Real-Time Statistics – How to arm your DB2 for 24x7

© 2009 SOFTWARE ENGINEERING GMBH 1

Real-Time Statistics–

How to arm your DB2 for 24x7

Ulf HeinrichCentral Canadian DB2 User’s Group June 8 - 9, 2009


Overview

� Real-Time Statistics basics� Real-Time Statistics advanced� Real-Time Statistics vs. DB2 Catalog Statistics� Tips and Tricks


Real-Time Statistics (RTS) basics

What is Real-Time Statistics (RTS)?

� Collect real time statistics for table and index spaces� Existence of two DB2 tables allows easy interpretation� Statistics externalized based on certain events� Counters

The values reflect the amount of object level activity that has occurred since last COPY, REORG, RUNSTATS

� Very important!!!


What is Real-Time Statistics (RTS) ?

� V7 or later (integrated into DB2 Catalog within DB2 9)� Capture statistics in memory and periodically written to the RTS

tables� SYSIBM.(SYS)TABLESPACESTATS for tables

� One row per table space/partition� SYSIBM.(SYS)INDEXSPACESTATS for indexes

� One row per index space/partition� Tables reside in a segmented table space (� PBG)

(DSNRTSTS/SYSRTSTS)� Table spaces reside in the DSNRTSDB/DSNDB06 database



Object name Description

DSNRTSDB/DSNDB06 Database for Real-Time Statistics objects

DSNRTSTS/SYSRTSTS Table space for Real-Time Statistics objects

SYSIBM.(SYS)TABLESPACESTATS Table for statistics on table spaces and table space partitions

SYSIBM.(SYS)INDEXSPACESTATS Table for statistics on index spaces and index space partitions

SYSIBM.TABLESPACESTATS_IX Unique index on SYSIBM.(SYS)TABLESPACESTATS(columns DBID, PSID, and PARTITION)

(SYSIBM.DSNRTX01 DBID, PSID, PARTITION and INSTANCE)

SYSIBM.INDEXSPACESTATS_IX Unique index on SYSIBM.INDEXSPACESTATS(columns DBID, ISOBID, and PARTITION)

(SYSIBM.DSNRTX02 DBID, ISOBID,PARTITION and INSTANCE)



How are they activated?

RTS processing will always happen in DBM1 address space… , but externalization has to be activated

� “Enabling” RTS prior to DB2 9� Create objects via DSNTESS � Explicit START DATABASE(DSNRTSDB) enables Real-Time

Statistics externalization

� “Enabling” RTS with DB2 9� DB2 9 already provides them



How are they accessed/processed?

� DB2 itself updates the RTS through non-SQL procedures

� RTS tables can be queried by standard SQL

� RTS tables can be processed by IBM supplied stored procedure� DSNACCOR/DSNACCOX

- Allows to narrow scope on utility and object (-type)- Checks RTS based on predefined formulas- Recommends objects for REORG, RUNSTATS, COPY- Exception table for general excludes



� Working with RTS� DBM1 allocates RTS blocks for each updated object

� At first update since the pageset/partition is opened� RTS runs in DBM1 address space

� CPU time is included in DBM1's SRB time� The system task is created during START DB2

� Free RTS blocks when� Pagesets/Partitions are closed� After statistics are written to RTS tables

� In a data sharing system, statistics are collected by each member

Real-Time Statistics (RTS) advanced


� Affecting RTS� CREATE/DROP table space� Insert / Update / Delete� Massdelete only updates massdelete counters� Rollback� REORG - online REORG triggers changes during Log Apply� RUNSTATS� COPY� LOAD � REBUILD - sets REORG counters to zero� RECOVER - sets utility timestamps to null� Trigger may cause statistics updated for other tables



� Externalizing the RTS� RTS manager externalizes in-memory statistics to the RTS

Tables on a timer interval� STATSINT in ZPARM - default 30 minutes (DB2 9 15 min.)� REAL TIME STATS in DSNTIPO install panel

� STOP DATABASE SPACENAM command� Flush in-memory statistics for all target objects

� STOP DATABASE(DSNRTSDB)� Flush all in-memory statistics

� STOP DB2 MODE(QUIESCE)� A utility operation (e.g. LOAD, REORG, RUNSTATS, COPY,

REBUILD, RECOVER)



� No externalization of the RTS� STOP DB2 MODE(FORCE)� Utilities that have a RTS-object in the utility list� limited for TEMP and Work Files Database� Read only objects� DEFINE NO objects � at the Tracker Site



