db2 performance primer baltimore/washington db2 users group december 10, 2003 michael murray senior...

DB2 Performance Primer

Baltimore/Washington DB2 Users Group

December 10, 2003

Michael MurraySenior Consultant

[email protected]

Presentation Overview

How Does DB2 Get Data? Index Considerations Tablespace Considerations Tune the SQL to Get the Biggest Bang

for your Buck Access Paths – What are the Choices?

DB2 SubsystemDatabase

Tablespace

Table

Page

Page

Row

Indexspace

Index

Page

Page

What is a Page?

4K page, maximum number of data bytes on the page 4,074. Maximum row size 4,056. Row size greater than 2,020 bytes will end up with just one row per page.

4K

8K

16K

32K

GETPAGE

Physical I/O

Your Data

Row Limits

PSID – page set identifier

DBM1 Address Space

SQL, DDL, DML, DCL Optimization Data Manager Relational Data System Buffer Manager Sort Pool EDM Pool RID Pool Bind/Rebind IRLM Interaction

Locking IRLM

Directory Catalog

WorkFile User Data

DSNDB01 DSNDB06

DSNDB07

Database ServicesDBM1

SQL

stored procedures

DB2 Stogroups

STOGROUP GPRVVOL

Volume B2RP03

Volume B2RP02

Volume B2RP01

CREATE STOGROUP GSMSVOL VOLUMES(“*”) VCAT S0;

CREATE STOGROUP GPRVVOL VOLUMES(B2RP01 ,B2RP02 ,B2RP03) VCAT P0;

Non-SMS User Managed Stogroup

SMS Managed Stogroup

SMS Allocations

indexspacevolume PBP2

Storage Group I

cache

indexspacevolume PBP8

cache

tablespacevolume PB34

Storage Group T

cache

tablespacevolume PBL8

cache

ACS Routines

(4th node is NOT X or I) (4th node is X or I)

Tablespace or Indexspace Allocations (Create, Extent Allocation, Load, Reorg)

DB2

SMS

Buffer Pool Strategy

DSNDB07DSNDB01DSNDB06

BP0 BP7

Default Tablespace

BP48

Default Indexspace

BP49

CRM Indexes

BP5

CRM Tablespaces

BP8

ERP Indexes

BP3

ERP Tablespaces

BP6

Critical Path Indexes

BP1

Critical Path Tablespace

BP2

DSNDB04

BP4

Other Indexes

BP9

Other Tablespaces

BP10

32K Tablespaces

BP32K

Random Tablespaces

BP12

Buffer Manager

indexspace

tablespace

Hiperpool

Group Buffer Pool

BUFFER POOL DATA MANAGER

Relational Data System

STAGE 1 PREDICATES

STAGE 2 PREDICATES

sargableindexableGet Page Request

Physical I/O

(page not found)

(page not found)

(page not found)

(page fou

nd

)

(page fou

nd

)

cache

cache

DB2’s Work File Explained

DATA MANAGER

Relational Data System

STAGE 1 PREDICATES

STAGE 2 PREDICATES

sargableindexable

Filtered Result Set

DSNDB07

SORT required

CREATE INDEX DEFER NO

•No matching index•DISTINCT•ORDER BY•UNION•GROUP BY•Some Joins

SORT POOL

3. sort columns

1. selected columns2. calc/derived values

key columns, RIDs

BP7

sort assist hardware

Sort assist hardware?

Index Considerations

Clustering Vs. Non Clustering Unique Vs. Duplicate Piecesize with NPI’s Uniqueness, Performance,

RI, Sorting Table Size Minimize I/O

1 2 5 7 1015

PRT B PRT L PRT M SG M/L SG S C

# Indexes

Index Limits based on # of pages? What's the I/O rate per page? Is this even realistic?

