for the session, run the following SQL statement:

ALTER SESSION SET EVENTS '10046 trace name context forever, level 8';

18.4.4.4 Guideline for Interpreting the Resolution of Statistics

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

18.4.4.5 Recursive SQL Statements

Sometimes, to execute a SQL statement issued by a user, Oracle Database must issue additional SQL statements. Such statements are called recursive calls or recursive SQL. For example, if you insert a row into a table that has insufficient space to hold that row, then the database makes recursive calls to allocate the space dynamically. The database also generates recursive calls when data dictionary information is not available in memory and so must be retrieved from disk.

If recursive calls occur while the SQL Trace facility is enabled, then TKPROF produces statistics for the recursive SQL statements and marks them clearly as recursive SQL statements in the output file. You can suppress the listing of Oracle Database internal recursive calls (for example, space management) in the output file by setting the SYS command-line parameter to NO. 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, consider the statistics for that statement and those for recursive calls caused by that statement.

Note:

Recursive SQL statistics are not included for SQL-level operations.

18.4.4.6 Library Cache Misses in TKPROF

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, then TKPROF does not list the statistic. In "Sample TKPROF Output", the statement resulted in one library cache miss for the parse step and no misses for the execute step.

18.4.4.7 Statement Truncation in SQL Trace

The following SQL statements are truncated to 25 characters in the SQL Trace file:

SET ROLE
GRANT
ALTER USER
ALTER ROLE
CREATE USER
CREATE ROLE

18.4.4.8 Identification of User Issuing the SQL Statement in TKPROF

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 if the statement was issued by multiple users, then 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.

18.4.4.9 Execution Plan in TKPROF

If you specify the EXPLAIN parameter on the TKPROF statement line, then TKPROF uses the EXPLAIN PLAN statement 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.

See Also:

Chapter 7, "Reading Execution Plans" for more information about interpreting execution plans

18.4.4.10 Deciding Which Statements to Tune

You must determine which SQL statements use the most CPU or disk resource. If the TIMED_STATISTICS parameter is enabled, then you can find high CPU activity in the CPU column. If TIMED_STATISTICS is not enabled, then check the QUERY and CURRENT columns.

With the exception of locking problems and inefficient PL/SQL loops, neither the CPU time nor the elapsed time is necessary to find problem statements. The key is the number of block visits, both query (that is, subject to read consistency) and current (that is, not subject to read consistency). Segment headers and blocks that are going to be updated are acquired in current mode, but all query and subquery processing requests the data in query mode. These are precisely the same measures as the instance statistics CONSISTENT GETS and DB BLOCK GETS. You can find high disk activity in the disk column.

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         0
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 

If it is acceptable to have 7.01 CPU seconds 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.

The output indicates that 10 unnecessary parse call were made (because 11 parse calls exist for this single statement) and that array fetch operations were performed. More rows were fetched than there were fetches performed. A large gap between CPU and elapsed timings indicates Physical I/Os.

See Also:

"Examples of TKPROF Statement" for examples of finding resource intensive statements

18.4.5 Step 5: Storing SQL Trace Facility Statistics

You might want to keep a history of the statistics generated by the SQL Trace facility for an 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 TKPROF_TABLE.

After running TKPROF, run this script to store the statistics in the database.

18.4.5.1 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, then TKPROF does not generate a script.

18.4.5.2 Editing the TKPROF Output SQL Script

After TKPROF has created the SQL script, you might want to edit the script before running it. If you have created an output table for previously collected statistics, and if you want to add new statistics to this table, then remove the CREATE TABLE statement from the script. The script then inserts the new rows into the existing table.

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

18.4.5.3 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);

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.

The columns in Table 18-5 help you identify a row of statistics.

Table 18-5 TKPROF_TABLE Columns for Identifying a Row of Statistics

Column Description

SQL_STATEMENT

This is the SQL statement for which the SQL Trace facility collected the row of statistics. Because this column has data type LONG, you cannot use it in expressions or WHERE clause conditions.

DATE_OF_INSERT

This is the date and time when the row was inserted into the table. This value is different from the time when the SQL Trace facility collected the statistics.

DEPTH

This indicates the level of recursion at which the SQL statement was issued. For example, a value of 0 indicates that a user issued the statement. A value of 1 indicates that Oracle Database generated the statement as a recursive call to process a statement with a value of 0 (a statement issued by a user). A value of n indicates that Oracle Database generated the statement as a recursive call to process a statement with a value of n-1.

