The document discusses using Oracle 10053 trace files to analyze the Cost Based Optimizer's decision making process. It provides information on enabling 10053 traces, the structure and contents of 10053 trace files, and examples of using traces to understand why a particular execution plan was chosen. The document also covers newer tracing options introduced in Oracle 11g and how 10053 traces can help optimize SQL statements and learn about the CBO.

1. Doug Burns dougburns@yahoo.com
http://oracledoug.com
@orcldoug
#OTW
#OakTable

2.  Introduction
 What
 How
 Why
 Structure
 Example
 Conclusions and References
01/10/2013

3.  Who am I?
 Why am I talking?
 Setting Expectations
01/10/2013

4.  I am Doug
 Doug I am << Dr Seuss Edition
 Actually I am Douglas
 … or, if you're Scottish, Dougie or Doogie
 I'm not from England
 You will have probably noticed that already
 I don't know many Scottish people who do glowing introductions about
their all-round genius!
 But, amongst other things, I am …
01/10/2013

5. 01/10/2013

6. 01/10/2013

7. 01/10/2013

8.  A long time ago in a galaxy far, far away ….
 "A look under the hood of CBO: The 10053 Event"
 Wolfgang Breitling (see References)
 Time passes & beers are consumed & conversations follow …
 You almost never need to use 10053 trace files
 They are far too long and complex to understand
 … and yet …
 I find myself using them more often
 I think they're becoming easier to understand
01/10/2013

9. 01/10/2013

10.  10053 files, like most Oracle trace files are
 Useful in specific situations
 Very detailed and informative
 Relatively easy to generate
 They are also
 Usually unnecessary
 Undocumented
 Subject to change over time
 Complex in places
01/10/2013

11.  Introduction
 What
 How
 Why
 Structure
 Example
 Conclusions and References
01/10/2013

12.  Contains a record of the Cost Based Optimizer decision
making process and the various inputs used
 Hard Parse Time
 As we'll see, it contains
 Server configuration items that influence the CBO
 Object and System Statistics used by calculations
 Execution Plan Steps that were considered and accepted
▪ Resulting in final overall execution plan
 Execution Plan Steps that were considered and rejected
▪ Including the reasons why
01/10/2013

13.  Introduction
 What
 How
 Why
 Structure
 Example
 Conclusions and References
01/10/2013

14.  By enabling event 10053 using any of the usual methods
 Run (or Explain) the SQL statement
 Disable event
 Find trace file in user_dump_dest
01/10/2013
show parameter user_dump_dest
ALTER SESSION SET tracefile_identifier='EXAMPLE1_10053';
ALTER SESSION SET events '10053 trace name context forever, level 1';
SELECT * FROM dual;
ALTER SESSION SET events '10053 trace name context off';

15.  The statement must be hard-parsed
 The statement must not have been run before
 Plan has been aged out of cursor cache
 Shared pool has been flushed
 New version of the statement by adding a unique comment
01/10/2013
show parameter user_dump_dest
ALTER SESSION SET tracefile_identifier='EXAMPLE1_10053_1';
ALTER SESSION SET events '10053 trace name context forever, level 1';
SELECT /* EXAMPLE1_1 */ * FROM dual;
ALTER SESSION SET events '10053 trace name context off';

16.  Oracle 11g introduces a new tracing infrastructure
 Can be accessed using
 ALTER SESSION
 ORADEBUG
 DBMS_SQLDIAG.DUMP_TRACE
▪ Does not require Diagnostics Pack license
01/10/2013

17.  Replacement for original method of setting event 10053
 Main 10053-related Options
 SQL_Compiler and SQL_Optimizer
01/10/2013
show parameter user_dump_dest
ALTER SESSION SET tracefile_identifier='EXAMPLE1_2_OPTTRACE';
ALTER SESSION SET events 'trace [SQL_Compiler.*]';
SELECT /* EXAMPLE1_2 */ * FROM dual;
ALTER SESSION SET events 'trace [SQL_Compiler.*] off';

18.  There are also sub-options
01/10/2013
SQL> oradebug doc component SQL_Compiler
SQL_Compiler SQL Compiler
SQL_Parser SQL Parser (qcs)
SQL_Semantic SQL Semantic Analysis (kkm)
SQL_Optimizer SQL Optimizer
SQL_Transform SQL Transformation (kkq, vop, nso)
SQL_MVRW SQL Materialized View Rewrite
SQL_VMerge SQL View Merging (kkqvm)
SQL_Virtual SQL Virtual Column (qksvc, kkfi)
SQL_APA SQL Access Path Analysis (apa)
SQL_Costing SQL Cost-based Analysis (kko, kke)
SQL_Parallel_Optimization SQL Parallel Optimization (kkopq)
SQL_Code_Generator SQL Code Generator (qka, qkn, qke,
kkfd, qkx)
SQL_Parallel_Compilation SQL Parallel Compilation (kkfd)
SQL_Expression_Analysis SQL Expression Analysis (qke)
SQL_Plan_Management SQL Plan Managment (kkopm)
MPGE MPGE (qksctx)

