1. Understanding
how
Adap1ve
Cursor
Sharing
(ACS)
produces
mul1ple
Op1mal
Plans
Carlos
Sierra

2. Carlos
Sierra
• Consultant/Developer/DBA
• Oracle
Performance
• SQLTXPLAIN
(SQLT)
• SQL
Tuning
• Tools
Enkitec
(c)
2014
2

3. Topics
• Adap1ve
Cursor
Sharing
(ACS)
– Mechanics
– Demos
Enkitec
(c)
2014
3

4. Plan
Flexibility
Allies
• CBO
Parameters
• CBO
Sta1s1cs
• Dynamic
Sampling
• Cardinality
Feedback
• Cursor
Sharing
• Adap%ve
Cursor
Sharing
(ACS)
Enkitec
(c)
2014
4

5. Plan
Stability
Tools
• CBO
Hints
• Stored
Outlines
• SQL
Profiles
• SQL
Plan
Management
(SPM)
Enkitec
(c)
2014
5

6. Cursor
Sharing
• Use
of
Bind
Variables
instead
of
Literals
– AND
p.prod_category
LIKE
'So[ware%’
– AND
p.prod_category
LIKE
:b5
• Goal:
Reduce
Hard
Parsing
– Improve
Scalability
• Reduce
CPU
u1liza1on
• Reduce
Shared
Memory
footprint
Enkitec
(c)
2014
6

7. Cursor
Sharing
Shortcomings
• Flipping
Plans
– Exacerbated
by
Histograms
on
Skewed
Data
– AND
c.cust_marital_status
=
:b2
• :b2
:=
‘married’
• :b2
:=
‘widow’
– Plan
is
computed
at
hard
parse
• Plan
becomes
a
long
term
moving
target
Enkitec
(c)
2014
7

8. Adap1ve
Cursor
Sharing
(ACS)
• 11g+
• Mul1ple
Op1mal
Plans
per
SQL
– As
per
“Selec1vity”
of
Predicates
• :b2
:=
‘married’
(close
to
60%
maybe)
• :b2
:=
‘widow’
(this
one
is
more
selec1ve)
Enkitec
(c)
2014
8

9. ACS
Challenges
• Minimize
Resources
Impact
– Monitor
only
a
subset
of
SQL
Statements
– Ac1vate
ACS
only
for
a
subset
of
the
monitored
SQL
– Share
Execu1ons
Plans
through
a
“Selec1vity
Profile”
Enkitec
(c)
2014
9
All
Statements
Bind
Sensi1ve
Bind
Aware
ACS

10. Becoming
Bind
Sensi1ve
1. SQL
has
Range
Predicates
on
Bind
Variables
– AND
c.cust_year_of_birth
BETWEEN
:b3
AND
:b4
– AND
p.prod_category
LIKE
:b5
2. SQL
has
Equality
Predicates
on
Bind
Variables
and
Column
has
a
Histogram
– AND
c.cust_marital_status
=
:b2
– AND
TO_CHAR(s.1me_id,
'YYYY')
=
:b6
Enkitec
(c)
2014
10

11. Becoming
Bind
Aware
1. Rows
Processed
change
substan1ally
between
Execu1ons
– Between
a
few
rows
to
millions
2. Rows
Processed
oscillate
significantly
between
Execu1ons
– Between
a
few
rows
and
a
few
thousand
– Between
a
few
thousand
and
millions
Enkitec
(c)
2014
11

12. ACS
Monitoring
• V$SQL
(State)
– is_shareable
– is_bind_sensi1ve
– is_bind_aware
• V$SQL_CS_STATISTICS
(Rows
Processed)
• V$SQL_CS_HISTOGRAM
(3
Buckets
S/M/L)
• V$SQL_CS_SELECTIVITY
(Selec1vity
Profile)
Enkitec
(c)
2014
12

13. Rows
Processed
• v$sql_cs_sta1s1cs.rows_processed
• Updated
only
at
hard
parse
• A
measure
of
amount
of
work
on
Execu1on
Plan
• Three
sizes:
S/M/L
– 0:
Small
– 1:
Medium
– 2:
Large
Enkitec
(c)
2014
13

14. Rows
Processed
• v$sql_cs_sta1s1cs.rows_processed
• Updated
only
at
hard
parse
• A
measure
of
amount
of
work
on
Execu1on
Plan
• Three
sizes:
S/M/L
– 0:
Small
(less
than
1K
rows)
– 1:
Medium
(between
1k
and
1m
rows)
– 2:
Large
(more
than
1m
rows)
Enkitec
(c)
2014
14

15. ACS
Buckets
• v$sql_cs_histogram.bucket_id
– 0:
Small
– 1:
Medium
– 2:
Large
• v$sql_cs_histogram.count
– Incremented
with
each
Execu1on
as
per
• v$sql_cs_sta1s1cs.rows_processed
Enkitec
(c)
2014
15

