System statistics in oracle database ?

 

In oracle database system statistics provide the optimizer with information about the system hardware and workload information , such cpu speed , i/o performance .

this statistic help the cost based optimizer make better decision when generating the execution plan  .

Why Gather System Statistics?

• To provide the optimizer with accurate information about the system's performance.
• To improve query execution plans by accounting for CPU and I/O costs.
• To adapt the optimizer's behavior to the specific hardware and workload of the database.

Types of System Statistics

NOWORKLOAD Statistics:

Collected when the database is idle or under minimal workload.

Provides baseline hardware characteristics like CPU speed and I/O performance.

Default system statistics provided by Oracle.

WORKLOAD Statistics:

Collected during a representative workload period.

Provides information about the system's performance under actual workload conditions.

Useful for databases with specific workload patterns.

Start gathering statistics:

BEGIN

  DBMS_STATS.GATHER_SYSTEM_STATS('START');

END;

/

Stop gathering statistics:

BEGIN

  DBMS_STATS.GATHER_SYSTEM_STATS('STOP');

END;

/

Best Practices

Choose the Right Type of Statistics:

Use NOWORKLOAD statistics for general-purpose systems.

Use WORKLOAD statistics for systems with specific workload patterns.

Gather Statistics During Representative Workloads:

For WORKLOAD statistics, ensure the workload period reflects typical database usage.

Monitor and Update Regularly:

Gather system statistics periodically or after significant hardware changes (e.g., CPU or storage upgrades).

Backup Existing Statistics:

Before gathering new statistics, back up the current system statistics to restore them if needed.

How to create pluggable database in oracle ?

 create pluggable database in oracle 

SQL> show con_name 

CON_NAME

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

CDB$ROOT

SQL> 

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

2 PDB$SEED   READ ONLY  NO

3 PDB   READ WRITE NO

SQL> 

SQL> 

SQL> 

SQL> 

SQL> create pluggable database demo1 admin user demo1 identified by demo1

  2  file_name_convert=('/u01/app/oracle/oradata/DB1/pdbseed','/u01/app/oracle/oradata/demo1');   

Pluggable database created.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

2 PDB$SEED   READ ONLY  NO

3 PDB   READ WRITE NO

4 DEMO1   MOUNTED

SQL> alter pluggable database demo1 open read write;

Pluggable database altered.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

2 PDB$SEED   READ ONLY  NO

3 PDB   READ WRITE NO

4 DEMO1   READ WRITE NO

SQL> 

SQL> 

SQL>       

SQL> alter session set container=demo1;

Session altered.

SQL> show con_name 

CON_NAME

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

DEMO1

SQL> 

SQL> 

SQL> 

SQL> select name from v$pdbs;

NAME

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

DEMO1

SQL> 

how to drop pluggable database in oracle ?

 Drop pluggable database in oracle

=> connect to the container database 

=> close the pluggable database 

=> unplug the pluggable database (optional)

=> drop the pluggable database 

    .if we are using the command without including datafiles , this only remove pdb not underline datafiles etc .

SQL> alter session set container =cdb$root;

Session altered.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

 2 PDB$SEED   READ ONLY  NO

 3 PDB   READ WRITE NO

 4 DEMO1   READ WRITE NO

SQL> 

SQL> alter pluggable database demo1 close immediate;

Pluggable database altered.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

 2 PDB$SEED   READ ONLY  NO

 3 PDB   READ WRITE NO

 4 DEMO1   MOUNTED

SQL> drop pluggable database demo1 including datafiles;

Pluggable database dropped.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

 2 PDB$SEED   READ ONLY  NO

 3 PDB   READ WRITE NO

SQL> 

How to check and list pluggable database in oracle ?

 

SQL> 

SQL> select name from v$pdbs;

NAME

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

PDB$SEED

PDB

SQL> 

SQL> select pdb_name from cdb_pdbs;

PDB_NAME

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

PDB

PDB$SEED

SQL> 

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

2 PDB$SEED   READ ONLY  NO

3 PDB   READ WRITE NO

SQL> 

SQL> 

Oracle Error : ORA-65040: operation not allowed from within a pluggable database

 

ORA-65040: operation not allowed from within a pluggable database

SQL> drop pluggable database demo1 including datafiles;

drop pluggable database demo1 including datafiles

*

ERROR at line 1:

ORA-65040: operation not allowed from within a pluggable database

SQL> 

Solution :

=> connect to the container database 

=> close the pluggable database 

=> unplug the pluggable database (optional)

=> drop the pluggable database 

    .if we are using the command without including datafiles , this only remove pdb not underline datafiles etc .

SQL> alter session set container =cdb$root;

Session altered.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

2 PDB$SEED   READ ONLY  NO

3 PDB   READ WRITE NO

4 DEMO1   READ WRITE NO

SQL> 

SQL> alter pluggable database demo1 close immediate;

Pluggable database altered.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

2 PDB$SEED   READ ONLY  NO

3 PDB   READ WRITE NO

4 DEMO1   MOUNTED

SQL> drop pluggable database demo1 including datafiles;

Pluggable database dropped.

SQL> show pdbs

    CON_ID CON_NAME   OPEN MODE  RESTRICTED

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

2 PDB$SEED   READ ONLY  NO

3 PDB   READ WRITE NO

SQL>