Oracle® Database Performance Tuning Guide 10g Release 2 (10.2) Part Number B14211-01 |
|
|
View PDF |
This chapter discusses Oracle automatic SQL tuning features.
This chapter contains the following sections:
See Also:
Oracle Database 2 Day DBA for information on monitoring and tuning SQL statementsAutomatic SQL Tuning is a new capability of the query optimizer that automates the entire SQL tuning process. Using the newly enhanced query optimizer to tune SQL statements, the automatic process replaces manual SQL tuning, which is a complex, repetitive, and time-consuming function. The Automatic SQL Tuning features are exposed to the user with the SQL Tuning Advisor.
This section covers the following topics:
The enhanced query optimizer has two modes:
In normal mode, the optimizer compiles the SQL and generates an execution plan. The normal mode of the optimizer generates a reasonable execution plan for the vast majority of SQL statements. Under normal mode the optimizer operates with very strict time constraints, usually a fraction of a second, during which it must find a good execution plan.
In tuning mode, the optimizer performs additional analysis to check whether the execution plan produced under normal mode can be further improved. The output of the query optimizer is not an execution plan, but a series of actions, along with their rationale and expected benefit for producing a significantly superior plan. When called under the tuning mode, the optimizer is referred to as the Automatic Tuning Optimizer. The tuning performed by the Automatic Tuning Optimizer is called Automatic SQL Tuning.
Under tuning mode, the optimizer can take several minutes to tune a single statement. It is both time and resource intensive to invoke the Automatic Tuning Optimizer every time a query has to be hard-parsed. The Automatic Tuning Optimizer is meant to be used for complex and high-load SQL statements that have non-trivial impact on the entire system. The Automatic Database Diagnostic Monitor (ADDM) proactively identifies high-load SQL statements which are good candidates for Automatic SQL Tuning. See Chapter 6, "Automatic Performance Diagnostics".
Automatic SQL Tuning includes four types of tuning analysis:
The query optimizer relies on object statistics to generate execution plans. If these statistics are stale or missing, the optimizer does not have the necessary information it needs and can generate poor execution plans. The Automatic Tuning Optimizer checks each query object for missing or stale statistics, and produces two types of output:
Recommendations to gather relevant statistics for objects with stale or no statistics.
Because optimizer statistics are automatically collected and refreshed, this problem may be encountered only when automatic optimizer statistics collection has been turned off. See "Automatic Statistics Gathering".
Auxiliary information in the form of statistics for objects with no statistics, and statistic adjustment factor for objects with stale statistics.
This auxiliary information is stored in an object called a SQL Profile.
The query optimizer can sometimes produce inaccurate estimates about an attribute of a statement due to lack of information, leading to poor execution plans. Traditionally, users have corrected this problem by manually adding hints to the application code to guide the optimizer into making correct decisions. For packaged applications, changing application code is not an option and the only alternative available is to log a bug with the application vendor and wait for a fix.
Automatic SQL Tuning deals with this problem with its SQL Profiling capability. The Automatic Tuning Optimizer creates a profile of the SQL statement called a SQL Profile, consisting of auxiliary statistics specific to that statement. The query optimizer under normal mode makes estimates about cardinality, selectivity, and cost that can sometimes be off by a significant amount resulting in poor execution plans. SQL Profile addresses this problem by collecting additional information using sampling and partial execution techniques to verify and, if necessary, adjust these estimates.
During SQL Profiling, the Automatic Tuning Optimizer also uses execution history information of the SQL statement to appropriately set optimizer parameter settings, such as changing the OPTIMIZER_MODE
initialization parameter setting from ALL_ROWS
to FIRST_ROWS
for that SQL statement.
The output of this type of analysis is a recommendation to accept the SQL Profile. A SQL Profile, once accepted, is stored persistently in the data dictionary. Note that the SQL Profile is specific to a particular query. If accepted, the optimizer under normal mode uses the information in the SQL Profile in conjunction with regular database statistics when generating an execution plan. The availability of the additional information makes it possible to produce well-tuned plans for corresponding SQL statement without requiring any change to the application code.