USER_ID

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

CURSOR_NUM

Oracle Database uses this column value to keep track of the cursor to which each SQL statement was assigned.


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 "Sample TKPROF Output".

SELECT * FROM TKPROF_TABLE;

Sample output appears as follows:

DATE_OF_INSERT CURSOR_NUM DEPTH USER_ID PARSE_CNT PARSE_CPU PARSE_ELAP
-------------- ---------- ----- ------- --------- --------- ---------- 
21-DEC-2012          1      0     8         1        16         22

PARSE_DISK PARSE_QUERY PARSE_CURRENT PARSE_MISS EXE_COUNT EXE_CPU 
---------- ----------- ------------- ---------- --------- ------- 
    3          11           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 
--------- ---------- ---------- ----------- ------------- ---------- 
     2        20          2          2            4           10 

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

18.5 Guidelines for Avoiding Traps in TKPROF Interpretation

This section describes some fine points of TKPROF interpretation:

18.5.1 Guideline for Avoiding the Argument Trap

If you are not aware of the values being bound at run time, then it is possible to fall into the argument trap. EXPLAIN PLAN cannot determine the type of a bind variable from the text of SQL statements, and it always assumes that the type is VARCHAR. If the bind variable is actually a number or a date, then TKPROF can cause implicit data conversions, which can cause inefficient plans to be executed. To avoid this situation, experiment with different data types in the query, and perform the conversion yourself.

18.5.2 Guideline for Avoiding 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    0.10        0.18        0         0       0        0
Execute      1    0.00        0.00        0         0       0        0
Fetch        1    0.11        0.21        2       101       0        1

Misses in library cache during parse: 1
Parsing user id: 01 (USER1)

Rows     Execution Plan
e----     --------- ----
   0     SELECT STATEMENT
   1       TABLE ACCESS (BY ROWID) OF 'CQ_NAMES'
   2         INDEX (RANGE SCAN) OF 'CQ_NAMES_NAME' (NON_UNIQUE) 

18.5.3 Guideline for Avoiding 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 must 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       0.06         0.10        0      0       0    0
Execute         1       0.02         0.02        0      0       0    0 
Fetch           1       0.23         0.30       31     31       3    1

Misses in library cache during parse: 0
Parsing user id: 02  (USER2)

Rows     Execution Plan
-------  ---------------------------------------------------
      0  SELECT STATEMENT
   2340    TABLE ACCESS (BY ROWID) OF 'CQ_NAMES'
      0      INDEX (RANGE SCAN) OF 'CQ_NAMES_NAME' (NON-UNIQUE)

Two statistics suggest that the query might have been executed with 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.

Generating a new trace file gives the following data:

SELECT name_id
FROM cq_names 
WHERE name = 'FLOOR'; 

call    count    cpu   elapsed  disk  query current     rows
-----  ------ ------  -------- ----- ------ -------    -----
Parse       1   0.01      0.02     0      0       0        0
Execute     1   0.00      0.00     0      0       0        0
Fetch       1   0.00      0.00     0      2       0        1

Misses in library cache during parse: 0
Parsing user id: 02  (USER2)

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 CPU time and 20 milliseconds of elapsed time, but the query apparently took no time at all to execute and perform the fetch. These anomalies arise because the clock tick of 10 milliseconds is too long relative to the time taken to execute and fetch the data. In such cases, it is important to get lots of executions of the statements, so that you have statistically valid numbers.

18.5.4 Guideline for Avoiding the Time Trap

Sometimes, as in the following example, you might 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      0.06       0.24        0        0       0           0
Execute        1      0.62      19.62       22      526      12           7
Fetch          0      0.00       0.00        0        0       0           0

Misses in library cache during parse: 1
Parsing user id: 02  (USER2)

Rows     Execution Plan
-------  ---------------------------------------------------
      0  UPDATE STATEMENT
  2519  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. On the one hand, comparative data is essential when the interference is contributing only a short delay (or a small increase in block visits in the previous example). However, if the interference contributes only modest overhead, and if the statement is essentially efficient, then its statistics may not require analysis.

18.6 Sample TKPROF Output

This section provides an example of TKPROF output. Portions have been edited out for brevity.

18.6.1 Sample TKPROF Header

TKPROF: Release 12.1.0.0.2
 
Copyright (c) 1982, 2012, Oracle and/or its affiliates.  All rights reserved.
 
