This document provides a summary of techniques for tuning SQL and database performance. It begins by discussing the importance of properly understanding the user requirement before focusing on SQL tuning. Various SQL tuning techniques are then demonstrated, such as adding indexes, partitioning, and materialized views. The document emphasizes the need to avoid side effects from tuning and stresses tuning the overall user experience rather than just the SQL. Diagnostic techniques like ASH and wait events are also covered.

1. Connor McDonald
OracleDBA
co.uk
1
@connor_mc_d
connormcdonald.wordpress.com

2. 2

4. gratuitous book plug
4

5. bio slide
5

7. 7

8. 8

9. you should look cool
9

10. 10

11. 11
Dump of memory from 0x07246400 to 0x07248400
1064B4C00 06A20000 08C0000A 0A07C47E 00020506 [...........~....]
1064B4C10 34BC0000 01000000 00030CBF 0A07C47C [4..............|]
1064B4C20 0002EC28 00020300 00000000 0004001D [...(............]
...
1064B6BF0 C10B02C1 0B06436F 6E6E6F72 C47E0605 [......Connor.~..]
table or index
block size
database version created in
relative block address

12. 12

13. sounds sexy right ?
13

14. 14

15. if you are tuning SQL ...
15

16. ... you are failing
16

17. 17

18. why ?
18

19. real example
19

20. 20

21. 21
"last transaction for all accounts"

22. problem
22

23. 23

24. make it faster ...
24

25. "it’s a SQL problem"
25

26. 26
SQL> desc ACCOUNT
Name Null? Type
----------------------------------- -------- ------------------------
ACCOUNT_NUM NOT NULL NUMBER(8)
CURRENT_BALANCE NOT NULL NUMBER(14,2)
...
SQL> desc TRANSACTIONS
Name Null? Type
----------------------------------- -------- -------------------
TXN_SEQ NOT NULL NUMBER(11)
TXN_TS NOT NULL TIMESTAMP(6)
TXN_TYPE NOT NULL VARCHAR2(10)
ACCOUNT_NUM NOT NULL NUMBER(8)
AMOUNT NOT NULL NUMBER(11,2)

27. existing code
27

28. 28
SQL> select ACCOUNT_NUM, max(TXN_TS) LAST_TS
2 from TRANSACTIONS, ACCOUNT
3 where <joins etc>
4 group by ACCOUNT_NUM
5 order by 1;

29. 29
SQL> select ACCOUNT_NUM, max(TXN_TS) LAST_TS
2 from TRANSACTIONS
3 group by ACCOUNT_NUM
4 order by 1;
simplified

30. 30
SQL> select ACCOUNT_NUM, max(TXN_TS) LAST_TS
2 from TRANSACTIONS t
3 group by ACCOUNT_NUM
4 order by 1;
--------------------------------------------------
| Id | Operation | Name |
--------------------------------------------------
| 0 | SELECT STATEMENT | |
| 1 | TABLE ACCESS FULL | TRANSACTIONS |
--------------------------------------------------

31. tuning attempt #1
31

32. 32
SQL> select /*+ PARALLEL(t 16) */
2 ACCOUNT_NUM, max(TXN_TS) LAST_TS
3 from TRANSACTIONS t
4 group by ACCOUNT_NUM
5 order by 1;

33. worked...
33

34. ... storage meltdown
34

35. tuning attempt #2
35

36. 36
create index TRANSACTIONS_IX on TRANSACTIONS (
account_num, txn_ts )
SQL> select ACCOUNT_NUM, max(TXN_TS) LAST_TS
2 from TRANSACTIONS t
3 group by ACCOUNT_NUM
4 order by 1;
--------------------------------------------------
| Id | Operation | Name |
--------------------------------------------------
| 0 | SELECT STATEMENT | |
| 1 | INDEX FAST FULL SCAN| TRANSACTIONS_IX |
--------------------------------------------------

37. worked...
37

38. ... oltp impact
38

39. tuning attempt #3
39

40. 40
CREATE TABLE TRANSACTIONS
(
...
)
PARTITION BY RANGE (TXN_TS)
INTERVAL( NUMTOYMINTERVAL(1,'MONTH'))
(
PARTITION P1 VALUES LESS THAN (TIMESTAMP' 2009-01-01 00:00:00')
PARTITION P2 VALUES LESS THAN (TIMESTAMP' 2009-06-01 00:00:00')
...
);

41. 41
SQL> select ACCOUNT_NUM, max(TXN_TS) LAST_TS
2 from TRANSACTIONS t
3 where TXN_TS > add_months(sysdate,-12)
4 group by ACCOUNT_NUM
5 order by 1;

42. 42
---------------------------------------------------------------
| Id | Operation | Name |Pstart| Pstop |
--------------------------------------------------------------
| 0 | SELECT STATEMENT | | | |
| 1 | PARTITION RANGE ITER..| | 127 | 138 |
|* 2 | TABLE ACCESS FULL | TRANSACTIONS | 127 | 138 |
-------------------------------------------------------------

43. worked ...
43

44. ... changed the function
44

45. 45

47. tuning attempt #4
47

48. 48
Jul Aug Sep Oct

49. 49
SQL> insert into GTT_LAST_TXN
2 select ACCOUNT_NUM, max(TXN_TS) LAST_TS
3 from TRANSACTIONS t
4 where TXN_TS >= trunc(sysdate,'MM')
5 group by ACCOUNT_NUM;
for i in (
select ACCOUNT_NUM from ACCOUNTS
minus
select ACCOUNT_NUM from GTT_LAST_TXN
)
insert into GTT_LAST_TXN
select /*+ INDEX_DESC(t (account_num, txn_ts)) */ MAX(TXN_TS)
from TRANSACTIONS t
where ACCOUNT_NUM = i.ACCOUNT_NUM
and TXN_TS < trunc(sysdate,'MM')

50. worked ...
50

51. ... complexity !
51

52. problem
52

53. 53
SQL> select ...
2 from ...
3 where ...

54. the requirement
54

55. 55
"we have an interest in recent
activity for account holders"
"last transaction for all accounts"

56. promotional material
56
"we haven't seen you in a while,
here's a discount on ...."

57. 57

58. manual examination
58

59. tuning attempt #5
59

60. 60
SQL> desc ACCOUNT
Name Null? Type
----------------------------------- -------- ---------------
ACCOUNT_NUM NOT NULL NUMBER(8)
CURRENT_BALANCE NOT NULL NUMBER(14,2)
...
...
...
MODIFICATION_TS NOT NULL TIMESTAMP(6)

61. optimistic locking
61

62. 62
select ..., MODIFICATION_TS
into ..., :prev_modtstamp
from ACCOUNT
where ...
update ACCOUNT
set ...
where ACCOUNT_NUM = :b1
and MODIFICATION_TS = :prev_modtstamp
if SQL%NOTFOUND then
msg('Row has been changed by another user, please requery');
end if;

63. 63
SQL> select ACCOUNT_NUM,
2 MODIFICATION_TS approx_last_usage
3 from ACCOUNT

64. that's it !
64

65. later ...
65

66. 66
SQL> desc ACCOUNT
Name Null? Type
------------------------------- -------- --------------
ACCOUNT_NUM NOT NULL NUMBER(8)
CURRENT_BALANCE NOT NULL NUMBER(14,2)
...

67. 67
update ACCOUNT
set ...
where ACCOUNT_NUM = :b1
and MODIFICATION_TS = :prev_modtstamp
LAST_TXN_TS = systimestamp
LARGEST_TXN_AMT = greatest(TXN_AMT,LARGEST_TXN_AMT)
BALANCE_CEILING = greatest(BALANCE,BALANCE_CEILING)
BALANCE_FLOOR = least(BALANCE,BALANCE_FLOOR)

68. 68
SQL> desc ACCOUNT
Name Null? Type
----------------------------------- -------- ---------------
ACCOUNT_NUM NOT NULL NUMBER(8)
CURRENT_BALANCE NOT NULL NUMBER(14,2)
LAST_WITHDRAWAL_TS TIMESTAMP(6)
LAST_DEPOSIT_TS TIMESTAMP(6)
LAST_TXN_TS TIMESTAMP(6)
LARGEST_TXN_AMT NUMBER(14,2)
BALANCE_CEILING NUMBER(14,2)
BALANCE_FLOOR NUMBER(14,2)

69. minimal cost
69

70. (semi) automate
70
"we haven't seen you in a while,
here's a discount on ...."

