Oracle Database has automated several common maintenance tasks typically performed by database administrators. These automated maintenance tasks are performed when the system load is expected to be light. You can enable and disable individual maintenance tasks, and can configure when these tasks run and what resource allocations they are allotted.
In this chapter:
Enabling Automated SQL Tuning in Oracle 11g. SYSAUTOSQLTUNINGTASK is the default name of the Automatic SQL Tuning task. You can use this query DBAADVISORLOG to check the execution time of the same. You can also use Enterprise Manager to manage the features regarding Automatic SQL Tuning. From the main database page, navigate to the. Automatic SQL Tuning in Oracle Database 11g Release 1; Adaptive Query Optimization in Oracle Database 12c (12.1 and 12.2) EXECUTEAUTOTUNINGTASK The EXECUTEAUTOTUNINGTASK procedure and function manually initiate the SYSAUTOSQLTUNINGTASK task. The only difference between the two is the function returns the task name, which is useful if you don't specify one, as it.
Oracle Database automatically runs the SQL Tuning Advisor on selected high-load SQL statements from the Automatic Workload Repository (AWR) that qualify as tuning candidates. This task, called Automatic SQL Tuning, runs in the default maintenance windows on a nightly basis. Aug 18, 2016 Occasionally, when running the 'SYSAUTOSQLTUNINGTASK' warning messages such as the following may appear in the alert log: 'Process 0x%p appears to be hung in Auto SQL Tuning task' 'Current time =%u, process death time =%u' 'Attempting to kill process 0x%p with OS pid =%s' 'OSD kill skipped for process%p' 'OSD kill succeeded for process. The Oracle docs note this on automatic maintenance tasks: 'In Oracle 11g, there is no GATHERSTATSJOB. It has been now incorporated into DBMSAUTOTASKADMIN job along with Automatic segment advisor and Automatic tuning advisor. Jul 26, 2017 SQL Optimization is intimidating for a lot of people. Even when you have great tools like Quest SQL Optimizer, people can be reluctant to hop into a different UI with so many powerful options. Thankfully, the Auto-Optimizer feature in Toad for Oracle makes tuning SQL a snap, and you don't have to leave the familiar Toad UI.
Note:
This chapter explains how to administer automated maintenance tasks using PL/SQL packages. An easier way is to use the graphical interface of Enterprise Manager.To manage automatic maintenance tasks with Enterprise Manager:
- Access the Database Home Page.See Oracle Database 2 Day DBA or the Oracle Enterprise Manager Grid Control online help for instructions.
- On the Database Home Page, click Server to display the Server page.
- Under the Oracle Scheduler section, click Automated Maintenance Tasks to configure maintenance tasks, or Windows to configure maintenance windows.
About Automated Maintenance Tasks
Automated maintenance tasks are tasks that are started automatically at regular intervals to perform maintenance operations on the database. An example is a task that gathers statistics on schema objects for the query optimizer. Automated maintenance tasks run in maintenance windows, which are predefined time intervals that are intended to occur during a period of low system load. You can customize maintenance windows based on the resource usage patterns of your database, or disable certain default windows from running. You can also create your own maintenance windows.
Oracle Database has three predefined automated maintenance tasks:
- Automatic Optimizer Statistics Collection--Collects optimizer statistics for all schema objects in the database for which there are no statistics or only stale statistics. The statistics gathered by this task are used by the SQL query optimizer to improve the performance of SQL execution.See Also:Oracle Database Performance Tuning Guide for more information on automatic statistics collection
- Automatic Segment Advisor—Identifies segments that have space available for reclamation, and makes recommendations on how to defragment those segments.You can also run the Segment Advisor manually to obtain more up-to-the-minute recommendations or to obtain recommendations on segments that the Automatic Segment Advisor did not examine for possible space reclamation.See Also:'Using the Segment Advisor' for more information.
- Automatic SQL Tuning Advisor--Examines the performance of high-load SQL statements, and makes recommendations on how to tune those statements. You can configure this advisor to automatically implement SQL profile recommendations.See Also:Oracle Database Performance Tuning Guide for more information on SQL Tuning Advisor
By default, all three automated maintenance tasks are configured to run in all maintenance windows.