The scope of a SQL Profile can be controlled by the CATEGORY
profile attribute. This attribute determines which user sessions can apply the profile. You can view the CATEGORY
attribute for a SQL Profile in CATEGORY
column of the DBA_SQL_PROFILES
view. By default, all profiles are created in the DEFAULT
category. This means that all user sessions where the SQLTUNE_CATEGORY
initialization parameter is set to DEFAULT
can use the profile.
By altering the category of a SQL profile, you can determine which sessions are affected by the creation of a profile. For example, by setting the category of a SQL Profile to DEV
, only those users sessions where the SQLTUNE_CATEGORY
initialization parameter is set to DEV
can use the profile. All other sessions do not have access to the SQL Profile and execution plans for SQL statements are not impacted by the SQL profile. This technique enables you to test a SQL Profile in a restricted environment before making it available to other user sessions.
It is important to note that the SQL Profile does not freeze the execution plan of a SQL statement, as done by stored outlines. As tables grow or indexes are created or dropped, the execution plan can change with the same SQL Profile. The information stored in it continues to be relevant even as the data distribution or access path of the corresponding statement change. However, over a long period of time, its content can become outdated and would have to be regenerated. This can be done by running Automatic SQL Tuning again on the same statement to regenerate the SQL Profile.
SQL Profiles apply to the following statement types:
SELECT
statements
UPDATE
statements
INSERT
statements (only with a SELECT
clause)
DELETE
statements
CREATE
TABLE
statements (only with the AS
SELECT
clause)
MERGE
statements (the update or insert operations)
A complete set of functions are provided for management of SQL Profiles. See "SQL Profiles".
Indexes can tremendously enhance performance of a SQL statement by reducing the need for full table scans on large tables. Effective indexing is a common tuning technique. The Automatic Tuning Optimizer also explores whether a new index can significantly enhance the performance of a query. If such an index is identified, it recommends its creation.
Because the Automatic Tuning Optimizer does not analyze how its index recommendation can affect the entire SQL workload, it also recommends running a the SQLAccess Advisor utility on the SQL statement along with a representative SQL workload. The SQLAccess Advisor looks at the impact of creating an index on the entire SQL workload before making any recommendations. See "Automatic SQL Tuning Features".
The Automatic Tuning Optimizer identifies common problems with structure of SQL statements than can lead to poor performance. These could be syntactic, semantic, or design problems with the statement. In each of these cases the Automatic Tuning Optimizer makes relevant suggestions to restructure the SQL statements. The alternative suggested is similar, but not equivalent, to the original statement.
For example, the optimizer may suggest to replace UNION
operator with UNION
ALL
or to replace NOT
IN
with NOT
EXISTS
. An application developer can then determine if the advice is applicable to their situation or not. For instance, if the schema design is such that there is no possibility of producing duplicates, then the UNION
ALL
operator is much more efficient than the UNION
operator. These changes require a good understanding of the data properties and should be implemented only after careful consideration.
The Automatic SQL Tuning capabilities are exposed through a server utility called the SQL Tuning Advisor. The SQL Tuning Advisor takes one or more SQL statements as an input and invokes the Automatic Tuning Optimizer to perform SQL tuning on the statements. The output of the SQL Tuning Advisor is in the form of an advice or recommendations, along with a rationale for each recommendation and its expected benefit. The recommendation relates to collection of statistics on objects, creation of new indexes, restructuring of the SQL statement, or creation of SQL Profile. A user can choose to accept the recommendation to complete the tuning of the SQL statements.
The SQL Tuning Advisor input can be a single SQL statement or a set of statements. For tuning multiple statements, a SQL Tuning Set (STS) has to be first created. An STS is a database object that stores SQL statements along with their execution context. An STS can be created manually using command line APIs or automatically using Oracle Enterprise Manager. See "SQL Tuning Sets".
This section cover the following topics related to the SQL Tuning Advisor:
The input for the SQL Tuning Advisor can come from several sources. These input sources include:
Automatic Database Diagnostic Monitor
The primary input source is the Automatic Database Diagnostic Monitor (ADDM). By default, ADDM runs proactively once every hour and analyzes key statistics gathered by the Automatic Workload Repository (AWR) over the last hour to identify any performance problems including high-load SQL statements. If a high-load SQL is identified, ADDM recommends running SQL Tuning Advisor on the SQL. See "Automatic Database Diagnostic Monitor".