TS Type Number PagesPartitioned big > 5,000,000Partitioned large < 5,000,000

> 200,000Partitioned medium < 200,000

> 5,000Segmented medium - large > 5,000

< 500,000Segmented small < 5,000Code Tables –Segmented or Partitioned

< 200

Peaks > 13,999 Feet Located in US

Indexes: Clustered Index on: Elevation (desc), State, Peak Name Non-Clustered Index on: Peak Name Unique PK Index on: Latitude, Longitude

Peak Name State Elevation Latitude Longitude RatingMount McKinley AK 20320 630410N 1510013W VERY DIFFICULT

Mount Bear AK 14831 611702N 1410832W MODERATE

Mount Whitney CA 14494 363438N 1181733W MODERATE

Mount Harvard CO 14420 385528N 1061912W EASY

Mount Rainier WA 14410 465110N 1214531W DIFFICULT

Goal of indexes is to minimize I/O

Elevation (desc)

State Peak Name

ROOT Page

CLUSTERED INDEX Page 552

14831 AK Mount Bear

14420 CO Mount Harvard

p. 501, 2

p. 502, 2

LEAF & DATA Page

Page 553

14270 CO Grays Peak

14196 CO Mount Yale p. 504, 2

p. 503, 2

Page 554

14110 CO Pikes Peak

14059 CO Sunlight Peak

p. 505, 2

Page 555

14037 CO Little Bear Peak

14000 CA Thunderbolt Peak

p. 507, 2

NON-LEAF Page

Page 717

14420 CO Mount Harvard

14196 CO Mount Yale

14059 CO Sunlight Peak

14000 CA Thunderbolt Peak

p. 553, 2

p. 554, 2

p. 552, 2

p. 508, 2

20320 AK Mount McKinley …

14831 AK Mount Bear …

Page 502

14494 CA Mount Whitney …

14420 CO Mount Harvard …

Page 503

14410 WA Mount Rainier …

14270 CO Grays Peak …

Page 504

14255 CO Longs Peak …

14196 CO Mount Yale …

Page 505

14172 CO Mount Bross …

14110 CO Pikes Peak …

Page 506

14080 CA Starlight Peak …

14059 CO Sunlight Peak …

Page 507

14058 CA Split Mountain …

14037 CO Little Bear Peak …

Page 508

14000 CA Thunderbolt Peak …

Page 501

14005 CO Mount o/t Holy Cross …

p. 555, 2

p. 506, 2

Peak Name p. 401, 2

Page 301

Little Bear Peak

Mount Bear p. 402, 2

ROOT Page

NON-LEAF Page

LEAF Page

NON-CLUSTERED INDEX 20320 AK Mount McKinley …


Page 502



Page 503



Page 504



Page 505



Page 506



Page 507



Page 508



DATA Page

Page 501

p. 403, 2

Page 302

Mount Harvard

Mount o/t Holy Cross p. 404, 2

p. 405, 2

Page 303

Mount Whitney

Pikes Peak p. 406, 2

p. 407, 2

Page 304

Starlight Peak

Thunderbolt Peak p. 408, 2

p. 301, 2

Page 201

Mount Bear


p. 303, 2

Page 202

Pikes Peak


p. 201, 2

Page 101

Mount o/t Holy Cross


p. 503, 2

Page 401

Grays Peak

Little Bear Peak p. 507, 2

p. 504, 1

Page 402

Longs Peak

Mount Bear p. 501, 2

p. 505, 1

Page 403

Mount Bross

Mount Harvard p. 502, 2

p. 501, 1

Page 404

Mount McKinley


p. 503, 1

Page 405

Mount Rainier

Mount Whitney p. 502, 1

p. 504, 2

Page 406

Mount Yale

Pikes Peak p. 505, 2

p. 507, 1

Page 407

Split Mountain

Starlight Peak p. 506, 1

p. 506, 2

Page 408

Sunlight Peak

