Oracle 11g architecture Quick Reference

How to find all child tables of a table in Oracle??

Sometimes it’s useful to find out all the dependent/child tables for a particular table. The SQL statement below will work for an Oracle database:

SELECT
  a.owner,a.table_name, a.constraint_name
FROM
  sys.all_constraints a,
  (SELECT owner,constraint_name from sys.all_constraints
    WHERE
     owner = 'OWNER' and
     table_name = 'TABLE_NAME' and
     constraint_type in ('P','U')
  ) b
WHERE
  a.constraint_type = 'R' and
  a.r_constraint_name = b.constraint_name and
  a.r_owner = b.owner

Where  OWNER is the owner/schema to which the table belongs andTABLE_NAME is the table to be reported on.

HUNG IN AUTO SQL TUNING TASK

Issue-
In 11.2.0.3 database , we get alert in EM related to metric “Generic Operational Error” or "Generic Operational Error Status ". Occasionally when running Automatic SQL Tuning the following messages may appear in the alert log:
Error-

These messages indicate that an auto kill of a "hung"/long running tuning task has taken place.

This is a protective measure purely to avoid the task from over-running its time limit because of a single task and  protects a the system from harm caused by such over-running.

Since this is an expected activity to prevent over-running there is no fix as such.  
Instead as a workaround, you could:
FIX 1 :Give the task more time to complete (the following example would set the per statement timeout to 6 hours (21600 seconds)):
BEGIN
  DBMS_SQLTUNE.set_tuning_task_parameter('SYS_AUTO_SQL_TUNING_TASK', 'LOCAL_TIME_LIMIT', 21600);
 END;

/
Note
If you increase the per-statement time limit (LOCAL_TIME_LIMIT) then you need to stay within the bounds of the time limit for the entire task (TIME_LIMIT). The duration of the TIME_LIMIT parameter must be at least equal or greater than the LOCAL_TIME_LIMIT. When the maintenance window closes the SQL Tuning Advisor is stopped.
FIX 2 :
Disable the automatic tuning process and the messages will not appear anymore (though obviously the auto tuning will also no longer occur - you could manually execute the job as desired later). 
To disable the job:
connect / as sysdba

BEGIN
DBMS_AUTO_TASK_ADMIN.DISABLE(
client_name => 'sql tuning advisor',
operation => NULL,
window_name => NULL);
END;
/
To re-enable in future:
connect / as sysdba

BEGIN
DBMS_AUTO_TASK_ADMIN.ENABLE(
client_name => 'sql tuning advisor',
operation => NULL,
window_name => NULL);
END;

/
Source : 
How to Avoid or Prevent "Process 0x%p appears to be hung in Auto SQL Tuning task" Messages (Doc ID 1344499.1)

How to get PASSWORD changed time for an Oracle user??

SELECT name, ctime, ptime
FROM sys.user$
WHERE name = 'TEST_SUH';

How to check if your Oracle client is 32 bit or 64 bit?

SOLUTION 1:
If logged into SQL Plus, the banner will tell you 64-bit if the 64-bit version is installed. If it does not specify 64-bit then it is 32-bit (even though it does not explicitly say so).

SOLUTION 2:
You can specifically query the info by running the following:
SELECT * FROM V$VERSION;

The banner will tell you 64-bit if the 64-bit version is installed. If it does not specify 64-bit then it is 32-bit.
SOLUTION 3:
Run the query to check the following:
select distinct address from v$sql where rownum<2;
If the address returned is 16 characters long, it is 64 bit.
If it is 32 bit you will get an 8 character address.

SOLUTION 4:
If the two directories $ORACLE_HOME/lib32 and $ORACLE_HOME/lib are existing then it is 64 bit. If there is only an ORACLE_HOME/lib directory then it is 32 bit client.
*Headsup: In newer versions of the client, the library is not included and this directory may not exist.

How to find total number of Oracle schema objects and its size??

select obj.owner "Owner", obj_cnt "Objects", decode(seg_size, NULL, 0, seg_size) "size MB" from (select owner, count(*) obj_cnt from dba_objects group by owner) obj, (select owner, ceil(sum(bytes)/1024/1024) seg_size
from dba_segments group by owner) seg where obj.owner = seg.owner(+)
order by 3 desc ,2 desc, 1;

How to run SQL Tuning Adviser manually??

Step 1: Replace SQL_ID and TASK_NAME (Unique):

DECLARE

  l_sql_tune_task_id  VARCHAR2(100);

BEGIN

  l_sql_tune_task_id := DBMS_SQLTUNE.create_tuning_task (

                          sql_id      => 'XXXXX',

                          scope       => DBMS_SQLTUNE.scope_comprehensive,

                          time_limit  => 1800,

                          task_name   => 'XXXXX_A',

                          description => 'Tuning task for statement 8p9qh5xwgc3fx_B in AWR.');

  DBMS_OUTPUT.put_line('l_sql_tune_task_id: ' || l_sql_tune_task_id);

END;

/

Step 2: Validate if SQL Tuning Task is created or not (Status should be INITIAL):

select * from dba_advisor_log  where task_name='XXXXX_A' order by task_id desc;

Step 3: Run the Advisor

EXEC DBMS_SQLTUNE.execute_tuning_task('XXXXX_A');

Step 4: Check the status in other session using command below: (It should show EXECUTING)

select * from dba_advisor_log  where task_name='XXXXX_A' order by task_id desc;

Step 5: Once the Advisor task is completed. Generate report using command below:

SELECT DBMS_SQLTUNE.report_tuning_task(‘XXXXX_A') AS recommendations FROM dual;

Step 6: Analyze the report and implement the solution if necessary.

Source: Thanks Arbind!!!