71. too focused on the SQL
71

72. so...
72

73. if you don't tune SQL ...
73

74. ...what are you tuning ?
74

75. 75
HERE

76. user experience
76

77. UX
77

78. screen...
78

79. ... user experience
79

80. report....
80

81. ... user experience
81

82. nightly batch...
82

83. ... user experience
83

84. all solutions shown ...
84
denormalised
indexes
structure
horse power

85. ... all valid
85

86. as long as
86

87. tuning the requirement
87

88. tuning the user experience
88

89. SQL as a means, not an end
89

90. </rant>
90

91. so if we're "failing"…
91

92. …why talk about
92

93. 93

94. 94

95. sql tuning is ...
95

96. 96

97. stop the bleeding...
97

98. ...until find a cure
98

99. but ... without
99

100. ... side effects
100

101. every pain problem
101

102. 102

103. ... side effects
103

104. 104
constipation
dizziness
drowsiness
headache
lightheadedness
nausea
mood swingssweating
vomitingrash
itching
difficulty breathing
tightness in the chest
swelling of the mouth
confusion
disorientation
fainting
irregular heartbeat
hallucinations
seizures
sudden chest pain
unusual bruising or bleeding
blurred vision

105. "This is not a complete list"
105

106. triage
106
find the (likely) pain
stop the bleeding
avoid side effects
work toward cure

107. find
107

108. 108

109. where not too look ...
109
(maybe)

110. server
110

111. "server CPU is 45%"
111
"buffer cache is 99%"

112. too high level
112

113. user experience
113

114. "no problems last 15 minutes"
114

115. Statspack
115
(maybe)

116. hourly...
116

117. sql trace
117

118. definitive ... but
118

119. (maybe) intrusive
119

120. (maybe) user experience
120

121. "please repeat"
121

122. targetted
122

123. much easier
123

124. instrumented
124

125. 125
procedure MY_PROC(...) is
begin
dbms_application_info.set_module('MY_PROC');
dai.set_client_info(' p_parm1 = '||p_parm1);
dai.set_client_info(' p_parm2 = '||p_parm2);
select ...
update ...
dai.set_action('now loading changes');
...
end;

126. diagnostic pack

127. v$active_session_history
127

128. amazing
128

129. every active session...
129

130. ...every second
130

131. 131
SQL> desc V$ACTIVE_SESSION_HISTORY
Name Null? Type
------------------------------- -------- -------------------
SAMPLE_ID NUMBER
SAMPLE_TIME TIMESTAMP(3)
IS_AWR_SAMPLE VARCHAR2(1)
SESSION_ID NUMBER
SESSION_SERIAL# NUMBER
SESSION_TYPE VARCHAR2(10)
FLAGS NUMBER
USER_ID NUMBER
SQL_ID VARCHAR2(13)
IS_SQLID_CURRENT VARCHAR2(1)
SQL_CHILD_NUMBER NUMBER
SQL_OPCODE NUMBER
SQL_OPNAME VARCHAR2(64)
FORCE_MATCHING_SIGNATURE NUMBER
TOP_LEVEL_SQL_ID VARCHAR2(13)
TOP_LEVEL_SQL_OPCODE NUMBER
SQL_PLAN_HASH_VALUE NUMBER
SQL_PLAN_LINE_ID NUMBER
SQL_PLAN_OPERATION VARCHAR2(30)

132. "This morning, my screen froze
for 3 mins running Pay Adjustment..."
132

133. 133
SQL> select sql_id,
2 sql_exec_id,
3 count(*)
4 from v$active_session_history
5 where program = 'Finance.exe'
6 and module = 'PayAdjust'
7 and sample_time >
timestamp '2013-08-20 08:00:00'
8 and sql_id is not null
9 group by
10 sql_id,
11 sql_exec_id
12 order by 3 desc ;

134. 134
SQL_ID SQL_EXEC_ID COUNT(*)
------------- ----------- ----------
087jnbt3bg3fn 33562711 178
9n2nx15wj6tb3 33512732 39
7nvh5pd4y5nqu 33562791 36
7nvh5pd4y5nqu 33562735 30
7nvh5pd4y5nqu 33562736 29
6b5r2j5p2z7kk 33671666 14
6b5r2j5p2z7kk 33670545 12
7nvh5pd4y5nqu 33562689 11
bamffwpy8v8bt 33554432 9
...

135. 135
# cd $ORACLE_HOME/rdbms/admin
# sqlplus / as sysdba @ashrpt

136. 136

137. very very cool
137

138. 138
SQL> select sql_fulltext
2 from v$sql
3 where sql_id = '087jnbt3bg3fn';
SQL_FULLTEXT
-----------------------------------------------
SELECT ...
FROM ...

139. 139
latching

140. 140
woeful metaphor

143. 143
same with memory

144. SGA

145. 145
latches

146. 146
serialised access
aka, someone waits

147. SGA
protected by

148. SGA
protected by
1) get latch

149. SGA
protected by
2) access memory

150. SGA
protected by
3) release latch

151. 151
what protects the latch ?

152. 152
latch acquisition atomic

153. you can do better
153

154. 154
SQL> select sql_fulltext
2 from v$sqlstats
3 where sql_id = '087jnbt3bg3fn';
SQL_FULLTEXT
-----------------------------------------------
SELECT ...
FROM ...

155. "The column definitions for columns in V$SQLSTATS are
identical to those in the V$SQL and V$SQLAREA views.
However, the V$SQLSTATS view differs from V$SQL and
V$SQLAREA in that it is faster, more scalable, and has a
greater data retention (the statistics may still appear in
this view, even after the cursor has been aged out of the
shared pool)."
155

156. 156
found your sql...

157. SQL> select e.department_id, sum(salary)
2 from emp e,
3 job_hist j
4 where e.employee_id = j.employee_id
5 and extract(year from e.hire_date) > 1985
6 and j.end_date > j.start_date + 1
7 and j.start_date >= e.hire_date
8 group by e.department_id
157

158. stop
158

159. optimizer got it wrong...
159

160. or
160

161. ... it cannot run better
161
legitimate response

162. be like the optimizer
162
only smarter

163. what does it do ?
163

164. we can see !
164

165. 10053
165

166. don't panic....
166

167. 167
SQL> alter session set events =
2 '10053 trace name context forever, level 1';
Session altered.
SQL> explain plan for
2 select e.empno, d.dname
3 from emp e,
4 dept d
5 where e.deptno = d.deptno
6 and e.ename like '%A%'
7 and d.deptno != 5;
Explained.

168. 168
SQL> select p.tracefile
2 from v$session s, v$process p
3 where s.paddr = p.addr
4 and s.sid = sys_context('USERENV','SID');
TRACEFILE
----------------------------------------------
/u01/app/oracle/diag/..../MYDB_ora_2994270.trc

169. 169
---------------------
QUERY BLOCK SIGNATURE
---------------------
signature (): qb_name=SEL$1 nbfros=2 flg=0
fro(0): flg=4 objn=51562 hint_alias="D"@"SEL$1"
fro(1): flg=4 objn=51564 hint_alias="E"@"SEL$1"
******************************************
----- Current SQL Statement (sql_id=gvg2yvpdr4uaw) -----
explain plan for
select e.empno, d.dname
from emp e,
dept d
where e.deptno = d.deptno
and e.ename like '%A%'
and d.deptno != 5
*******************************************

170. 170
******************************
PARAMETERS
******************************
Compilation Environment Dump
optimizer_mode_hinted = false
optimizer_features_hinted = 0.0.0
parallel_execution_enabled = true
parallel_query_forced_dop = 0
parallel_dml_forced_dop = 0
parallel_ddl_forced_degree = 0
parallel_ddl_forced_instances = 0
_query_rewrite_fudge = 90
optimizer_features_enable = 11.2.0.2
_optimizer_search_limit = 5

171. 171
Considering Query Transformations
**************************
*************************
Common Subexpression elimination
Order-by elimination
Join Elimination
*************************
SQL:******* UNPARSED QUERY IS *******
SELECT "E"."EMPNO" "EMPNO","D"."DNAME" "DNAME"
FROM "SCOTT"."EMP" "E","SCOTT"."DEPT" "D"
WHERE "E"."DEPTNO"="D"."DEPTNO"
AND "E"."ENAME" LIKE '%A%'
AND "D"."DEPTNO"<>5

172. 172
Predicate Move-Around (PM)
**************************
"E"."DEPTNO"="D"."DEPTNO" AND
"E"."ENAME" LIKE '%A%'
AND "D"."DEPTNO"<>5
...
finally:
"E"."DEPTNO"="D"."DEPTNO" AND
"E"."ENAME" LIKE '%A%' AND
"D"."DEPTNO"<>5 AND
"E"."DEPTNO"<>5

173. 173
SINGLE TABLE ACCESS PATH
Single Table Cardinality Estimation for EMP[E]
Table: EMP Alias: E
Card: Original: 14.000000 Rounded: 1 Computed: 0.70
Access Path: TableScan
Cost: 4.00 Resp: 4.00 Degree: 0
Cost_io: 4.00 Cost_cpu: 41081
Resp_io: 4.00 Resp_cpu: 41081
Best:: AccessPath: TableScan
Cost: 4.00 Degree: 1 Resp: 4.00 Card: 0.70 Bytes: 0