Thunderbolt Peak p. 508, 2NON-LEAF Page

p. 461, 2

Page 331

370116N 1182520W

370539N 1183124W p. 462, 2

ROOT Page

NON-LEAF Page

LEAF Page

PRIMARY NON-CLUSTERED INDEX 20320 AK Mount McKinley …


Page 502



Page 503



Page 504



Page 505



Page 506



Page 507



Page 508



DATA Page

Page 501

LatitudeLongitude

p. 463, 2

Page 332

373738N 1073543W

385039N 1061848W p. 464, 2

p. 465, 2

Page 333

392007N 1060625W

393802N 1054901W p. 466, 2

p. 467, 2

Page 334

465110N 1214531W

630410N 1510013W p. 468, 2

p. 331, 2

Page 281

370539N 1183124W

385039N 1061848W p. 332, 2

p. 333, 2

Page 282

393802N 1054901W

630410N 1510013W p. 334, 2

p. 281, 2

Page 101

385039N 1061848W

630410N 1510013W p. 282, 2

p. 502, 1

Page 461

363438N 1181733W

370116N 1182520W p. 507, 1

p. 506, 1

Page 462

370539N 1183119W

370539N 1183124W p. 508, 2

p. 507, 2

Page 463

373400N 1052948W

373738N 1073543W p. 506, 2

p. 505, 2

Page 464

385026N 1050238W

385039N 1061848W p. 504, 2

p. 502, 2

Page 465

385528N 1061912W

392007N 1060625W p. 505, 1

p. 508, 1

Page 466

392805N 1062845W

393802N 1054901W p. 503, 2

p. 504, 1

Page 467

401517N 1053655W

465110N 1214531W p. 503, 1

p. 501, 2

Page 468

611702N 1410832W

630410N 1510013W p. 501, 1NON-LEAF Page

Adding Columns to an Index

Improves filtering Provides index only access Increases matched columns Provides a sequence to avoid SORTS Increases cluster ratio Helps in index screening Is the increased RID chain length negatively

impacting your non-read transactions?

Index Statistics

Indexes & Stats: PK Index on: Latitude, Longitude, Climber_ID, Strt_DT NPI: Climber_ID, Summit, O2, Guided RUNSTATS TABLESPACE dbname.tsname INDEX(ALL)

1st Column & Fullkey Cardinality on all indexesTop 10 most frequent values for 1st column of all indexes

RUNSTATS INDEX owner.ixname FREQVAL xx NUMCOLS xxGive me the top 15 climbed peaks (FREQVAL 15 NUMCOLS 2 for PK index)

LATITUDE LONGITUDE CLIMBER_ID STRT_DT END_DT TB_TIME SUMMIT O2 GUIDED630410N 1510013W CA000015 4/20/2001 5/28/2001 11:00 YES YES NO630410N 1510013W CA000015 2/11/2000 3/13/2000 10:00 NO NO YES630410N 1510013W CE000008 2/7/2000 3/22/2000 12:00 YES YES NO630410N 1510013W CE000008 3/3/1999 4/16/1999 13:00 YES YES YES630410N 1510013W CE000008 1/14/1998 3/14/1998 15:30 NO YES YES630410N 1510013W CJ000033 3/17/2002 5/13/2002 14:30 YES NO NO630410N 1510013W CJ000033 12/19/2000 2/14/2001 15:00 NO YES YES630410N 1510013W CR000039 2/14/2002 4/9/2002 13:30 YES NO NO630410N 1510013W CR000039 3/30/2001 5/12/2001 14:00 YES NO YES630410N 1510013W CR000039 1/7/1999 3/10/1999 13:00 NO NO NO

PEAKS CLIMBED TABLE

SELECT CLIMBER_ID, LATITUDE, LONGITUDE, O2, GUIDED FROM PEAKS_CLIMBEDWHERE CLIMBER_ID = ‘CE000008’ AND SUMMIT = ‘YES’

ORDER BY O2, GUIDED WITH UR;

SORT Required?

