Implications
of Setting
Oracle9iR2’s
Statistical Collection Level
James F. Koopmann
Co-Founder & Chief Architect
dbDoctor Inc.
Colorado
www.dbdoctor.net
Jkoopmann@dbdoctor.net
james_koopmann@yahoo.com
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
1
Content
1. Why statistics are important, Who Needs them ?
2. What is the new method of setting up statistical collections.
3. How you can see what your settings are currently
4. How you can change your settings.
5. A test scenario for determining system impact of collecting statistics.
6. SPFILE Usage
7. Various Examples
8. Information exchange
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
2
Why Do We Care About Statistics, Who Needs Them
TRUE or FALSE
Collecting Statistics
will
make my
database run faster
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
3
Why Do We Care About Statistics, Who Needs Them
TRUE or FALSE
Collecting Statistics
will in the future
make my
database run faster
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
4
Why Do We Care About Statistics, Who Needs Them
It’s All About Problem Detection
What Are Problems?
1.
Problems are anything that causes us, or our database discomfort.
2.
Problems are anything that occurs in relation to the database that is a deviation from the norm.
A few questions to ask yourself
1.
If a batch job runs one hour longer than normal, is it a problem if no one knows about it?
2.
If you take down the listener and no one tries to connect to your database, is it a problem?
3.
If the database is down and isn’t being used, is it a problem?
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
5
Why Do We Care About Statistics, Who Needs Them
It’s All About Problem Detection
Lazy man method of finding problems
a. You can find problems by snooping around in the database
b. You can find problems from user complaints
c. You can find problems when the system crashes or is unavailable
d. Use of rudimentary statistics (wall clock, system feel)
Intelligent method of finding problems
a. Realizes that aggregate statistics aren’t enough
b. Has a method of detecting change, where have I been and where am I going.
c. Hard and fast statistics (V$ tables, iostat, vmstat, …).
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
6
Why Do We Care About Statistics, Who Needs Them
The Problem with Problems
1.
We have to fix them
2.
Mistakes are common and we can’t rid ourselves of them
3.
a.
Be compassionate
b.
Be humble
Receive new ideas with an open but analytical mind
a.
Research for yourself
b.
Have reliable sources
4. Validate what you have heard or read
a.
don’t take for granted everything you read or hear
b.
“Your mileage may vary”
5. Accept only after validation
a.
This is the best part, you can count on what you have learned
b.
You can use new knowledge to validate other scenarios
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
7
New to Oracle9iR2
STATISTICS_LEVEL
Controls Collection of Advisories and Statistics
1.
2.
3.
4.
5.
6.
7.
8.
Shared Pool Advice
Buffer Cache Advice
PGA Advice
MTTR Advice
Segment Level Statistics
Timed Statistics
Timed OS Statistics
Plan Execution Statistics
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
8
New to Oracle9iR2
STATISTICS_LEVEL is a Dynamic Parameter
DYNAMIC
Parameter can be modified using the ALTER SESSION or ALTER SYSTEM statement while an instance is
running.
Syntax we are all familiar with
ALTER SESSION SET parameter_name = value
1.
2.
Change the value of a parameter for the duration of the session.
The value of this parameter does not change for other sessions in the instance.
ALTER SYSTEM SET parameter_name = value
1.
2.
Change the value of the parameter for all current and future sessions.
Record the change in the alert.log
ALTER SYSTEM SET parameter_name = value [DEFERRED]
1.
2.
Change only applies to future sessions that will connect to the database.
Record the change in the alert.log
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
9
New to Oracle9iR2
V$STATISTICS_LEVEL
Column
STATISTICS_NAME
Values(?)
DESCRIPTION
Description
Name of the statistics/advisory.
Description of what the statistics/advisory does and
what it can be used for.
SESSION_STATUS
ENABLED|DISABLED
Status of the statistics/advisory for this session.
SYSTEM_STATUS
ENABLED|DISABLED
Status of the statistics/advisory system-wide.
ACTIVATION_LEVEL
BASIC|TYPICAL|ALL
Indicates the level of STATISTICS_LEVEL than enable
this statistics/advisory
STATISTICS_VIEW_NAME
If there is a single view externalizing this
statistics/advisory, the name of that view.If there is
no such a view, this column is empty. If there are
multiple views involved, the DESCRIPTION column should
mention the view names.
