1. EVOLUTION OF THE ORACLE OPTIMIZER THINKING
Jurijs Velikanovs
7+ years Oracle DBA, OCP 7/8/8i/9i, OCA 9iAS R2

2. DEMO! Topics: Definition of database optimizer
Death of RBO or Why CBO is better
Limitations of earlier CBO versions
Some ways to workaround 8i +
9i Revolution
DEMO!

3. About myself Introduction 8 years as Oracle DBA
Master degree in computer since
8 years as Oracle DBA
OCP 7/8/8i/9i, OCA 9iAS R2
Oracle9i Database Administrator Certified Master
7+ in IT Alise
First line Oracle support analyst
Development DBA, Consultant
DBA Teamleader

4. About IT Alise Introduction ~200 employees Main working directions
10+ years experience in Oracle development
~200 employees
Main working directions
Oracle Custom Development
Oracle eBusiness Suite implementation
Oracle Expert services

5. Definition of database optimizer

6. Definition of optimizer
Oracle9i Database Concepts “The optimizer determines the most efficient way to run a SQL statement.”

7. Definition of optimizer
Nowadays it means my opinion ”If application design reflects business needs you don’t have to think about particular SQL performance”
I. Optimizer will find optimal path himself
II. You still have to think about application design

8. Death of RBO ! or Why CBO is Better ?

9. DEMO!
INDEX & RBO 
tfc1/2/3.sql

10. Technically can’t choose optimal way
RBO
Technically can’t choose optimal way
Don’t know anything about data distribution
There is set of rules
You have to think about execution plan writing SQL
Stabile life. SQL executes equally: yesterday/today/tomorrow
RBO is dead 
But what would say CBO? DEMO tfc2.sql

11. CBO How CBO found the way? Main Characteristics
DEMO event tfc4.sql
PARAMETERS USED BY THE OPTIMIZER
BASE STATISTICAL INFORMATION
SINGLE TABLE ACCESS PATH
OPTIMIZER STATISTICS AND COMPUTATIONS
GENERAL PLANS
Main Characteristics
Works using statistics
Looks through “all” possible paths
Calculates COST and choose path with lowest cost
There a lot of assumption

12. Limitations of earlier CBO versions

13. DB_FILE_MULTIBLOCK_READ_COUNT
FULL SCAN cost
DEMO tfc4sql
‘adjusted’ multi-block read value for COST calculation
number of blocks / aMBRC
Some blocks can be in memory
Don’t do MBR across extents
Oracle don’t believe you (MBRC)
All IO are equal
Single block read = Multiblock read time

14. Limitations of earlier CBO (COST)
All IO are equal
Single block read = Multiblock read time
Think in PIO units
LIO = PIO (buffer pool?)
All Join operations speed are equal
Full Scan = Nested Loop = Hash Join = Merge Join …
All other operation ignored
Comparization, Functions, …

15. Some ways to workaround 8i +

16. Some ways to workaround 8i +
Think in PIO units
LIO = PIO (buffer pool?)
OPTIMIZER_INDEX_CACHING (o_i_c)
Measurement 0-100%
Default value are far from real world = 0%
How many blocks accessible via “db file sequential read” are in the cache
'buffer cache hit ratio'

17. Some ways to workaround 8i +
All IO are equal
Single block read = Multiblock read time
OPTIMIZER_INDEX_COST_ADJ (o_i_c_a)
Measurement %
Default value are far from real world = 100%
“db file sequential read” cost * o_i_c_a = REAL COST
“db file sequential reads” / ”db file scattered read”
DEMO tfc5sql

18. Do not underestimate parameters impact
Conclusion 8i
Do not underestimate parameters impact
DB_FILE_MULTIBLOCK_READ_COUNT
OPTIMIZER_INDEX_CACHING
OPTIMIZER_INDEX_COST_ADJ
Default values far from real world needs
OPTIMIZER_INDEX_CACHING=0%
OPTIMIZER_INDEX_COST_ADJ=100%

19. 9i Revolution

20. 9i Revolution = SYSTEM_STATS
Compute
DBMS_STATS. GATHER_SYSTEM_STATS(gathering_mode => 'START');
DO THE LOAD …
DBMS_STATS. GATHER_SYSTEM_STATS(gathering_mode => 'STOP');
Retrieve
select * from sys.aux_stats$;
DEMO ss.sql

21. Part 1: Multi block reads
Statistics computed
SREADTIM: Average time for a single-block read request in milliseconds
MREADTIM: Average time for a multi-block read request in milliseconds
MBRC: Average number of blocks in a multi-block read.
FullScan time = MREADTIM * BLOKS / MBRC
Cost = FullScan time /SREADTIM
Cost = Response time measured in single block reads
DEMO tfc6.sql

22. Part 2: CPU Costing Model
Statistics computed
CPUSPEED: Oracle calibration of system CPU speed
Costing formula (Oracle9i Database Performance Tuning Guide and Reference) :
COST = ( #SRds * SREADTIM + #MRds * MREADTIM + #CPUCycles / CPUSPEED ) / SREADTIM
CPUCycles
Virtually every operation have cost in terms of CPU usage
HASH/SORT/PREDICATES SEARCH/IRS/IUS/TFS...
There is internal Oracle table for operation calibration
Model allows measure CPU usage
DEMO ss1.sql

23. Conclusion
It is really REVOLUTION!
RBO is dead !!!
The CBO keeps evolving
Statistics & Parameters are essential
Lot of wrong assumptions in earlier versions
9i+ revolutionary switch SYS_STATs
There are still assumptions
Design is most important!
And now you can have time for design!

24. Jurijs Velikanovs Q&A +371-9268222 J.Velikanovs@alise.lv

26. Show Time
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