High-load SQL statements
The second most important input source is the high-load SQL statements captured in Automatic Workload Repository (AWR). The AWR takes regular snapshots of the system activity including high-load SQL statements ranked by relevant statistics, such as CPU consumption and wait time. A user can view the AWR and identify the high-load SQL of interest and run SQL Tuning Advisor on them. By default, the AWR retains data for the last seven days. This means that any high-load SQL that ran within the retention period of the AWR can be located and tuned using this feature. See "Automatic Workload Repository".
Cursor cache
The third likely source of input is the cursor cache. This source is used for tuning recent SQL statements that are yet to be captured in the AWR. The cursor cache and AWR together provide the capability to identify and tune high-load SQL statements from the current time going as far back as the AWR retention allows, which by default is at least 7 days.
SQL Tuning Set
Another possible input source for the SQL Tuning Advisor is the SQL Tuning Set. A SQL Tuning Set (STS) is a database object that stores SQL statements along with their execution context. An STS can include SQL statements that are yet to be deployed, with the goal of measuring their individual performance, or identifying the ones whose performance falls short of expectation. When a set of SQL statements are used as input, a SQL Tuning Set (STS) has to be first constructed and stored. See "SQL Tuning Sets".
SQL Tuning Advisor provides options to manage the scope and duration of a tuning task. The scope of a tuning task can be set to limited or comprehensive.
If the limited option is chosen, the SQL Tuning Advisor produces recommendations based on statistics checks, access path analysis, and SQL structure analysis. SQL Profile recommendations are not generated.
If the comprehensive option is selected, the SQL Tuning Advisor carries out all the analysis it performs under limited scope plus SQL Profiling. With the comprehensive option you can also specify a time limit for the tuning task, which by default is 30 minutes.
After analyzing the SQL statements, the SQL Tuning Advisor provides advice on optimizing the execution plan, the rationale for the proposed optimization, the estimated performance benefit, and the command to implement the advice. You simply have to choose whether or not to accept the recommendations to optimize the SQL statements.
The recommended interface for the SQL Tuning Advisor is the Oracle Enterprise Manager.
The SQL Tuning Advisor may be used to tune a single or multiple SQL statements. When tuning multiple SQL statements, Oracle Enterprise Manager will automatically create a SQL Tuning Set (STS) from a user-defined set of SQL statements. An STS is a database object that stores SQL statements along with their execution context. An STS can be created manually using command line APIs, or automatically using Oracle Enterprise Manager. See "SQL Tuning Sets".
To run a SQL Tuning Advisor Task using Oracle Enterprise Manager:
On the Database Home page, click the Advisor Central link under Related Links.
The Advisor Central page appears.
Under Advisors, click SQL Tuning Advisor.
The SQL Tuning Advisor Links page appears.
To run a SQL tuning task on:
High-load SQL statement, click Top Activity. The Top Activity page appears. Under Top SQL, select the top SQL statement to tune and click Schedule SQL Tuning Advisor.
SQL statement within a historical 24 hour period, click Period SQL. The Period SQL page appears. Under Historical Interval Selection, click on the band below the chart to select the historical 24 hour interval for which you want to view SQL statements that ran on the database instance. Under Detail for Selected 24 Hour Interval, select the SQL statement to tune and click Schedule SQL Tuning Advisor.
SQL Tuning Set, click SQL Tuning Sets. The SQL Tuning Sets page appears. Select the SQL Tuning Set to tune and click Schedule SQL Tuning Advisor.
For information on SQL Tuning Sets, see "SQL Tuning Sets".
Under Scope, select the scope of tuning to perform.
A limited scope will only take approximately one second to tune each SQL statement but will not recommend a SQL Profile. A comprehensive scope will perform a complete analysis and recommend a SQL Profile when appropriate but may take much longer. When running a comprehensive tuning task, you can set a time limit (in minutes) in the Total Time Limit field.
