Mallik034: October 2022

Tuesday, October 11, 2022

Is flushing shared pool and buffer cache is good?

Flushing shared pool and buffer cache is not recommended and we should not perform on PROD environment

Flush Shared pool meaning flushing cached execution plan and SQL Queries from memory.

Flush buffer cache meaning flushing cached data from memory.

Database restart which internally flush both shared pool and buffer cache.

Flushing the data buffer cache & Shared pool is not recommend on Production Environment.

It may lead to increase the performance overhead, especially on RAC databases.

Flush buffer cache may lead to disk I/0 overhead.

https://docs.oracle.com/database/121/ARPLS/d_result_cache.htm#ARPLS202

1. Before flushing shared pool and buffer cache

[root@oraclelab1 ~]# su - oracle

Last login: Fri Aug 26 18:47:01 IST 2022 on pts/1

[oracle@oraclelab1 ~]$

[oracle@oraclelab1 ~]$ ps -ef|grep smon

oracle 4467 1 0 Aug09 ? 00:00:19 ora_smon_DEVDB

[oracle@oraclelab1 ~]$

[oracle@oraclelab1 ~]$ . oraenv

ORACLE_SID = [oracle] ? DEVDB

The Oracle base has been set to /u01/app/oracle

[oracle@oraclelab1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 19.0.0.0.0 - Production on Sat Aug 27 01:56:44 2022

Version 19.14.0.0.0

Connected to:

Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production

Version 19.14.0.0.0

SQL> select count(*) from v$sql;

COUNT(*)

----------

7049

SQL> exec dbms_result_cache.memory_report;

PL/SQL procedure successfully completed.

SQL> set serveroutput on;

SQL> exec dbms_result_cache.memory_report;

R e s u l t C a c h e M e m o r y R e p o r t

[Parameters]

Block Size = 1K bytes

Maximum Cache Size = 18048K bytes (18048 blocks)

Maximum Result Size = 902K bytes (902 blocks)

[Memory]

Total Memory = 800200 bytes [0.085% of the Shared Pool]

... Fixed Memory = 12424 bytes [0.001% of the Shared Pool]

... Dynamic Memory = 787776 bytes [0.084% of the Shared Pool]

....... Overhead = 165184 bytes

....... Cache Memory = 608K bytes (608 blocks)

........... Unused Memory = 12 blocks

........... Used Memory = 596 blocks

............... Dependencies = 11 blocks (11 count)

............... Results = 585 blocks

................... SQL = 3 blocks (3 count)

................... PLSQL = 6 blocks (6 count)

................... Invalid = 576 blocks (576 count)

PL/SQL procedure successfully completed.

2. After flushing shared pool and buffer cache

SQL> startup force;

ORACLE instance started.

Total System Global Area 3690985848 bytes

Fixed Size 8903032 bytes

Variable Size 989855744 bytes

Database Buffers 2684354560 bytes

Redo Buffers 7872512 bytes

Database mounted.

Database opened.

SQL> select count(*) from v$sql;

COUNT(*)

----------

445

SQL> set serveroutput on;

SQL> exec dbms_result_cache.memory_report;

R e s u l t C a c h e M e m o r y R e p o r t

[Parameters]

Block Size = 1K bytes

Maximum Cache Size = 18048K bytes (18048 blocks)

Maximum Result Size = 902K bytes (902 blocks)

[Memory]

Total Memory = 202648 bytes [0.022% of the Shared Pool]

... Fixed Memory = 5848 bytes [0.001% of the Shared Pool]

... Dynamic Memory = 196800 bytes [0.021% of the Shared Pool]

....... Overhead = 164032 bytes

....... Cache Memory = 32K bytes (32 blocks)

........... Unused Memory = 25 blocks

........... Used Memory = 7 blocks

............... Dependencies = 5 blocks (5 count)

............... Results = 2 blocks

................... Invalid = 2 blocks (2 count)

PL/SQL procedure successfully completed.

SQL>

Manually flush buffer cache & shared pool cache without bouncing the database:

Standalone Database:

alter system flush buffer_cache;

alter system flush shared_pool;

RAC Database:

alter system flush buffer_cache global;

alter system flush shared_pool global;

Regards,

Mallik

Check or get the Execution plan from SQL ID

Get the Execution plan from SQL ID!!!

Check the Execution plan from SQL ID!!!

High level steps

1. Get the SQL ID for the SQL Statement
2. Get the explain plain or execution plan for the SQL ID.

1. Get the SQL ID for the SQL Statement

- First you need to execute the SQL statement to get the SQL ID from v$sql view.