About Maintenance Windows
A maintenance window is a contiguous time interval during which automated maintenance tasks are run. Maintenance windows are Oracle Scheduler windows that belong to the window group named
MAINTENANCE_WINDOW_GROUP
. A Scheduler window can be a simple repeating interval (such as 'between midnight and 6 a.m., every Saturday'), or a more complex interval (such as 'between midnight and 6 a.m., on the last workday of every month, excluding company holidays').When a maintenance window opens, Oracle Database creates an Oracle Scheduler job for each maintenance task that is scheduled to run in that window. Each job is assigned a job name that is generated at run time. All automated maintenance task job names begin with
ORA$AT
. For example, the job for the Automatic Segment Advisor might be called ORA$AT_SA_SPC_SY_26
. When an automated maintenance task job finishes, it is deleted from the Oracle Scheduler job system. However, the job can still be found in the Scheduler job history.Note:
To view job history, you must log in as the SYS
user.In the case of a very long maintenance window, all automated maintenance tasks except Automatic SQL Tuning Advisor are restarted every four hours. This feature ensures that maintenance tasks are run regularly, regardless of window size.
The framework of automated maintenance tasks relies on maintenance windows being defined in the database. Table 26-1 lists the maintenance windows that are automatically defined with each new Oracle Database installation.
See Also:
- 'About Jobs and Supporting Scheduler Objects' for more information on windows and groups.
Configuring Automated Maintenance Tasks
To enable or disable specific maintenance tasks in any subset of maintenance windows, you can use the
DBMS_AUTO_TASK_ADMIN
PL/SQL package.This section contains the following topics:
Enabling and Disabling Maintenance Tasks for all Maintenance Windows
You can disable a particular automated maintenance task for all maintenance windows with a single operation. You do so by calling the
DISABLE
procedure of the DBMS_AUTO_TASK_ADMIN
PL/SQL package without supplying the window_name
argument. For example, you can completely disable the Automatic SQL Tuning Advisor task as follows:To enable this maintenance task again, use the
ENABLE
procedure, as follows:The task names to use for the
client_name
argument are listed in the DBA_AUTOTASK_CLIENT
database dictionary view.To enable or disable all automated maintenance tasks for all windows, call the
ENABLE
or DISABLE
procedure with no arguments.See Also:
- Oracle Database PL/SQL Packages and Types Reference for more information on the
DBMS_AUTO_TASK_ADMIN
PL/SQL package.
Enabling and Disabling Maintenance Tasks for Specific Maintenance Windows
By default, all maintenance tasks run in all predefined maintenance windows. You can disable a maintenance task for a specific window. The following example disables the Automatic SQL Tuning Advisor from running in the window
MONDAY_WINDOW
:Configuring Maintenance Windows
You may want to adjust the predefined maintenance windows to a time suitable to your database environment or create a new maintenance window. You can customize maintenance windows using the
DBMS_SCHEDULER
PL/SQL package.This section contains the following topics:
Modifying a Maintenance Window
The
DBMS_SCHEDULER
PL/SQL package includes a SET_ATTRIBUTE
procedure for modifying the attributes of a window. For example, the following script changes the duration of the maintenance window SATURDAY_WINDOW
to 4 hours:Note that you must use the
DBMS_SCHEDULER.DISABLE
subprogram to disable the window before making changes to it, and then re-enable the window with DBMS_SCHEDULER.ENABLE
when you are finished. If you change a window when it is currently open, the change does not take effect until the next time the window opens.See Also:
'Managing Job Scheduling and Job Priorities with Windows' for more information about modifying windows.Creating a New Maintenance Window
To create a new maintenance window, you must create an Oracle Scheduler window object and then add it to the window group
MAINTENANCE_WINDOW_GROUP
. You use the DBMS_SCHEDULER
.CREATE_WINDOW
package procedure to create the window, and the DBMS_SCHEDULER
.ADD_GROUP_MEMBER
procedure to add the new window to the window group.The following example creates a maintenance window named
EARLY_MORNING_WINDOW
. This window runs for one hour daily between 5 a.m. and 6 a.m.See Also:
- Oracle Database PL/SQL Packages and Types Reference for information on the
DBMS_SCHEDULER
package
Removing a Maintenance Window
To remove an existing maintenance window, remove it from the
MAINTENANCE_WINDOW_GROUP
window group. The window continues to exist but no longer runs automated maintenance tasks. Any other Oracle Scheduler jobs assigned to this window continue to run as usual.The following example removes
