DBA Commands and Concepts That Every Developer Should Know

DBA Commands and Concepts
That Every Developer Should
Know
Presented by: Alex Zaballa, Oracle DBA

Alex Zaballa
http://alexzaballa.blogspot.com/
@alexzaballa147 and counting…
https://www.linkedin.com/in/alexzaballa

Worked for 7 years in Brazil as a Developer
Worked 8 years for the Ministry of Finance
In Angola as a DBA
March - 2007 until March - 2015

DBA Commands and Concepts That Every
Developer Should Know

Oracle Flashback Query
• Flashback Query (SELECT AS OF)
 AS OF TIMESTAMP
• Flashback Version Query
 VERSIONS BETWEEN { SCN | TIMESTAMP } start
AND end
• Flashback Transaction Query
 SELECT FROM flashback_transaction_query

• Retrieve old versions of procedures:
select text from dba_source
as of timestamp systimestamp - interval '5' minute
where name='MY_PROC' order by line;

The maximum available versions are dependent on the
UNDO_RETENTION parameter.
The default is 900 seconds (15 minutes).

Oracle Flashback Table
Reinstating an accidentally dropped table.
Parameter recyclebin = on (default).

SELECT OWNER,OBJECT_NAME,
ORIGINAL_NAME, TYPE, DROPTIME
FROM DBA_RECYCLEBIN
WHERE ORIGINAL_NAME='TAB_TEST';
FLASHBACK TABLE TAB_TEST TO BEFORE DROP;
Oracle Flashback Table

RMAN Table Recovery in 12c
RMAN enables you to recover one or more
tables or table partitions to a specified point in
time.

RMAN Table Recovery in 12c
RMAN> RECOVER TABLE HR.REGIONS
UNTIL TIME "TO_DATE('01/10/2013
09:33:39','DD/MM/RRRR HH24:MI:SS')"
AUXILIARY DESTINATION '/tmp/backups'

Schema Management
DDL Wait Option
SQL> alter table invoice add (code number);
alter table invoice add (code number)
*
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT
specified or timeout expired

Schema Management
DDL Wait Option
Parameter DDL_LOCK_TIMEOUT (default = 0)
It will wait for N seconds.
In that N seconds, it continually re-tries the DDL
operation until it's successful or this time
expires.

Schema Management
Adding Columns with a Default Value
Table T1  3 millions rows
10.2.0.4.0 > alter table t1 add C_DDL number default 42 not null;
Table altered.
Elapsed: 00:00:48.53
11.2.0.3.0> alter table t1 add C_DDL number default 42 not null;
Table altered.
Elapsed: 00:00:00.04

Rollback
How much longer?
select *
from v$session_longops
where sid = sid_of_the_session_doing_rollback

Rollback
SID : 26
SERIAL# : 30832
OPNAME : Transaction Rollback
TARGET :
TARGET_DESC : xid:0x000e.01c.00000012
SOFAR : 1211
TOTALWORK : 21244
UNITS : Blocks
START_TIME : 15-nov-2015 16:20:07
LAST_UPDATE_TIME : 15-nov-2015 16:21:24
TIME_REMAINING : 55
ELAPSED_SECONDS : 5
CONTEXT : 0
MESSAGE : Transaction Rollback: .... USERNAME
: alex_zaballa
SQL_ADDRESS : 00000000DF79A840
SQL_HASH_VALUE : 72257521
SQL_ID : 4wv9a0h24x3zj

Pending Statistics
We have the option of keeping the newly gathered statistics in a pending
state for testing purposes, until you choose to publish them.
Set table preferences:
begin
dbms_stats.set_table_prefs (
ownname => 'SCOTT',
tabname => 'EMP',
pname => 'PUBLISH',
pvalue => 'FALSE'
);
end;
Collect the statistics.

Pending Statistics
select num_rows,
to_char(last_analyzed,'dd/mm/rrrr hh24:mi:ss')
from all_tab_pending_stats
where table_name = 'EMP';

Pending Statistics
alter session set
optimizer_use_pending_statistics = true;
Test the queries.

Pending Statistics
If it’s ok:
dbms_stats.publish_pending_stats('SCOTT', 'EMP');
Or:
dbms_stats.delete_pending_stats(’SCOTT',’EMP');

Restore Statistics from History
Check the retention:
select
DBMS_STATS.GET_STATS_HISTORY_RETENTION
from dual;
Default is 31 days.