Colvalue CardF FrequencyFAK 2 0.1250CA 4 0.2500CO 9 0.5625WA 1 0.0625

SELECT PEAKNAME FROM PEAKS WHERE STATE = ‘CO’;



Page 502



Page 503



Page 504



Page 505



Page 506



Page 507



Page 508



Page 501

p. 501, 1

Page 307

AK 20320

p. 501, 2AK 14831

p. 502, 1

Page 308

CA 14494

p. 506, 1CA 14080

p. 507, 1

Page 309

CA 14058

p. 508, 2CA 14000

p. 502, 2

Page 310

CO 14420

p. 503, 2CO 14270

p. 504, 1

Page 311

CO 14255

p. 504, 2CO 14196

p. 505, 1

Page 312

CO 14172

p. 505, 2CO 14110

p. 506, 2

Page 313

CO 14059

p. 507, 2CO 14037

p. 508, 1

Page 314

CO 14005

p. 503, 1WA 14410

Colvalue CardF FrequencyFAK 21 0.2308CA 15 0.1648CO 54 0.5934WA 1 0.0110

SELECT PEAKNAME FROM PEAKS WHERE STATE = ‘CO’ AND ELEVATION =‘14110’;

ColGroupColNo CardF FrequencyFAK 20320 1 0.0625AK 14831 1 0.0625CA xxxxx 1 0.0625CO xxxxx 1 0.0625WA xxxxx 1 0.0625

ColGroupColNo CardF FrequencyFAK xxxxx 1 0.0110CA xxxxx 1 0.0110CA 14162 2 0.0220CA 14000 2 0.0220CO xxxxx 1 0.0110CO 14265 2 0.0220CO 14162 2 0.0220CO 14042 2 0.0220CO 14014 2 0.0220CO 14005 2 0.0220CO 14197 3 0.0330WA 14410 1 0.0110

RUNSTATS INDEX DB2.STELEV FREQVAL 10 NUMCOLS 2

RUNSTATS TABLESPACE dbname.tsname INDEX(ALL)

DATA PageLEAF Page

CREATE INDEX DB2.STELEV ON DB2.PEAKS STATE, ELEVATION DEFER YES PIECESIZE 2G;

List Prefetch



Page 502



Page 503



Page 504



Page 505



Page 506


14059 CA Sunlight Peak …

Page 507



Page 508



Page 501

p. 502, 1

Page 461

363438N 1181733W

370116N 1182520W p. 507, 1

p. 506, 1

Page 462

370539N 1183119W

370539N 1183124W p. 508, 2

p. 507, 2

Page 463

373400N 1052948W

373738N 1073543W p. 506, 2

p. 505, 2

Page 464

385026N 1050238W

385039N 1061848W p. 504, 2

p. 502, 2

Page 465

385528N 1061912W

392007N 1060625W p. 505, 1

p. 508, 1

Page 466

392805N 1062845W

393802N 1054901W p. 503, 2

p. 504, 1

Page 467

401517N 1053655W

465110N 1214531W p. 503, 1

p. 501, 2

Page 468

611702N 1410832W

630410N 1510013W p. 501, 1

p. 502, 1

RID LIST

363438N 1181733W

370116N 1182520W p. 507, 1

p. 506, 1370539N 1183119W

370539N 1183124W p. 508, 2

373738N 1073543W p. 506, 2

p. 502, 1

Sorted RID LIST

363438N 1181733W

p. 506, 1370539N 1183119W

370539N 1183124W p. 508, 2

373738N 1073543W p. 506, 2

physical I/O order

370116N 1182520W p. 507, 1

(poor cluster ratio)

= unwanted disk head movement

SELECT ELEVATION, PEAKNAME FROM PEAKS WHERE LATITUDE IN (‘363438N’,’370116N’,’370539N’,’373738N’)

Tablespace TypesSegmented Tablespace - 3 table example

Segmented Tablespace - 1 table example

Spacemap keeps track of segments (pages) by table. Spacemap page in a segmented tablespace helps when a program deletes without a where clause by marking those segments logically deleted. Spacemap page also makes segments tied to dropped tables accessible. Segsize between 4-64 increasing in increments of 4. See recommendations in notes section.

