Category: Performance Tunning

How to Create SQL Plan Baseline from AWR

In another post How to Create SQL Plan Baseline from Cursor Cache. Here we will demonstrate how to create SQL plan baseline from AWR.

By using the SQL in Find Oracle SQL Execution History Details, we get the best execution plan for sql_id=’6fqb4wf9sgfyv’ and plan_hash_value= 815656277.

Create STS (  SQL Tuning Set )

 BEGIN  
  DBMS_SQLTUNE.CREATE_SQLSET (  
     sqlset_name  => 'STS_6fqb4wf9sgfyv',  
     description  => 'SQL Tuning Set for 6fqb4wf9sgfyv');  
 END;

Load the Good Plan into STS

DECLARE  
  cur sys_refcursor;  
 BEGIN  
  OPEN cur FOR  
   SELECT VALUE(P)  
   FROM TABLE(   dbms_sqltune.select_workload_repository(begin_snap=>101300,end_snap=>101304,basic_filter=>'sql_id = ''6fqb4wf9sgfyv''',attribute_list=>'ALL')  
        ) p;  
    DBMS_SQLTUNE.LOAD_SQLSET( sqlset_name=> 'STS_6fqb4wf9sgfyv', populate_cursor=>cur);  
  CLOSE cur;  
 END;  

  /
PL/SQL procedure successfully completed.

Check the Good SQL Loaded into STS

SQL>  select OWNER,NAME,DESCRIPTION,STATEMENT_COUNT from DBA_SQLSET where OWNER='SYS' and NAME='STS_6fqb4wf9sgfyv';

OWNER                          NAME
------------------------------ ------------------------------
DESCRIPTION                                                                                                                                                                                                                                  STATEMENT_COUNT
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------------
SYS                            STS_6fqb4wf9sgfyv
SQL Tuning Set for 6fqb4wf9sgfyv                                                                                                                                                                                                                   1

SQL> select * from table(dbms_xplan.display_sqlset('STS_6fqb4wf9sgfyv','6fqb4wf9sgfyv'));
...
..
.

Load the Plan From STS

SQL> DECLARE
 good_plans pls_integer;
 BEGIN
  good_plans := DBMS_SPM.LOAD_PLANS_FROM_SQLSET(
   sqlset_name => 'STS_6fqb4wf9sgfyv',
   basic_filter=>'plan_hash_value = ''815656277'''
   );
 END;   

 /

PL/SQL procedure successfully completed.

Check the Plan Loaded Successfully

SQL> select SQL_HANDLE,PLAN_NAME,ENABLED,ACCEPTED,FIXED,REPRODUCED,AUTOPURGE,OPTIMIZER_COST , EXECUTIONS,ELAPSED_TIME,CPU_TIME from DBA_SQL_PLAN_BASELINES where SQL_TEXT like 'SELECT O.ORDER_ID, O.ORDER_RE%';

SQL_HANDLE                     PLAN_NAME                      ENA ACC FIX REP AUT OPTIMIZER_COST EXECUTIONS ELAPSED_TIME   CPU_TIME
------------------------------ ------------------------------ --- --- --- --- --- -------------- ---------- ------------ ----------
SQL_4e7889c88773e98f           SQL_PLAN_4wy49t23r7ucgbe7808e2 YES YES NO  YES YES         229777          1     61311779   53542413

SQL>  SELECT * FROM   TABLE(DBMS_XPLAN.display_sql_plan_baseline(plan_name=>'SQL_PLAN_4wy49t23r7ucgbe7808e2'));

SQL>  SELECT * FROM   TABLE(DBMS_XPLAN.display_sql_plan_baseline(sql_handle=>'SQL_4e7889c88773e98f'));
Advertisement

How to Check Oracle Database Table and Index Fragmentation

The following posts demonstrated how to check fragmentations in PostgreSQL:
How to Identify Fragmentation in PostgreSQL RDS
Code to Report Table Index Schema or Database Fragmentation in PostgreSQL

This post will show how to check table and index fragmentations in Oracle database.

Subscribe to get access

Read more of this content when you subscribe today.

Subscribe

Find Oracle SQL Execution History Details

DBAs are always asked about the database performance issues, which are mostly caused by some SQL queries’ execution plan changes.

This post demonstrates how to get a SQL query performance details like executions, disk/physical read/write, cpu time, elapsed time and waiting time, etc.

With the help of those statistics of a specific SQL query, DBA can easily identify the issue, and remediate it by applying SQL plan baselines.

Subscribe to get access

Read more of this content when you subscribe today.

Subscribe
Log in

How to Find Bind Variable Values of Oracle SQL Query

A couple of ways to retrieve bind variables in real time or from history

Oracle database captures a SQL query bind variables and their  values periodically, and the default capture bind variables interval is 900 seconds(15 minutes), which is modifiable but facing performance concerns.

Parameter Description                 Session Value  Instance Value
------------------------------------- -------------- --------------- 
_cursor_bind_capture_interval              900           900
interval(in seconds) between two bind 
capture for a cursor
SQL>alter system set "_cursor_bind_capture_interval"=30 scope=both;

Oracle intends to minimize the impact on database performance, and makes the capturing interval a pretty big value( like 15 minutes). So it is not a very reliable method to retrieve bind variables from Oracle database views.

Please note you need have licenses of “Oracle Diagnostics & Tuning Packs” if you query dba_hist_****** and v$sql_monitor in this post.

There are a couple of ways to retrieve bind variables in real time or from history.

Subscribe to get access

Read more of this content when you subscribe today.

Subscribe

dbms_spm.drop_sql_plan_baseline Fails With ‘ORA-14552: Cannot Perform A DDL, Commit Or Rollback Inside A Query Or DML

SYMPTOM

Drop a sql execution plan baseline with following errors:

SQL> select dbms_spm.drop_sql_plan_baseline(sql_handle=>    -
                       'SQL_89d3699974845bdb') from dual;
select dbms_spm.drop_sql_plan_baseline(sql_handle=>        -
                       'SQL_89d3699974845bdb') from dual
*
ERROR at line 1:
ORA-14552: cannot perform a DDL,commit or rollback inside 
           a query or DML
ORA-06512: at "SYS.DBMS_SPM", line 1210
ORA-06512: at "SYS.DBMS_SPM", line 1200
ORA-06512: at line 1

dbms_spm.drop_sql_plan_baseline updates dictionary tables. So you should not use it in a query.

SOLUTION

SQL> exec :xx :=dbms_spm.drop_sql_plan_baseline(sql_handle=>   -
                                   'SQL_89d3699974845bdb');

PL/SQL procedure successfully completed.

SQL> select :xx from dual;

:XX
----------
1

SQL> print :xx

XX
----------
1
Drop all sql execution plan baselines.
SQL> set serveroutput on
SQL> declare
     v_count pls_integer;
     v_sql_handle varchar2(50);
     cursor c1 is
     select sql_handle from dba_sql_plan_baselines
         where sql_handle like 'SQL_%';
     begin
        open c1 ;
        loop
            fetch c1 into v_sql_handle;
            exit when c1%notfound;
            v_count := dbms_spm.drop_sql_plan_baseline( 
                             sql_handle=>v_sql_handle );
           dbms_output.put_line(v_count);
      end loop;
  end;

 /
1
1
..
.
PL/SQL procedure successfully completed.

SQL> select count(*) from dba_sql_plan_baselines;

    COUNT(*)
 ----------
         0