174. 174
Access path analysis for DEPT
***************************************
SINGLE TABLE ACCESS PATH
Single Table Cardinality Estimation for DEPT[D]
Using prorated density: 0.208333 of col #1 as
selectvity of out-of-range/non-existent value pred
Table: DEPT Alias: D
Card: Original: 4.000000 Rounded: 3 Computed: 3.17
Access Path: TableScan
Cost: 4.00 Resp: 4.00 Degree: 0
Cost_io: 4.00 Cost_cpu: 36467
Resp_io: 4.00 Resp_cpu: 36467
Best:: AccessPath: TableScan
Cost: 4.00 Degree: 1 Resp: 4.00 Card: 3.17 Bytes: 0

175. 175
Join order[1]: EMP[E]#0 DEPT[D]#1
***************
Now joining: DEPT[D]#1
***************
NL Join
Outer table: Card: 0.70 Cost: 4.00 Resp: 4.00 Degree: 1
Bytes: 13
Access path analysis for DEPT
Access Path: TableScan
Access Path: index (UniqueScan)
Index: PK_DEPT

176. 176
SM Join
SM cost: 10.01
Outer table: EMP Alias: E
resc: 4.00 card 0.70 bytes: 13 deg: 1 resp: 4.00
Inner table: DEPT Alias: D
resc: 4.00 card: 3.17 bytes: 13 deg: 1 resp: 4.00
HA Join
HA cost: 8.51
resc: 8.51 resc_io: 8.00 resc_cpu: 4367998
resp: 8.51 resp_io: 8.00 resp_cpu: 4367998
Best:: JoinMethod: NestedLoop
Cost: 5.01 Degree: 1 Resp: 5.01 Card: 0.55 Bytes: 26

177. 177
Join order[2]: DEPT[D]#1 EMP[E]#0
***************
Now joining: EMP[E]#0
***************
NL Join
...
SM Join
...
HA Join
...

178. 178
------------------------------------------------+---------------+
| Id | Operation | Name | Rows | Cost |
------------------------------------------------+----------------
| 0 | SELECT STATEMENT | | | 5 |
| 1 | NESTED LOOPS | | | |
| 2 | NESTED LOOPS | | 1 | 5 |
| 3 | TABLE ACCESS FULL | EMP | 1 | 4 |
| 4 | INDEX UNIQUE SCAN | PK_DEPT | 1 | 0 |
| 5 | TABLE ACCESS BY INDEX ROWID | DEPT | 1 | 1 |
------------------------------------------------+---------------+

179. the optimizer does ...
179

180. can I write it better ?
180
CONSIDERING QUERY TRANSFORMATIONS

181. where should I start ?
181
SINGLE TABLE ACCESS PATH

182. what should I join to (next) ?
182
Join order[1]: EMP[E]#0 DEPT[D]#1

183. how should I join ?
183
NL Join
HA Join
SM Join

184. we follow its lead
184

185. what is the real query
185

186. 186
SQL> set autotrace traceonly stat
SQL> select * from STUFF
2 where CREATED > sysdate
Statistics
------------------------------------------
651 recursive calls
0 db block gets
2243 consistent gets
24 physical reads

187. 12c
187

188. 188
SQL> variable c clob
SQL> begin
2 dbms_utility.expand_sql_text
3 ( 'select * from STUFF '||
4 'where created > sysdate',:c);
5 end;
6 /
PL/SQL procedure successfully completed.
SQL> print c

189. 189
SQL> create or replace
2 view STUFF as
3 select
4 o.owner,
5 o.created,
6 s.bytes,
7 s.tablespace_name
8 from
9 dba_segments s,
10 all_objects o
11 where o.owner = s.owner
12 and o.object_name = s.segment_name;
View created.

190. 190
SELECT "A1"."OWNER" "OWNER",
"A1"."NAME" "NAME",
"A1"."CREATED" "CREATED",
"A1"."BYTES" "BYTES",
"A1"."TABLESPACE_NAME" "TABLESPACE_NAME"
FROM (SELECT "A2"."OWNER" "OWNER",
"A2"."OBJECT_NAME" "NAME",
"A2"."CREATED" "CREATED",
"A3"."BYTES" "BYTES",
"A3"."TABLESPACE_NAME" "TABLESPACE_NAME" FROM (SELECT "A4"
."OWNER" "OWNER",
"A4"."SEGMENT_NAME" "SEGMENT_NAME",
"A4"."PARTITION_NAME" "PARTITION_NAME",
"A4"."SEGMENT_TYPE" "SEGMENT_TYPE",
"A4"."SEGMENT_SUBTYPE" "SEGMENT_SUBTYPE",
"A4"."TABLESPACE_NAME" "TABLESPACE_NAME",
"A4"."HEADER_FILE" "HEADER_FILE",
"A4"."HEADER_BLOCK" "HEADER_BLOCK",
DECODE(BITAND("A4"."SEGMENT_FLAGS",131072),131072,
"A4"."BLOCKS",DECODE(BITAND("A4"."SEGMENT_FLAGS",1),1,
"SYS"."DBMS_SPACE_ADMIN"."SEGMENT_NUMBER_BLOCKS"("A4"."TABLESPACE_ID",
"A4"."RELATIVE_FNO",
"A4"."HEADER_BLOCK",
"A4"."SEGMENT_TYPE_ID",
"A4"."BUFFER_POOL_ID",
"A4"."SEGMENT_FLAGS",
"A4"."SEGMENT_OBJD",
"A4"."BLOCKS"),
"A4"."BLOCKS"))*"A4"."BLOCKSIZE" "BYTES",
DECODE(BITAND("A4"."SEGMENT_FLAGS",131072),131072,
"A4"."BLOCKS",DECODE(BITAND("A4"."SEGMENT_FLAGS",1),1,
"SYS"."DBMS_SPACE_ADMIN"."SEGMENT_NUMBER_BLOCKS"("A4"."TABLESPACE_ID",
"A4"."RELATIVE_FNO",

191. 191
"A4"."HEADER_BLOCK",
"A4"."SEGMENT_TYPE_ID",
"A4"."BUFFER_POOL_ID",
"A4"."SEGMENT_FLAGS",
"A4"."SEGMENT_OBJD",
"A4"."BLOCKS"),
"A4"."BLOCKS")) "BLOCKS",DECODE(BITAND("A4"."SEGMENT_FLAGS",131072),131072,
"A4"."EXTENTS",DECODE(BITAND("A4"."SEGMENT_FLAGS",1),1,
"SYS"."DBMS_SPACE_ADMIN"."SEGMENT_NUMBER_EXTENTS"("A4"."TABLESPACE_ID",
"A4"."RELATIVE_FNO",
"A4"."HEADER_BLOCK",
"A4"."SEGMENT_TYPE_ID",
"A4"."BUFFER_POOL_ID",
"A4"."SEGMENT_FLAGS",
"A4"."SEGMENT_OBJD",
"A4"."EXTENTS"),
"A4"."EXTENTS")) "EXTENTS",
"A4"."INITIAL_EXTENT" "INITIAL_EXTENT",
"A4"."NEXT_EXTENT" "NEXT_EXTENT",
"A4"."MIN_EXTENTS" "MIN_EXTENTS",
"A4"."MAX_EXTENTS" "MAX_EXTENTS",
"A4"."MAX_SIZE" "MAX_SIZE",
"A4"."RETENTION" "RETENTION",
"A4"."MINRETENTION" "MINRETENTION",
"A4"."PCT_INCREASE" "PCT_INCREASE",
"A4"."FREELISTS" "FREELISTS",
"A4"."FREELIST_GROUPS" "FREELIST_GROUPS",
"A4"."RELATIVE_FNO" "RELATIVE_FNO",
DECODE("A4"."BUFFER_POOL_ID",1,'KEEP',2,'RECYCLE','DEFAULT') "BUFFER_POOL",
DECODE("A4"."FLASH_CACHE",1,'KEEP',2,
'NONE','DEFAULT') "FLASH_CACHE",DECODE("A4"."CELL_FLASH_CACHE",1,'KEEP',2,'NONE','DEFAULT')
"CELL_FLASH_CACHE"
FROM ( (SELECT NVL("A199"."NAME",'SYS') "OWNER",
"A198"."NAME" "SEGMENT_NAME",

