db2 production virtualisation with profiles

DB2 Production VirtualisationWith Profiles

Baltimore/Washington DB2 Users GroupDecember 11, 2012Jim Dee, BMC Software

© Copyright 04/22/2023 BMC Software, Inc 2

Agenda

Why do we need a production clone?What does our clone need to be a true model of productionThings we can do in realityThings we should virtualizeVirtualization help from IBM/DB2Virtualization difficultiesWhat’s still missing


Why do we need a production clone?

Either to MEASURE performance in a production-like environmentOr to ESTIMATE performance in a production-like environmentOr to COMPARE one set of access paths with another

A “production clone” is a subsystem that looks and behaves in exactly the same way as the real production subsystem(s)


MEASURE performance

We want to KNOW- How expensive an application, program or SQL statement will be- How long it will run for- Do we have capacity


ESTIMATE performance

We want to ESTIMATE- How expensive an application, program or SQL statement will be- How long it will run for- Does this new/changed situation still look OK


COMPARE access paths

We assume what we have in production is OKWhen we change something of the environment- What gets better?- What gets worse

Things like- New versions of DB2 or z/OS- Perhaps even maintenance- New versions of the application- Tuning recomendations


What does our clone need to be a true model of production

For ESTIMATING (and COMPARING):- All objects defined identically to production

Same statistics as production- ALL of them

Identical bufferpool configurationsIdentical sort pool, RID pool, statement cache, EDMPOOL- Complete this list at your leisure

Same maintenance level of DB2- And everything else?


What else is needed

For ESTIMATING (and COMPARING):- Same versions of programs, packages, SQL

UNLESS we are validating new versions, of course


What does our clone need to be a true model of production

For MEASURING:- Everything that was needed for ESTIMATING

plus....

- ALL of the data or at least a representative sized sample

- Some sort of capture/replay technology


Things we can do in reality

Copying object definitions is easy- Set PRI/SEC quantities to low value- Or (better) add DEFINE NO

Copying object stats is also easy (tools help!)Setting the DB2 configurations MIGHT be possible- Use the “same” dsnzparm etc as production?

Hopefully our maintenance levels are close togetherThe same (or new) programs/SQL as appropriate


Things we’d like to virtualize

Number of cpusPower of cpuszIIP and zAAP configurations

Anything else?


Things that don’t matter (much)

With DB2 it’s sometimes hard to know just what IS important- And what isn’t

DB2 probably uses more z/OS features than any other z/OS software- And it’s using mostly them for performance gains


Virtualization difficulties

So how DO you make one LPAR look like another?Your clone DB2 is highly unlikely to be running on the same physical kit as your production subsystemSo we really need some way of “fooling” the clone DB2 into behaving as if the environment WAS the same as production


Virtualization help from IBM/DB2

Some time ago IBM introduced the concept of virtual indexesEntries in DSN_VIRTUAL_INDEXES could define index changes to be taken into account during Explain- Creation of new indexes- Dropping of existing indexes

These entries can be enabled or disabled allowing quite involved “what if” analyses to be carried out- Pity you can’t run “virtual Runstats” though- The stats are key to index choices



This is not really virtualisation of another environmentMore of support for “what if” tuning hypotheses

And there was something fundamental missing......



Enter PM26475 (for DB2 9)And PM26973 (for DB2 10)

These are “let’s fool DB2” apars allowing virtualization of some of the environmental aspects- Sort pool, RID pool, all bufferpools- Cpu speed and number of cpus

Can all be specified as virtual values- Affecting EXPLAIN only and NOT bind


Virtualization in DB2 9 and 10

So this virtualisation helps with ESTIMATINGBut not MEASURING- A simulated cpu cannot run at the speed that it’s simulating!- Neither can DB2 be expected to run parallel tasks on virtual cpus


Virtualization in dsnzparm

Two new parameters are added to the DSN6SPRM macro- SIMULATED_CPU_CPEED

“the microseconds of task or service request block (SRB) execution time per service unit for the CPU being simulated”

- SIMULATED_CPU_COUNT “the number the of local CPUs being simulated”

These parameters are on-line changeable with –SET SYSPARM


Virtualization using PROFILES

A new area that has not been taken up by many sites are the new monitoring profile possibilitiesMonitoring profiles are INCREDIBLY powerfulCan allow surgical overrides of system parameters at STATEMENT level


