11g surprises

The first two surprises after my first 11g installation was the new location of alert.log file and AMM changed yet again. I didn't run 11g beta program, so the two surprises could be old story for many others.

Just in case you wonder where's my alert.log files and what is memory_target parameter. Check following two metalink docs for full explanation.

Automatic Memory Management(AMM) on 11g
Doc ID:
Note:443746.1

Finding alert.log file in 11g
Doc ID:
Note:438148.1

explain plan - a note for myself

Just a quick note for myself. I used to generate explain plan from sqlplus using autotrace, it's time to switch to use dbms_xplan package instead. Well it's never too late to do the right thing anyway.

SQL> explain plan for select empno,sal from emp;
Explained.
SQL> select * from table(dbms_xplan.display);

LOG Miner by Example

Come across a post in OTN forum today where DBMS Direct has a pretty good demonstration of how to use Logminer. Thought it's might be a good idea to post it here as future quick reference for myself or anyone need it.

First check if you have SUPPLEMENTAL Logging enabled,

SELECT SUPPLEMENTAL_LOG_DATA_MIN FROM V$DATABASE;

If not,

ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;

Choose the Dictionary Option, there're three options you can choose.

Tell Logminer to use current online catalog as dictionary,

EXECUTE DBMS_LOGMNR.START_LOGMNR(-
OPTIONS => DBMS_LOGMNR.DICT_FROM_ONLINE_CATALOG);

Or extract Dictionary to the Redo Log Files,
you set this option if you can't access sourcce database while you do log mining.

EXECUTE DBMS_LOGMNR_D.BUILD( -
OPTIONS=> DBMS_LOGMNR_D.STORE_IN_REDO_LOGS);

Or extract Dictionary to a Flat File,
this option is for backward compatibility and not recommended if you can use other two.

EXECUTE DBMS_LOGMNR_D.BUILD('dictionary.ora', -
'/oracle/database/', -
DBMS_LOGMNR_D.STORE_IN_FLAT_FILE);

Now find a list of recent redo logfiles you want to mine,
you could choose to let Logminer use control file automatically build the list of redo logfiles needed.

ALTER SESSION SET NLS_DATE_FORMAT = 'DD-MON-YYYY HH24:MI:SS';

EXECUTE DBMS_LOGMNR.START_LOGMNR( -
STARTTIME => '01-Jan-2007 08:30:00', -
ENDTIME => '01-Jan-2007 08:45:00', -
OPTIONS => DBMS_LOGMNR.DICT_FROM_ONLINE_CATALOG + -
DBMS_LOGMNR.CONTINUOUS_MINE);

Or manually pick which one you want to analysis

SQL> SELECT NAME FROM V$ARCHIVED_LOG WHERE COMPLETION_TIME > TRUNC(SYSDATE);

/oracle/edb/oraarch/edb/1_3703_608486264.dbf
/oracle/edb/oraarch/edb/1_3704_608486264.dbf
/oracle/edb/oraarch/edb/1_3705_608486264.dbf
/oracle/edb/oraarch/edb/1_3706_608486264.dbf
/oracle/edb/oraarch/edb/1_3707_608486264.dbf
/oracle/edb/oraarch/edb/1_3708_608486264.dbf
/oracle/edb/oraarch/edb/1_3710_608486264.dbf
/oracle/edb/oraarch/edb/1_3709_608486264.dbf
/oracle/edb/oraarch/edb/1_3711_608486264.dbf
/oracle/edb/oraarch/edb/1_3712_608486264.dbf

10 rows selected.

Add the logfiles for analysis.

EXECUTE DBMS_LOGMNR.ADD_LOGFILE(LOGFILENAME => '/oracle/edb/oraarch/edb/1_3712_608486264.dbf',OPTIONS => DBMS_LOGMNR.NEW);

EXECUTE DBMS_LOGMNR.ADD_LOGFILE(LOGFILENAME => '/oracle/edb/oraarch/edb/1_3711_608486264.dbf');

Start LogMiner to populate the V$LOGMNR_CONTENTS view

EXECUTE DBMS_LOGMNR.START_LOGMNR();

Format the SQLplus output for better viewing,

SQL> set lines 200
SQL> set pages 0
SQL> col USERNAME format a10
SQL> col SQL_REDO format a30
SQL> col SQL_UNDO format a30

And there we go,

1 SELECT username,
2 SQL_REDO, SQL_UNDO ,to_char(timestamp,'DD/MM/YYYY HH24:MI:SS') timestamp
3* FROM V$LOGMNR_CONTENTS where rownum< username="'TEST'">

SQL> /

USERNAME SQL_REDO SQL_UNDO
---------- ------------------------------ ------------------------------
TIMESTAMP
-------------------
TEST insert into "TEST"."KI_TEST delete from "TEST"."KI_TEST
_RES7"("MASTER_ID","WAFER_ID", _RES7" where "MASTER_ID" = '18
"DIE_NUM","TEST_NUM","RESULT") 8199' and "WAFER_ID" = '15' an
values ('188199','15','0,144' d "DIE_NUM" = '0,144' and "TES
,'4','.83555'); T_NUM" = '4' and "RESULT" = '.
83555' and ROWID = 'AAAOnaAAZA
AAECZAEV';
01/11/2007 09:23:59

