Sherlock holmes for dba’s

Sherlock Holmes for DBA’s

Kellyn Pot’Vin
Sr. Technical Consultant
Enkitec

Denver DBA
 Kellyn Pot’Vin,
 Westminster, Colorado
 Oracle ACE, Sr. Technical Specialist at Enkitec
 Multi-Platform DBA
 Specialize in performance and management
of large enterprise environments.
 Board of directors for RMOUG, Director of
Training Days 2013, KSCOPE DB Track Lead
2013
 Blog: DBAKevlar.com
 Twitter: @DBAKevlar

Challenges for Today’s DBA
 Added Complexity by Less Manual
Configurations in Environment.
 Added Roles to DBA’s, either requiring
more specializing and/or overall
knowledge required.
 Added Features, systems.
 More open source solutions required,
outside of standard design.

The Pitfall of All Optimization:
The “Tinsel Monkey”

“Tinsel” vs. “Valuable”
 Tinsel = anything that is shiny-
◦ graphs from EM without investigation.
◦ costs without research verifying are valid.
◦ Assumptions without proof.
 Tuning “Tinsel” results in no productive gain
in performance in the database.
 Valuable optimization=Performance Gain.
 Performance gain should equal time savings.
 Time is gold.

What is Performance “Gold”
 Performance optimization that-
◦ saves valuable time to a long running process.
◦ Saves users valuable time to their work day.
◦ Saves results in value to the business.
◦ Re-allocates valuable resources, (memory, I/O
or sessions) back to the database.
 Optimizing that saves time from
maintenance work that can be re-
allocated back to the business processing.

Saving DBA Time
 Sharing knowledge- Optimization should
never be viewed as a “mystery process”
or “voodoo”.
 Developers and Analysts should have
access to DBA Performance Views.
 Ability to create explain plans.
 Access to Enterprise Manager “Top
Activity” and drill downs.

Goals for the Attendee
 AWR, ASH and Tracing Knowledge.
 Steps to trouble-shooting an issue.

Over all, the goal of this session is for you
to always, ALWAYS, ALWAYS base any
changes you make on data and proof.
NEVER base changes on assumptions,
guesses or because you “read it
somewhere”.

Presentation Agenda
 Architecture
 History
 Reports
◦ ADDM
◦ ASH
◦ AWR
◦ Explain Plans
 Trace Files
◦ 10046
◦ 10053

AWR Repository
 Used not only by the AWR reports
◦ Automatic Database Diagnostic Monitor, (ADDM
Reporting)
◦ SQL Tuning Advisor
◦ Segment Advisor
 By default, snapshots every hour. Retention
is for 7 days. Both are modifiable.
 Snapshots can be taken at any time:
EXEC DBMS_WORKLOAD_REPOSITORY.create_snapshot;

Running Tuning Pack Reports
 Through Enterprise Manager
 $ORACLE_HOME/rdbms/admin
◦ ADDM- addmrpt.sql
◦ ASH- ashrpt.sql
◦ AWR- awrrpt.sql
◦ SQL_ID Specific AWR- awrsqrpt.sql
 These reports can be in HTML or TEXT
versions.
 Require the Tuning and Management Pack
license.

AWR Reports
Statspack on “Steroids”
 As detailed snapshot of database depending on
intervals of snapshot setup, (hourly be default.)
 Introduced in Oracle 10g
 Evolution to statspack, requests for performance
reporting improvements.
 “Always on” approach to performance metrics
with requirement of non-locking collection
process.
 Requires Management Tuning Pack License from
Oracle.

Running AWR from Enterprise
Manager

• Post logging into the database, click on
Performance.
• From Performance  AWR  AWR Report

ASH Report
 Best in smaller timeslots.
 Includes SQL_ID, object information and timeline of
waits.
 Samples each active database session every second.
 Data is held in buffer in memory.
 Built into the Oracle kernel and accessed through the
v$active_session_history view.
 In an AWR snapshot, 1 row in 10 from ASH buffer is
placed into the AWR repository.
 Managed by the MMNL, (Memory Monitor Lite)
 Should not be used to track occurrence.

Running ASH Report from
Enterprise Manager
• ASH is always by time, not snapshot.
• Set start date and time.
• End date and time
• Generate report

ADDM Report High Lights
“Just the Facts” Report
 Produced from AWR Snapshots
 Broken down by “Findings and
Recommendations”
 Identifies high-level misconfigurations.
 Lists what “Is Not an Impact”
 Do NOT recommend for non-DBA
Personnel.