16. Rows
Processed
and
ACS
Buckets
IF
v$sql_cs_statistics.rows_processed
<
1K
THEN
v$sql_cs_histogram.count(0)++
ELSIF
v$sql_cs_statistics.rows_processed
<
1M
THEN
v$sql_cs_histogram.count(1)++
ELSE
v$sql_cs_histogram.count(2)++
END
IF
Enkitec
(c)
2014
16

17. Becoming
Bind
Aware
1. Small
and
Large
buckets
have
a
value
– bucket_id.count(0)
>
0
AND
bucket_id.count(2)
>
0
2. Two
adjacent
buckets
have
same
non-­‐zero
value
– bucket_id.count(0)
=
bucket_id.count(1)
>
0
– bucket_id.count(1)
=
bucket_id.count(2)
>
0
Enkitec
(c)
2014
17

18. Rows
Processed
per
Execu1on
• 10(0)…
50(0)…
3,000,000(2)…
BA
• 30(0)…
3,000(1)…
BA
• 2,000,000(2)…
1(0)…
BA
• 0(0)…
10,000(1)…
BA
• 3,000(1)…
2,000(1)…
200(0)…
300(0)…
BA
• 10…
100…
500…
2,000…
3,000…
5,000…
BA
• rows_processed(bucket_id)…
Bind
Aware(BA)
Enkitec
(c)
2014
18

19. WHY
becoming
BA
is
important?
• Mul1ple
Op1mal
Plans
are
created
a[er
Cursor
becomes
Bind
Aware
Enkitec
(c)
2014
19

20. Sample
Query
(1)
SELECT
p.prod_subcategory_desc
subcatagory,
SUM(amount_sold)
amount_sold
FROM
sh.customers
c,
sh.products
p,
sh.sales
s
WHERE
c.cust_gender
=
'M'
AND
c.cust_marital_status
=
'single'
AND
c.cust_year_of_birth
BETWEEN
1913
AND
1990
AND
p.prod_category
LIKE
'Software%'
AND
TO_CHAR(s.time_id,
'YYYY')
=
'2001'
AND
s.cust_id
=
c.cust_id
AND
s.prod_id
=
p.prod_id
GROUP
BY
p.prod_subcategory_desc
ORDER
BY
p.prod_subcategory_desc;
Enkitec
(c)
2014
20

21. Sample
Query
(2)
• Based
on
Sample
Schema
SH
– With
CBO
Histograms
in
all
Columns
• Not
a
requirement
for
this
ACS
test
• 3
Tables
with
Filter
Predicates
• 2
Joins
• 6
possible
Join
Orders
• Several
possible
Execu1on
Plans
Enkitec
(c)
2014
21

22. Demo
1
• 5
Execu1ons
of
Sample
Query
using
Literals
– Different
values
for
each
Execu1on
• Sequence
1,
2,
3,
4
and
5
– Each
Execu1on
performs
a
Hard
Parse
– Each
Execu1on
computes
a
“new”
Plan
– Each
seems
to
be
an
“Op1mal”
Plan
Enkitec
(c)
2014
22

23. Demo
2
• 5
Execu1ons
of
Sample
Query
using
Binds
– Different
values
for
each
Execu1on
• Sequence
1,
2,
3,
4
and
5
– Each
Execu1on
performs
a
Hard
Parse
• Forced
with
a
Cursor
Flush
before
the
Execu1on
– Each
computes
a
“new”
Op1mal
Plan
• Almost
same
as
“with
Literals”
Enkitec
(c)
2014
23

24. Demo
2
Results
Query
Rows
Processed
ACS
Bucket
Plan
Hash
Value
1
1,483,124
2
2048551027
2
1,272,154
2
3022804314
3
1,014,876
2
2326939410
4
716,168
1
2163719564
5
530
0
2163719564
Enkitec
(c)
2014
24

25. Demo
3
• 5
Execu1ons
of
Sample
Query
using
Binds
– Different
values
for
each
Execu1on
• Sequence
1,
2,
3,
4
and
5
– No
Cursor
Flush
between
Execu1ons
– First
Execu1on
computes
a
“new”
Op1mal
Plan
– All
Execu1ons
use
same
Plan…
Enkitec
(c)
2014
25

26. Demo
3
Results
Query
Rows
Processed
ACS
Bucket
Op%mal
Plan
ACS
Aware
Executed
1
1,483,124
2
2048551027
N
2048551027
2
1,272,154
2
3022804314
N
2048551027
3
1,014,876
2
2326939410
N
2048551027
4
716,168
1
2163719564
N
2048551027
5
530
0
2163719564
N
2048551027
Enkitec
(c)
2014
26

27. Demo
4
• 5
Execu1ons
of
Sample
Query
using
Binds
– Different
values
for
each
Execu1on
• Sequence
5,
4,
3,
2
and
1
– No
Cursor
Flush
between
Execu1ons
– Cursor
becomes
Bind
Aware
a[er
2nd
Execu1on
– All
Execu1ons
used
an
Op1mal
Plan
Enkitec
(c)
2014
27