SESSION_SETTABLE
Whether this statistics/advisory can be set at the
session level.
YES|NO.
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
10
New to Oracle9iR2
V$STATISTICS_LEVEL
SQL> SELECT statistics_name, statistics_view_name, description FROM v$statistics_level
STATISTICS_NAME
STATISTICS_VIEW_NAME DESCRIPTION
------------------------- --------------------- ---------------------------------------Shared Pool Advice
V$SHARED_POOL_ADVICE Predicts the impact of different values of
shared_pool_size on elapsed parse time saved
Buffer Cache Advice
V$DB_CACHE_ADVICE
Predicts the impact of different cache sizes on
number of physical reads
PGA Advice
V$PGA_TARGET_ADVICE
Predicts the impact of different values of
pga_aggregate_target on the performance of
memory intensive SQL operators
MTTR Advice
V$MTTR_TARGET_ADVICE
Predicts the impact of different MTTR settings
on number of physical I/Os
Segment Level Statistics
V$SEGSTAT
Enables gathering of segment access statistics
Timed Statistics
Enables gathering of timed statistics
Timed OS Statistics
Enables gathering of timed operating system
statistics
Plan Execution Statistics V$SQL_PLAN_STATISTICS Enables collection of plan execution statistics
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
11
SPFILE
Is the Init.ora File Going Away ?
1. Simplified Parameter Management
2. Change in STARTUP Sequence
3. Push to Migrate from Parameter File
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
12
SPFILE
DO You Have One?
SQL> show parameter spfile
NAME
TYPE
VALUE
--------------------------- --------- -------------spfile
string
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
13
SPFILE
How Do I Get One?
Help, I Want My INIT.ORA
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
14
SPFILE
Items to Consider
•
•
•
•
•
•
Must be SYSOPER or SYSDBA to create one
Occasionally save you SPFILE
SPFILE is a binary file
SHUTDOWN / STARTUP to recognize
ORA-12547: TNS:lost contact
ALTER SYSTEM RECOGNIZE command
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
15
SPFILE
Setting a Parameter
ALTER SYSTEM SET
DEFERRED, changes the value for the parameter for sessions connecting after the statement is
issued.
SCOPE, specifies when the change will take effect.
1.
MEMORY - the change takes effect immediately but is not available after next startup
2.
SPFILE - the change is made in the server parameter file only and available after
next startup
3.
BOTH
- MEMORY + SPFILE, this is the default
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
16
SPFILE
Resetting a Parameter
ALTER SYSTEM RESET
Switch to default statistics_level
alter system set statistics_level=typical scope=memory;
alter system reset statistics_level scope=spfile sid=‘*’;
Switch timed_statistics to be under statistics_level control
alter system set timed_statistics=true scope=memory;
alter system reset timed_statistics scope=spfile sid=‘*’;
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
17
SPFILE
Setting a Parameter that is a List of Strings
alter system set control_files=
'/u01/app/oracle/oradata/saigon/control01.ctl',
'/u01/app/oracle/oradata/saigon/control02.ctl',
'/u01/app/oracle/oradata/saigon/control03.ctl'
scope=spfile;
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
18
STATISTICS_LEVEL
Dynamic Parameters
Parameter
ALTER
SESSION
ALTER
SYSTEM
ALTER
SYSTEM
…DEFERRED
STATISTICS_LEVEL
Db_cache_advice
Timed_statistics
Timed_os_statistics
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
19
STATISTICS_LEVEL
Three Settings
Statistic / Advisory
BASIC
TYPICAL
ALL
Override
SESSION
SPFILE
Shared Pool Advice
Buffer Cache Advice
db_cache_advice
PGA Advice
MTTR Advice
Segment Level Statistics
timed_statistics
Timed Statistics
