db2 performance primer_new

7/30/2019 DB2 Performance Primer_New

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DB2 Performance Primer

Baltimore/Washington DB2 Users Group

December 10, 2003

Michael Murray

Senior Consultant

[email protected]


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Presentation Overview

How Does DB2 Get Data? Index Considerations

Tablespace Considerations

Tune the SQL to Get the Biggest Bangfor your Buck

Access Paths What are the Choices?


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DB2 SubsystemDatabase

Tablespace

Table

Page

Page

Row

Indexspace

Index

Page

Page


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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

PSIDpage set identifier


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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


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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


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SMS Allocations

indexspace

volume PBP2

Storage Group I

cache

indexspacevolume PBP8

cache

tablespace

volume 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


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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

RandomTablespaces

BP12


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DB2s Work File Explained

DATA MANAGER

Relational Data System

STAGE 1 PREDICATES

STAGE 2 PREDICATES

sargableindexable

Filtered Result Set

DSNDB07

SORTrequired

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

hardwareSort assist

hardware?


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Index Considerations

Clustering Vs. Non Clustering

Unique Vs. Duplicate

Piecesize with NPIs

Uniqueness, Performance,RI, Sorting

Table Size

Minimize I/O

1 25 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 Pages

Partitioned big > 5,000,000

Partitioned large < 5,000,000

> 200,000

Partitioned medium < 200,000

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

< 500,000

Segmented small < 5,000

Code Tables

Segmented or Partitioned

< 200


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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 Rating

Mount 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


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Elevation (desc)

State

Peak Name

ROOT Page

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


14196 CO Mount Yale



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


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


Page 507

14058 CA Split Mountain


Page 508


Page 501

14005 CO Mount o/t Holy Cross

p. 555, 2

p. 506, 2


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Peak Namep. 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 14831 AK Mount Bear

Page 502



Page 503


14270 CO Grays Peak

Page 504

14255 CO Longs Peak

14196 CO Mount Yale

Page 505


14110 CO Pikes Peak

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, 2Page 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


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p. 461, 2

Page 331

370116N 1182520W

370539N 1183124W p. 462, 2

ROOT Page

NON-LEAF Page

LEAF Page

PRIMARY NON-CLUSTERED INDEX20320 AK Mount McKinley

14831 AK Mount Bear

Page 502



Page 503


14270 CO Grays Peak

Page 504

14255 CO Longs Peak

14196 CO Mount Yale

Page 505


14110 CO Pikes Peak

Page 506



Page 507



Page 508



DATA Page

Page 501

Latitude

Longitude

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 1054901W630410N 1510013W p. 334, 2

p. 281, 2Page 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


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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?


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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 GUIDED

630410N 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 YES

630410N 1510013W CE000008 2/7/2000 3/22/2000 12:00 YES YES NO

630410N 1510013W CE000008 3/3/1999 4/16/1999 13:00 YES YES YES

630410N 1510013W CE000008 1/14/1998 3/14/1998 15:30 NO YES YES

630410N 1510013W CJ000033 3/17/2002 5/13/2002 14:30 YES NO NO

630410N 1510013W CJ000033 12/19/2000 2/14/2001 15:00 NO YES YES

630410N 1510013W CR000039 2/14/2002 4/9/2002 13:30 YES NO NO

630410N 1510013W CR000039 3/30/2001 5/12/2001 14:00 YES NO YES

630410N 1510013W CR000039 1/7/1999 3/10/1999 13:00 NO NO NO

PEAKS CLIMBED TABLE

SELECT CLIMBER_ID, LATITUDE,

LONGITUDE, O2, GUIDED FROMPEAKS_CLIMBED

WHERE CLIMBER_ID = CE000008 AND

SUMMIT = YES

ORDER BY O2, GUIDED WITH UR;

SORT

Required?


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Colvalue CardF FrequencyF

AK 2 0.1250

CA 4 0.2500

CO 9 0.5625

WA 1 0.0625

SELECT PEAKNAME FROM PEAKS

WHERE STATE = CO;


14831 AK Mount Bear

Page 502



Page 503


14270 CO Grays Peak

Page 504

14255 CO Longs Peak

14196 CO Mount Yale

Page 505


14110 CO Pikes Peak

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 FrequencyF

AK 21 0.2308

CA 15 0.1648CO 54 0.5934

WA 1 0.0110


WHERE STATE = CO AND

ELEVATION =14110;

ColGroupColNo CardF FrequencyF

AK 20320 1 0.0625

AK 14831 1 0.0625

CA xxxxx 1 0.0625

CO xxxxx 1 0.0625

WA xxxxx 1 0.0625

ColGroupColNo CardF FrequencyF

AK xxxxx 1 0.0110CA xxxxx 1 0.0110

CA 14162 2 0.0220

CA 14000 2 0.0220

CO xxxxx 1 0.0110

CO 14265 2 0.0220

CO 14162 2 0.0220

CO 14042 2 0.0220

CO 14014 2 0.0220

CO 14005 2 0.0220

CO 14197 3 0.0330

WA 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;


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List Prefetch


14831 AK Mount Bear

Page 50214494 CA Mount Whitney


Page 503


14270 CO Grays Peak

Page 504

14255 CO Longs Peak 14196 CO Mount Yale

Page 505


14110 CO Pikes Peak

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, 1Page 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 1050238W385039N 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

physicalI/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)


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Tablespace Types

Segmented 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 thosesegments 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.