19.  What if you want to trace just one SQL statement that a
Session executes?
 Perhaps inside a PL/SQL procedure or function
 Can also specify SQL_ID
 Still relies on Hard Parse
01/10/2013
show parameter user_dump_dest
ALTER SESSION SET tracefile_identifier='EXAMPLE2_OPTTRACE';
ALTER SESSION SET events 'trace [SQL_Compiler.*][sql:37cv4d33vbu8h]';
SELECT /* EXAMPLE1_2 */ * FROM dual;
ALTER SESSION SET events 'trace [SQL_Compiler.*] off';

20.  What if you want to trace just one SQL statement and you
don't know which session will execute it?
 Can enable System-wide tracing using ALTER SYSTEM
 Still relies on Hard Parse
01/10/2013
show parameter user_dump_dest
ALTER SYSTEM SET events 'trace [SQL_Compiler.*][sql:bhqn6d93r5r03]';
ALTER SYSTEM SET events 'trace [SQL_Compiler.*] off';

21.  Solves several issues
 Can show optimizer trace file for a statement that has already been
executed and exists in the cursor cache
 Can force hard parse of the statement
 Can only use Optimizer or Compiler
01/10/2013
BEGIN
dbms_sqldiag.dump_trace(
p_sql_id => '37cv4d33vbu8h',
p_child_number => 0,
p_component => 'Compiler',
p_file_id => 'EXAMPLE1_OPTTRACE');
END;
/

22. 01/10/2013
Enabling tracing for cur#=10 sqlid=8rhfhbwtndmgc recursive
Parsing cur#=10 sqlid=8rhfhbwtndmgc len=61
sql=/* SQL Analyze(216,0) */ SELECT /* EXAMPLE1_2 */ * FROM dual
End parsing of cur#=10 sqlid=8rhfhbwtndmgc
Semantic Analysis cur#=10 sqlid=8rhfhbwtndmgc
OPTIMIZER INFORMATION
******************************************
----- Current SQL Statement for this session (sql_id=8rhfhbwtndmgc) -----
/* SQL Analyze(216,0) */ SELECT /* EXAMPLE1_2 */ * FROM dual
----- PL/SQL Stack -----
----- PL/SQL Call Stack -----
object line object
handle number name
0xee579040 145 package body SYS.DBMS_SQLTUNE_INTERNAL
0xee579040 12085 package body SYS.DBMS_SQLTUNE_INTERNAL
0xee814bc0 1229 package body SYS.DBMS_SQLDIAG
0xe8c34ab0 2 anonymous block
*******************************************

23.  Introduction
 What
 How
 Why
 Structure
 Example
 Conclusions and References
01/10/2013

24.  Many ways of viewing the execution plan used for a
statement
 10046 Trace File
 DBMS_XPLAN - combined with /*+ gather_plan_statistics */
 Real-Time SQL Monitoring
 Modern options allow comparison of Estimated vs. Actual
row source cardinalities
 E-Rows vs. A-Rows
 Experience and data knowledge allow educated guesses
about what is 'going wrong'
01/10/2013

25.  No real overhead
 Only happens at hard parse
 Sounds crazy, but even if it doesn't help you, it doesn't hurt to
look
 As long as you don't look for too long!
01/10/2013

26.  You've never wondered why that optimiser won't play?
 Sometimes they are the only way of knowing why the CBO
made a specific decision
 Particularly useful tools here are trace files for 'good' and
'bad' plans and a visual diff tool
 They are a great way of learning about the CBO and
particularly any new features
 Oracle Support/Optimizer Development Group!
01/10/2013

27.  Introduction
 What
 How
 Why
 Structure
 Example
 Conclusions and References
01/10/2013

28.  Standard Trace File Pre-amble
 Query Block Assignment
 SQL Plan Management
 Parallel Query/Auto-DOP
 Predicate Move-Around
 Optimizer Information
 Query Transformations
 Peeked Binds
 Statistics
 Computations – Access Paths and Join Orders
 SQL Statement and Execution Plan dump
01/10/2013

