Oracle Query Optimization

1. Oracle
Query
Optimizer
Hyderabad
–
30th
May
2015

2. About
me…
Vivek
Sharma,
Blog
url
:
h3p://viveklsharma.wordpress.com
Email
:
vlsharma@hotmail.com
A
Regular
Speaker
for
AIOUG
Speaker
of
the
Year
–
Sangam
2012

3. • Cursors
• SelecMvity
• Cardinality
Key
Concepts…

4. • Cursors
• SelecMvity
• Cardinality
Key
Concepts…
Client
/
Applica-on
Handle
Server
Process
Memory
Private
SQL
Area
SGA
Library
Cache
Shared
SQL
Area

5. Syntax
/
Seman-cs
Checks
Sharable
Parent
Cursor
Available
?
Execute
Store
Parent
Cursor
in
Library
Cache
Query
Transforma-on
/
Execu-on
Plans
Store
child
Cursor
in
Library
Cache
Sharable
Child
Cursor
Available
?
N
N
Y
Y
Life
4me
of
a
Cursor…

6. Syntax
/
Seman-cs
Checks
Sharable
Parent
Cursor
Available
?
Execute
Store
Parent
Cursor
in
Library
Cache
Query
Transforma-on
/
Execu-on
Plans
Store
child
Cursor
in
Library
Cache
Sharable
Child
Cursor
Available
?
N
N
Y
Y
Life
4me
of
a
Cursor…

7. • Cursors
• SelecMvity
• Cardinality
Key
Concepts…
ü Value
between
0
and
1
ü Represents
FracMon
or
%age
of
rows
filtered
ü Drives
the
Access
Path
ü With
no-­‐histograms,
it
is
Density
or
1/Num_DisMnct
ü Close
to
0
–
Low
/
Close
to
1
-­‐
High

8. • Cursors
• SelecMvity
• Cardinality
Key
Concepts…
ü Number
of
rows
returned
by
an
OperaMon
ü Drives
Access
Order
ü SelecMvity
*
Num_Rows

9. Introduc4on
to
Query
Op4mizer…
SQL
Query
OpMmizer
Object
StaMsMcs
System
StaMsMcs
Database
Design
Fixed
Plans
ExecuMon
Environment
Bind
Variables
Dynamic
Sampling
Cardinality
Feedback
ExecuMon
Plan

10. Object
Sta4s4cs…
• Table
StaMsMcs
o num_rows
o Blocks
• Index
StaMsMcs
o blevel
o leaf_blocks
o clustering_factor
• Column
StaMsMcs
o num_disMnct
o num_nulls
o density
(1/num_disMnct)
o low_value
o high_value
• ParMMon
Level
StaMsMcs
o Single
ParMMon
Scan
• Global
StaMsMcs
(Table
Level)
o All
or
MulMple
ParMMons
Scan
• Histograms
o Frequency
Based
o Height
Balanced
o Top
Frequency
o Hybrid
With
Frequency
1/(2*num_rows)

11. Object
Sta4s4cs
(Cardinality
-­‐
No
Nulls)…
Statistics Values
Num_rows 1000
Num_distinct 10 (low 1 and high 10)
Blocks 39
Predicate ORG_ID 1
Density (org_id) 0.1 (No Nulls)
SQL> select id, name from aioug where org_id = 1;
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------
Plan hash value: 1667281916
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 100 | 1800 | 12 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| AIOUG | 100 | 1800 | 12 (0)| 00:00:01 |
---------------------------------------------------------------------------

12. Statistics Values
Num_rows 1000
Num_distinct 10 (low 1 and high 10)
Blocks 39
Density (org_id) 0.1 (No Nulls)
Base Selectivity 0.1 * ((1000-0)/1000) = 0.1
Cardinality 0.1 * 1000 = 100
Object
Sta4s4cs
(Cardinality
-­‐
No
Nulls)…