28. Demo
4
Results
Query
Rows
Processed
ACS
Bucket
Op%mal
Plan
Bind
Aware
Executed
5
530
0
2163719564
N
2163719564
4
716,168
1
2163719564
N
2163719564
3
1,014,876
2
2326939410
Y
2326939410
2
1,272,154
2
3022804314
Y
3022804314
1
1,483,124
2
2048551027
Y
2048551027
Enkitec
(c)
2014
28

29. Demo
5
• 5
Execu1ons
of
Sample
Query
using
Binds
– Different
values
for
each
Execu1on
• Sequence
5,
1,
2,
3
and
4
– No
Cursor
Flush
between
Execu1ons
– Cursor
becomes
Bind
Aware
a[er
2nd
Execu1on
– All
but
one
Execu1ons
used
an
Op1mal
Plan
Enkitec
(c)
2014
29

30. Demo
5
Results
Query
Rows
Processed
ACS
Bucket
Op%mal
Plan
Bind
Aware
Executed
5
530
0
2163719564
N
2163719564
1
1,483,124
2
2048551027
N
2163719564
2
1,272,154
2
3022804314
Y
3022804314
3
1,014,876
2
2326939410
Y
2326939410
4
716,168
1
2163719564
Y
2163719564
Enkitec
(c)
2014
30

31. Controlling
ACS
with
CBO
Hint
• /*+
BIND_AWARE
*/
– Bypasses
the
monitoring
phase
of
a
Bind
Sensi1ve
SQL
• /*+
NO_BIND_AWARE
*/
– Turns
off
ACS
for
given
SQL
Enkitec
(c)
2014
31

32. Controlling
ACS
with
SQL
Patch
• SYS.DBMS_SQLDIAG_INTERNAL.I_CREATE_PATCH
– sql_text
– hint_text
=>
BIND_AWARE
• Script
sqlpch.sql
Enkitec
(c)
2014
32

33. ACS
Plan
Selec1on
• On
every
Execu1on
of
Bind
Aware
Cursor
– Compute
Selec1vity
of
each
qualifying
Predicate
– Search
Selec1vity
within
Range
of
values
on
ACS
Selec1vity
Profile
– If
within
Range,
lookup
Child
Number
and
use
its
Plan
– Else,
Hard
Parse
and
Execute
newly
computed
Plan
• If
same
as
exis1ng
Plan,
then
update
Selec1vity
Profile
• Else,
create
Selec1vity
Profile
for
new
Child
Number
Enkitec
(c)
2014
33

34. Selec1vity
Profile
(1)
• v$sql_cs_selec1vity
– predicate
– range_id
• low
and
high
(selec1vi1es)
– child_number
Enkitec
(c)
2014
34

35. Selec1vity
Profile
(2)
CHILD
PREDICATE
RANGE_ID
LOW
HIGH
-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐
-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐
-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐
-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐
-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐
1
<=B4
0
0.860941
1.052262
1
=B1
0
0.602369
0.736229
1
=B2
0
0.455337
0.556523
1
>=B3
0
0.182445
0.222988
1
B5
0
0.306250
0.374306
2
<=B4
0
0.892666
1.091036
2
=B1
0
0.297574
0.363702
2
=B2
0
0.455337
0.556523
2
>=B3
0
0.077947
0.095268
2
B5
0
0.306250
0.374306
3
<=B4
0
0.836835
1.022798
3
=B1
0
0.297574
0.363702
3
=B2
0
0.002085
0.002548
3
>=B3
0
0.221447
0.270657
3
B5
0
0.306250
0.374306
Enkitec
(c)
2014
35

36. ACS
Summary
• ACS
is
capable
of
producing
mul1ple
Op1mal
Execu1on
Plans
per
SQL
• During
ramp-­‐up
sub
Op1mal
Plans
may
happen
• ACS
Metadata
resides
in
Memory
(not
Persistent)
• ACS
provides
desirable
Plan
Flexibility
• ACS
does
not
address
the
Plan
Stability
concern
Enkitec
(c)
2014
36

37. ACS
Suggested
Strategy
• Use
sys.dbms_sqldiag_internal.i_create_patch
to
SQL
Patch
with
BIND_AWARE
the
SQL
on
Baselines
Enkitec
(c)
2014
37

38. SPM
Suggested
Strategy
• Use
dbms_applica1on_info.set_module
in
your
code
to
set
MODULE
and
ACTION
• Use
dbms_spm.load_plans_from_cursor_cache
filtering
with
MODULE
or
ACTION
• Use
dbms_spm.evolve_sql_plan_baseline
to
verify
and
evolve
periodically
good
performing
Plans
Enkitec
(c)
2014
38

39. References
(1)
• Using
SQL
Patch
to
add
hints
to
a
packaged
applica1on
– hxps://blogs.oracle.com/op1mizer/entry/
how_can_i_hint_a
Enkitec
(c)
2014
39

40. References
(2)
• Oracle®
Database
PL/SQL
Packages
and
Types
Reference
– 11g
Release
2
(11.2)
– Part
Number
E25788-­‐04
Enkitec
(c)
2014
40

41. Contact
Informa1on
• carlos.sierra@enkitec.com
• carlos-­‐sierra.net
• @csierra_usa
Enkitec
(c)
2014
41