29. 01/10/2013
Trace file
/app/ora/local/admin/TEST1102/diag/rdbms/TEST1102_doug/TEST1102/trace/TEST1102_ora_1
450_DOUG_TEST2.trc
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options
ORACLE_HOME = /app/ora/local/product/11.2.0.2/db_4
System name: Linux
Node name: doug
Release: 2.6.18-194.11.4.el5
Version: #1 SMP Fri Sep 17 04:57:05 EDT 2010
Machine: x86_64
Instance name: TEST1102
Redo thread mounted by this instance: 1
Oracle process number: 52
Unix process pid: 1450, image: oracle@doug
*** 2013-03-18 10:59:58.774
*** SESSION ID:(139.79) 2013-03-18 10:59:58.774
*** CLIENT ID:() 2013-03-18 10:59:58.774
*** SERVICE NAME:(SYS$USERS) 2013-03-18 10:59:58.774
*** MODULE NAME:(TOAD 10.6.1.3) 2013-03-18 10:59:58.774
*** ACTION NAME:() 2013-03-18 10:59:58.774

30. 01/10/2013
Registered qb: SEL$1 0xad486a80 (PARSER)
---------------------
QUERY BLOCK SIGNATURE
---------------------
signature (): qb_name=SEL$1 nbfros=1 flg=0
fro(0): flg=4 objn=116 hint_alias="DUAL"@"SEL$1"
SPM: statement not found in SMB
**************************
Automatic degree of parallelism (ADOP)
**************************
Automatic degree of parallelism is disabled: Parameter.
PM: Considering predicate move-around in query block SEL$1 (#0)
**************************
Predicate Move-Around (PM)
**************************

31. 01/10/2013
OPTIMIZER INFORMATION
******************************************
----- Current SQL Statement for this session (sql_id=a5ks9fhw2v9s1) -----
select * from dual
*******************************************
Legend
The following abbreviations are used by optimizer trace.
CBQT - cost-based query transformation
JPPD - join predicate push-down
OJPPD - old-style (non-cost-based) JPPD
FPD - filter push-down
PM - predicate move-around
CVM - complex view merging
SPJ - select-project-join
SJC - set join conversion
SU - subquery unnesting
OBYE - order by elimination
OST - old style star transformation
ST - new (cbqt) star transformation
CNT - count(col) to count(*) transformation
JE - Join Elimination
JF - join factorization
SLP - select list pruning

32.  Oracle 8.1.7 ≈ 50
 Oracle 11.2.0.3 > 300
01/10/2013
***************************************
PARAMETERS USED BY THE OPTIMIZER
********************************
*************************************
PARAMETERS WITH ALTERED VALUES
******************************
Compilation Environment Dump
_pga_max_size = 2097152 KB
*************************************
PARAMETERS WITH DEFAULT VALUES
******************************
Compilation Environment Dump
optimizer_mode_hinted = false
optimizer_features_hinted = 0.0.0
***************************************
PARAMETERS IN OPT_PARAM HINT
****************************

33.  The Optimizer Development group are Busy Bees!
 As they introduce fixes, they number them and store
information about them in V$SYSTEM_FIX_CONTROL
 Can enable/disable … http://tinyurl.com/5r9zrse
 Coskan Blog Post
01/10/2013
Bug Fix Control Environment
fix 3834770 = 1
fix 3746511 = enabled
fix 4519016 = enabled
fix 3118776 = enabled
fix 4488689 = enabled
fix 2194204 = disabled
fix 2660592 = enabled

34. 01/10/2013
Considering Query Transformations on query block SEL$1 (#0)
**************************
Query transformations (QT)
**************************
JF: Checking validity of join factorization for query block SEL$1 (#0)
JF: Bypassed: not a UNION or UNION-ALL query block.
ST: not valid since star transformation parameter is FALSE
TE: Checking validity of table expansion for query block SEL$1 (#0)
TE: Bypassed: No partitioned table in query block.
CBQT bypassed for query block SEL$1 (#0): no complex view, sub-queries or UNION
(ALL) queries.
CBQT: Validity checks failed for a5ks9fhw2v9s1.
CSE: Considering common sub-expression elimination in query block SEL$1 (#0)
 Exadata/11g Upgrade project
 optimizer_features_enable – 10.2.0.4
 Cost-based query transformation
 http://tinyurl.com/c6wdhxv - Jonathan Lewis Blog Post

35. 01/10/2013
*************************
Common Subexpression elimination (CSE)
*************************
CSE: CSE not performed on query block SEL$1 (#0).
OBYE: Considering Order-by Elimination from view SEL$1 (#0)
***************************
Order-by elimination (OBYE)
***************************
OBYE: OBYE bypassed: no order by to eliminate.
CVM: Considering view merge in query block SEL$1 (#0)
query block SEL$1 (#0) unchanged
Considering Query Transformations on query block SEL$1 (#0)
**************************
Query transformations (QT)
**************************
JF: Checking validity of join factorization for query block SEL$1 (#0)
JF: Bypassed: not a UNION or UNION-ALL query block.
ST: not valid since star transformation parameter is FALSE
TE: Checking validity of table expansion for query block SEL$1 (#0)
TE: Bypassed: No partitioned table in query block.
CBQT bypassed for query block SEL$1 (#0): no complex view, sub-queries or UNION
(ALL) queries.
CBQT: Validity checks failed for a5ks9fhw2v9s1.

