Tuesday, February 23, 2010

Using "sys_context" function

We were planning to restrict an DB user so that it can
a. only create session
b. have insert only into a table MYTABLE
c. Can insert on that table(MYTABLE) only from several selected servers

Point a & b are easy to resolve. But for pint c we had to do some this extra.
In order to implement point c we created a trigger on table MYTABLE which used function sys_context to collect & IP from the session and use these information for authentication. My trigger was as below:

create or replace trigger mytrg
before insert on MYTABLE
for each row
declare
var_ip varchar2(50);
var_count_ip number;
var_user varchar2(50);
begin
select sys_context('USERENV', 'IP_ADDRESS') into var_ip from dual;
select count(*) into var_count_ip from servers where ip = var_ip;
select user into var_user from dual;
if var_user = 'ALERTSENDER' and (var_ip is null or var_count_ip <>
RAISE_APPLICATION_ERROR(-20001,
'ERROR:' || var_ip ||
':NOT AN AUTHENTICATED IP');
else
--OTHER NORMAL OPERATIONS
end if;
end;


Detailed List of Locked Object

I order to find details of all locked object at any moment we can use below query:

select c.USERNAME,b.owner,b.object_name,b.object_type,
decode(a.LOCKED_MODE,
0,
'none',
1,'null',
2,'Row- Share',
3,'Row-exclusive',
4,'Share',
5,'Share /Row- exclusive',
6,'exclusive') LOCKED_MODE,
c.SID, c.SERIAL#,d.SPID, c.OSUSER,c.PROGRAM,c.MACHINE
from v$locked_object a, dba_objects b, v$session c, v$process d
where a.OBJECT_ID = b.object_id
and a.SESSION_ID = c.SID
and c.PADDR = d.ADDR;

Tuesday, February 16, 2010

Foreign Key Constraints Referencing to a Table

We had a table to purge with primary key.
Problem is we need to backup purged data which includes data from all the child tables referencing with foreign keys to that table.
Now I had to find all the child tables and their foreign key columns. I used below query to resolve this problem:

select a.owner,
a.constraint_name,
a.constraint_type,
a.table_name,
b.column_name,
a.r_owner,
a.r_constraint_name
from dba_constraints a, dba_cons_columns b
where a.owner = 'MYUSER'
and a.owner = b.owner
and a.constraint_name = b.constraint_name
and a.r_constraint_name in
(select constraint_name
from dba_constraints
where table_name = 'MYTABLE'
and owner = 'MYUSER');


http://bytes.com/topic/oracle/answers/644008-query-find-primary-foreign-keys
http://www.databasejournal.com/features/oracle/article.php/3665591/Finding-Foreign-Key-Constraints-in-Oracle.htm

Monday, February 15, 2010

Execution Plan & Estimate Temporary Tablespace Usages

One of our developer was informing that he need extra space on temporary tablespace as one of his adhoc query is running for 2 hours (and may run for 10 hours) and consuming huge amount of temp space.

Database was Oracle 11gR2 on RHEL5.
Now problem is how can I estimate that how much space should I add ? I tried with execution plan
as below:

sqlplus user/pass@DB

sql> delete from myuser.plan_table;

sql> commit;

sql> explain plan for
select * from .....


sql> select * from myuser.plan_table;


But I could not find any field that said about Temp Usage.
Then searching the web I became know that Older version of plan table(I found default) don't have that field. It should be created manually and than explain the a query:

cd /ORAIN/oracle/product/11.2.0/dbhome_1/rdbms/admin/


sqlplus user/pass@DB

sql> drop myuser.plan_table purge;

sql> @utlxplan.sql

Table created.

sql> delete from myuser.plan_table;

sql> commit;

sql> explain plan for
select * from .....


sql> select * from myuser.plan_table;

Here TEMP_SPACE column will show the estimated space usage. Then I added the extra Temp space according to the value [added more than estimated for safety purpose] showed by column TEMP_SPACE and it worked.


Recent optimizer statistics should be gathered for Tables and Indexes used the query for which plan is being generated in order to get more accurate result.

http://oradbatips.blogspot.com/2008/02/tip-69-estimate-temp-usage-without.html
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:12519780526076