Automatic SQL Tuning Set in Oracle 21c

The SQL tuning sets introduced in Oracle 10g and DBMS_SQLTUNE package used to manage SQL Tuning. You can use SQL tuning sets to group statements into a single object and use as input to tuning tools.

The below command can be used to create a SQL Tuning set

EXEC DBMS_SQLTUNE.create_sqlset(sqlset_name => 'SQL_Tuning_Set1');

BEGIN
DBMS_SQLTUNE.CREATE_SQLSET (
sqlset_name => 'SQL_Tuning_Set1',
description => 'SQL Tuning Set 1’);
END;

You can use UPDATE_SQLSET procedure to update the attributes of the SQL statements in the SQL tuning Sets

You can use below query to find the SQL Tuning sets owned by the user

SQL> SELECT NAME, STATEMENT_COUNT, DESCRIPTION FROM USER_SQLSET;

You can use DELETE_SQLSET procedure to deletes all the statements in SQL Tuning set

BEGIN
DBMS_SQLTUNE.DELETE_SQLSET ( sqlset_name => 'SQL_Tuning_Set1');
END;
/

You can use DROP_SQLSET procedure command the SQL Tuning set using below command

BEGIN
DBMS_SQLTUNE.DROP_SQLSET( sqlset_name => 'SQL_Tuning_Set1');
END;
/

You can also transfer the SQL tuning sets following steps create, pack, transfer, and unpack by using use below procedures. You can use datapump or export/import to export/import from source to destination database.

DBMS_SQLTUNE.create_stgtab_sqlset – create a stage
DBMS_SQLTUNE.pack_stgtab_sqlset – To pack SQL tuning sets
DBMS_SQLTUNE.unpack_stgtab_sqlset – To unpack SQL Tuning Sets

In Oracle 11g, further enhancements added to use SQL tuning sets with SQL Performance Analyzer. The DBMS_SQLPA package helps to build and compare two different version of the workload performance.

You can use CREATE_ANALYSIS_TASK to create an analysis task for SQL tuning set or for a single statement or single statement from the workload repository with range of snapshots

You can use below examples…

variable v_task VARCHAR2(64);
variable v_tset_task VARCHAR2(64);

-- SQL Text

EXEC :v_task := DBMS_SQLPA.CREATE_ANALYSIS_TASK(

sql_text => select dname, count(*) from dept, emp where dept.deptno = emp.deptno);

-- SQL ID

EXEC :v_task := DBMS_SQLPA.CREATE_ANALYSIS_TASK( SQL_ID => 'cv1d34ds5kdd4');

--Workload repository

exec :v_task := DBMS_SQLPA.CREATE_ANALYSIS_TASK( BEGIN_SNAP => 1, END_SNAP => 2,

SQL_ID => 'cv1d34ds5kdd4');

-- SQL Tuning Set

EXEC :v_tset_task := DBMS_SQLPA.CREATE_ANALYSIS_TASK( SQLSET_NAME => 'SQL_Tuning_Set1', order_by => 'BUFFER_GETS' );

You can use CANCEL_ANALYSIS_TASK procedure to cancel the task.

EXEC DBMS_SQLPA.CANCEL_ANALYSIS_TASK(:v_task);

In Oracle 21c, Automatic SQL tuning automates the entire SQL tuning processes. The automated SQL Tuning sets (ASTS) is a system generated execution plan and performance metrics, it is useful for repairing SQL performance regression when using SQL Plan management.

This feature is introduced in 19c RU 19.7 onwards and available with AWR . You can use ASTS with SQL plan management to implement entire workflow without manual intervention.

You can run below query dba_sqlset_Statements to view statements in ASTS

SQL> SELECT SQL_TEXT FROM DBA_SQLSET_STATEMENTS WHERE SQLSET_NAME = 'SYS_AUTO_STS';

You can use below commands to enable/Disable ASTS

BEGIN

DBMS_AUTO_TASK_ADMIN.ENABLE(

CLIENT_NAME => 'ASTS CAPTURE TASK',

OPERATION => NULL,

WINDOW_NAME => NULL);

END;

/

BEGIN

DBMS_AUTO_TASK_ADMIN.DISABLE(

CLIENT_NAME => 'ASTS CAPTURE TASK',

OPERATION => NULL,

WINDOW_NAME => NULL);

END;

/

Thanks & Regards

http://oracleracexpert.com

PGA Memory are not eligible to receive ORA-4036 interrupts

Users may receive ORA-04036 errors when PGA_AGGREGATE_LIMIT has been exceeded but some processes using the most PGA and you will see the errors written in the trace files as well.

ARC1 (PID:42467): Archived Log entry 10265 added for T-1.S-10440 ID 0xb264618a LAD:1
2022-05-15T02:07:49.670543-07:00
PGA_AGGREGATE_LIMIT has been exceeded but some processes using the most PGA
memory are not eligible to receive ORA-4036 interrupts. Further occurrences
of this condition will be written to the trace file of the DBRM process.

When you encounter this issue, the sessions consuming the PGA will be terminated until the bottleneck is cleared . Note that Oracle can exceed the amount of RAM without PGA_AGGREGATE_LIMIT which may lead to RAM buffer paging and RAC node eviction errors

The V$PGA_TARGET_ADVICE will help to predict how the cache hit percentage and over allocation count statistics displayed by the V$PGASTAT performance view

SQL> select pga_target_for_estimate, pga_target_factor, estd_time  from v$pga_target_advice;

The below query can help to get PGA Target advice by querying v$pga_target_advice_histogram

SQL> SELECT LOW_OPTIMAL_SIZE/1024 "LOW VALUE IN KB", (HIGH_OPTIMAL_SIZE+1)/1024 "HIGH VALUE IN KB", ESTD_OPTIMAL_EXECUTIONS "OPTIMAL VALUE IN KB ", ESTD_ONEPASS_EXECUTIONS "ONE PASS EXECUTION", ESTD_MULTIPASSES_EXECUTIONS "MULTI-PASS EXECUTION "

FROM  V$PGA_TARGET_ADVICE_HISTOGRAM

WHERE PGA_TARGET_FACTOR = 2 AND ESTD_TOTAL_EXECUTIONS != 0

ORDER BY 1;

By default PGA_AGGREGATE_LIMIT is set to 2GB, when you receive the errors, I would suggest to double the value or set the appropriate value required for your environment.

You can run below command to get PGA_AGGREGATE_LIMIT and increase the value

SQL> show parameter PGA_AGGREGATE_LIMIT
SQL> alter system set PGA_AGGREGATE_LIMIT=<xGB> scope=spfile;

Sometimes users may receive below errors when PGA_AGGREGATE_LIMIT set to zero. Make sure you set the non-zero and appropriate value.

ORA-04036: PGA memory used by the instance exceeds PGA_AGGREGATE_LIMIT
REP-0069: Internal error
REP-57054: In-process job terminated:Terminated with error:
REP-300: PGA memory used by the instance exceeds PGA_AGGREGATE_LIMIT

Users may experience "Database Crash" in Oracle 19c versions when USING DBMS_STATS.GATHER_TABLE_STATS . This is due to a Oracle product defect Bug:30846782 which is fixed in 21.1.

As a workaround you may try to reduce the memory usage, set hidden parameter "_fix_control"='20424684:OFF'.

At session level:
alter session set "_fix_control"='20424684:OFF';
At Instance level:
alter system set "_fix_control"='20424684:OFF';

Thanks & Regards,

http://oracleracexpert.com, Oracle ACE.