DBA Commands and Concepts That Every Developer Should Know - Part 2

DBA Commands and Concepts That
Every Developer Should Know
Part 2
Alex Zaballa
Part 2
Palestrante
Part 2
Alex Zaballa

2
Alex Zaballa
http://alexzaballa.blogspot.com/
@alexzaballa
https://www.linkedin.com/in/alexzaballa
275 and counting…

3
Alex Zaballa
http://alexzaballa.blogspot.com/
@alexzaballa
https://www.linkedin.com/in/alexzaballa
275 and counting…

5 5
3 Membership Tiers
• Oracle ACE Director
• Oracle ACE
• Oracle ACE Associate
bit.ly/OracleACEProgram
500+ Technical Experts
Helping Peers Globally
Connect:
Nominate yourself or someone you know: acenomination.oracle.com
@oracleace
Facebook.com/oracleaces
oracle-ace_ww@oracle.com

7
Oracle Database Multilingual Engine – Beta 12.2
Initial beta with JavaScript Stored Procedures
http://www.oracle.com/technetwork/database/multilingua
l-engine/overview/index.html

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9

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http://www.oracle.com/technetwork/pt/articles/database-
performance/odb-12-2-multilingual-4394909-ptb.html

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Oracle Database 18c is NOT an Autonomous Database!
https://oracle-base.com/blog/2018/01/03/oracle-database-18c-is-not-an-autonomous-database/

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Autonomous Database - DW
https://juliandontcheff.wordpress.com/2018/03/28/dba-internals-of-the-oracle-autonomous-database/
“You cannot create indexes on columns, you cannot partition
tables, you cannot create materialized views, etc. Not even
database links. You will get an error message: ORA-00439:
feature not enabled: Partitioning or ORA-01031: insufficient
privileges.”

16
count(1) vs count(*)
What is the difference between count(1) and count(*) ?

17
Nothing
count(1) vs count(*)

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Should you gather System Statistics?
https://blogs.oracle.com/optimizer/should-you-gather-system-statistics

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22

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“There is an exceptional case to consider. Databases supporting a pure data
warehouse workload on an Oracle Exadata Database Machine can benefit
from system statistics gathered using the EXADATA option.”

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MBRC
Should I change DB_FILE_MULTIBLOCK_READ_COUNT?

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MBRC
“Oracle recommends using the default unset value, which allows the
Optimizer to calculate the cost as a value of 8, but to use the maximum I/O
request size (usually 1MB) during Full Scan operations.
Starting with Oracle 10gR2, the CBO can automatically determine an
optimal value for the environment.
Setting MBRC to any value makes CBO to use such value but also limits the
number of blocks Oracle can read at once. If the parameter is unset, the
optimizer uses maximum I/O request size up to 128 (usually 1MB) during
Full Scan operations.”

29
MBRC + SYSTEM STATS + EXADATA
EXEC DBMS_STATS.GATHER_SYSTEM_STATS(‘EXADATA’);
***Most of the time the FULL TABLE SCAN is more performant than an INDEX SCAN on
Exadata
Why?
Smartscan

30
MBRC + SYSTEM STATS + EXADATA
Exadata + DW:
• Do not set MBRC
• Collect system stats in Exadata mode
Exadata + OLTP:
• Do not set MBRC
• Do not collect system stats

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MBRC + SYSTEM STATS
Regular Database + DW:
• Do not set MBRC
Regular Database + OLTP :
• Do not set MBRC
*****

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List of valid values for Oracle Database parameters

33

35
How about hidden parameters?

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37

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Parameter values – Another session

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Parameter values – Another session

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Not optimizer related?

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Row-by-row
https://blog.jooq.org/2018/04/19/the-performance-difference-between-sql-row-by-row-updating-batch-updating-and-bulk-updating/

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Analyzing Tables
https://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_4005.htm

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Explain Plan
It does not actually execute the SQL statement.
Runtime factors can influence choice of plan:
• Dynamic Sampling
• Bind Variable Peeking
• Adaptive Features

60
Now what?
• DBMS_XPLAN.DISPLAY_CURSOR
• V$SQL_PLAN%

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DBMS_XPLAN.DISPLAY_CURSOR
• SQL_ID
• CURSOR_CHILD_NO (default 0)
• FORMAT
TYPICAL = DEFAULT
ALL = TYPICAL + QB + PROJECTION + ALIAS + REMOTE
ADVANCED = ALL + OUTLINE + BINDS
ALLSTATS = IOSTATS + MEMSTATS (all executions)
ALLSTATS LAST (last execution)
ADAPTIVE (12c)