36. 01/10/2013
SYSTEM STATISTICS INFORMATION
-----------------------------
Using NOWORKLOAD Stats
CPUSPEEDNW: 1416 millions instructions/sec (default is 100)
IOTFRSPEED: 4096 bytes per millisecond (default is 4096)
IOSEEKTIM: 10 milliseconds (default is 10)
MBRC: -1 blocks (default is 32)
***************************************
BASE STATISTICAL INFORMATION
***********************
Table Stats::
Table: DUAL Alias: DUAL
#Rows: 1 #Blks: 1 AvgRowLen: 2.00 ChainCnt: 0.00
Access path analysis for DUAL
***************************************
SINGLE TABLE ACCESS PATH
Single Table Cardinality Estimation for DUAL[DUAL]
Table: DUAL Alias: DUAL
Card: Original: 1.000000 Rounded: 1 Computed: 1.00 Non Adjusted: 1.00
Access Path: TableScan
Cost: 2.00 Resp: 2.00 Degree: 0
Cost_io: 2.00 Cost_cpu: 9893
Resp_io: 2.00 Resp_cpu: 9893
Best:: AccessPath: TableScan
Cost: 2.00 Degree: 1 Resp: 2.00 Card: 1.00 Bytes: 0

37. 01/10/2013
OPTIMIZER STATISTICS AND COMPUTATIONS
***************************************
GENERAL PLANS
***************************************
Considering cardinality-based initial join order.
Permutations for Starting Table :0
Join order[1]: DUAL[DUAL]#0
***********************
Best so far: Table#: 0 cost: 2.0005 card: 1.0000 bytes: 2
***********************
(newjo-stop-1) k:0, spcnt:0, perm:1, maxperm:2000
*********************************
Number of join permutations tried: 1
*********************************
 This is the section that gets very complicated very quickly!

38. 01/10/2013
Plan Table
============
-------------------------------------+-----------------------------------+
| Id | Operation | Name | Rows | Bytes | Cost | Time |
-------------------------------------+-----------------------------------+
| 0 | SELECT STATEMENT | | | | 2 | |
| 1 | TABLE ACCESS FULL | DUAL | 1 | 2 | 2 | 00:00:01 |
-------------------------------------+-----------------------------------+
Content of other_xml column
===========================
db_version : 11.2.0.2
parse_schema : RRS_CORE_DBO
plan_hash : 272002086
plan_hash_2 : 4017058736
Outline Data:
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.2')
DB_VERSION('11.2.0.2')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
FULL(@"SEL$1" "DUAL"@"SEL$1")
END_OUTLINE_DATA
*/

39.  Introduction
 What
 How
 Why
 Structure
 Example
 Conclusions and References
01/10/2013

40.  Introduction
 What
 How
 Why
 Structure
 Example
 Conclusions and References
01/10/2013

41.  Many ways of viewing the execution plan used for a
statement
 All show you the numbers that the CBO is using and the
resulting plan
 EXPLAIN Plan etc
 Some show you the real numbers
 SQL Monitor Reports and other Plan Statistics approaches
 Only a optimizer trace file can truly show you why there is a
discrepancy
 Sometimes ;-)
01/10/2013

42.  Cost Based Oracle Fundamentals - Appendix
 Jonathan Lewis
http://tinyurl.com/bxxl6
 Under the hood of the CBO
 Wolfgang Breitling
http://tinyurl.com/bxxl6
 Using new 11g tracing infrastructure to generate files
 Optimizer Development Group (Maria Colgan)
http://tinyurl.com/brcryva and http://tinyurl.com/cr5kz8t
 Greg Rahn
http://tinyurl.com/bupmehx
01/10/2013

43.  My Blog Posts
 http://oracledoug.com
 Recent Blog Post
 http://jonathanlewis.wordpress.com
 Thanks
 Wolfgang Breitling
 Maria Colgan & Greg Rahn
 Jonathan Lewis
 To you, for listening
01/10/2013

44. Doug Burns dougburns@yahoo.com
http://oracledoug.com
@orcldoug
#OTW
#OakTable