Statistics available for the table:
SELECT OWNER,
TABLE_NAME,
STATS_UPDATE_TIME
FROM dba_tab_stats_history
WHERE table_name='MY_TABLE';

Begin
dbms_stats.restore_table_stats(
'SCOTT',
'EMP',
‘08-NOV-15 11.38.05.015640 AM +08:00’);
End;

Export and Import schema statistics
begin
dbms_stats.CREATE_STAT_TABLE( ownname=>user
, stattab=>'MY_STATS_TABLE'
);
end;
begin
dbms_stats.export_schema_stats( ownname=>user
, statid=>'CURRENT_STATS'
);
End;
EXPDP / IMPDP
begin
dbms_stats.import_schema_stats( ownname=>user
, statid=>'CURRENT_STATS'
);
End;

Explain Plan
How many people are using
Explain Plan ?

Explain Plan
Explain Plan Lies

Explain Plan
Explain Plan just try to predict the Plan.
AUTOTRACE experiences a similar "problem”, especially when
the SQL statement uses bind variables.

Explain Plan
Solution ?
DBMS_XPLAN.DISPLAY_CURSOR

DBMS_APPLICATION_INFO
Allows programs to add information to the
V$SESSION.
Use SET_MODULE to set the name for the program that
the user is currently executing. Optionally you can also
set an action name.
Use SET_ACTION for subsequent processing.
Use SET_CLIENT_INFO for any additional information.

Row-by-Row Processing vs Bulk
Processing
Instead of fetching a single row at a time it is
possible to use the bulk features.

Oracle Virtual Private Database (VPD)
• VPD enables you to create security policies to control
database access at the row and column level.
• VPD adds a dynamic WHERE clause to a SQL statement.
• VPD enforces security directly on database tables,
views, or synonyms.

Oracle Virtual Private Database (VPD)
Original Select:
SELECT * FROM ORDERS;
VPD policy dynamically appends:
SELECT * FROM ORDERS
WHERE COMPANY_ID = 1;

Extended Data Types
SQL> create table tabela_teste(campo01
varchar2(4001));
*
ERROR at line 1:
ORA-00910: specified length too long for its
datatype

Extended Data Types
- VARCHAR2 : 32767 bytes
- NVARCHAR2 : 32767 bytes
- RAW : 32767 bytes

Extended Data Types
SHUTDOWN IMMEDIATE;
STARTUP UPGRADE;
ALTER SYSTEM SET max_string_size=extended;
@?/rdbms/admin/utl32k.sql
SHUTDOWN IMMEDIATE;
STARTUP;
**Once you switch to extended data types you can't switch back

SQL Text Expansion
SQL> variable retorno clob
SQL> begin
dbms_utility.expand_sql_text( input_sql_text
=> 'select * from emp', output_sql_text=>
:retorno );
end;

SQL Text Expansion
• Views
• VPDs

Identity Columns
CREATE TABLE tabela_teste (
id NUMBER GENERATED ALWAYS AS IDENTITY,
coluna1 VARCHAR2(30));

Identity Columns
id NUMBER GENERATED BY DEFAULT AS IDENTITY,

Identity Columns
id NUMBER GENERATED BY DEFAULT ON NULL AS
IDENTITY,

UTL_CALL_STACK
This package allow programmatic access to the call
stack and error stack.
Before 12c: DBMS_UTILITY.FORMAT_CALL_STACK

READ Object Privilege and READ ANY
TABLE System Privilege
What is the difference to SELECT and SELECT
ANY TABLE?

SELECT and SELECT ANY TABLE provides the
ability to lock rows:
LOCK TABLE table_name IN EXCLUSIVE MODE;
SELECT ... FROM table_name FOR UPDATE;

SQL> grant select on scott.emp to teste;
Grant succeeded.
SQL> lock table scott.emp in exclusive mode;
Table(s) Locked.

SQL> grant read on scott.emp to teste;
Grant succeeded.
SQL> lock table scott.emp in exclusive mode;
lock table scott.emp in exclusive mode
*
ERROR at line 1:
ORA-01031: insufficient privileges

Virtual Columns
“Virtual columns appear to be normal table
columns, but their values are derived rather
than being stored on disc.”

Online Table Redefinition
(DBMS_REDEFINITION)
You can change the structure of a table that is
already in use and is impossible to get a
maintenance downtime.

DBA Commands and Concepts That Every Developer Should Know

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