EARLY_MORNING_WINDOW
from the window group:See Also:
- Oracle Database PL/SQL Packages and Types Reference for information on the
DBMS_SCHEDULER
package
Configuring Resource Allocations for Automated Maintenance Tasks
This section contains the following topics on resource allocation for maintenance windows:
See Also:
Chapter 27, 'Managing Resources with Oracle Database Resource Manager'About Resource Allocations for Automated Maintenance Tasks
By default, all predefined maintenance windows use the resource plan
DEFAULT_MAINTENANCE_PLAN
. Automated maintenance tasks run under its subplan ORA$AUTOTASK_SUB_PLAN
. This subplan divides its portion of total resource allocation equally among the maintenance tasks.DEFAULT_MAINTENANCE_PLAN
defines the following resource allocations:Consumer Group/subplan | Level 1 | Level 2 | Maximum Utilization Limit |
---|---|---|---|
ORA$AUTOTASK_SUB_PLAN | - | 25% | 90 |
ORA$DIAGNOSTICS | - | 5% | 90 |
OTHER_GROUPS | - | 70% | |
SYS_GROUP | 75% | - |
In this plan, any sessions in the
SYS_GROUP
consumer group get priority. (Sessions in this group are sessions created by user accounts SYS
and SYSTEM
.) Any resource allocation that is unused by sessions in SYS_GROUP
is then shared by sessions belonging to the other consumer groups and subplans in the plan. Of that allocation, 25% goes to maintenance tasks, 5% goes to background processes performing diagnostic operations, and 70% goes to user sessions. The maximum utilization limit for ORA$AUTOTASK_SUB_PLAN
and ORA$DIAGNOSTICS
is 90. Therefore, even if the CPU is idle, this group/plan cannot be allocated more than 90% of the CPU resources.To reduce or increase resource allocation to the automated maintenance tasks, you make adjustments to
DEFAULT_MAINTENANCE_PLAN
. See 'Changing Resource Allocations for Automated Maintenance Tasks' for more information.Note that as with any resource plan, the portion of an allocation that is not used by a consumer group or subplan is available for other consumer groups or subplans. Note also that the Database Resource Manager does not begin to limit resource allocations according to resource plans until 100% of CPU is being used.
Note:
Although DEFAULT_MAINTENANCE_PLAN
is the default, you can assign any resource plan to any maintenance window. If you do change a maintenance window resource plan, ensure that you include the subplan ORA$AUTOTASK_SUB_PLAN
and the consumer group ORA$DIAGNOSTICS
in the new plan.See Also:
Chapter 27, 'Managing Resources with Oracle Database Resource Manager' for more information on resource plans.Changing Resource Allocations for Automated Maintenance Tasks
To change the resource allocation for automated maintenance tasks within a maintenance window, you must change the percentage of resources allocated to the subplan
ORA$AUTOTASK_SUB_PLAN
in the resource plan for that window. (By default, the resource plan for each predefined maintenance window is DEFAULT_MAINTENANCE_PLAN
.) You must also adjust the resource allocation for one or more other subplans or consumer groups in the window's resource plan such that the resource allocation at the top level of the plan adds up to 100%. For information on changing resource allocations, see Chapter 27, 'Managing Resources with Oracle Database Resource Manager'.Automated Maintenance Tasks Reference
This section contains the following reference topics for automated maintenance tasks:
Predefined Maintenance Windows
By default there are seven predefined maintenance windows, each one representing a day of the week. The weekend maintenance windows,
SATURDAY_WINDOW
and SUNDAY_WINDOW
, are longer in duration than the weekday maintenance windows. The window group MAINTENANCE_WINDOW_GROUP
consists of these seven windows. The list of predefined maintenance windows is given in Table 26-1.Table 26-1 Predefined Maintenance Windows
Window Name | Description |
---|---|
MONDAY_WINDOW | Starts at 10 p.m. on Monday and ends at 2 a.m. |
TUESDAY_WINDOW | Starts at 10 p.m. on Tuesday and ends at 2 a.m. |
WEDNESDAY_WINDOW | Starts at 10 p.m. on Wednesday and ends at 2 a.m. |
THURSDAY_WINDOW | Starts at 10 p.m. on Thursday and ends at 2 a.m. |
FRIDAY_WINDOW | Starts at 10 p.m. on Friday and ends at 2 a.m. |
SATURDAY_WINDOW | Starts at 6 a.m. on Saturday and is 20 hours long. |
SUNDAY_WINDOW | Starts at 6 a.m. on Sunday and is 20 hours long. |
Automated Maintenance Tasks Database Dictionary Views
Table 26-2 displays information about database dictionary views for automated maintenance tasks:
Table 26-2 Automated Maintenance Tasks Database Dictionary Views
View Name | Description |
---|---|