Trace file: /disk1/oracle/log/diag/rdbms/orcla/orcla/trace/orcla_ora_917.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
********************************************************************************

18.6.2 Sample TKPROF Body

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.01       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      0.01       0.00          0          0          0           0

Misses in library cache during parse: 1
Optimizer mode: FIRST_ROWS
Parsing user id: 44  

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1       28.59         28.59
********************************************************************************

select condition 
from
 cdef$ where rowid=:1

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          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      0.00       0.00          0          2          0           1

Misses in library cache during parse: 1
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 1)

Rows     Row Source Operation
-------  ---------------------------------------------------
      1  TABLE ACCESS BY USER ROWID OBJ#(31) (cr=1 r=0 w=0 time=151 us)

********************************************************************************

SELECT last_name, job_id, salary
  FROM employees
WHERE salary =
  (SELECT max(salary) FROM employees)

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.02       0.01          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        2      0.00       0.00          0         15          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        4      0.02       0.01          0         15          0           1

Misses in library cache during parse: 1
Optimizer mode: FIRST_ROWS
Parsing user id: 44  

Rows     Row Source Operation
-------  ---------------------------------------------------
      1  TABLE ACCESS FULL EMPLOYEES (cr=15 r=0 w=0 time=1743 us)
      1   SORT AGGREGATE (cr=7 r=0 w=0 time=777 us)
    107    TABLE ACCESS FULL EMPLOYEES (cr=7 r=0 w=0 time=655 us)

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       2        0.00          0.00
  SQL*Net message from client                     2        9.62          9.62
********************************************************************************

********************************************************************************
 delete
         from stats$sqltext st
        where (hash_value, text_subset) not in
             (select --+ hash_aj
                     hash_value, text_subset
                from stats$sql_summary ss
               where (   (   snap_id     < :lo_snap
                          or snap_id     > :hi_snap
                         )
                         and dbid            = :dbid
                         and instance_number = :inst_num
                     )
                  or (   dbid            != :dbid
                      or instance_number != :inst_num)
              )

call     count       cpu    elapsed       disk      query    current rows
------- ------  -------- ---------- ---------- ---------- ---------- ----------
Parse        1      0.00       0.00          0          0          0          0
Execute      1     29.60      60.68     266984      43776     131172      28144
Fetch        0      0.00       0.00          0          0          0          0
------- ------  -------- ---------- ---------- ---------- ---------- ----------
total        2     29.60      60.68     266984      43776     131172      28144

Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: 22

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  DELETE  (cr=43141 r=266947 w=25854 time=60235565 us)
  28144   HASH JOIN ANTI (cr=43057 r=262332 w=25854 time=48830056 us)
  51427    TABLE ACCESS FULL STATS$SQLTEXT (cr=3465 r=3463 w=0 time=865083 us)
 647529    INDEX FAST FULL SCAN STATS$SQL_SUMMARY_PK 
                      (cr=39592 r=39325 w=0 time=10522877 us) (object id 7409)

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file sequential read                      8084        0.12          5.34
  direct path write                             834        0.00          0.00
  direct path write temp                        834        0.00          0.05
  db file parallel read                           8        1.53          5.51
  db file scattered read                       4180        0.07          1.45
  direct path read                             7082        0.00          0.05
  direct path read temp                        7082        0.00          0.44
  rdbms ipc reply                                20        0.00          0.01
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1        0.00          0.00
********************************************************************************

18.6.3 Sample TKPROF Summary

OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        4      0.04       0.01          0          0          0           0
Execute      5      0.00       0.04          0          0          0           0
Fetch        2      0.00       0.00          0         15          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total       11      0.04       0.06          0         15          0           1

Misses in library cache during parse: 4
Misses in library cache during execute: 1
Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       6        0.00          0.00
  SQL*Net message from client                     5       77.77        128.88

OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS

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          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      0.00       0.00          0          2          0           1

Misses in library cache during parse: 1
    5  user  SQL statements in session.
    1  internal SQL statements in session.
    6  SQL statements in session.
********************************************************************************
Trace file: main_ora_27621.trc
Trace file compatibility: 9.00.01
Sort options: default
       1  session in tracefile.
       5  user  SQL statements in trace file.
       1  internal SQL statements in trace file.
       6  SQL statements in trace file.
       6  unique SQL statements in trace file.
      76  lines in trace file.
     128  elapsed seconds in trace file.