Creating Explain Plans
Creating an Explain plan:
EXPLAIN PLAN FOR <SQL STATEMENT>;
SELECT PLAN_TABLE_OUTPUT from
table(dbms_xplan.display(‘plan_ta
ble’,null,’basic’));
Preferred:
SELECT * FROM
TABLE(DBMS_XPLAN.DISPLAY);
From a previous run, using SQL_ID:
SELECT * FROM
TABLE(DBMS_XPLAN.DISPLAY_AWR(‘SQL_I
D’));

Trace Events and Levels
Event Level Description
10046 0 No statistics generated

Standard trace output including parsing, executes and fetches
10046 1 plus more
10046 2 Same as Level 1
10046 4 Level 1 + Bind Variables
10046 8 Level 1 + Waits
10046 12 Level 1 + Bind Variables & Waits

Added in 11g to generate STAT line dumps for each
execution. STAT dumping has been amended in 11g so that
they are not aggregated across all executions but are dumped
10046 16 after execution.
10053 1 Dump Optimizer Statistics and Computations
10053 2 Dump Optimizer Computations only

Tracing: 10046
 10046
alter session set events '10046 trace name
context forever, level 8';
exec
dbms_system.set_sql_trace_in_session(<sid>,<s
erial#>,TRUE);
exec
dbms_system.set_ev(<sid>,<serial#>,10046,12,'
');

Tracing:10053
Alter session set events '10053 trace
name context forever, level 1';
OR
begin
DBMS_SQLDIAG.DUMP_TRACE(p_sql_id=>‘<sql
_id>',
p_child_number=>0,
p_component=>'Optimizer',
p_file_id=>‘<distinguish trace
name>');
end;
/

Trace Files are Too Big/Complex
 Become familiar with TKPROF for 10046
trace files.
 If tracing often, sell cost effectiveness like
advanced trace assistance tools like
Method R’s “Mr. Trace”.
 Become confident in how to find bind
variable, sql_id and column data values in
a trace file.
 Become friends with find/search.. 

Real Life Scenario 1
Developer notices that performance is poor in
two standard transformation process.
Process utilizes CTAS, (create table as)
Believes parallel process is being degraded to
serial due to limitations in CPU resources in
database.
First Step?
Second Step?

Scenario 1, Step 1
 Explain plan of first CTAS shows that
although SQL has parallel hints in “select”
section, no parallel was designated in
“create table” section of statement.
 Second process showed parallel in explain
plan, but processing via Enterprise
Manager did show only one process
active for majority of time, other parallel
slaves waiting.

Scenario 1, Step 2
 10046, level 8 trace of second process.
 Trace file clearly shows single slave
session busy on function call, where
parallel at all other processing.
 Inspection of code showed function
needed to be created with
“parallel_enable” clause addition.

11g Upgrade recently performed in
environment.
Overall performance good, but number of large
DML processes degrading.
Elapsed time extended, but time extension is
spread across each transaction in the overall
processing.
First step?
Second step?

Scenario 2, Step 1
 AWR reports show significant increase in
times.
 IO has increased, physical reads on tables
involved in DML shown as increase.
 No change in explain plans, utilizing 10g
plans or new plans show no
improvement.

Scenario 2, Step 2
 10053 trace, level 1 by SQL_ID’s of DML
involved.
 Discovered in the trace file, full scans of
tables due to following 11g parameter:
 CELL_OFFLOAD_PROCESSING=TRUE
 Per the MOS note- High 'ksv master wait'
And 'ASM File Metadata Operation' Waits
In Non-Exadata 11g [ID 1308282.1]

 Users complain of performance
degradation of main processing in data
mart when larger, heavy concurrent
processes.
 Same code executed in database when
degradation occurs.
 AWR shows adequate SGA, PGA hit, high
I/O.
 First step? Second Step?

Scenario 3, First Step:
 Memory and PGA show fine, yet high I/O, inspect the memory
,workarea and temp:
select vst.sql_text, swa.sql_id, swa.sid,
swa.tablespace
, swa.operation_type
, trunc(swa.work_area_size/1024/1024) "PGA MB"
, trunc(swa.max_mem_used/1024/1024)"Mem MB"
, trunc(swa.tempseg_size/1024/1024)"Temp MB"
from v$sql_workarea_active swa, v$session vs,
v$sqltext vst
where swa.sid=vs.sid
and swa.sql_id=vs.sql_id
and vs.sql_id=vst.sql_id
and vst.piece=0
order by swa.sql_id;

Scenario 3, Second Step:
 Workarea shows no PGA allocated,
considering the size of temp table created
as part of the CTAS, hash joins and hash
group by sort.
 Performed 10048 trace of session.
 Action Plan: Traced session and noted the
following, which was then located in
procedure call: alter session set
WORKAREA_SIZE_POLICY =
MANUAL;

Optimization Data
 Database Level:
◦ AWR Reports
◦ ASH Reports
◦ ADDM Reports
◦ Enterprise Manager
◦ Queries
 Session Level:
◦ Explain Plans
◦ Traces
◦ Queries

Design of an Optimization Exercise
 Collect top 10 list of database
performance challenges.
 Review with peers and user base.
 Create top 10 list that incorporates both
the DBA list of top 10 and the User list.
 Divide the list into “low-hanging fruit” and
those that will demand extensive
resources to correct.
 Review the database again only after the
“low-hanging fruit” has been addressed.

Summary
 Optimization is not an exact science, but
following logical steps when scenarios
develop is key.
 Always optimize for time savings
 Research to produce data, (proof) behind
any optimize goaled exercise to eliminate
wasted effort before an exercise is
commenced.

Thank you
Kellyn Pot’Vin
Website: http://dbakevlar.com
and http://enkitec.com
Email: dbakevlar@gmail.com or kpotvin@enkitec.com
Twitter: @DBAKevlar
Facebook and LinkedIn: Kellyn Pot’Vin

Sherlock holmes for dba’s

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