TEST insert into "TEST"."KI_TEST delete from "TEST"."KI_TEST
_RES7"("MASTER_ID","WAFER_ID", _RES7" where "MASTER_ID" = '18
"DIE_NUM","TEST_NUM","RESULT") 8199' and "WAFER_ID" = '15' an
values ('188199','15','0,144' d "DIE_NUM" = '0,144' and "TES
,'5','.70222'); T_NUM" = '5' and "RESULT" = '.
70222' and ROWID = 'AAAOnaAAZA
AAECZAEW';
01/11/2007 09:23:59

TEST insert into "TEST"."KI_TEST delete from "TEST"."KI_TEST
_RES7"("MASTER_ID","WAFER_ID", _RES7" where "MASTER_ID" = '18
"DIE_NUM","TEST_NUM","RESULT") 8199' and "WAFER_ID" = '15' an
values ('188199','15','0,144' d "DIE_NUM" = '0,144' and "TES
,'6','.82502'); T_NUM" = '6' and "RESULT" = '.
82502' and ROWID = 'AAAOnaAAZA
AAECZAEX';
01/11/2007 09:23:59

TEST insert into "TEST"."KI_TEST delete from "TEST"."KI_TEST
_RES7"("MASTER_ID","WAFER_ID", _RES7" where "MASTER_ID" = '18
"DIE_NUM","TEST_NUM","RESULT") 8199' and "WAFER_ID" = '15' an
values ('188199','15','0,144' d "DIE_NUM" = '0,144' and "TES
,'7','1.4818'); T_NUM" = '7' and "RESULT" = '1
.4818' and ROWID = 'AAAOnaAAZA
AAECZAEY';
01/11/2007 09:23:59


Reference:
Oracle Document
Using LogMiner to Analyze Redo Log Files

Orginal Post in OTN

LOGGING/NOLOGGING

One of the common misconception is if you set NOLOGGING on a table or index, then no future DML operations (insert, update, delete etc) on this object will be recorded in logfiles.

Actually the real meaning of NOLOGGING is whatever operations are performed on the object with the NOLOGGING option, will NOT be recorded in logfiles.

However, not all operations support NOLOGGING mode, the following is a list of operations that support NOLOGGING:

direct load (SQL*Loader)
direct-load
INSERT CREATE TABLE ... AS SELECT
CREATE INDEX
ALTER TABLE ... MOVE PARTITION
ALTER TABLE ... SPLIT PARTITION
ALTER INDEX ... SPLIT PARTITION
ALTER INDEX ... REBUILD
ALTER INDEX ... REBUILD PARTITION
INSERT, UPDATE, and DELETE on LOBs in NOCACHE NOLOGGING mode stored out of line


It also recommended to do a backup of subject object after NOLOGGING operation. When you do media recovery of the object using backup copy before NOLOGGING operation, the extent invalidation records mark a range of blocks as logically corrupt, because the redo data is not fully logged. The similar situation apply to Data Guard setup. That's also one of reason why Data Guard setup require you to set force logging.

Howard has been talking about the use of _disable_logging parameter to temporary disable redo logging while bulking loading. However this parameter should be used with extreme caution.

Howard's post about _disable_logging

Some thing about Shared Pool

Here's a good presentation, explaining the internal structure of shared pool and how lock, pin and latch are handled.

http://www.perfvision.com/papers/unit6_shared_pool.ppt

Set SQL*Plus Prompt

Since most DBAs will use SQL*Plus more than any tools else, it will be convenience if you can set your SQL*Plus prompt to show your current login user and SID instead of this "SQL>". Especially if you have mulitple instances running under same Oracle installation.

To do this, you need to include following in your glogin.sql

set term off
define sql_prompt=idle
column user_sid new_value sql_prompt
select lower(user) '@' '&_CONNECT_IDENTIFIER' user_sid from dual;
set sqlprompt '&sql_prompt> '
set term on

When you login you will see this,

sqlplus scott/tiger
scott@dev

If you are on 10g, it becomes much easier by only this,

set sqlprompt '_user@&_connect_identifier>'

Getting a job as a Junior DBA - series

Unfortunately, due to some unspecified events happened early 2008, Howard decide to withdraw his contribution to Oracle community. More info here
The interview series link is no longer valid. I wish I had cut/pasted it :(

One of the most common Q I saw new DBA ask in Oracle forum is what kind of questions employer will ask during a job interview? I tried to sum a few questions I have been asked during job interviews as a job candidate.

Howard Rogers has nice serie in his blog from interviewer's prospective.
Getting a job as a Junior DBA

Frankly if you ask me, I don't want to work for him :) However that doesn't change the fact it's a nice reading.