Under Schedule, select Immediately to run the SQL tuning task immediately or Later to schedule a specific time in the future and click OK.
Depending on your selection, the SQL tuning task will either run immediately or at its scheduled time.
Once the SQL tuning task has been scheduled, various actions can be performed in the Advisor Central page:
To view results for a completed SQL tuning task, select the SQL Tuning Advisor task and click View Result.
To delete a SQL tuning task, select the SQL Tuning Advisor task and click Delete.
To reschedule a SQL tuning task, select the SQL Tuning Advisor task. Select Re-schedule from the Actions pull-down menu and click Go.
To interrupt a running SQL tuning task, select the SQL Tuning Advisor task. Select Interrupt from the Actions pull-down menu and click Go.
To cancel a scheduled SQL tuning task, select the SQL Tuning Advisor task. Select Cancel from the Actions pull-down menu and click Go.
To change the expiration of a SQL tuning task, select the SQL Tuning Advisor task. Select Change Expiration from the Actions pull-down menu and click Go.
To edit a scheduled SQL tuning task, select the SQL Tuning Advisor task. Select Edit from the Actions pull-down menu and click Go.
See Also:
Oracle Enterprise Manager Concepts and online help for information about monitoring and diagnostic tools available with Oracle Enterprise ManagerWhile the recommended interface for the SQL Tuning Advisor is the Oracle Enterprise Manager Database Control, the advisor can be administered with procedures in the DBMS_SQLTUNE
package. To use the APIs, the user must be granted specific privileges.
See Also:
Oracle Database PL/SQL Packages and Types Reference for information on the security model for theDBMS_SQLTUNE
packageRunning SQL Tuning Advisor using DBMS_SQLTUNE
package is a multi-step process:
Create a SQL Tuning Set (if tuning multiple SQL statements)
Create a SQL tuning task
Execute a SQL tuning task
Display the results of a SQL tuning task
Implement recommendations as appropriate
A SQL tuning task can be created for a single SQL statement. For tuning multiple statements, a SQL Tuning Set (STS) has to be first created. An STS is a database object that stores SQL statements along with their execution context. An STS can be created manually using command line APIs or automatically using Oracle Enterprise Manager. See "SQL Tuning Sets".
Figure 12-2 shows the steps involved when running the SQL Tuning Advisor using the DBMS_SQLTUNE
package.
This section covers the following topics:
See Also:
Oracle Database PL/SQL Packages and Types Reference for detailed information on theDBMS_SQLTUNE
packageYou can create tuning tasks from the text of a single SQL statement, a SQL Tuning Set containing multiple statements, a SQL statement selected by SQL identifier from the cursor cache, or a SQL statement selected by SQL identifier from the Automatic Workload Repository.
For example, to use the SQL Tuning Advisor to optimize a specified SQL statement text, you need to create a tuning task with the SQL statement passed as a CLOB argument. For the following PL/SQL code, the user HR has been granted the ADVISOR
privilege and the function is run as user HR on the employees
table in the HR schema.
DECLARE my_task_name VARCHAR2(30); my_sqltext CLOB; BEGIN my_sqltext := 'SELECT /*+ ORDERED */ * ' || 'FROM employees e, locations l, departments d ' || 'WHERE e.department_id = d.department_id AND ' || 'l.location_id = d.location_id AND ' || 'e.employee_id < :bnd'; my_task_name := DBMS_SQLTUNE.CREATE_TUNING_TASK( sql_text => my_sqltext, bind_list => sql_binds(anydata.ConvertNumber(100)), user_name => 'HR', scope => 'COMPREHENSIVE', time_limit => 60, task_name => 'my_sql_tuning_task', description => 'Task to tune a query on a specified employee'); END; /
In this example, 100 is the value for bind variable :bnd
passed as function argument of type SQL_BINDS
, HR
is the user under which the CREATE_TUNING_TASK
function analyzes the SQL statement, the scope is set to COMPREHENSIVE
which means that the advisor also performs SQL Profiling analysis, and 60 is the maximum time in seconds that the function can run. In addition, values for task name and description are provided.