13. Object
Sta4s4cs
(Cardinality
Few
Nulls)…
Statistics Values
Num_rows 1000
Num_distinct 10 (low 1 and high 10)
Blocks 39
Predicate ORG_ID_N 1
Density (org_id_n) 0.1 (100 Nulls)
SQL> select id, name from aioug where org_id_n = 1;
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------
Plan hash value: 1667281916
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 90 | 1620 | 12 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| AIOUG | 90 | 1620 | 12 (0)| 00:00:01 |
---------------------------------------------------------------------------

14. Object
Sta4s4cs
(Cardinality
Few
Nulls)…
Statistics Values
Num_rows 1000
Num_distinct 10 (low 1 and high 10)
Blocks 39
Density (org_id_n) 0.1 (100 Nulls)
Base Selectivity 0.1 * ((1000-100)/1000) = 0.09
Cardinality 0.09 * 1000 = 90

15. Out
of
Bound
(Cardinality
-­‐
No
Nulls)…
Statistics Values
Num_rows 1000
Num_distinct 10 (low 1 and high 10)
Blocks 39
Predicate ORG_ID 14
Density (org_id) 0.1 (No Nulls)
SQL> select id, name from aioug where org_id = 14;
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------
Plan hash value: 1667281916
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 56 | 1008 | 11 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| AIOUG | 56 | 1008 | 11 (0)| 00:00:01 |
---------------------------------------------------------------------------

16. Statistics Values
Num_rows 1000
Num_distinct 10 (low 1 and high 10)
Blocks 39
Density (org_id) 0.1 (No Nulls)
Base Selectivity 0.1 * ((1000-0)/1000) = 0.1
Required Value (org_id) 14
Out of Bound Factor ((14-10)/(10-1)) = 0.44444
Cardinality (0.1 * 1000) –
(0.1*1000*0.4444) = 56
Out
of
Bound
(Cardinality
-­‐
No
Nulls)…

17. • utl_raw.cast_to_*
• dbms_stats.convert_raw_value
Low
&
High
Value
(Deciphering)…
select column_name, low_value, high_value from dba_tab_columns
where owner='SCOTT' and table_name='AIOUG' order by 1;
COLUMN_NAME LOW_VALUE HIGH_VALUE
-------------------- ----------------------- -----------------------
ID C102 C20B
NAME 41477349586C68677566 7A7073484A505A44544F
ORG_ID C102 C10B
ORG_ID_N C102 C10B

18. Object
Sta4s4cs…
• Table
StaMsMcs
o num_rows
o Blocks
• Index
StaMsMcs
o blevel
o leaf_blocks
o clustering_factor
• Column
StaMsMcs
o num_disMnct
o num_nulls
o density
(1/num_disMnct)
o low_value
o high_value
• ParMMon
Level
StaMsMcs
o Single
ParMMon
Scan
• Global
StaMsMcs
(Table
Level)
o All
or
MulMple
ParMMons
Scan
• Histograms
o Frequency
Based
o Height
Based
o Top
Frequency
o Hybrid
(12c)
With
Frequency
1/(2*num_rows)

19. Index
Sta4s4cs
(low
Clustering
Factor)…
Statistics
Indexed Column ORG_ID ORG_ID_M
Num_rows 1000 1000
Blevel 1 1
Leaf_Blocks 2 2
Clustering_Factor 34 337
SQL> select id, name from aioug where org_id = 1;
Plan hash value: 1442557996
-------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)|
-------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 100 | 5 (0)|
| 1 | TABLE ACCESS BY INDEX ROWID BATCHED| AIOUG | 100 | 5 (0)|
| 2 | INDEX RANGE SCAN | AIOUG_ORG_ID_IDX | 100 | 1 (0)|
-------------------------------------------------------------------------------------

20. Index
Sta4s4cs
(High
Clustering
Factor)…
SQL> select id, name from aioug where org_id_m = 1;
Plan hash value: 1667281916
--------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)|
--------------------------------------------------------
| 0 | SELECT STATEMENT | | 100 | 12 (9)|
| 1 | TABLE ACCESS FULL| AIOUG | 100 | 12 (9)|
--------------------------------------------------------
Statistics
Indexed Column ORG_ID ORG_ID_M
Num_rows 1000 1000
Blevel 1 1
Leaf_Blocks 2 2
Clustering_Factor 34 337