DBA_AUTOTASK_CLIENT_JOB | Contains information about currently running Scheduler jobs created for automated maintenance tasks. It provides information about some objects targeted by those jobs, as well as some additional statistics from previous instantiations of the same task. Some of this additional data is taken from generic Scheduler views. |
DBA_AUTOTASK_CLIENT | Provides statistical data for each automated maintenance task over 7-day and 30-day periods. |
DBA_AUTOTASK_JOB_HISTORY | Lists the history of automated maintenance task job runs. Jobs are added to this view after they finish executing. |
DBA_AUTOTASK_WINDOW_CLIENTS | Lists the windows that belong to MAINTENANCE_WINDOW_GROUP , along with the Enabled or Disabled status for the window for each maintenance task. Primarily used by Enterprise Manager. |
DBA_AUTOTASK_CLIENT_HISTORY | Provides per-window history of job execution counts for each automated maintenance task. This information is viewable in the Job History page of Enterprise Manager. |
See Also:
'Resource Manager Data Dictionary Views' for column descriptions for views.This chapter discusses the automatic SQL tuning features of Oracle Database. Automatic SQL tuning automates the manual process, which is complex, repetitive, and time-consuming.
This chapter contains the following sections:
- See Also:Oracle Database 2 Day + Performance Tuning Guide for information about using the automatic SQL tuning features of Oracle Database with Oracle Enterprise Manager
17.1 Automatic Tuning Optimizer
When SQL statements are executed by the Oracle database, the query optimizer is used to generate the execution plans of the SQL statements. The query optimizer operates in two modes: a normal mode and a tuning mode.
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 improved further. 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 running in the tuning mode, the optimizer is referred to as the Automatic Tuning Optimizer.
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 SQL tuning. See Chapter 6, 'Automatic Performance Diagnostics'. The automatic SQL tuning feature of Oracle Database also automatically identifies problematic SQL statements and implements tuning recommendations during system maintenance windows as an automated maintenance task.
The Automatic Tuning Optimizer performs four types of tuning analysis:
17.1.1 Statistics 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 Optimizer Statistics Collection'.
- 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.
Oracle Query Performance Tuning
17.1.2 SQL Profiling
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. Fresh stuff 4 you. 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.See Also:
Oracle Database Reference for information on the SQLTUNE_CATEGORY
initialization parameterIt 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. In general, it is not necessary to refresh the SQL profiles. However, over a long period of time, its content can become outdated and may need to be regenerated. This can be done by running the SQL Tuning Advisor again on the same statement to regenerate the SQL Profile.
SQL Profiles apply to the following statement types:
SELECT
statementsUPDATE
statementsINSERT
statements (only with aSELECT
clause)DELETE
statementsCREATE
TABLE
statements (only with theAS
SELECT
clause)MERGE
statements (the update or insert operations)
A complete set of functions are provided for management of SQL Profiles. See 'SQL Profiles'.
17.1.3 Access Path Analysis
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 the SQL Access Advisor utility on the SQL statement along with a representative SQL workload. The SQL Access Advisor looks at the impact of creating an index on the entire SQL workload before making any recommendations. See 'Automatic SQL Tuning Features'.
17.1.4 SQL Structure Analysis
The Automatic Tuning Optimizer identifies common problems with structure of SQL statements that 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.17.2 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 a SQL profile. You can choose to accept the recommendation to complete the tuning of the SQL statements.
Oracle Database can automatically tune SQL statements by identifying problematic SQL statements and implementing tuning recommendations using the SQL Tuning Advisor during system maintenance windows. You can also run the SQL Tuning Advisor selectively on a single or a set of SQL statements that have been identified as problematic.
17.3 Automatic SQL Tuning Advisor
Oracle Database automatically runs the SQL Tuning Advisor on selected high-load SQL statements from the Automatic Workload Repository (AWR) that qualify as tuning candidates. This task, called Automatic SQL Tuning, runs in the default maintenance windows on a nightly basis. You can customize attributes of the maintenance windows, including start and end time, frequency, and days of the week.