192. 192
"A198"."SUBNAME" "PARTITION_NAME",
"A196"."OBJECT_TYPE" "SEGMENT_TYPE",
"A195"."TYPE#" "SEGMENT_TYPE_ID",DECODE(BIT
AND("A195"."SPARE1",2097408),2097152,'SECUREFILE',256,'ASSM','MSSM') "SEGMENT_SUBTYPE",
"A197"."TS#" "TABLESPACE_ID",
"A197"."NAME" "TABLESPACE_NAME",
"A197"."BLOCKSIZE" "BLOCKSIZE",
"A194"."FILE#" "HEADER_FILE",
"A195"."BLOCK#" "HEADER_BLOCK",
"A195"."BLOCKS"*"A197"."BLOCKSIZE" "BYTES",
"A195"."BLOCKS" "BLOCKS",
"A195"."EXTENTS" "EXTENTS",
"A195"."INIEXTS"*"A197"."BLOCKSIZE" "INITIAL_EXTENT",
"A195"."EXTSIZE"*"A197"."BLOCKSIZE" "NEXT_EXTENT",
"A195"."MINEXTS" "MIN_EXTENTS",
"A195"."MAXEXTS" "MAX_EXTENTS",DECODE(BITAND("A195"."SPARE1",4194304),4194304,
"A195"."BITMAPRANGES",NULL) "MAX_SIZE",TO_CHAR(DECODE(
BITAND("A195"."SPARE1",2097152),2097152,
DECODE("A195"."LISTS",0,'NONE',1,'AUTO',2,'MIN',3,'MAX',4,'DEFAULT','INVALID'),NULL))
"RETENTION",DECODE(BITAND("A195"."SPARE1",2097152),2097152,
"A195"."GROUPS",NULL) "MINRETENTION",DECODE(BITAND("A197"."FLAGS",3),1,TO_NUMBER(NULL),
"A195"."EXTPCT") "PCT_INCREASE",DECODE(BITAND("A197"."FLAGS",32),32,
TO_NUMBER(NULL),DECODE("A195"."LISTS",0,1,
"A195"."LISTS"))
"FREELISTS",DECODE(BITAND("A197"."FLAGS",32),32,TO_NUMBER(NULL),DECODE("A195"."GROUPS",0,1,
"A195"."GROUPS")) "FREELIST_GROUPS",
"A195"."FILE#" "RELATIVE_FNO",BITAND("A195"."CACHEHINT",3) "BUFFER_POOL_ID",
BITAND("A195"."CACHEHINT",12)/4 "FLASH_CACHE",BITAND("A195"."CACHEHINT",48)/16 "CELL_FLASH_CACHE",
NVL("A195"."SPARE1",0)
"SEGMENT_FLAGS",DECODE(BITAND("A195"."SPARE1",1),1,
"A195"."HWMINCR",
"A198"."DATAOBJ#") "SEGMENT_OBJD" FROM "SYS"."USER$" "A199",
"SYS"."OBJ$" "A198",
"SYS"."TS$" "A197", ( (SELECT

193. 193
DECODE(BITAND("A209"."PROPERTY",8192),8192,'NESTED TABLE','TABLE') "OBJECT_TYPE",
2 "OBJECT_TYPE_ID",5 "SEGMENT_TYPE_ID",
"A209"."OBJ#" "OBJECT_ID",
"A209"."FILE#" "HEADER_FILE",
"A209"."BLOCK#" "HEADER_BLOCK",
"A209"."TS#" "TS_NUMBER" FROM "SYS"."TAB$" "A209" WHERE BITAND("A209"."PROPERTY",1024)=0) UNI
ON ALL (SELECT 'TABLE PARTITION' "OBJECT_TYPE",19 "OBJECT_TYPE_ID",5 "SEGMENT_TYPE_ID",
"A208"."OBJ#" "OBJECT_ID",
"A208"."FILE#" "HEADER_FILE",
"A208"."BLOCK#" "HEADER_BLOCK",
"A208"."TS#" "TS_NUMBER" FROM "SYS"."TABPART$" "A208") UNION ALL
(SELECT 'CLUSTER' "OBJECT_TYPE",3 "OBJECT_TYPE_ID",5 "SEGMENT_TYPE_ID",
"A207"."OBJ#" "OBJECT_ID",
"A207"."FILE#" "HEADER_FILE",
"A207"."BLOCK#" "HEADER_BLOCK",
"A207"."TS#" "TS_NUMBER" FROM "SYS"."CLU$" "A207") UNION ALL
(SELECT DECODE("A206"."TYPE#",8,'LOBINDEX','INDEX') "OBJECT_TYPE",1 "OBJECT_TYPE_ID",6
"SEGMENT_TYPE_ID",
"A206"."OBJ#" "OBJECT_ID",
"A206"."FILE#" "HEADER_FILE",
"A206"."BLOCK#" "HEADER_BLOCK",
"A206"."TS#" "TS_NUMBER" FROM "SYS"."IND$" "A206" WHERE "A206"."TYPE#"=1 OR
"A206"."TYPE#"=2 OR
"A206"."TYPE#"=3 OR
"A206"."TYPE#"=4 OR
"A206"."TYPE#"=6 OR
"A206"."TYPE#"=7 OR
"A206"."TYPE#"=8 OR
"A206"."TYPE#"=9) UNION ALL
(SELECT 'INDEX PARTITION'
"OBJECT_TYPE",20 "OBJECT_TYPE_ID",6 "SEGMENT_TYPE_ID",
"A205"."OBJ#" "OBJECT_ID",
"A205"."FILE#" "HEADER_FILE",
"A205"."BLOCK#" "HEADER_BLOCK",

194. 194
"A205"."TS#" "TS_NUMBER" FROM "SYS"."INDPART$" "A205") UNION ALL
(SELECT 'LOBSEGMENT' "OBJECT_TYPE",21 "OBJECT_TYPE_ID",8 "SEGMENT_TYPE_ID",
"A204"."LOBJ#" "OBJECT_ID",
"A204"."FILE#" "HEADER_FILE",
"A204"."BLOCK#" "HEADER_BLOCK",
"A204"."TS#" "TS_NUMBER" FROM "SYS"."LOB$" "A204" WHERE BITAND("A204"."PROPERTY",64)=0 OR
BITAND("A204"."PROPERTY",128)=128) UNION ALL
(SELECT 'TABLE SUBPARTITION' "OBJECT_TYPE",34 "OBJECT_TYPE_ID",5 "SEGMENT_TYPE_ID",
"A203"."OBJ#" "OBJECT_ID",
"A203"."FILE#" "HEADER_FILE",
"A203"."BLOCK#" "HEADER_BLOCK",
"A203"."TS#" "TS_NUMBER" FROM "SYS"."TABSUBPART$" "A203") UNION ALL
(SELECT 'INDEX SUBPARTITION' "OBJECT_TYPE",35 "OBJECT_TYPE_ID",6 "SEGMENT_TYPE_ID",
"A202"."OBJ#" "OBJECT_ID",
"A202"."FILE#" "HEADER_FILE",
"A202"."BLOCK#" "HEADER_BLOCK",
"A202"."TS#" "TS_NUMBER" FROM "SYS"."INDSUBPART$" "A202") UNION ALL
(SELECT DECODE("A201"."FRAGTYPE$",'P','LOB PARTITION','LOB SUBPARTITION')
"OBJECT_TYPE",DECODE("A201"."FRAGTYPE$",'P',40,41) "OBJECT_TYPE_ID",8 "SEGMENT_TYPE_ID",
"A201"."FRAGOBJ#" "OBJECT_ID",
"A201"."FILE#" "HEADER_FILE",
"A201"."BLOCK#" "HEADER_BLOCK",
"A201"."TS#" "TS_NUMBER" FROM "SYS"."LOBFRAG$" "A201")) "A196",
"SYS"."SEG$" "A195",
"SYS"."FILE$" "A194" WHERE "A195"."FILE#"="A196"."HEADER_FILE" AND
"A195"."BLOCK#"="A196"."HEADER_BLOCK" AND
"A195"."TS#"="A196"."TS_NUMBER" AND
"A195"."TS#"="A197"."TS#" AND
"A198"."OBJ#"="A196"."OBJECT_ID" AND
"A198"."OWNER#"="A199"."USER#"(+) AND
"A195"."TYPE#"="A196"."SEGMENT_TYPE_ID" AND
"A198"."TYPE#"="A196"."OBJECT_TYPE_ID" AND
"A195"."TS#"="A194"."TS#" AND