Virtualization using PROFILES

In our case, PROFILES are used to create virtual environments

We create a new profile in DSN_PROFILE_TABLEWe then add profile attributes in DSN_PROFILE_ATTRIBUTES- SORT_POOL_SIZE, MAX_RID_BLOCKS, BP0, BP8K2 etc etc

And –START the profile- With –START PROFILE


Step by Step (1)

First you need to create a DSN_PROFILE_TABLE- See current doc

Then you need to add a row for your profile- This is keyed on PROFILE_ID- Which is

“INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY NOT NULL”- So you can’t choose your profile id!


Step by Step (2)

Then you need to create a DSN_PROFILE_ATTRIBUTES_TABLE- See current doc

Profile attributes are- Keyed on PROFILE_ID- And require entries in KEYWORDS plus

ATTRIBUTE1/ATTRIBUTE2/ATTRIBUTE3- Depending on what you are modelling


Step by Step (3)

Now create both DSN_PROFILE_HISTORY and DSN_PROFILE_ATTRIBUTES_HISTORYThese will eventually contain an audit trail of activated profiles


Step by Step (4)

Now –START the profileNote – you just say-START PROFILEProfileid is NOT mentionedDB2 starts ALL profilesCheck DSN_PROFILE_HISTORY to find out whether YOUR profileid was started


Step by Step (5)

Look for REJECTED - DUPLICATED SCOPE SPECIFIED REJECTED - INVALID SCOPE SPECIFIED REJECTED - NO VALID RECORD FOUND IN ATTRIBUTE TABLE orACCEPTED


Step by Step (5)

Because you start ALL profiles, you need to be careful of what others are specifyingIt is also possible to “restart” profiles- -START PROFILE when profiles are already active- Refreshed all profiles according to what is in the profile tables

Check the history table to make sure conflicts have not appeared


Step by Step (6)

Stopping profiles is easy-STOP PROFILE

BUT, how do you stop only YOUR profileid?- Sorry – you can’t

You COULD change your profileid to have PROFILE_ENABLED = ‘N’- Then issue another –START PROFILE- This should terminate YOUR profileid- But what else have you changed…..?


Some problems with profiles

Did you notice that we don’t start A profile- We start ALL the profiles defined in DSN_PROFILE_TABLE- Where PROFILE_ENABLED = “Y”

Wouldn’t it have been useful to be able to start specific profiles?- Then we could have defined different profiles for different virtualizations- This also means we must be VERY careful what else we are activating when

we START our profile


Some other problems

And you have to ask why the simulated cpu speed and cpu count values are in dsnzparm- And everything else is part of a profile?

Have you guessed yet where to get these values from?- You could talk to your friendly sysprog....


Some other problems

Well, the APAR shows you how

SET CURRENT DEGREE='ANY‘;

EXPLAIN ALL SET QUERYNO=6475 FOR SELECT * FROM SYSIBM.SYSDUMMY1;

SELECT HEX(SUBSTR(IBM_SERVICE_DATA,17,2)) AS CPU_COUNT, HEX(SUBSTR(IBM_SERVICE_DATA,69,4)) AS CPU_SPEED, HEX(SUBSTR(IBM_SERVICE_DATA,13,4)) AS RIDPOOL, HEX(SUBSTR(IBM_SERVICE_DATA,9,4)) AS SORT_POOL FROM PLAN_TABLE WHERE QUERYNO=6475;


Some other problems

BUT, it seems that CPU_COUNT is only populated when a query actually chooses a parallel access path


Did DB2 even notice?

When you have a running profile and/or dsnzparm changesAfter an EXPLAIN, look at REASON in your DSN_STATEMNT_TABLE- If DB2 took notice- You will see “PROFILEID nnn”

(quoting the relevant profile id)


Some other problems

It seems that IBM consider it likely that any ONE modelling subsystem will only be modelling ONE production subsystem- If you want to model multiple targets in a single DB2, YOU will have to

manage all the attribute settings- And different dsnzparms as well


What’s still missing

It’s still not possible to simulate zIIPs or zAAPs

BUT it is perhaps harsh to complainWhat we have been provided with is MUCH more useful than we had before

Questions??


Learn more at www.bmc.com

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