See Also:
Oracle Database Administrator's Guide for information about automated maintenance taskOnce automatic SQL tuning begins, which by default runs for at most one hour during a maintenance window, the following steps are performed:
- Identify SQL candidates in the AWR for tuning.Oracle Database analyzes statistics in the AWR and generates a list of potential SQL statements that are eligible for tuning. These statements include repeating high-load statements that have a significant impact on the system. Only SQL statements that have an execution plan with a high potential for improvement will be tuned. Recursive SQL and statements that have been tuned recently (in the last month) are ignored, as are parallel queries, DMLs, DDLs, and SQL statements with performance problems that are caused by concurrency issues. The SQL statements that are selected as candidates are then ordered based on their performance impact. The performance impact of a SQL statement is calculated by summing the CPU time and the I/O times captured in the AWR for that SQL statement in the past week.
- Tune each SQL statement individually by calling the SQL Tuning Advisor.During the tuning process, all recommendation types are considered and reported, but only SQL profiles can be implemented automatically.
- Test SQL profiles by executing the SQL statement.If a SQL profile is recommended, test the new SQL profile by executing the SQL statement both with and without the SQL profile. If the performance improvement improves at least threefold, the SQL profile will be accepted (when the
ACCEPT_SQL_PROFILES
task parameter is set toTRUE
). Otherwise, only the recommendation to create a SQL profile will be reported in the automatic SQL tuning reports. - Optionally implement the SQL profiles provided they meet the criteria of threefold performance improvement.Note that other factors are considered when deciding whether or not to implement the SQL profile. For example, a SQL profile is not implemented if the objects referenced in the SQL statement have stale optimizer statistics. You can identify which SQL profiles have been implemented automatically as their type will be set to
AUTO
in theDBA_SQL_PROFILES
view.If SQL plan management is used and there is already an existing plan baseline for the SQL statement, a new plan baseline will be added when a SQL profile is created. As a result, the new and improved SQL execution plan will be used by the optimizer immediately after the SQL profile is created. For information about SQL plan management, see Chapter 15, 'Using SQL Plan Management'.
At any time during or after the automatic SQL tuning process, you can view the results using the automatic SQL tuning report. This report describes in detail all the SQL statements that were analyzed, the recommendations generated, and the SQL profiles that were automatically implemented.
Figure 17-1 illustrates the steps performed by Oracle Database during the automatic SQL tuning process.
Figure 17-1 Automatic SQL Tuning
Description of 'Figure 17-1 Automatic SQL Tuning'
This section contains the following topics:
17.3.1 Enabling and Disabling Automatic SQL Tuning
Automatic SQL tuning runs as part of the automated maintenance tasks infrastructure.
To enable automatic SQL tuning, use the
ENABLE
procedure in the DBMS_AUTO_TASK_ADMIN
package:To disable automatic SQL tuning, use the DISABLE procedure in the DBMS_AUTO_TASK_ADMIN package:
You can pass a specific window name using the
window_name
parameter to enable or disable the task in certain maintenance windows only.Setting the
STATISTICS_LEVEL
parameter to BASIC
will disable automatic statistics gathering by the AWR and, as a result, also disable automatic SQL tuning.See Also:
- Oracle Database Administrator's Guide for information about the AutoTask infrastructure
- Oracle Database PL/SQL Packages and Types Reference for information about the
DBMS_AUTO_TASK_ADMIN
package
17.3.2 Configuring Automatic SQL Tuning
The behavior of the automatic SQL tuning task can be configured using the
DBMS_SQLTUNE
package. To use the APIs, the user needs at least the ADVISOR
privilege.In addition to configuring the standard behavior of the SQL Tuning Advisor, the
DBMS_SQLTUNE
package enables you to configure automatic SQL tuning by specifying the task parameters using the SET_TUNING_TASK_PARAMETER
procedure. Because the automatic tuning task is owned by SYS, only the SYS user can set the task parameters.Table 17-2 lists the parameters that are specific to automatic SQL tuning which can be configured.