The CREATE_TUNING_TASK
function returns the task name that you have provided or generates a unique task name. You can use the task name to specify this task when using other APIs. To view the task names associated with a specific owner, you can run the following:
SELECT task_name FROM DBA_ADVISOR_LOG WHERE owner = 'HR';
After you have created a tuning task, you need to execute the task and start the tuning process. For example:
BEGIN DBMS_SQLTUNE.EXECUTE_TUNING_TASK( task_name => 'my_sql_tuning_task' ); END; /
You can check the status of the task by reviewing the information in the USER_ADVISOR_TASKS view or check execution progress of the task in the V$SESSION_LONGOPS
view. For example:
SELECT status FROM USER_ADVISOR_TASKS WHERE task_name = 'my_sql_tuning_task';
You can check the execution progress of the SQL Tuning Advisor in the V$ADVISOR_PROGRESS
view. For example:
SELECT sofar, totalwork FROM V$ADVISOR_PROGRESS WHERE user_name = 'HR' AND task_name = 'my_sql_tuning_task';
See Also:
Oracle Database Reference for information on the V$ADVISOR_PROGRESS viewAfter a task has been executed, you display a report of the results with the REPORT_TUNING_TASK
function. For example:
SET LONG 1000 SET LONGCHUNKSIZE 1000 SET LINESIZE 100 SELECT DBMS_SQLTUNE.REPORT_TUNING_TASK( 'my_sql_tuning_task') FROM DUAL;
The report contains all the findings and recommendations of Automatic SQL Tuning. For each proposed recommendation, the rationale and benefit is provided along with the SQL commands needed to implement the recommendation.
Additional information about tuning tasks and results can be found in DBA views. See "SQL Tuning Information Views".
You can use the following APIs for managing SQL tuning tasks:
INTERRUPT_TUNING_TASK
to interrupt a task while executing, causing a normal exit with intermediate results
RESUME_TUNING_TASK
to resume a previously interrupted task
CANCEL_TUNING_TASK
to cancel a task while executing, removing all results from the task
RESET_TUNING_TASK
to reset a task while executing, removing all results from the task and returning the task to its initial state
DROP_TUNING_TASK
to drop a task, removing all results associated with the task
A SQL Tuning Set (STS) is a database object that includes one or more SQL statements along with their execution statistics and execution context, and could include a user priority ranking. The SQL statements can be loaded into a SQL Tuning Set from different SQL sources, such as the Automatic Workload Repository, the cursor cache, or custom SQL provided by the user. An STS includes:
A set of SQL statements
Associated execution context, such as user schema, application module name and action, list of bind values, and the cursor compilation environment
Associated basic execution statistics, such as elapsed time, CPU time, buffer gets, disk reads, rows processed, cursor fetches, the number of executions, the number of complete executions, optimizer cost, and the command type
Associated execution plans and row source statistics for each SQL statement (optional)
SQL statements can be filtered using the application module name and action, or any of the execution statistics. In addition, the SQL statements can be ranked based on any combination of execution statistics.
A SQL Tuning Set can be used as input to the SQL Tuning Advisor, which performs automatic tuning of the SQL statements based on other input parameters specified by the user. SQL Tuning Sets are transportable across databases and can be exported from one system to another, allowing for the transfer of SQL workloads between databases for remote performance diagnostics and tuning. When poorly performing SQL statements are encountered on a production system, it may not be desirable for developers to perform their investigation and tuning activities on the production system directly. This feature allows the DBA to transport the offending SQL statements to a test system where the developers can safely analyze and tune them. To transport SQL Tuning Sets, use the DBMS_SQLTUNE
package procedures.
This section covers the following topics:
To manage the SQL Tuning Sets through Oracle Enterprise Manager Database Control:
On the Database Home page, click the Advisor Central link under Related Links.
The Advisor Central page appears.
Under Advisors, click SQL Tuning Advisor.
The SQL Tuning Advisor Links page appears.
To view and create SQL Tuning Sets, click SQL Tuning Sets.
The SQL Tuning Sets page appears. Existing SQL Tuning Sets are displayed on this page.