Timed OS Statistics
timed_os_statistics
Plan Execution Statistics
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
20
Take a Look at Your Settings
Override Control (V$PARAMETER)
SQL> SELECT name, value, isses_modifiable,
issys_modifiable,isdefault,ismodified
FROM v$parameter
WHERE NAME IN ('statistics_level','db_cache_advice',
'timed_statistics', 'timed_os_statistics');
NAME
----------------------
statistics_level
timed_statistics
timed_os_statistics
db_cache_advice
VALUE
-------
TYPICAL
FALSE
0
OFF
ISSES_MODIFIABLE
----------------
TRUE
TRUE
TRUE
FALSE
TRUE = Default Value
(NO SPFILE entry)
FALSE = SPFILE entry
ISSYS_MODIFIABLE
----------------
IMMEDIATE
IMMEDIATE
IMMEDIATE
IMMEDIATE
ISDEFAULT
---------
ISMODIFIED
---------
TRUE
TRUE
TRUE
TRUE
FALSE
FALSE
FALSE
FALSE
FALSE
= Not Modified since startup
MODIFIED
= ALTER SESSION
SYSTEM_MOD = ALTER SYSTEM
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
21
Take a Look at Your Settings
Override Control (V$STATISTICS_LEVEL)
SQL> SELECT statistics_name, session_status, system _status
activation_level, session_settable
FROM v$statistics_level
Am I Collecting
STATISTICS
NAME
------------------------Buffer Cache Advice
MTTR Advice
PGA Advice
Segment Level Statistics
Shared Pool Advice
Timed Statistics
Plan Execution Statistics
Timed OS Statistics
SESSION
STATUS
-------ENABLED
ENABLED
ENABLED
ENABLED
ENABLED
ENABLED
DISABLED
DISABLED
SYSTEM
STATUS
-------ENABLED
ENABLED
ENABLED
ENABLED
ENABLED
ENABLED
DISABLED
DISABLED
What Level in
STATISTICS_LEVEL to
Activate
ACTIVATION
LEVEL
---------TYPICAL
TYPICAL
TYPICAL
TYPICAL
TYPICAL
TYPICAL
ALL
ALL
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
SESSION
SETTABLE
-------NO
NO
NO
NO
NO
YES
YES
YES
22
Take a Look at Your Settings
Don’t Get Confused
•
If there is an entry in SPFILE then setting STATISTICS_LEVEL will not have an impact on that
statistic or advisory.
•
Even if the setting in the SPFILE is the DEFAULT, it will still not be under the control of the
STATISTICS_LEVEL parameter.
•
When looking at v$parameter and v$statistics_level after you have made changes, you may get
confused.
•
ALTER SYSTEM command will override any ALTER SESSION command
•
RESET any parameters that you want to be controlled by the new STATISTICS_LEVEL
parameter.
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
23
Take a Look at Your Settings
Oracle Gets Confused
The setting of timed_os_statistics to anything other than 0 (zero) or 5 will switch the
SESSION_STATUS & SYSTEM_STATUS in V$STATISTICS_LEVEL to UNKNOWN
NAME
----------------------
VALUE
-------
timed_os_statistics
STATISTICS
NAME
-------------------------
Timed OS Statistics
10
ISSES_MODIFIABLE
----------------
ISSYS_MODIFIABLE
----------------
TRUE
SESSION
STATUS
--------
UNKNOWN
ISDEFAULT
---------
IMMEDIATE
SYSTEM
STATUS
---------
ACTIVATION
LEVEL
----------
UNKNOWN
ISMODIFIED
---------
FALSE
FALSE
SESSION
SETTABLE
--------
ALL
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
YES
24
Human Impact
The Most Hated Statements
1. You must set TIMED_STATISTICS to TRUE
in the parameter file.
2. I recommend using timed statistics.
3. Doing this will have a small negative effect
on system performance.
4. You will incur minimal resource overhead
5. You cannot afford to be without the information
that timed statistics provides.
6. Gathering OS statistics is very expensive.
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
25
Human Impact
Typical Responses
1. Sorry, Oracle Support does not have any specific
benchmark information.
2. Contact ___________, they may have benchmark
information.
3. Can anyone else share their input and experiences.
4.
My Technical Consultant has not seen any specific
benchmarks on this.