Table 17-1 SET_TUNING_TASK_PARAMETER Automatic SQL Tuning Parameters
Parameter | Description |
---|---|
ACCEPT_SQL_PROFILE | Specifies whether to accept SQL profiles automatically. |
MAX_SQL_PROFILES_PER_EXEC | Specifies the limit of SQL profiles that are accepted for each automatic SQL tuning task. Consider setting the limit of SQL profiles that are accepted for each automatic SQL tuning task based on the acceptable level of changes that can be made to the system on a daily basis. |
MAX_AUTO_SQL_PROFILES | Specifies the limit of SQL profiles that are accepted in total. |
EXECUTION_DAYS_TO_EXPIRE | Specifies the number of days for which to save the task history in the advisor framework schema. By default, the task history is saved for 30 days before it expires. |
To configure automatic SQL tuning, run the
SET_TUNING_TASK_PARAMETER
procedure in the DBMS_SQLTUNE
package:In this example, the automatic SQL tuning task is configured to automatically accept SQL profiles recommended by the SQL Tuning Advisor.
See Also:
- 'Configuring a SQL Tuning Task' for information about other parameters that can be configured for a SQL tuning task
- Oracle Database PL/SQL Packages and Types Reference for information about the
DBMS_SQLTUNE
package
17.3.3 Viewing Automatic SQL Tuning Reports
The automatic SQL tuning report is generated using the
DBMS_SQLTUNE
.REPORT_AUTO_TUNING_TASK
function and contains information about all executions of the automatic SQL tuning task. To run this report, you need the ADVISOR
privilege and SELECT privileges on the DBA_ADVISOR
views. Unlike the standard SQL tuning report generated using the DBMS_SQLTUNE
.REPORT_TUNING_TASK
function, which only contains information about a single task execution of the SQL Tuning Advisor, the automatic SQL tuning report contains information about multiple executions of the automatic SQL tuning task.To view the automatic SQL tuning report, run the
REPORT_AUTO_TUNING_TASK
function in the DBMS_SQLTUNE
package:In this example, a text report is generated to display all SQL statements that were analyzed in the most recent execution, including recommendations that were not implemented, and all sections of the report are included.
See Also:
Oracle Database PL/SQL Packages and Types Reference for information about the DBMS_SQLTUNE
packageDepending on the sections that were included in the report, you can view information about the automatic SQL tuning task in the following sections of the report:
- General informationThe general information section provides a high-level description of the automatic SQL tuning task, including information about the inputs given for the report, the number of SQL statements tuned during the maintenance, and the number of SQL profiles that were created
- SummaryThe summary section lists the SQL statements (by their SQL identifiers) that were tuned during the maintenance window and the estimated benefit of each SQL profile, or their actual execution statistics after test executing the SQL statement with the SQL profile
- Tuning findingsThis section contains the following information about each SQL statement analyzed by the SQL Tuning Advisor:
- All findings associated with each SQL statement
- Whether the profile was accepted on the system, and why
- Whether the SQL profile is currently enabled on the system
- Detailed execution statistics captured when testing the SQL profile
- Explain plansThis section shows the old and new explain plans used by each SQL statement analyzed by the SQL Tuning Advisor.
- ErrorsThis section lists all errors encountered by the automatic SQL tuning task.
17.4Reactive Tuning Using the SQL Tuning Advisor
The SQL Tuning Advisor can be invoked manually for on-demand tuning of one or more SQL statements. To tune multiple statements, you need to create a SQL tuning set (STS). A SQL tuning set is a database object that stores SQL statements along with their execution context. You can create a SQL tuning set using command line APIs or Oracle Enterprise Manager. See 'SQL Tuning Sets'.
This section contains the following topics:
17.4.1 Input Sources
The input for the SQL Tuning Advisor can come from several sources. These input sources include:
- Automatic Database Diagnostic MonitorThe 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 'Overview of the Automatic Database Diagnostic Monitor'.
- Automatic Workload RepositoryThe second most important input source is the 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.You can view the AWR and manually identify high-load SQL statements and run the SQL Tuning Advisor on them, though this is done automatically by Oracle Database as part of the automatic SQL tuning process. By default, the AWR retains data for the last eight days. Any high-load SQL that ran within the retention period of the AWR can be located and tuned using this method. See 'Overview of the Automatic Workload Repository'.
- Cursor cacheThe 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 8 days.
- SQL Tuning SetAnother 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'.
17.4.2 Tuning Options
The 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.
17.4.3 Advisor Output
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.