A SQL Tuning Set can be created from SQL statements selected from Period SQL, snapshots, or preserved snapshot sets.
To create a SQL Tuning Set from:
Period SQL, select Period SQL from the Create SQL Tuning Set From pull-down menu and click Go. The Period SQL page appears. Under Historical Interval Selection, click on the band below the chart to select the historical 24 hour interval for which you want to view SQL statements that will be used in the STS. Under Detail for Selected 24 Hour Interval, select the desired SQL statements and click Create SQL Tuning Set.
Snapshots, select Snapshots from the Create SQL Tuning Set From pull-down menu and click Go. The Snapshots page appears. Under Select Beginning Snapshot, select the start point for the range of snapshots containing the SQL statements to be used in the STS. From the Actions pull-down menu, select Create SQL Tuning Set and click Go.
Preserved snapshot set, select Preserved Snapshot Sets from the Create SQL Tuning Set From pull-down menu and click Go. The Preserved Snapshot Sets page appears. Select the preserved snapshot set containing the SQL statements to be used in the STS. From the Actions pull-down menu, select Create SQL Tuning Set and click Go.
The Create SQL Tuning Set page appears.
To create the STS, click OK. For STS created using snapshots, first select the end point for the range of snapshots before clicking OK.
The created STS will now appear on the SQL Tuning Sets page.
To view the SQL statements contained in a STS, select the STS on the SQL Tuning Sets page and click View.
See Also:
Oracle Enterprise Manager Concepts and online help for information about monitoring and diagnostic tools available with Oracle Enterprise ManagerWhile SQL Tuning Sets are usually handled by Oracle Enterprise Manager as part of the Automatic SQL Tuning process, SQL Tuning Sets can be managed with DBMS_SQLTUNE
package procedures. The SQL Tuning Sets APIs allow you to mange SQL Tuning Sets to determine performance information about SQL statements running on your system. Typically you would use the STS operations in the following sequence:
Create a new STS
Load the STS
Select the STS to review the contents
Update the STS if necessary
Create a tuning task with the STS as input
Transporting the STS to another system if necessary
Drop the STS when finished
To use the APIs, you need the ADMINISTER SQL TUNING SET
system privilege to manage SQL Tuning Sets that you own, or the ADMINISTER
ANY
SQL
TUNING
SET
system privilege to manage any SQL Tuning Sets.
Figure 12-3 shows the steps involved when using SQL Tuning Sets APIs.
This section covers the following topics:
See Also:
Oracle Database PL/SQL Packages and Types Reference for detailed information on theDBMS_SQLTUNE
packageThe CREATE_SQLSET
procedure is used to create an empty STS object in the database. For example, the following procedure creates an STS object that could be used to tune I/O intensive SQL statements during a specific period of time:
BEGIN DBMS_SQLTUNE.CREATE_SQLSET( sqlset_name => 'my_sql_tuning_set', description => 'I/O intensive workload'); END; /
where my_sql_tuning_set
is the name of the STS in the database and 'I/O intensive workload'
is the description assigned to the STS.
The LOAD_SQLSET
procedure populates the STS with selected SQL statements. The standard sources for populating an STS are the workload repository, another STS, or the cursor cache. For both the workload repository and STS, there are predefined table functions that can be used to select columns from the source to populate a new STS.
In the following example, procedure calls are used to load my_sql_tuning_set
from an AWR baseline called peak
baseline
. The data has been filtered to select only the top 30 SQL statements ordered by elapsed time. First a ref cursor is opened to select from the specified baseline. Next the statements and their statistics are loaded from the baseline into the STS.
DECLARE baseline_cursor DBMS_SQLTUNE.SQLSET_CURSOR; BEGIN OPEN baseline_cursor FOR SELECT VALUE(p) FROM TABLE (DBMS_SQLTUNE.SELECT_WORKLOAD_REPOSITORY( 'peak baseline', NULL, NULL, 'elapsed_time', NULL, NULL, NULL, 30)) p; DBMS_SQLTUNE.LOAD_SQLSET( sqlset_name => 'my_sql_tuning_set', populate_cursor => baseline_cursor); END; /
The SELECT_SQLSET
table function reads the contents of the STS. After an STS has been created and populated, you can browse the SQL in the STS using different filtering criteria. The SELECT_SQLSET
procedure is provided for this purpose.