195. 195
"A195"."FILE#"="A194"."RELFILE#") UNION ALL
(SELECT NVL("A193"."NAME",'SYS') "OWNER",
"A191"."NAME" "SEGMENT_NAME",NULL "PARTITION_NAME",
DECODE("A190"."TYPE#",1,'ROLLBACK',10,'TYPE2 UNDO') "SEGMENT_TYPE",
"A190"."TYPE#" "SEGMENT_TYPE_ID",NULL "SEGMENT_SUBTYPE",
"A192"."TS#" "TABLESPACE_ID",
"A192"."NAME" "TABLESPACE_NAME",
"A192"."BLOCKSIZE" "BLOCKSIZE",
"A189"."FILE#" "HEADER_FILE",
"A190"."BLOCK#" "HEADER_BLOCK",
"A190"."BLOCKS"*"A192"."BLOCKSIZE" "BYTES",
"A190"."BLOCKS" "BLOCKS",
"A190"."EXTENTS" "EXTENTS",
"A190"."INIEXTS"*"A192"."BLOCKSIZE" "INITIAL_EXTENT",
"A190"."EXTSIZE"*"A192"."BLOCKSIZE" "NEXT_EXTENT",
"A190"."MINEXTS" "MIN_EXTENTS",
"A190"."MAXEXTS" "MAX_EXTENTS",DECODE(BITAND("A190"."SPARE1",4194304),4194304,
"A190"."BITMAPRANGES",NULL) "MAX_SIZE",NULL "RETENTION",NULL "MINRETENTION",
"A190"."EXTPCT"
"PCT_INCREASE",DECODE(BITAND("A192"."FLAGS",32),32,TO_NUMBER(NULL),DECODE("A190"."LISTS",0,1,
"A190"."LISTS")) "FREELISTS",DECODE(BITAND("A192"."FLAGS",32),32,TO_NUMBER(NULL),
DECODE("A190"."GROUPS",0,1,"A190"."GROUPS")) "FREELIST_GROUPS",
"A190"."FILE#" "RELATIVE_FNO",BITAND("A190"."CACHEHINT",3)
"BUFFER_POOL_ID",BITAND("A190"."CACHEHINT",12)/4 "FLASH_CACHE",
BITAND("A190"."CACHEHINT",48)/16 "CELL_FLASH_CACHE",NVL("A190"."SPARE1",0) "SEGMENT_FLAGS",
"A191"."US#" "SEGMENT_OBJD" FROM "SYS"."USER$" "A193","SYS"."TS$" "A192",
"SYS"."UNDO$" "A191",
"SYS"."SEG$" "A190",
"SYS"."FILE$" "A189" WHERE "A190"."FILE#"="A191"."FILE#" AND
"A190"."BLOCK#"="A191"."BLOCK#" AND
"A190"."TS#"="A191"."TS#" AND
"A190"."TS#"="A192"."TS#" AND
"A190"."USER#"="A193"."USER#"(+) AND
("A190"."TYPE#"=1 OR
"A190"."TYPE#"=10) AND
"A191"."STATUS$"<>1 AND

196. 196
"A191"."TS#"="A189"."TS#" AND
"A191"."FILE#"="A189"."RELFILE#") UNION ALL
(SELECT NVL("A188"."NAME",'SYS') "OWNER",
TO_CHAR("A185"."FILE#")||'.'||TO_CHAR("A186"."BLOCK#") "SEGMENT_NAME",NULL "PARTITION_NAME",
DECODE("A186"."TYPE#",2,'DEFERRED ROLLBACK',3,
'TEMPORARY',4,'CACHE',9,'SPACE HEADER','UNDEFINED') "SEGMENT_TYPE",
"A186"."TYPE#" "SEGMENT_TYPE_ID",NULL "SEGMENT_SUBTYPE",
"A187"."TS#" "TABLESPACE_ID",
"A187"."NAME" "TABLESPACE_NAME",
"A187"."BLOCKSIZE" "BLOCKSIZE",
"A185"."FILE#" "HEADER_FILE",
"A186"."BLOCK#" "HEADER_BLOCK",
"A186"."BLOCKS"*"A187"."BLOCKSIZE" "BYTES",
"A186"."BLOCKS" "BLOCKS",
"A186"."EXTENTS" "EXTENTS",
"A186"."INIEXTS"*"A187"."BLOCKSIZE" "INITIAL_EXTENT",
"A186"."EXTSIZE"*"A187"."BLOCKSIZE" "NEXT_EXTENT",
"A186"."MINEXTS" "MIN_EXTENTS",
"A186"."MAXEXTS" "MAX_EXTENTS",DECODE(BITAND("A186"."SPARE1",4194304),4194304,
"A186"."BITMAPRANGES",NULL) "MAX_SIZE",NULL
"RETENTION",NULL "MINRETENTION",DECODE(BITAND("A187"."FLAGS",3),1,TO_NUMBER(NULL),
"A186"."EXTPCT")
"PCT_INCREASE",DECODE(BITAND("A187"."FLAGS",32),32,TO_NUMBER(NULL),DECODE("A186"."LISTS",0,1,
"A186"."LISTS"))
"FREELISTS",DECODE(BITAND("A187"."FLAGS",32),32,TO_NUMBER(NULL),DECODE("A186"."GROUPS",0,1,
"A186"."GROUPS")) "FREELIST_GROUPS",
"A186"."FILE#" "RELATIVE_FNO",BITAND("A186"."CACHEHINT",3)
"BUFFER_POOL_ID",BITAND("A186"."CACHEHINT",12)/4 "FLASH_CACHE",BITAND("A186"."CACHEHINT",48)/16
"CELL_FLASH_CACHE",NVL("A186"."SPARE1",0) "SEGMENT_FLAGS",
"A186"."HWMINCR" "SEGMENT_OBJD" FROM "SYS"."USER$"
"A188",
"SYS"."TS$" "A187",
"SYS"."SEG$" "A186",
"SYS"."FILE$" "A185" WHERE "A186"."TS#"="A187"."TS#" AND
"A186"."USER#"="A188"."USER#"(+) AND
"A186"."TYPE#"<>1 AND
"A186"."TYPE#"<>5 AND

197. 197
"A186"."TYPE#"<>6 AND
"A186"."TYPE#"<>8 AND
"A186"."TYPE#"<>10 AND
"A186"."TYPE#"<>11 AND
"A186"."TS#"="A185"."TS#"
AND
"A186"."FILE#"="A185"."RELFILE#") UNION ALL
(SELECT NVL("A184"."NAME",'SYS') "OWNER",'HEATMAP' "SEGMENT_NAME",
NULL "PARTITION_NAME",'SYSTEM STATISTICS' "SEGMENT_TYPE",
"A182"."TYPE#" "SEGMENT_TYPE_ID",NULL "SEGMENT_SUBTYPE",
"A183"."TS#" "TABLESPACE_ID",
"A183"."NAME" "TABLESPACE_NAME",
"A183"."BLO
CKSIZE" "BLOCKSIZE",
"A181"."FILE#" "HEADER_FILE",
"A182"."BLOCK#" "HEADER_BLOCK",
"A182"."BLOCKS"*"A183"."BLOCKSIZE" "BYTES",
"A182"."BLOCKS" "BLOCKS",
"A182"."EXTENTS" "EXTENTS",
"A182"."INIEXTS"*"A183"."BLOCKSIZE" "INITIAL_EXTENT",
"A182"."EXTSIZE"*"A183"."BLOCKSIZE" "NEXT_EXTENT",
"A182"."MINEXTS" "MIN_EXTENTS",
"A182"."MAXEXTS" "MAX_EXTENTS",DECODE(BITAND("A182"."SPARE1",4194304),4194304,
"A182"."BITMAPRANGES",NULL) "MAX_SIZE",NULL "RETENTION",NULL
"MINRETENTION",DECODE(BITAND("A183"."FLAGS",3),1,TO_NUMBER(NULL),
"A182"."EXTPCT") "PCT_INCREASE",DECODE(BITAND("A183"."FLAGS",32),32,TO_NUMBER(NULL),DEC
ODE("A182"."LISTS",0,1,
"A182"."LISTS"))
"FREELISTS",DECODE(BITAND("A183"."FLAGS",32),32,TO_NUMBER(NULL),DECODE("A182"."GROUPS",0,1,
"A182"."GROUPS")) "FREELIST_GROUPS",
"A182"."FILE#" "RELATIVE_FNO",BITAND("A182"."CACHEHINT",3) "BUFFER_POOL_ID",
BITAND("A182"."CACHEHINT",12)/4 "FLASH_CACHE",BITAND("A18
2"."CACHEHINT",48)/16 "CELL_FLASH_CACHE",NVL("A182"."SPARE1",0) "SEGMENT_FLAGS",
"A182"."HWMINCR" "SEGMENT_OBJD" FROM "SYS"."USER$" "A184",