Columns of SYSIBM.TABLESPACESTATS (DB2 7 and 8)DBNAME CHAR( 8) NOT NULL, NAME CHAR( 8) NOT NULL, PARTITION SMALLINT NOT NULL, DBID SMALLINT NOT NULL, PSID SMALLINT NOT NULL, UPDATESTATSTIME TIMESTAMP NOT NULL WITH DEFAULT,TOTALROWS FLOAT , NACTIVE INTEGER , SPACE INTEGER , EXTENTS SMALLINT , LOADRLASTTIME TIMESTAMP , REORGLASTTIME TIMESTAMP , REORGINSERTS INTEGER , REORGDELETES INTEGER , REORGUPDATES INTEGER , REORGUNCLUSTINS INTEGER , REORGDISORGLOB INTEGER , REORGMASSDELETE INTEGER , REORGNEARINDREF INTEGER , REORGFARINDREF INTEGER , STATSLASTTIME TIMESTAMP , STATSINSERTS INTEGER , STATSDELETES INTEGER , STATSUPDATES INTEGER , STATSMASSDELETE INTEGER , COPYLASTTIME TIMESTAMP , COPYUPDATEDPAGES INTEGER , COPYCHANGES INTEGER , COPYUPDATELRSN CHAR(6) FOR BIT DATA,

COPYUPDATETIME TIMESTAMP



Columns of SYSIBM.SYSTABLESPACESTATS (DB2 9)UPDATESTATSTIME TIMESTAMP NOT NULL WITH DEFAULT,NACTIVE INTEGER,NPAGES INTEGER,EXTENTS SMALLINT,LOADLASTTIME TIMESTAMP,REORGLASTTIME TIMESTAMP,REORGINSERTS INTEGER,REORGDELETES INTEGER,REORGUPDATES INTEGER,REORGDISORGLOB INTEGER,REORGUNCLUSTINS INTEGER,REORGMASSDELETE INTEGER,REORGNEARINDREF INTEGER,REORGFARINDREF INTEGER,STATSLASTTIME TIMESTAMP,STATSINSERTS INTEGER,STATSDELETES INTEGER,STATSUPDATES INTEGER,STATSMASSDELETE INTEGER,COPYLASTTIME TIMESTAMP,COPYUPDATEDPAGES INTEGER,COPYCHANGES INTEGER,COPYUPDATELRSN CHAR(6) FOR BIT DATA,COPYUPDATETIME TIMESTAMP,IBMREQD CHAR(1) NOT NULL,DBID SMALLINT NOT NULL,PSID SMALLINT NOT NULL,PARTITION SMALLINT NOT NULL,INSTANCE SMALLINT NOT NULL WITH DEFAULT 1,SPACE BIGINT,TOTALROWS BIGINT,DATASIZE BIGINT,UNCOMPRESSEDDATASIZE BIGINT,DBNAME VARCHAR(24) NOT NULL,NAME VARCHAR(24) NOT NULL



Columns of SYSIBM.INDEXSPACESTATS (DB2 7 and 8)DBNAME CHAR( 8) NOT NULL, INDEXSPACE CHAR( 8) NOT NULL, PARTITION SMALLINT NOT NULL, DBID SMALLINT NOT NULL, ISOBID SMALLINT NOT NULL, PSID SMALLINT NOT NULL, UPDATESTATSTIME TIMESTAMP NOT NULL WITH DEFAULTTOTALENTRIES FLOAT , NLEVELS SMALLINT , NACTIVE INTEGER , SPACE INTEGER , EXTENTS SMALLINT , LOADRLASTTIME TIMESTAMP , REBUILDLASTTIME TIMESTAMP , REORGLASTTIME TIMESTAMP , REORGINSERTS INTEGER , REORGDELETES INTEGER , REORGAPPENDINSERT INTEGER , REORGPSEUDODELETES INTEGER , REORGMASSDELETE INTEGER , REORGLEAFNEAR INTEGER , REORGLEAFFAR INTEGER , REORGNUMLEVELS INTEGER , STATSLASTTIME TIMESTAMP , STATSINSERTS INTEGER , STATSDELETES INTEGER , STATSMASSDELETE INTEGER , COPYLASTTIME TIMESTAMP , COPYUPDATEDPAGES INTEGER , COPYCHANGES INTEGER , COPYUPDATELRSN CHAR(6) FOR BIT DATA, COPYUPDATETME TIMESTAMP