5. Take a look at the guide and if necessary we will try
to get some development resources
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
26
System Impact
Test Scenarios
Statistic / Advisory
Shared Pool Advice
Buffer Cache Advice
PGA Advice
BASIC
TYPICAL
Why
ALL
1. Reduce stress
associated with
statistical collection
2. Who else will help
MTTR Advice
Segment Level Statistics
3. Validate for myself
Timed Statistics
Timed OS Statistics
Plan Execution Statistics
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
27
System Impact
Basic Terminology
Throughput
User / Job
Request
(workload)
(v$sysstat)
LGWR wait for redo copy,
log file sync,
Sorts, Reads, Writes, Enqueues, Redo
activity, Buffer cache activity, Parsing,… db file sequential read,…
Resource Usage
(v$sysstat)
Wait Times
(v$system_event)
Database
Completes
Request
User
User
Decides
Queues
What to
Next
Do Next Transaction
Coffee
Break
Think
Time
Database Response Time
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
28
System Impact
Test Scenarios (workload types)
execute count, Total number of calls (user and recursive) that executed SQL statements
calls to get snapshot scn: kcmgss, Number of times a snapshot system change number (SCN) was
allocated. The SCN is allocated at the start of a transaction.
session logical reads, The sum of db_block_gets and consistent_gets.
db block gets, Number of times a CURRENT block was requested
consistent gets, Number of times a consistent read was requested for a block.
db block changes, This statistic counts the total number of changes that were part of an update or delete
operation that were made to all blocks in the SGA. This approximates total database work. It statistic
indicates the rate at which buffers are being dirtied.
user commits, Number of user commits. When a user commits a transaction, the redo generated that
reflects the changes made to database blocks must be written to disk. Commits often represent the closest
thing to a user transaction rate.
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
29
System Impact
Test Scenarios (workload types)
Statistic
BASIC
timed_statistics
TYPICAL
TYPICAL / BASIC
ALL
ALL / TYPICAL
execute count
520370
505683
(2.82%)
498753
(1.37%)
4.15%
calls to get snapshot scn:
kcmgss
703731
682467
(3.02%)
674396
(1.18%)
4.17%
1087327
1052570
(3.20%)
1041518
(1.05%)
4.21%
446278
431281
(3.36%)
427297
(0.92%)
4.25%
39405
38323
(2.75%)
37766
(1.45%)
4.16%
session logical reads
db block changes
user commits
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
ALL / BASIC
30
System Impact
Test Scenarios (wait types)
Statistic
Total Waits
Total Timeouts
Total Time Waited
BASIC
timed_statistics
TYPICAL
TYPICAL / BASIC
ALL
ALL / TYPICAL
ALL / BASIC
44451
42719
(3.90%)
42558
(.38%)
(4.26%)
39272
(3.23%)
38859
(1.05%)
(4.25%)
634
(7.04%)
655
(-3.31%)
(3.96%)
40584
682
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
31
System Impact
Test Scenarios (resource types)
Statistic
BASIC
timed_statistics
TYPICAL
redo blocks written
146059
141432
139607
3.17%
1.29%
4.42%
redo entries
224570
216854
214942
3.44%
0.88%
4.29%
68865028
66699016
65852920
3.15%
1.27%
4.37%
40685
39394
38970
3.17%
1.08%
4.22%
change write time
1238
1227
1221
0.89%
0.49%
1.37%
enqueue requests
143264
137748
137173
3.85%
0.42%
4.25%
8
33
20
-312.50%
39.39%
-150.00%
consistent changes
7162
6460
6833
9.80%
-5.77%
4.59%
physical reads
3210
2778
3116
13.46%
-12.17%
2.93%
physical writes
3297
2946
3040
10.65%
-3.19%
7.79%
parse count (total)
4818
4545
4680
5.67%
-2.97%
2.86%
sorts (memory)
1937
1830
1885
5.52%
-3.01%
2.68%
sorts (rows)
4251
4244
4243
0.16%
0.02%
0.19%
table fetch by rowid
11975
11041
11505
7.80%
-4.20%
3.92%
table scan blocks gotten
85358
82778
81920
3.02%
1.04%
4.03%
400388
386772
383741
3.40%
0.78%
4.16%
17
16
17
5.88%
-6.25%
0.00%
122229
118631
117138
2.94%
1.26%
4.17%
redo size
redo writes
enqueue waits
table scan rows gotten
table scans (long tables)
table scans (short tables)
ALL
TYPICAL / BASIC
ALL / TYPICAL
ALL / BASIC
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
32
System Impact
More Data
Give Me a Call
file:///C:/temp/Vsysstat.htm
file:///C:/temp/Vsysstat_xls.htm
file:///C:/oradoc/920doc/server.920/a96536/apc2.htm
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
33
Buffer Cache Advisory
Defined
Why:
Disk is slow, memory is fast
What:
Use to size the buffer caches
When:
Performance is bad
Where:
Populates V$DB_CACHE_ADVICE
for each buffer cache in use
(2K, 4K, 8K, 16K, 32K, KEEP, RECYCLE)
How:
db_cache_advice / statistics_level
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
34
Buffer Cache Advisory
A Tried and True Friend
Calculate Buffer Cache Hit Ratio
SQL> SELECT name, block_size,
100*(1 - (physical_reads / (db_block_gets+consistent_gets))) buffhit
FROM v$buffer_pool_statistics;
How we size the buffer cache
1.