198. 198
"SYS"."TS$" "A183",
"SYS"."SEG$" "A182",
"SYS"."FILE$" "A181" WHERE "A182"."TS#"="A183"."TS#" AND
"A182"."USER#"="A184"."USER#"(+) AND
"A182"."TYPE#"=11 AND
"A182"."TS#"="A181"."TS#" AND
"A182"."FILE#"="A181"."RELFILE#")) "A4") "A3", (SELECT "A5"."NAME" "OWNER",
"A6"."NAME" "OBJECT_NAME",
"A6"."SUBNAME" "SUBOBJECT_NAME",
"A6"."OBJ#" "OBJECT_ID",
"A6"."DATAOBJ#" "DATA_OBJECT_ID",DECODE("A6"."TYPE#",0,'NEXT OBJECT',1,'INDEX',
2,'TABLE',3,'CLUSTER',4,'VIEW',5,'SYNONYM
',6,'SEQUENCE',7,'PROCEDURE',8,'FUNCTION',9,'PACKAGE',11,'PACKAGE BODY',12,
'TRIGGER',13,'TYPE',14,'TYPE BODY',19,'TABLE PARTITION',20,'INDEX PARTITION',
21,'LOB',22,'LIBRARY',23,'DIRECTORY',24,'QUEUE',28,'JAVA SOURCE',29,'JAVA CLASS',30,
'JAVA RESOURCE',32,'INDEXTYPE',33,'OPERATOR',34,
'TABLE SUBPARTITION',35,'INDEX SUBPARTITION',40,'LOB PARTITION',41,'LOB SUBPARTITION',42
,NVL( (SELECT 'REWRITE EQUIVALENCE' "'REWRITEEQUIVALENCE'" FROM SYS."SUM$" "A52" WHERE "A52"."OBJ#"="A6"."OBJ#" AND
BITAND("A52"."XPFLAGS",8388608)=8388608),'MATERIALIZED VIEW'),43,'DIMENSION',
44,'CONTEXT',46,'RULE SET',47,'RESOURCE PLAN',48,'CONSUMER GROUP',55,'XML SCHEMA',56,'JAVA
DATA',57,'EDITION',59,'RULE',
60,'CAPTURE',61,'APPLY',62,'EVALUATION CONTEXT',66,'JOB',67,'PROGRAM',68,'JOB CLASS',69,
'WINDOW',72,'SCHEDULER GROUP',74,'SCHEDULE',79,'CHAIN',81,'FILE GROUP',82,'MINING
MODEL',87,'ASSEMBLY',90,'CREDENTIAL',92,'CUBE
DIMENSION',93,'CUBE',94,'MEASURE FOLDER',95,'CUBE BUILD PROCESS',100,'FILE WATCHER',
101,'DESTINATION',114,'SQL TRANSLATION PROFILE',115,'UNIFIED AUDIT POLICY','UNDEFINED') "OBJECT_TYPE",
"A6"."CTIME" "CREATED",
"A6"."MTIME" "LAST_DDL_TIME",TO_CHAR("A6"."STIME",'YYYY-MM-DD:HH24:MI:SS') "TIMESTAMP",DEC
ODE("A6"."STATUS",0,'N/A',1,'VALID','INVALID') "STATUS",DECODE(BITAND("A6"."FLAGS",2),0,'N',2,'Y','N')
"TEMPORARY",DECODE(BITAND("A6"."FLAGS",4),0,'N',4,'Y','N') "GENERATED",DECODE(BITAND("A6"."FLAGS",16),0,'N',16,'Y','N')
"SECONDARY",
"A6"."NAMESPACE" "NAMESPACE",
"A6"."DEFINING_EDITION" "EDITION_NAM
E",DECODE(BITAND("A6"."FLAGS",196608),65536,'METADATA LINK',131072,'OBJECT LINK','NONE') "SHARING",
CASE WHEN ("A6"."TYPE#"=4 OR
"A6"."TYPE#"=5 OR

199. 16 ...
199
more
pages

200. reading a single table
200

201. should I use an index ?
201

202. full scan versus index
202

203. 203
SQL> select *
2 from STUDENT
3 where gender = 'W';

204. full scan
(dba_extents)
File 1, Block 271, 512 blocks
File 2, Block 234, 256 blocks
etc

205. indexed access
W, File 1, Block 37, Row 4
W, File 1, Block 437, Row 11
Sue
Jane
POOL_IX (POOL_TYPE) STUDENT

206. what will a full scan cost ?
206

207. 207
SQL> select blocks
2 from dba_tables
3 where owner = 'SCOTT'
4 and table_name = 'STUDENT';
BLOCKS
----------
9083

208. dbms_space
208

209. 209
SQL> select value
2 from v$parameter
3 where name = 'db_file_multiblock_read_count';
VALUE
---------------
128

210. IO cost blocks / blocks at a time
210

211. adjusted downwards
211

212. adj = 1.6765 x orig0.6581
212
Ack: Wolfgang Brietling, 2001

213. 128
213
41

214. 214
SQL> set autotrace traceonly explain
SQL> select /*+ no_cpu_costing */ * from STUDENT;
-----------------------------------------------------
| Id | Operation | Name | Rows | Cost |
-----------------------------------------------------
| 0 | SELECT STATEMENT | | 531K| 224 |
| 1 | TABLE ACCESS FULL| STUDENT | 531K| 224 |
-----------------------------------------------------
9083 / 41 = 221

215. 215
SQL> set autotrace traceonly explain
SQL> select /*+ no_cpu_costing */ * from STUDENT;
-----------------------------------------------------
| Id | Operation | Name | Rows | Cost |
-----------------------------------------------------
| 0 | SELECT STATEMENT | | 531K| 224 |
| 1 | TABLE ACCESS FULL| STUDENT | 531K| 224 |
-----------------------------------------------------
9083 / 41 = 221

216. "digest" the rows
216

217. 217

218. 218
SQL> set autotrace traceonly explain
SQL> select * from STUDENT;
-----------------------------------------------------
| Id | Operation | Name | Rows | Cost |
-----------------------------------------------------
| 0 | SELECT STATEMENT | | 531K| 1586 |
| 1 | TABLE ACCESS FULL| STUDENT | 531K| 1586 |
-----------------------------------------------------

219. what will a index scan cost ?
219

220. a few blocks +
220

221. 221
SQL> select AVG_LEAF_BLOCKS_PER_KEY
2 from USER_INDEXES
3 where INDEX_NAME = 'STUDENT_IX'
AVG_LEAF_BLOCKS_PER_KEY
-----------------------
6

222. approximation
222

223. the easiest way

224. run a few...
valid use of hints

225. understanding joins

226. nested loops
hash
sort merge
index join
and-equal
btree-bitmap conversion
bitmap join

227. other complexities
bloom filters
parallel

228. nested loop

229. "for each row in outer,
check for row in inner"

230. for (i=1; i<100; i++)
for (j=1; j<100; j++)
for (k=1; k<100; k++)
...
...

231. demo

235. cost

236. effort = L1 + M * L2
=
cost to Lookup rows
in outer table
number of rows Matching
criteria in outer table
cost of Lookup matching row
in inner table

237. High M ... no good
effort = L1 + M * L2
=

238. High L2 ... no good
effort = L1 + M * L2
=

239. High L1 ... no good maybe
effort = L1 + M * L2

240. sort merge

241. demo

245. merge

247. cost

248. effort = S1 + S2 + M
sort table 1 (hold result)
sort table 2 (hold result)
merge results (not held*)

249. risks

250. RAM
SQL> select value * 0.05 / 1024 sort_kb
2 from v$parameter
3 where name = 'pga_aggregate_target';
SORT_KB
----------
2457.6

251. single pass

252. really big sorts

253. multipass sorts

254. detection

255. SQL> select * from v$mystat / v$sesstat / v$sysstat
2 where name like 'work%';
NAME VALUE
----------------------------------- ----------
workarea executions - optimal 12
workarea executions - onepass 0
workarea executions - multipass 0

256. why sort merge ?

257. non-equality joins
where t1.name > t2.name

258. hash joins

259. 7.3

260. 260
SQL> select value
2 from v$parameter
3 where name = 'hash_join_enabled';
VALUE
----------------------
true

261. 261

262. "best" join
262

263. divide and conquer
263

264. demo
264

265. 265

266. 266

267. much larger hash
267

268. = and != only
268

269. nested loop
good selectivity into each table
small numbers of (result) rows
first row fast
269

270. hash join
the "best" join (theory)
270

271. sort merge
rarely seen
partial joins
271

272. 272
back to our problem SQL

273. SQL> select e.department_id, sum(salary)
2 from emp e,
3 job_hist j
4 where e.employee_id = j.employee_id
5 and extract(year from e.hire_date) > 1985
6 and j.end_date > j.start_date + 1
7 and j.start_date >= e.hire_date
8 group by e.department_id
273

274. 274
v$sql_plan

275. -----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)|
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 36M| 2742M| | 10998 (48)|
| 1 | HASH GROUP BY | | 36M| 2742M| | 10998 (48)|
|* 2 | HASH JOIN | | 36M| 2742M| 3728K| 9137 (37)|
|* 3 | TABLE ACCESS FULL| JOB_HIST | 88761 | 2687K| | 147 (3)|
|* 4 | TABLE ACCESS FULL| EMP | 877K| 40M| | 3028 (2)|
-----------------------------------------------------------------------------
275

276. 276
now what ?