In the following example, the SQL statements in the STS are displayed for statements with a disk-reads to buffer-gets ratio greater than or equal to 75%.
SELECT * FROM TABLE(DBMS_SQLTUNE.SELECT_SQLSET( 'my_sql_tuning_set', '(disk_reads/buffer_gets) >= 0.75'));
Additional details of the SQL Tuning Sets that have been created and loaded can also be displayed with DBA views, such as DBA_SQLSET
, DBA_SQLSET_STATEMENTS
, and DBA_SQLSET_BINDS
.
SQL statements can be updated and deleted from a SQL Tuning Set based on a search condition. In the following example, the DELETE_SQLSET
procedure deletes SQL statements from my_sql_tuning_set
that have been executed less than fifty times.
BEGIN DBMS_SQLTUNE.DELETE_SQLSET( sqlset_name => 'my_sql_tuning_set', basic_filter => 'executions < 50'); END; /
SQL Tuning Sets can be transported to another system by first exporting the STS from one system to a staging table, then importing the STS from the staging table into another system.
To transport a SQL Tuning Set:
Use the CREATE_STGTAB_SQLSET
procedure to create a staging table where the SQL Tuning Sets will be exported.
The following example shows how to create a staging table named staging_table
.
BEGIN DBMS_SQLTUNE.CREATE_STGTAB_SQLSET( table_name => 'staging_table' ); END; /
Use the PACK_STGTAB_SQLSET
procedure to export SQL Tuning Sets into the staging table.
The following example shows how to export a SQL Tuning Set named my_sts
to the staging table.
BEGIN DBMS_SQLTUNE.PACK_STGTAB_SQLSET( sqlset_name => 'my_sts', staging_table_name => 'staging_table'); END; /
Move the staging table to the system where the SQL Tuning Sets will be imported using the mechanism of choice (such as datapump or database link).
On the system where the SQL Tuning Sets will be imported, use the UNPACK_STGTAB_SQLSET
procedure to import SQL Tuning Sets from the staging table.
The following example shows how to import SQL Tuning Sets contained in the staging table.
BEGIN DBMS_SQLTUNE.UNPACK_STGTAB_SQLSET( sqlset_name => '%', replace => TRUE, staging_table_name => 'staging_table'); END; /
The DROP_SQLSET
procedure is used to drop an STS that is no longer needed. For example:
BEGIN DBMS_SQLTUNE.DROP_SQLSET( sqlset_name => 'my_sql_tuning_set' ); END; /
You can use the following APIs to manage an STS:
Updating the attributes of SQL statements in an STS
The UPDATE_SQLSET
procedure updates the attributes of SQL statements (such as PRIORITY
or OTHER
) in an existing STS identified by STS name and SQL identifier.
Capturing the full system workload
The CAPTURE_CURSOR_CACHE_SQLSET
function enables the capture of the full system workload by repeatedly polling the cursor cache over a specified interval. This function is a lot more efficient than repeatedly using the SELECT_CURSOR_CACHE
and LOAD_SQLSET
procedures to capture the cursor cache over an extended period of time. This function effectively captures the entire workload, as opposed to the AWR—which only captures the workload of high-load SQL statements—or the LOAD_SQLSET
procedure, which accesses the data source only once.
Adding and removing a reference to an STS
The ADD_SQLSET_REFERENCE
function adds a new reference to an existing STS to indicate its use by a client. The function returns the identifier of the added reference. The REMOVE_SQLSET_REFERENCE
procedure is used to deactivate an STS to indicate it is no longer used by the client.
While SQL Profiles are usually handled by Oracle Enterprise Manager as part of the Automatic SQL Tuning process, SQL Profiles can be managed through the DBMS_SQLTUNE
package. To use the SQL Profiles APIs, you need the CREATE
ANY
SQL_PROFILE
, DROP
ANY
SQL_PROFILE
, and ALTER
ANY
SQL_PROFILE
system privileges.