DBA Commands and Concepts That Every Developer Should Know - Part 2

DBMS_XPLAN
Display plan for the last SQL executed:
select * from table(dbms_xplan.display_cursor());

Display plan for one specific SQL
Get SQL_ID:

SQL MONITOR
• Introduced in Oracle Database 11g.
• Automatically started when a SQL statement either runs in
parallel or has consumed at least 5 seconds of combined CPU
and I/O.
• Hint /*+ MONITOR */

• Oracle Enterprise Manager
• EM Database Express (12c)
• SQL Developer
• Command Line
**Part of the Oracle Tuning Pack
SQL MONITOR

•select dbms_sqltune.report_sql_monitor(
• sql_id => 'gjabwvvr07w09',
• report_level=>'ALL',
• type => 'ACTIVE') from dual;
SQL MONITOR

72
SQLT (SQLTXPLAIN) Diagnostic Tool
(Doc ID 215187.1)
• Pros: Supported by Oracle
• Cons: Requires Installation

73
SQLT (SQLTXPLAIN) Diagnostic Tool
(Doc ID 215187.1)

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SQLD360
• Pros: No Installation
• Cons: Might miss some information under
rare circumstances

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SQLTXPLAIN vs SQLd360
https://mauro-pagano.com/2017/04/29/sqltxplain-vs-sqld360-differences-and-similarities/

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SQLD360 – how to USE
• Download the free tool:
https://github.com/mauropagano/sqld360/
• Execution:
SQL> sqld360.sql <sql_id> [N|D|T]

81
If you want to know more:
https://mauro-pagano.com/category/sqld360/
SQLD360

83
Full table scan
https://www.slideshare.net/MauroPagano3/
full-table-scan-friend-or-foe

84
Full table scan

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https://richardfoote.wordpress.com/2008/05/12/index-scan-
or-full-table-scan-the-magic-number-magic-dance/
Full table scan

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https://richardfoote.wordpress.com/2008/05/12/index-scan-
or-full-table-scan-the-magic-number-magic-dance/
• Clustering Factor  How well ordered the rows in the table are in relation to
the index.
• Selectivity of the query
• Number of table blocks
• Effective multiblock read count
• Relative cost of single vs. multiblock I/Os
• Parallelism
• Etc
Full table scan

87
Full table scan

88
• Not always good
• Not always bad
Full table scan

90
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.

93
If it’s ok:
Or:
Pending Statistics

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Restore Statistics from History

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Check the retention:
Default is 31 days.

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Statistics available for the table:

97
Restore:

102
PARALLEL DML
insert /*+ append parallel */ into tab1 select /*+ parallel */ * from
tab2 nologging;
15 minutes to complete.
create table tab1 as select /*+ parallel */ * from tab2 nologging;
2 minutes to complete.

106
Oracle Flashback Query
Retrieve old versions of procedures:

108
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.

109
Schema Management
DDL Wait Option

110
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

111
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
DDL Wait Option

112
Adding Columns with a Default Value

113
Adding Columns with a Default Value
The table SALES is about 400 million rows.
10.2.0.4.0  alter table sales add tax varchar2(2) default ‘XX’ not
null;
Elapsed: 00:41:00.00
11.2.0.4.0  alter table sales add tax varchar2(2) default ‘XX’ not
null;
Elapsed: 00:00:00.03

115
READ Object Privilege and READ ANY TABLE System
Privilege

116
Privilege
What is the difference to SELECT and SELECT ANY TABLE?

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

118
Privilege
SQL> grant select on scott.emp to teste;
Grant succeeded.
SQL> lock table scott.emp in exclusive mode;
Table(s) Locked.

119
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
Privilege

121
Extended Data Types
SQL> create table tabela_teste(campo01 varchar2(4001));
*
ERROR at line 1:
ORA-00910: specified length too long for its datatype

122
Extended Data Types
• VARCHAR2 : 32767 bytes
• NVARCHAR2 : 32767 bytes
• RAW : 32767 bytes

123
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

127
Temporary Undo
ALTER SESSION SET TEMP_UNDO_ENABLED = TRUE;
ALTER SYSTEM SET TEMP_UNDO_ENABLED = TRUE;

129
Longer Identifier Names
Starting with Oracle Database 12c Release 2 (12.2), the maximum
length of identifier names for most types of database objects has
been increased to 128 bytes.

134
PDB LOCKDOWN PROFILES
A security mechanism to restrict operations that are available to
local users connected to a specified PDB.

137
Thank You
Slides Available: http://www.slideshare.net/

DBA Commands and Concepts That Every Developer Should Know - Part 2

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