17.4.4Running the SQL Tuning Advisor
The recommended interface for running the SQL Tuning Advisor is the Oracle Enterprise Manager. Whenever possible, you should run the SQL Tuning Advisor using Oracle Enterprise Manager, as described in the Oracle Database 2 Day + Performance Tuning Guide. If Oracle Enterprise Manager is unavailable, you can run the SQL Tuning Advisor using 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 the DBMS_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 17-2 shows the steps involved when running the SQL Tuning Advisor using the
DBMS_SQLTUNE
package.Figure 17-2 SQL Tuning Advisor APIs
Description of 'Figure 17-2 SQL Tuning Advisor APIs'
This section covers the following topics:
See Also:
Oracle Database PL/SQL Packages and Types Reference for information about the DBMS_SQLTUNE
package17.4.4.1 Creating a SQL Tuning Task
You 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.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:17.4.4.2 Configuring a SQL Tuning Task
You can fine tune a SQL tuning task after it has been created by configuring its parameters using the
SET_TUNING_TASK_PARAMETER
procedure in the DBMS_SQLTUNE
package:In this example, the maximum time that the SQL tuning task can run is changed to 300 seconds.
Table 17-2 lists the parameters that can be configured using the
SET_TUNING_TASK_PARAMETER
procedure.Table 17-2 SET_TUNING_TASK_PARAMETER Procedure Parameters
Parameter | Description |
---|---|
MODE | Specifies the scope of the tuning task:
|
USERNAME | Username under which the SQL statement will be parsed |
DAYS_TO_EXPIRE | Number of days before the task is deleted |
DEFAULT_EXECUTION_TYPE | Default execution type if not specified by the EXECUTE_TUNING_TASK function when the task is executed |
TIME_LIMIT | Time limit (in number of seconds) before the task times out |
LOCAL_TIME_LIMIT | Time limit (in number of seconds) for each SQL statement |
TEST_EXECUTE | Determines if the SQL Tuning Advisor will test execute the SQL statements to verify the recommendation benefit:
|
BASIC_FILTER | Basic filter used for SQL tuning set |
OBJECT_FILTER | Object filter used for SQL tuning set |
PLAN_FILTER | Plan filter used for SQL tuning set |
RANK_MEASURE1 | First ranking measure used for SQL tuning set |
RANK_MEASURE2 | Second ranking measure used for SQL tuning set |
RANK_MEASURE3 | Third ranking measure used for SQL tuning set |
RESUME_FILTER | Extra filter used for SQL tuning set (besides BASIC_FILTER ) |
SQL_LIMIT | Maximum number of SQL statements to tune |
SQL_PERCENTAGE | Percentage filter of statements from SQL tuning set |
17.4.4.3 Executing a SQL Tuning Task
After you have created a tuning task, you need to execute the task and start the tuning process. For example:
Like any other SQL Tuning Advisor task, you can also execute the automatic tuning task
SYS_AUTO_SQL_TUNING_TASK
using the EXECUTE_TUNING_TASK
API. The SQL Tuning Advisor will perform the same analysis and actions as it would when run automatically. You can also pass an execution name to the API to name the new execution.17.4.4.4 Checking the Status of a SQL Tuning Task
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$SESSION_LONGOPS
view. For example:17.4.4.5Checking the Progress of the SQL Tuning Advisor
You can check the execution progress of the SQL Tuning Advisor in the
V$ADVISOR_PROGRESS
view. For example:See Also:
Oracle Database Reference for information on the V$ADVISOR_PROGRESS view17.4.4.6 Displaying the Results of a SQL Tuning Task
After a task has been executed, you display a report of the results with the
REPORT_TUNING_TASK
function. For example:The report contains all the findings and recommendations of the SQL Tuning Advisor. 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'.
17.4.4.7 Additional Operations on a SQL Tuning Task
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 resultsRESUME_TUNING_TASK
to resume a previously interrupted taskCANCEL_TUNING_TASK
to cancel a task while executing, removing all results from the taskRESET_TUNING_TASK
to reset a task while executing, removing all results from the task and returning the task to its initial stateDROP_TUNING_TASK
to drop a task, removing all results associated with the task
17.5SQL Tuning Sets
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 problematic 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.The recommended interface for managing SQL tuning sets is the Oracle Enterprise Manager. Whenever possible, you should manage SQL tuning sets using Oracle Enterprise Manager, as described in the Oracle Database 2 Day + Performance Tuning Guide. If Oracle Enterprise Manager is unavailable, you can manage SQL tuning sets using the
DBMS_SQLTUNE
package procedures. 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 17-3 shows the steps involved when using SQL Tuning Sets APIs.