Figure 12-4 shows the steps involved when using SQL Profiles APIs.
This section covers the following topics:
See Also:
Oracle Database PL/SQL Packages and Types Reference for detailed information on theDBMS_SQLTUNE
packageWhen the SQL Tuning Advisor recommends that a SQL Profile be used, you should accept the SQL Profile that is recommended. In cases where the SQL Tuning Advisor recommends that an index and a SQL Profile be used, both should be used. You can use the DBMS_SQLTUNE.ACCEPT_SQL_PROFILE
procedure to accept a SQL Profile recommended by the SQL Tuning Advisor. This creates and stores a SQL Profile in the database. For example:
DECLARE my_sqlprofile_name VARCHAR2(30); BEGIN my_sqlprofile_name := DBMS_SQLTUNE.ACCEPT_SQL_PROFILE ( task_name => 'my_sql_tuning_task', name => 'my_sql_profile',) force_match => TRUE); END;
In this example, my_sql_tuning_task
is the name of the SQL tuning task and my_sql_profile
is the name of the SQL Profile that you want to accept.
Typically, an accepted SQL Profile is associated with the SQL statement through a special SQL signature that is generated using a hash function. This hash function normalizes the SQL statement for case (changes the entire SQL statement to upper case) and white spaces (removes all extra whites spaces) before generating the signature. The same SQL Profile thus will work for all SQL statements that are essentially the same, where the only difference is in case usage and white spaces. However, by setting force_match
to true, the SQL Profile will additionally target all SQL statements that have the same text after normalizing literal values to bind variables. This may be useful for applications that use literal values rather than bind variables, since this will allow SQL with text differing only in its literal values to share a SQL Profile. If both literal values and bind variables are used in the SQL text, or if this parameter is set to false (the default value), literal values will not be normalized.
You can view information about a SQL Profile in the DBA_SQL_PROFILES
view.
You can alter the STATUS
, NAME
, DESCRIPTION
, CATEGORY
and FORCE_MATCH
attributes of an existing SQL Profile with the ALTER_SQL_PROFILE
procedure. For example:
BEGIN DBMS_SQLTUNE.ALTER_SQL_PROFILE( name => 'my_sql_profile', attribute_name => 'STATUS', value => 'DISABLED'); END; /
In this example, my_sql_profile
is the name of the SQL Profile that you want to alter. The status attribute is changed to disabled which means the SQL Profile is not used during SQL compilation.
You can drop a SQL Profile with the DROP_SQL_PROFILE
procedure. For example:
BEGIN DBMS_SQLTUNE.DROP_SQL_PROFILE(name => 'my_sql_profile'); END; /
In this example, my_sql_profile
is the name of the SQL Profile you want to drop. You can also specify whether to ignore errors raised if the name does not exist. For this example, the default value of FALSE
is accepted.
This section summarizes the views that you can display to review information that has been gathered for tuning the SQL statements. You need DBA privileges to access these views.
Advisor information views, such as DBA_ADVISOR_TASKS
, DBA_ADVISOR_FINDINGS
, DBA_ADVISOR_RECOMMENDATIONS
, and DBA_ADVISOR_RATIONALE
views.
SQL tuning information views, such as DBA_SQLTUNE_STATISTICS
, DBA_SQLTUNE_BINDS
, and DBA_SQLTUNE_PLANS
views.
SQL Tuning Set views, such as DBA_SQLSET
, DBA_SQLSET_BINDS
, DBA_SQLSET_STATEMENTS
, and DBA_SQLSET_REFERENCES
views.
Information on captured execution plans for statements in SQL Tuning Sets are displayed in the DBA_SQLSET_PLANS
and USER_SQLSET_PLANS
views.
SQL Profile information is displayed in the DBA_SQL_PROFILES
view.
Advisor execution progress information is displayed in the V$ADVISOR_PROGRESS
view.
Dynamic views containing information relevant to the SQL tuning, such as V$SQL
, V$SQLAREA
, V$SQLSTATS
, and V$SQL_BINDS
views.
See Also:
Oracle Database Reference for information on static data dictionary and dynamic views