- You can get the SQL ID from AWR report or ASH report or you can get from the current session

SQL> set pages 1000 lines 1000

SQL> SELECT * FROM EMP;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7839 KING 17-NOV-81 5000 10

7698 BLAKE MANAGER 7839 01-MAY-81 2850 30

7782 CLARK MANAGER 7839 09-JUN-81 2450 10

7566 JONES MANAGER 7839 02-APR-81 2975 20

7788 SCOTT ANALYST 7566 19-APR-87 3000 20

7902 FORD ANALYST 7566 03-DEC-81 3000 20

7369 SMITH CLERK 7902 17-DEC-80 800 20

7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30

7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30

7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30

7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30

7876 ADAMS CLERK 7788 23-MAY-87 1100 20

7900 JAMES CLERK 7698 03-DEC-81 950 30

7934 MILLER CLERK 7782 23-JAN-82 1300 10

14 rows selected.

SQL>

SQL> select sql_id from v$sql where sql_text like 'SELECT * FROM EMP';

SQL_ID

-------------

4ttqgu8uu8fus

2. Get the explain plain or execution plan for the SQL

SQL> select sql_id from v$sql where sql_text like 'SELECT * FROM EMP';

SQL_ID

-------------

4ttqgu8uu8fus

SQL> set line 200 pages 200

SQL> SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('&sqlid'));

SQL> Enter value for sqlid: 4ttqgu8uu8fus

old 1: SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('&sqlid'))

new 1: SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('4ttqgu8uu8fus'))

PLAN_TABLE_OUTPUT

-----------------------------------------------------------------------------

SQL_ID 4ttqgu8uu8fus, child number 0

-------------------------------------

SELECT * FROM EMP

Plan hash value: 3956160932

--------------------------------------------------------------------------

--------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | | | 3 (100)| |

| 1 | TABLE ACCESS FULL| EMP | 14 | 532 | 3 (0)| 00:00:01 |

--------------------------------------------------------------------------

13 rows selected.

SQL>

Demo 2: (Best Query)

SQL> SELECT * FROM EMP where EMPNO=7839;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7839 KING PRESIDENT 17-NOV-81 5000 10

SQL> select sql_id from v$sql where sql_text like 'SELECT * FROM EMP where EMPNO=7839';

SQL_ID

-------------

dm0ndwh8c28aj

SQL> set line 200 pages 200

SQL> SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('&sqlid'));

Enter value for sqlid: dm0ndwh8c28aj

old 1: SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('&sqlid'))

new 1: SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('dm0ndwh8c28aj'))

PLAN_TABLE_OUTPUT

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

SQL_ID dm0ndwh8c28aj, child number 0

-------------------------------------

SELECT * FROM EMP where EMPNO=7839

Plan hash value: 2949544139

--------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | | | 1 (100)| |

| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 38 | 1 (0)| 00:00:01 |

|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| |

--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

2 - access("EMPNO"=7839)

19 rows selected.

SQL>

Demo 3: (Bad Query)

SQL> set line 200 pages 200

SQL> SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('&sqlid'));

Enter value for sqlid: 071z8v8jqhyx4

old 1: SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('&sqlid'))

new 1: SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR ('071z8v8jqhyx4'))

PLAN_TABLE_OUTPUT

SQL_ID 071z8v8jqhyx4, child number 0

-------------------------------------

SELECT * FROM EMP where ENAME='KING'

Plan hash value: 3956160932

--------------------------------------------------------------------------

--------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | | | 3 (100)| |

|* 1 | TABLE ACCESS FULL| EMP | 1 | 38 | 3 (0)| 00:00:01 |

--------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - filter("ENAME"='KING')

18 rows selected.

SQL>

Regards,

Mallik

Mallik034

Tuesday, October 11, 2022

Is flushing shared pool and buffer cache is good?

Flushing shared pool and buffer cache is not recommended and we should not perform on PROD environment

1. Before flushing shared pool and buffer cache

2. After flushing shared pool and buffer cache

Check or get the Execution plan from SQL ID

Get the Execution plan from SQL ID!!!

Check the Execution plan from SQL ID!!!

1. Get the SQL ID for the SQL Statement
2. Get the explain plain or execution plan for the SQL ID.

1. Get the SQL ID for the SQL Statement

2. Get the explain plain or execution plan for the SQL

Demo 2: (Best Query)

Demo 3: (Bad Query)

Automation Script | Archivelog Generation Hourly Monitoring

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Tuesday, October 11, 2022

Is flushing shared pool and buffer cache is good?

Flushing shared pool and buffer cache is not recommended and we should not perform on PROD environment

1. Before flushing shared pool and buffer cache

2. After flushing shared pool and buffer cache

Check or get the Execution plan from SQL ID

Get the Execution plan from SQL ID!!!

Check the Execution plan from SQL ID!!!

1. Get the SQL ID for the SQL Statement2. Get the explain plain or execution plan for the SQL ID.

1. Get the SQL ID for the SQL Statement

2. Get the explain plain or execution plan for the SQL

Demo 2: (Best Query)

Demo 3: (Bad Query)

Automation Script | Archivelog Generation Hourly Monitoring

1. Get the SQL ID for the SQL Statement
2. Get the explain plain or execution plan for the SQL ID.