Figure 17-3 SQL Tuning Sets APIs
Description of 'Figure 17-3 SQL Tuning Sets APIs'
This section covers the following topics:
See Also:
Oracle Database PL/SQL Packages and Types Reference for information about the DBMS_SQLTUNE
package17.5.1 Creating a SQL Tuning Set
The
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: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.17.5.2 Loading a SQL Tuning Set
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, predefined table functions 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.17.5.3 Displaying the Contents of a SQL Tuning Set
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%.
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
.17.5.4 Modifying a SQL Tuning Set
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.17.5.5 Transporting a SQL Tuning Set
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 namedstaging_table
. Table names are case-sensitive. - 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 namedmy_sts
to the staging table. - 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.
17.5.6 Dropping a SQL Tuning Set
The
DROP_SQLSET
procedure is used to drop an STS that is no longer needed. For example:17.5.7 Additional Operations on SQL Tuning Sets
You can use the following APIs to manage an STS:
- Updating the attributes of SQL statements in an STSThe
UPDATE_SQLSET
procedure updates the attributes of SQL statements (such asPRIORITY
orOTHER
) in an existing STS identified by STS name and SQL identifier. - Capturing the full system workloadThe
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 theSELECT_CURSOR_CACHE
andLOAD_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 theLOAD_SQLSET
procedure, which accesses the data source only once. - Adding and removing a reference to an STSThe
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. TheREMOVE_SQLSET_REFERENCE
procedure is used to deactivate an STS to indicate it is no longer used by the client.
17.6SQL Profiles
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 ADMINISTER SQL MANAGEMENT OBJECT
privilege.Figure 17-4 shows the steps involved when using SQL Profiles APIs.
Figure 17-4 SQL Profiles APIs
Description of 'Figure 17-4 SQL Profiles APIs'
This section covers the following topics:
See Also:
Oracle Database PL/SQL Packages and Types Reference for information about the DBMS_SQLTUNE
package17.6.1 Accepting a SQL Profile
When 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: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.If SQL plan management is used and there is already an existing plan baseline for the SQL statement, a new plan baseline will be added when a SQL profile is created. If SQL plan management is not used, a new plan baseline will not be added when a SQL profile is created. There is no strict relationship between the SQL profile and the plan baseline. When hard parsing a SQL statement, the optimizer will use the SQL profile to select the best plan baseline from the ones available. In different conditions, the SQL profile may cause the optimizer to select different plan baselines. For information about SQL plan management, see Chapter 15, 'Using SQL Plan Management'.
You can view information about a SQL Profile in the
DBA_SQL_PROFILES
view.17.6.2 Altering a SQL Profile
You can alter the
STATUS
, NAME
, DESCRIPTION
, and CATEGORY
attributes of an existing SQL Profile with the ALTER_SQL_PROFILE
procedure. For example: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.17.6.3 Dropping a SQL Profile
What Is Sql Tuning
You can drop a SQL Profile with the
DROP_SQL_PROFILE
procedure. For example: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.17.7 SQL Tuning Information Views
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.
Sql Tuning Advisor In Oracle
- Advisor information views, such as
DBA_ADVISOR_TASKS
,DBA_ADVISOR_EXECUTIONS
,DBA_ADVISOR_FINDINGS
,DBA_ADVISOR_RECOMMENDATIONS
, andDBA_ADVISOR_RATIONALE
views. - SQL tuning information views, such as
DBA_SQLTUNE_STATISTICS
,DBA_SQLTUNE_BINDS
, andDBA_SQLTUNE_PLANS
views. - SQL Tuning Set views, such as
DBA_SQLSET
,DBA_SQLSET_BINDS
,DBA_SQLSET_STATEMENTS
, andDBA_SQLSET_REFERENCES
views. - Information on captured execution plans for statements in SQL Tuning Sets are displayed in the
DBA_SQLSET_PLANS
andUSER_SQLSET_PLANS
views. - SQL Profile information is displayed in the
DBA_SQL_PROFILES
view.TheTYPE
parameter shows if the SQL profile was created manually by the SQL Tuning Advisor (ifTYPE
=MANUAL
) or automatically by automatic SQL tuning (ifTYPE
=AUTO
). - 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$SQLSTATS
, andV$SQL_BINDS
views.See Also:Oracle Database Reference for information on static data dictionary and dynamic views