277. "where does it hurt ?"
277

278. 278

279. 279
where in the plan ...

280. SQL> select
2 DBMS_SQLTUNE.REPORT_SQL_MONITOR(
3 sql_id=>'d3ncuxj7629bf',
4 report_level=>'ALL',
5 type=>'HTML') as report
6 from dual;
280

284. options
284
rewrite the sql
hints
add indexes
remove indexes

285. rewrite the sql
285

286. ideally ... simply
286

287. 287
dynamic sampling

288. 288
cardinality is everything
288

289. 289

290. 290

291. 291
same with Oracle
291

292. 292
actual versus estimate
292

293. 293
SQL> select /*+ GATHER_PLAN_STATISTICS */ count(*)
2 from VEHICLES
3 where MAKE = 'FORD'
4 and MODEL = 'FOCUS';
COUNT(*)
----------
214468
293

294. 294
SQL> SELECT *
2 FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(
3 NULL, NULL, 'ALLSTATS LAST'));
-----------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows |
-----------------------------------------------------------------
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |
|* 2 | TABLE ACCESS FULL| VEHICLES| 1 | 220K| 214K|
-----------------------------------------------------------------
294

295. 295
295
if the estimate is wrong

296. 296
296
try dynamic sampling

297. 297
SQL> create table TOUGH_DATA as
2 select
3 rownum pk,
4 dbms_random.string('U',10) str
5 from dual
6 connect by level < 1000000
7 /
Table created.
SQL> exec dbms_stats.gather_table_stats(
user,'TOUGH_DATA')

298. 298
SQL> select count(*)
2 from TOUGH_DATA
3 where str like '%XX'
4 /
COUNT(*)
----------
1452
hard

299. 299
SQL> select count(*)
2 from TOUGH_DATA
3 where str like '%XX'
4 /
-------------------------------------------------
| Id | Operation | Name | Rows |
-------------------------------------------------
| 0 | SELECT STATEMENT | | 1 |
| 1 | SORT AGGREGATE | | 1 |
|* 2 | TABLE ACCESS FULL| TOUGH_DATA | 50000 |
-------------------------------------------------
5% assumption

300. 300
SQL> select /*+ dynamic_sampling(t 2) */ count(*)
2 from TOUGH_DATA t
3 where str like '%XX'
4 /
-------------------------------------------------
| Id | Operation | Name | Rows |
-------------------------------------------------
| 0 | SELECT STATEMENT | | 1 |
| 1 | SORT AGGREGATE | | 1 |
|* 2 | TABLE ACCESS FULL| TOUGH_DATA | 1252 |
-------------------------------------------------

301. more drastic measures
301

302. use hints
302

303. 303
"optimizer hints should only be
used with extreme care"
Maria Colgan, Oct 2012
Optimizer product manager

304. awesome hints
304

305. 305
gather_plan_statistics
dynamic_sampling
monitor
qb_name

306. query blocks
306

307. C#
PL/SQL
307

308. no comments
308

309. 309

310. "C# is self-documenting"
310

311. for (int i = 0; i < w.Count; ++i)
{
if (w[i].v > 0 && w[i].p > mddh)
{
m = Math.Max(m, w[i].d);
}
}
for (int i = 0; i < w.Count; ++i)
{
if (w[i].v > 0 && w[i].p > mddh)
{
w[i].d = m / w[i].d;
s += w[i].d;
}
}
311

312. query blocks =
self- documenting SQL
312

313. select emp.*
from emp,
( select trunc(hiredate,'YYYY'), max(empno) empno
from emp
where empno > 0
group by trunc(hiredate,'YYYY') ) x,
( select deptno, avg(sal)
from emp
group by deptno ) y
where x.empno = emp.empno
and y.deptno = emp.deptno
313

314. Id | Operation | Name |
----------------------------------------------|
0 | SELECT STATEMENT | |
1 | HASH JOIN | |
2 | TABLE ACCESS BY INDEX ROWID | EMP |
3 | NESTED LOOPS | |
4 | VIEW | |
5 | SORT GROUP BY | |
6 | TABLE ACCESS BY INDEX ROWID| EMP |
7 | INDEX FULL SCAN | E2 |
8 | INDEX RANGE SCAN | E1 |
9 | VIEW | |
10 | SORT GROUP BY | |
11 | TABLE ACCESS BY INDEX ROWID | EMP |
12 | INDEX RANGE SCAN | E2 |
314

315. select emp.*
from emp,
( select /*+ QB_NAME(YR_HIRE) */
trunc(hiredate,'YYYY'), max(empno) empno
from emp
where empno > 0
group by trunc(hiredate,'YYYY') ) x,
( select /*+ QB_NAME(AV_SAL) */
deptno, avg(sal)
from emp
group by deptno ) y
where x.empno = emp.empno
and y.deptno = emp.deptno
315

316. Id | Operation | Name | Query Block
----------------------------------------------|--------------
0 | SELECT STATEMENT | |
1 | HASH JOIN | |
2 | TABLE ACCESS BY INDEX ROWID | EMP |
3 | NESTED LOOPS | |
4 | VIEW | |
5 | SORT GROUP BY | |
6 | TABLE ACCESS BY INDEX ROWID| EMP |
7 | INDEX FULL SCAN | E2 |
8 | INDEX RANGE SCAN | E1 |
9 | VIEW | |
10 | SORT GROUP BY | |
11 | TABLE ACCESS BY INDEX ROWID | EMP |
12 | INDEX RANGE SCAN | E2 |
SEL$1
SEL$1
AV_SAL
AV_SAL
AV_SAL
AV_SAL
SEL$1
YR_HIRE
YR_HIRE
YR_HIRE
YR_HIRE
316

317. assist with other hints
317

318. select
/*+ QB_NAME(top)
INDEX(@yr_hire emp (empno))
FULL(@av_sal emp) */
emp.*
from emp,
( select /*+ QB_NAME(YR_HIRE) */
trunc(hiredate,'YYYY'), max(empno) empno
from emp
where empno > 0
group by trunc(hiredate,'YYYY') ) x,
( select /*+ QB_NAME(AV_SAL) */
deptno, avg(sal)
from emp
group by deptno ) y
where x.empno = emp.empno
and y.deptno = emp.deptno
318

319. sidebar
319

320. 320
select
/*+ QB_NAME(top)
INDEX(@yr_hire emp (empno))
FULL(@av_sal emp)
*/
INDEX(emp emp_ix)

321. cool hints
321

322. 322
first_rows_n
all_rows
leading
cardinality
statement_queueing
opt_param

323. assisting optimizer
323

324. dangerous hints
324

325. everything else...
325

326. 326
full
index
use_hash
use_nl
etc

327. suppressing the optimizer
327

328. undocumented hints
328

329. 329
selectivity
no_trigger

330. an invalid hint
330

331. is a comment
331

332. 332
SQL> select /*+ INDEX(accounts_pk) */
2 from ACCOUNTS
3 where ...
SQL> select /*+ INDEX(a) */
2 from ACCOUNTS
3 where ...
SQL> select /*+ INDEX(scott.accounts) */
2 from SCOTT.ACCOUNTS
3 where ...
SQL> select /* INDEX(A) */
2 from SCOTT.ACCOUNTS A
3 where ...

333. no error raised !
333

334. even if it IS valid ...
334

335. ... the (in)famous ignore issue
335

336. 336
SQL> select *
2 from emp e,
3 dept d
4 where e.deptno = d.deptno
5 and d.dname = 'SALES';
--------------------------------------------------------
| Id | Operation | Name | Rows |
--------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 |
| 1 | MERGE JOIN | | 5 |
|* 2 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 |
| 3 | INDEX FULL SCAN | PK_DEPT | 4 |
|* 4 | SORT JOIN | | 14 |
| 5 | TABLE ACCESS FULL | EMP | 14 |
--------------------------------------------------------

337. 337
"I want a hash join"

338. 338
SQL> select /*+ use_hash(d) */ *
2 from emp e,
3 dept d
4 where e.deptno = d.deptno
5 and d.dname = 'SALES';
--------------------------------------------------------
| Id | Operation | Name | Rows |
--------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 |
| 1 | MERGE JOIN | | 5 |
|* 2 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 |
| 3 | INDEX FULL SCAN | PK_DEPT | 4 |
|* 4 | SORT JOIN | | 14 |
| 5 | TABLE ACCESS FULL | EMP | 14 |
--------------------------------------------------------