21. Cost = blevel
+ ceil(leaf_blocks * index_selectivity)
+ ceil(clustering_factor * table_selectivity)
Cost
of
an
Index
Scan
Cost
of
a
Table
Scan
via
Index
CalculaMon
of
CF
(10
Row
3
Block
Table
with
an
Index)
Index Entry Table Block CF
A 1 1
A 1 1
A 2 2
B 3 3
B 1 4
C 3 5
C 2 6
C 2 6
D 1 7
D 3 8
Good
:
Near
to
Table.blocks
Bad
:
Near
to
Table.num_rows
Index
Sta4s4cs
(Clustering
Factor)…

22. • SREADTIM
• MREADTIM
• MBRC
• CPUSPEED
• IOSEEKTIM
• IOTRFSPEED
• CPUSPEEDNW
System
Sta4s4cs…
Workload
StaMsMcs
NoWorkload
StaMsMcs

23. System
Sta4s4cs
(workload)…
select pname, pval1
from sys.aux_stats$;
PNAME PVAL1
-------------------- ----------
SREADTIM 2
MREADTIM 5
CPUSPEED 500
MBRC 10
MAXTHR
SLAVETHR
Cost
=
IO_Cost
+
CPU
Cost
IO_Cost
=
ceil(#Blks/MBRC
*
Mread-m/Sread-m)
CPU
Cost
=
ceil(CPUSpeed
/
(CPUCycles
*
Sread-m)
+
_tablescan_cost_plus_one

24. System
Sta4s4cs
(workload)…
Statistics Values
Blocks 39
MBRC 10
Mreadtim / Sreadtim 5 / 2
SQL> select id, name from aioug where org_id = 1;
SQL> select operation, io_cost, cpu_cost, cost from plan_table
2 where operation='TABLE ACCESS';
OPERATION IO_COST CPU_COST COST
------------------------------ ---------- ---------- ----------
TABLE ACCESS 11 501736 12
SQL> select ceil(39/10*5/2), 1 "_table_scan_cost_plus_one" from dual;
CEIL(39/10*5/2) _table_scan_cost_plus_one
--------------- -------------------------
10 1

25. System
Sta4s4cs
(noworkload)…
select pname, pval1
from sys.aux_stats$;
PNAME PVAL1
-------------------- ----------
CPUSPEEDNW 2992.27468
IOSEEKTIM 10
IOTFRSPEED 4096
Cost
=
IO_Cost
+
CPU
Cost
IO_Cost
=
ceil(#Blks/MBRC
*
Mread-m/Sread-m)
CPU
Cost
=
ceil(CPUSpeed
/
(CPUCycles
*
Sread-m)
+
_tablescan_cost_plus_one
MBRC
=
db_file_mul-block_read_count
or
8
Sread-m
=
IOSeek-m
+
db_block_size
/
IOTrfspeed
Mread-m
=
IOSeek-m
+
dfmrc
or
8
*
db_block_size/IOTrfspeed

26. System
Sta4s4cs
(noworkload)…
Statistics Values
Blocks 39
Db_file_multiblock_read_count Non-default (=8)
Sreadtim 10 + (8192/4096) = 12
Mreadtim 10 + (8 * 8192/4096) = 26
SQL> select id, name from aioug where org_id = 1;
SQL> select operation, io_cost, cpu_cost, cost from plan_table
2 where operation='TABLE ACCESS';
OPERATION IO_COST CPU_COST COST
------------------------------ ---------- ---------- ----------
TABLE ACCESS 12 501736 12
SQL> select ceil(39/8*26/12), 1 "_table_scan_cost_plus_one" from dual
CEIL(39/8*26/12) _table_scan_cost_plus_one
---------------- -------------------------
11 1

27. • Extended
StaMsMcs
–
Dependant
Columns
• Histograms
–
Wherever
required
• FuncMons
on
Indexed
/
Non-­‐Indexed
Columns
• Deadly
Defaults
• Dynamic
Samplings
/
Cardinality
Feedback
• 10053
– OpMmizer
Workings
– Using
Prorated
Density
(Out
of
Bound)
Cri4cal
to
know
about…

28. THANK
YOU