Columns of SYSIBM.SYSINDEXSPACESTATS (DB2 9)UPDATESTATSTIMETIMESTAMP NOT NULL WITH DEFAULT,NLEVELS SMALLINT,NPAGES INTEGER,NLEAF INTEGER,NACTIVE INTEGER,SPACE INTEGER,EXTENTS SMALLINT,LOADRLASTTIME TIMESTAMP,REBUILDLASTTIMETIMESTAMP,REORGLASTTIME TIMESTAMP,REORGINSERTS INTEGER,REORGDELETES INTEGER,REORGAPPENDINSERT INTEGER,REORGPSEUDODELETES INTEGER,REORGMASSDELETEINTEGER,REORGLEAFNEAR INTEGER,REORGLEAFFAR INTEGER,REORGNUMLEVELS INTEGER,STATSLASTTIME TIMESTAMP,STATSINSERTS INTEGER,STATSDELETES INTEGER,STATSMASSDELETES INTEGER,COPYLASTTIME TIMESTAMP,COPYUPDATEDPAGES INTEGER,COPYCHANGES INTEGER,COPYUPDATELRSN CHAR(6) FOR BIT DATA,COPYUPDATETIME TIMESTAMP,IBMREQD CHAR(1) NOT NULL,DBID SMALLINT NOT NULL,ISOBID SMALLINT NOT NULL,PSID SMALLINT NOT NULL,PARTITION SMALLINT NOT NULL, INSTANCE SMALLINT NOT NULL WITH DEFAULT 1,TOTALENTRIES BIGINT, DBNAME VARCHAR(24) NOT NULL,NAME VARCHAR(128)NOT NULL,CREATOR VARCHAR(128)NOT NULL,INDEXSPACE VARCHAR(24) NOT NULL,LASTUSED DATE



� Real-Time Statistics are not used by the DB2 optimizer

� Real-Time Statistics are intended to provide youmost current object statistics on demand without anyoverhead

� Use RTS for threshold based database maintenance



RTS pertaining to backups:

� COPYLASTTIMEThe timestamp of the last full or incremental image copy on the table space or partition.

� COPYUPDATEDPAGESThe number of distinct pages that have been updated since the last COPY.

� COPYCHANGES The number of insert, delete, and update operations since the last COPY.

� COPYUPDATELRSN The LRSN or RBA of the first update after the last COPY.

� COPYUPDATETIME The timestamp of the first update after the last COPY.



DSNACCOR/DSNACCOX formulas to determine maintenance candidates

� Full COPY on table spaces� Full COPY on index space� Incremental COPY on table space� REORG on table space� REORG on index space� RUNSTATS on table space� RUNSTATS on index space� Extensive extents� Objects with exceptions (e.g. COPYPEND)



Execution within your job scheduler

Evaluation oftable spacesand indexes

Tailoringof utility JCL

Thresholds

RTS integration for the batch maintenance cycle

Start

QUIESCEREORGCOPY

MDB2ALTX MDB2SDB2

MDB2RUN

other

ALTER + REORGgenerates

Delete Copy Datasets

alters IX COPY YES/NO and generates

MODIFY MERGECOPY

MDB2RB MDB2MO MDB2MC

executes REBINDs

generates

MDB2LSTAMDB2MD

Delete Copy Datasets

generates checks the COPY statusEnd

generates

analyzes space usage

inserts

RTSRTS



Since object characteristics can be queried on demand, nowRTS even opens up

Real Time Maintenance on Demand

Goals:� Increased business agility� Runtime reduction for maintenance tasks� Real-time statistics also for volatile and clone objects� Less costs for gathering statistics



level 1cyclic

level 2re-activ

level 3automated

level 4on demand

level 5autonomic

staticmaintenance

jobs for allobjects

manualjob

building

totalmaintenance,

manualexecution

generatedmaintenance

jobs forspecificobjects

manualjob

building

selectivemaintenance,

manualexecution

generated,threshold

basedmaintenance

jobsautomated,thresholdbased jobgeneration


staticexecution

dynamicmaintenancejobs based onreal-time data

continuous,thresholdbased Jobgeneration


automatedexecution

dynamicmaintenance

integratedvia SLA‘s

continuous,DB2

basedgeneration

selectivemaintenanceautomatedexecution

pro

ced

ure

op

erat

ion

exec

uti

on

manual intervention

DB2 Database Maintenance – past, present, future



On Demand database maintenance benefits

� 24 x 7 data availability – even if database maintenance is required (RUNSTATS, COPY, REORG)

� Best availability and best performance� Immediately pinpointing urgent maintenance requirements� Direct execution of important Utility tasks

� faster Recovery� better performance (RUNSTATS, REORG on Indexes)� better load balancing making use of low workload periods� less “classic” batch window requirements