T bl S S


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Table Space Scans

Sequential I/O

Random I/O


ORDER BY RATING;


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.

S ti l D t ti


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Sequential Detection


14831 AK Mount Bear

Page 50214494 CA Mount Whitney


Page 503


14270 CO Grays Peak

Page 504

14255 CO Longs Peak

14196 CO Mount Yale

Page 505


14110 CO Pikes Peak

Page 506



Page 507



Page 508


Page 501

SELECT PEAKNAME

FROM PEAKS

WHERE STATE = CO;


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

SELECT PEAKNAME

FROM PEAKS

WHERE STATE = AK;

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

ACTIVE

6 out of 8

NOT

ACTIVE

3 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


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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.

T i SQL


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Tuning SQL

Tuning Steps

Static and Dynamic SQL

Get What You Need, Not What You Want

Reoptimization

Explain & Optimization Hints


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WHAT is Estimate & Select Access Path with Cheapest Estimated Cost

Proper statistics can reduce the amount of SQLtuning 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


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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

P f M i t C t l


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Performance, Maintenance, Control

ROLE ROLE DESCRIPTION0001 Database Ad ministrator

0002 System Programmer

0003 Application Programmer

0004 Data Modeler

EMP_ID ROLE PROJECT_1ST PROJECT_2ND77009134 0001 CLIENT REWRITE AGENT COMPENSATION

77009134 0003 CUST RETENTION

93989203 0002 AGENT COMPENSATION CUST RETENTION

99080622 0004 CLIENT REWRITE CUST RETENTION

DELETE RESTRICT

IT_ROLE (parent) PROJECT_ROLE (child)

EMP_ID ROLE PROJECT_1ST PROJECT_2ND

77009134 Database Administrator CLIENT REWRITE AGENT COMPENSATION

77009134 Application Programmer CUST RETENTION

93989203 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)


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Getting Your Way

REOPT(VARS) Useful when DB2s estimate of qualifying

rows would benefit if the real host variablewas 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 statementsto a few static packages.

Dynamic SQL statement level. Moregranular and easier to invoke on a smallerscale.

IFCID 0022 Did you get a better accesspath?

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

Sounds Great! Difficult to implement andmaintain.

DSNZPARM change to activate

Programmers should add QUERYNO to theircode.

How are you going to name and manage youropthints? CHAR(8)

After code has been bound with explain yes,need to update plan_table rows to add aOPTHINT.

To return to the good access path you havepreviously established, you would rebind yourpackage with OPTHINT(ohstring).

Verify hint is in use! SQL code +394,HINT_USED column of PLAN_TABLE, orQuery special register: CURRENT

OPTIMIZATION HINT

REOPTIMIZATION OPTIMIZATION HINTS

A P h


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Access Paths

More on QUERYNO = 103;

DB2s Choices

Understanding Predicates

Small Tables in Memory

Plan_Table Considerations

ACCESSTYPE in Plan Table


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ACCESSTYPE in Plan Table

RID = record identifier

ACCESNAME

R Table space scan, segmented tablespaceTable 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)

I1MATCHCOLS

PREFETCHNM Multiple index scan (same index twice or two different indexes)MX Qualifying RIDs for each index used in multiple index scanMI AND predicate, intersection of the qualifying RIDs from each indexMU OR predicate, union of the qualifying RIDs from each index OPTHINT

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)

P di t


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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

PEAKS T bl


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Peak Name State Elevation Latitude Longitude Rating

Mount 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

Grays Peak CO 14270 393802N 1054901W EASY

Longs Peak CO 14255 401517N 1053655W MODERATE

Mount Yale CO 14196 385039N 1061848W EASY

Mount Bross CO 14172 392007N 1060625W EASY

Pikes Peak CO 14110 385026N 1050238W EASY

Starlight Peak CA 14080 370539N 1183119W EASY

Sunlight Peak CO 14059 373738N 1073543W MODERATE

Split Mountain CA 14058 370116N 1182520W MODERATE

Little Bear Peak CO 14037 373400N 1052948W MODERATE

Mount o/t Holy Cross CO 14005 392805N 1062845W EASY MODERATE

Thunderbolt Peak CA 14000 370542N 1183124W EASY

PEAKS Table

Questions


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Questions...

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