Simple Tablespace - 1 table example

Simple Tablespaces can have multiple tables; however, rows can be intermingled. Use with caution on small static read only tables.

Partitioned Tablespace - NUMPARTS 18

Partitioned tablespaces allow only 1 table. Maximum number of partitions 254. Above 64 considered Large.

Table Space Scans

Sequential I/O

Random I/O

SELECT PEAKNAME FROM PEAKS ORDER BY RATING;

SELECT PEAKNAME FROM PEAKS WHERE STATE = ‘CA’ AND RATING = ‘MODERATE’;

AK

CA

CO

WA

LEGEND

Buffer Manager initiates a GETPAGE request for P1 through P16.

Buffer Manager initiates a GETPAGE request for P3 and P13.

Sequential Detection



Page 502



Page 503



Page 504



Page 505



Page 506



Page 507



Page 508


Page 501

SELECT PEAKNAME FROM PEAKSWHERE STATE = ‘CO’;


p. 507p. 502 p. 503 p. 504 p. 505 p. 506 p. 508 p. 532

SELECT PEAKNAME FROM PEAKSWHERE STATE = ‘AK’;

p. 564p. 501 p. 502 p. 522 p. 542 p. 562 p. 566 p. 583

ACTIVE6 out of 8

NOT ACTIVE3 out of 8

(data access sequential = 4 out of last 8 pages are page-sequential)

1 1 1 1 1 1 24

1 20 20 20 2 2 17

p. 570

p. 630

38

47

Minimize Logging

Default column placement from data model.

Blue represents static columns that do not change once the row is created

Purple represents column grouping updated associated to daily billing transactions

Teal represents column grouping updated associated to monthly inventory transactions

Dashed box represents variable data

Adjusted column placement taking logging considerations into play.

Tuning SQL

Tuning Steps Static and Dynamic SQL Get What You Need, Not What You Want Reoptimization Explain & Optimization Hints

WHAT is “Estimate & Select Access Path with Cheapest Estimated Cost ”

Proper statistics can reduce the amount of SQL tuning required

Lackluster statistics can be a Pandora's box!– REBIND DATE < RUNSTATS DATE– RUNSTATS performed yearly– EXPLAIN(NO)

Optimizer does not use Real Time Stats for access path selection

Better filtering = fewer rows returned

Get Only What You Need

data manager

relational data system

filtered result set

GETPAGE REQUEST

BP3

sort

DBM1 Address Space

buffer manger

DSNDB07

DASD

SELECT * FROM TBL

data manager

relational data system

filtered result set

GETPAGE REQUEST

BP3

sort

buffer manger

DSNDB07

DASD

SELECT C5,C6,C7 FROM TBL

Performance, Maintenance, Control

ROLE ROLE DESCRIPTION0001 Database Administrator0002 System Programmer0003 Application Programmer0004 Data Modeler

EMP_ID ROLE PROJECT_1ST PROJECT_2ND77009134 0001 CLIENT REWRITE AGENT COMPENSATION77009134 0003 CUST RETENTION93989203 0002 AGENT COMPENSATION CUST RETENTION99080622 0004 CLIENT REWRITE CUST RETENTION

DELETE RESTRICT

IT_ROLE (parent) PROJECT_ROLE (child)

EMP_ID ROLE PROJECT_1ST PROJECT_2ND77009134 Database Administrator CLIENT REWRITE AGENT COMPENSATION77009134 Application Programmer CUST RETENTION93989203 System Programmer AGENT COMPENSATION CUST RETENTION

PROJECT_ROLE (column constraint)

. DDL change to add a new role (data modeler)

. DBA involvement needed for the table change

. Better Performance, Tighter Control

. Insert new row to add a new role (data modeler)

. User, Programmer, or DBA can insert the row

. Slower performance

(DB2 RI)

Getting Your Way

REOPT(VARS) – – Useful when DB2’s estimate of qualifying

rows would benefit if the real host variable was available to the optimizer at execution

– Evaluate data values at runtime– Limit parts for partition scans– Influence join sequence

Reoptimization is done at open cursor Static SQL – package level. Consider

isolating/consolidating your reopt statements to a few static packages.