339. 339
/*+ use_hash(d) */
if joining into "d"...
use a hash join

340. we're not...
340

341. 341
--------------------------------------------------------
| Id | Operation | Name | Rows |
--------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 |
| 1 | MERGE JOIN | | 5 |
|* 2 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 |
| 3 | INDEX FULL SCAN | PK_DEPT | 4 |
|* 4 | SORT JOIN | | 14 |
| 5 | TABLE ACCESS FULL | EMP | 14 |
--------------------------------------------------------

342. 342
if joining into "d"...
we must be starting with "e"

343. 343
SQL> select /*+ leading(e) use_hash(d) */ *
2 from emp e,
3 dept d
4 where e.deptno = d.deptno
5 and d.dname = 'SALES';
---------------------------------------------------
| Id | Operation | Name | Rows | Bytes |
---------------------------------------------------
| 0 | SELECT STATEMENT | | 5 | 285 |
|* 1 | HASH JOIN | | 5 | 285 |
| 2 | TABLE ACCESS FULL| EMP | 14 | 518 |
|* 3 | TABLE ACCESS FULL| DEPT | 1 | 20 |
---------------------------------------------------

344. not enough hints
344

345. 345
"hints are like violence…
if they do not work, use more"

346. 346
SQL> select /*+ leading(e d b) use_hash(d) use_hash(b) */ *
2 from emp e,
3 dept d,
4 bonus b
5 where e.deptno = d.deptno
6 and d.dname = 'SALES'
7 and e.ename = b.ename;
---------------------------------------------
| Id | Operation | Name | Rows |
---------------------------------------------
| 0 | SELECT STATEMENT | | 1 |
|* 1 | HASH JOIN | | 1 |
|* 2 | HASH JOIN | | 5 |
| 3 | TABLE ACCESS FULL| EMP | 14 |
|* 4 | TABLE ACCESS FULL| DEPT | 1 |
| 5 | TABLE ACCESS FULL | BONUS | 1 |
---------------------------------------------

347. 347
SQL> select /*+ leading(e d b) use_hash(d) use_hash(b) */ *
2 from emp e,
3 dept d,
4 bonus b
5 where e.deptno = d.deptno
6 and d.dname = 'SALES'
7 and e.ename = b.ename;
---------------------------------------------
| Id | Operation | Name | Rows |
---------------------------------------------
| 0 | SELECT STATEMENT | | 1 |
|* 1 | HASH JOIN | | 1 |
| 2 | TABLE ACCESS FULL | BONUS | 1 |
|* 3 | HASH JOIN | | 5 |
| 4 | TABLE ACCESS FULL| EMP | 14 |
|* 5 | TABLE ACCESS FULL| DEPT | 1 |
---------------------------------------------

348. 348
---------------------------------------------
| Id | Operation | Name | Rows |
---------------------------------------------
| 0 | SELECT STATEMENT | | 1 |
|* 1 | HASH JOIN | | 1 |
|* 2 | HASH JOIN | | 5 |
| 3 | TABLE ACCESS FULL| EMP | 14 |
|* 4 | TABLE ACCESS FULL| DEPT | 1 |
| 5 | TABLE ACCESS FULL | BONUS | 1 |
---------------------------------------------
---------------------------------------------
| Id | Operation | Name | Rows |
---------------------------------------------
| 0 | SELECT STATEMENT | | 1 |
|* 1 | HASH JOIN | | 1 |
| 2 | TABLE ACCESS FULL | BONUS | 1 |
|* 3 | HASH JOIN | | 5 |
| 4 | TABLE ACCESS FULL| EMP | 14 |
|* 5 | TABLE ACCESS FULL| DEPT | 1 |
---------------------------------------------

349. join inputs
349

350. 350
SQL> select /*+ leading(e d b)
2 use_hash(d)
3 use_hash(b)
4 no_swap_join_inputs(b)
5 */
6 *
7 from emp e,
8 dept d,
9 bonus b
10 where e.deptno = d.deptno
11 and d.dname = 'SALES'
12 and e.ename = b.ename;

351. problem ...
351

352. 352
/*+ no_swap_join_inputs (b) */

353. option 1
353

354. fully specify hints
354

355. 355
SQL> SELECT *
2 from table(dbms_xplan.display(.... ,
format=>'typical +OUTLINE))
/*+ BEGIN_OUTLINE_DATA
USE_HASH(@"SEL$1" "B"@"SEL$1")
USE_HASH(@"SEL$1" "D"@"SEL$1")
LEADING(@"SEL$1" "E"@"SEL$1" "D"@"SEL$1" "B"@"SEL$1")
FULL(@"SEL$1" "B"@"SEL$1")
FULL(@"SEL$1" "D"@"SEL$1")
FULL(@"SEL$1" "E"@"SEL$1")
OUTLINE_LEAF(@"SEL$1")
ALL_ROWS
DB_VERSION('11.2.0.2')
OPTIMIZER_FEATURES_ENABLE('11.2.0.2')
IGNORE_OPTIM_EMBEDDED_HINTS
END_OUTLINE_DATA
*/ Ack: M.Colgan
swap still possible !

356. option 2
356

357. sql baseline
357

358. just hints … better in 12c
358

359. add / remove indexes
359

360. side effects
360

361. 361
structural change

362. "an index will fix it..."
362

363. 363
SQL> select *
2 from SALES
3 where SALES_DATE > ...

364. 364

365. 365
SQL> create index SALES_IX
2 on SALES( SALES_DATE );
Index created.

366. 366
SQL> explain plan for
2 select * from SALES
3 where sales_date > ...;
--------------------------------------------------------
| Id | Operation | Name | Rows |
--------------------------------------------------------
| 0 | SELECT STATEMENT | | 950 |
| 1 | TABLE ACCESS BY INDEX ROWID| SALES | 950 |
|* 2 | INDEX RANGE SCAN | SALES_IX | 950 |
--------------------------------------------------------

367. 367

368. 368

369. 369
your query

370. 370
everyone elses queries

371. 371
real example

372. 372
SQL> create table T
2 as select * from all_objects;
Table created.
SQL> create index OBJ_IX on T ( OBJECT_ID);
Index created.
SQL> analyze table T estimate statistics;
Table analyzed.

373. 373
SQL> set autotrace traceonly explain
SQL> select * from T
2 where OWNER = 'SCOTT'
3 and created > sysdate - 1
4 /
---------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
---------------------------------------------------------------
| 0 | SELECT STATEMENT | | 6 | 546 | 281 (1)|
|* 1 | TABLE ACCESS FULL| T | 6 | 546 | 281 (1)|
---------------------------------------------------------------

374. 374
“Can I index OWNER..”

375. 375
SQL> create index NEW_IX on T ( owner);
Index created.
SQL> select * from T
2 where OWNER = 'SCOTT'
3 and created > sysdate - 1;
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 6 | 546 | 122 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| T | 6 | 546 | 122 (0)|
|* 2 | INDEX RANGE SCAN | NEW_IX | 4107 | | 10 (0)|
---------------------------------------------------------------------------

376. 376
existing code ?

377. 377
before the new index

378. 378
SQL> set autotrace traceonly explain
SQL> select * from T
2 where OWNER = 'SYS'
3 and OBJECT_ID between 10 and 8000
4 /
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 462 | 42042 | 143 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| T | 462 | 42042 | 143 (0)|
|* 2 | INDEX RANGE SCAN | OBJ_IX | 7851 | | 20 (0)|
---------------------------------------------------------------------------

379. 379
SQL> set autotrace traceonly stat
SQL> select * from T
2 where owner = 'SYS'
3 and object_id between 10 and 8000
4 /
4967 rows selected.
Statistics
-----------------------------------------------------
0 recursive calls
0 db block gets
784 consistent gets
15 physical reads

380. 380
after the new index

381. 381
SQL> select * from T
2 where owner = 'SYS'
3 and object_id between 10 and 8000
4 /
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 462 | 42042 | 122 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| T | 462 | 42042 | 122 (0)|
|* 2 | INDEX RANGE SCAN | NEW_IX | 4105 | | 10 (0)|
---------------------------------------------------------------------------
changed !

382. 382
SQL> set autotrace traceonly stat
SQL> select * from T
2 where owner = 'SYS'
3 and object_id between 10 and 8000
4 /
4967 rows selected.
Statistics
------------------------------------------------------
0 recursive calls
0 db block gets
1522 consistent gets
62 physical reads

383. 383
invisible indexesconsider

384. 384
SQL> alter index OWN_IX invisible;
Index altered.

385. 385
SQL> alter session set
2 optimizer_use_invisible_indexes = true;
Session altered.
SQL> [MY QUERY]
SQL> alter session set
2 optimizer_use_invisible_indexes = false;
Session altered.

386. wrap up
386

387. if you are tuning SQL ...
387
... you are failing

388. tuning the user experience
388

389. 389
find
stop
side effects
cure

390. 390

391. ORA-03113
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