Just issue the SQL to see the hit ratio
2.
Got smarter and diff’d between a start and end time
3.
Run a valid workload through system
4.
Come up with a ballpark estimate on size
5.
Increase buffer cache if hit ratio is low
6.
Done if hit ratio is high
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
35
Buffer Cache Advisory
Diff’d Buffer Cache Hit Ratio
SQL> SELECT b.name, b.block_size,
100*(1 - ((e.physical_reads-b.physical_reads) /
((e.db_block_gets-b.db_block_gets)+
(e.consistent_gets-b.consistent_gets)))) buffhit
FROM beg_buffer_pool_statistics b, end_buffer_pool_statistics e
WHERE b.name=e.name AND b.block_size=e.block_size;
How to diff
1.
Create table beg_buffer_pool_statistics as select * from v$buffer_pool_statistics
2.
Run workload through system
3.
Create table end_buffer_pool_statistics as select * from v$buffer_pool_statistics
4.
Issue above SQL
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
36
Buffer Cache Advisory
Use of V$DB_CACHE_ADVICE
SQL> SELECT name, block_size, size_for_estimate,
estd_physical_read_factor, estd_physical_reads
FROM V$DB_CACHE_ADVICE
WHERE advice_status = 'ON';
How to get the statistics
1.
Set db_cache_advice to ‘READY’
2.
Set db_cache_advice to ‘ON’
3.
Run a valid workload through system
4.
Issue above SQL
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
37
Buffer Cache Advisory
Output of V$DB_CACHE_ADVICE
BLOCK Cache Estd Phys
NAME
SIZE Size Read Factor
-------- ----- ----- ----------DEFAULT
8192
48
2.1133
DEFAULT
8192
96
1.7266
DEFAULT
8192
144
1.4763
DEFAULT
8192
192
1.3573
DEFAULT
8192
240
1.2801
DEFAULT
8192
288
1.2165
DEFAULT
8192
336
1.1686
DEFAULT
8192
384
1.1202
DEFAULT
8192
432
1.0877
DEFAULT
8192
480
1.0602
DEFAULT
8192
528
1.0196
DEFAULT
8192
544
1.00
1
DEFAULT
8192
576
.9765
DEFAULT
8192
624
.9392
DEFAULT
8192
672
.9216
DEFAULT
8192
720
.9013
DEFAULT
8192
768
.885
DEFAULT
8192
816
.8726
DEFAULT
8192
864
.8607
DEFAULT
8192
912
.8492
DEFAULT
8192
960
.8277
Estd Phys
Reads
---------343669940
280783364
240091867
220733606
208181172
197842182
190052917
182180544
176884743
172420984
165812231
162626093
158797352
152735392
149879874
146571255
143928671
141908868
139972381
138098490
134610328
Its all about reads
1. Don’t reduce the size of
your cache if you are
going to incur more
physical reads
CURRENT
2.
Don’t increase the size of
your cache if you are not
going to reduce the
number of reads
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
38
Comments
Concerns
Questions
Answers
Dos
Don’ts
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
39
Implications
of Setting
Oracle9iR2’s
Statistical Collection Level
James F. Koopmann
dbDoctor Inc.
Colorado
www.dbdoctor.net
Jkoopmann@dbdoctor.net
james_koopmann@yahoo.com
James F. Koopmann
Implications of Setting Oracle9iR2’s Statistics Collection Level
40