Dynamic SQL – statement level. More granular and easier to invoke on a smaller scale.

IFCID 0022 – Did you get a better access path?

Would static SQL benefit from being dynamic and taking advantage of dynamic cache?

Sounds Great! Difficult to implement and maintain.

DSNZPARM change to activate Programmers should add QUERYNO to their

code. How are you going to name and manage your

opthints? CHAR(8) After code has been bound with explain yes,

need to update plan_table rows to add a OPTHINT.

To return to the good access path you have previously established, you would rebind your package with OPTHINT(‘ohstring’).

Verify hint is in use! SQL code +394, HINT_USED column of PLAN_TABLE, or Query special register: CURRENT OPTIMIZATION HINT

REOPTIMIZATION OPTIMIZATION HINTS

Access Paths

More on QUERYNO = 103; DB2’s Choices Understanding Predicates Small Tables in Memory Plan_Table Considerations

ACCESSTYPE in Plan Table

RID = record identifier

ACCESNAME

R Table space scan, segmented tablespace

Table space scan, non-segmented tablespace

Table space scan, partition scan (scanning limited parts)

I mc=0

Non-matching index scan (scan of index leaf pages)

One fetch index access (min/max)

Perform 1 matching index scan for each value in (LIST)

I1

MATCHCOLS

PREFETCHN

M Multiple index scan (same index twice or two different indexes)

MX

Qualifying RIDs for each index used in multiple index scan

MI AND predicate, intersection of the qualifying RIDs from each index

MU OR predicate, union of the qualifying RIDs from each indexOPTHINT

INDEXONLY

PRIMARY_ACCESSTYPE

D Direct row access via ROWID (page#, rid). One getpage!

I mc>0

Matching index scan (using IX structure - root, non-leaf, leaf)

Predicates

Know Your Predicates– Indexable, matching predicates on index key columns

– Stage 1, not picked as matching but still refer to index columns (index screening)

– Stage 1, operating on a data page

– Stage 2, everything else

Application Programming and SQL GuideTable 68, page 629, DB2 for OS/390 and z/OS V7

Peak Name State Elevation Latitude Longitude Rating

Mount McKinley AK 20320 630410N 1510013W VERY DIFFICULTMount Bear AK 14831 611702N 1410832W MODERATEMount Whitney CA 14494 363438N 1181733W MODERATEMount Harvard CO 14420 385528N 1061912W EASYMount Rainier WA 14410 465110N 1214531W DIFFICULTGrays Peak CO 14270 393802N 1054901W EASYLongs Peak CO 14255 401517N 1053655W MODERATEMount Yale CO 14196 385039N 1061848W EASYMount Bross CO 14172 392007N 1060625W EASYPikes Peak CO 14110 385026N 1050238W EASYStarlight Peak CA 14080 370539N 1183119W EASYSunlight Peak CO 14059 373738N 1073543W MODERATESplit Mountain CA 14058 370116N 1182520W MODERATELittle Bear Peak CO 14037 373400N 1052948W MODERATEMount o/t Holy Cross CO 14005 392805N 1062845W EASY MODERATEThunderbolt Peak CA 14000 370542N 1183124W EASY

PEAKS Table

Questions...

db2 performance primer baltimore/washington db2 users group december 10, 2003 michael murray senior...

Documents

leaf page leaf page

cache slide

root page

mount harvard page

mount yale page

io slide

page request physical

grays peak page