DB2 CatalogStatistics

(Optimizer-)RUNSTATS

BIND

SELECT …FROM …WHERE …

ExecutableCode

Optimizer

RTS vs. DB2 Catalog Statistics

Historically we have two typesof RUNSTATS:

1. Optimizer RUNSTATS to improve performance




BIND


ExecutableCode

REBIND

Optimizer Optimizer






(Analytical-)RUNSTATS

Utility Decision(REORG, COPY etc)




2. Analytical RUNSTATS to analyze maintenance needs




Real-TimeStatistics




With RTS we now have two repositoriesRUNSTATS � DB2 catalog RTS � RTS objects


Real-TimeStatistics






� Stop using catalog statistics for analytical RUNSTATS

� Use Real-Time Statistics for accurate statistics

� Save CPU! Eliminate analytical RUNSTATS

� Eliminate the “lag” time

� Secure your optimizer base




BIND


ExecutableCode

REBIND Real-TimeStatistics

Optimizer Optimizer






Mini-BIND


DynamicStatement

Cache

Optimizer



0

5

10

15

20

25

30

Runtime in h forgenerationbased onanalyticalRUNSTATSRuntime in h forgenerationbased on RTS


Resulting savings from exploiting RTS

� RTS fully eliminates the need for analytical RUNSTATS


0

500

1000

1500

2000

2500

3000

3500

Number ofRUNSTATSbefore

No RUNSTATSneeded withRTS

0

5

10

15

20

Duration ofRUNSTATS in hbefore

Duration ofRUNSTATS withRTS



� RTS reduces the resource requirements to determineobjects that require database maintenance to zero



If you haven’t exploited threshold based maintenance already,the savings will be even more significant

- e.g. Full/incremental copies based on update rates- 77% elapsed time reduction- 74% CPU reduction

- e.g. RUNSTATS based on update rates- 83% elapsed and CPU reduction



RTS good practice� Avoid Timeouts or Deadlocks with RTS manager� Use Uncommitted Read lock isolation when accessing RTS

tables� For disaster recovery

• Recover RTS objects after DB2 Catalog and Directory objects are recovered

• Explicitly issue START DATABASE(DSNRTSDB) after RTS objects are recovered

Tips and Tricks


Omit weak points when enabling RTS� Validate table space, table and index definitions for orphans,

widows and null stats and inconsistencies� Data may not be accurate until a REORG/RUNSTATS/COPY

is done

V7: all values are null*V8/V9: all counters are zero (only updated if timestamp not null)

all timestamps are null*except REORGLASTTIME (creation timestamp)

* REORG, RUNSTATS, COPY required

Tips and Tricks


RTS initialisation

e.g. UPDATE SYSIBM.TABLESPACESTATS

SET REORGLASTTIME = ‘0001-01-01-00.00.00.000000’,REORGINSERTS = 0,REORGINSERTS = 0,REORGINSERTS = 0,REORGMASSDELETE = 0

WHERE REORGLASTTIME IS NULL;UPDATE SYSIBM.TABLESPACESTATS A

SET TOTALROWS(SELECT B.CARDF FROM SYSIBM.SYSTABLEPART B

WHERE A.DBNAME = B.DBNAMEAND A.NAME = B.TSNAMEAND A.PARTITION = B.PARTITION)

WHERE A.TOTALROWS is NULL;

Tips and Tricks


Other things to consider

� All in-memory statistics are lost in case of a DB2 abend� Unable to capture statistics when DSNRTSDB is stopped or

statistics tables are unavailable� Statistics could be inaccurate if running 3rd party vendor utilities

without flushing the in-memory statistics� Some stats may not be valid in a utility restart scenario� Use SHRLEVEL CHANGE when running utilities against RTS� Don't mix RTS objects with other user objects in a utility list operation

Tips and Tricks


RTS Benefits:

� Current statistics without the need for expensive RUNSTATS� Current object characteristics that can be used to trigger utilities

threshold based � New opportunities to do database maintenance in dynamic 24x7

environments� Statistics for volatile tables without compromising access paths� Provides individual data for clone and base table� RUNSTATS only required for the DB2 optimizer (BIND/REBIND)� Easy access via SQL or DSNACCOR/DSNACCOX

Tips and Tricks


Will LEO be back once upon a time?

DB2 Vnext goals

1. Save CPU time

2. Reduce disk space

3. Reduce software costs

4. Improve business agility

5. Improve productivity

Tips and Tricks


Questions?

Real-Time Statistics – How to arm your DB2 for 24x7

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