DB2 DIAGNOSE DISPLAY MEPL

DIAGNOSE is a DB2 for z/OS utility that, as the name suggests, is used in diagnosing problems. It generates information that is useful in diagnosing problems. But you should use this utility only under the direction of IBM Software Support staff, except for DIAGNOSE DISPLAY MEPL.

You can use the DISPLAY MEPL even without contacting IBM in the following scenario.

First of all, MEPL is an acronym for Module Entry Point List (MEPL). DIAGNOSE DISPLAY MEPL dumps module entry point lists to SYSPRINT.

Recently, we had an issue with a query after applying the maintenance RSU1304. I opened a SR (Service Request) with IBM and the support staff found a PTF in PE status. It took about 2 months to find a fix and eventually when I applied a PTF to fix the PTF in PE, it didn't work. The query still had the same problem.

IBM asked me to run this utility to find if the PTF is in fact applied to the subsystem that we were testing the query. The SYSPRINT from this utility didn't show the PTF. That's when I realized that the PTF was applied to the maintenance library, but the load module was not copied to the production run time library. After copying the load module from maintenance library to run time library, the query ran good.

Usually I do search the SMPPTS library to see if PTF that was applied recently is found, but that's not foolproof. This method of running the DIAGNOSE DISPLAY MEPL utility looks foolproof. Lesson learnt !!

Here is a sample job to run this utility:

//jobcard
//JOBLIB   DD  DISP=SHR,DSN=SYS2.DB2.DBxx.SDSNLOAD
//STEP0010 EXEC PGM=DSNUTILB,PARM='DBxx,MEPL',REGION=4M
//SYSPRINT DD SYSOUT=*
//SYSUDUMP DD SYSOUT=*
//SYSIN    DD  *
  DIAGNOSE DISPLAY MEPL
/*

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CBT Tape

Just a quick note about a freeware site for mainframers. Check this out: http://www.cbttape.org/.

The CBT tape is a collection of freeware for almost all open-source distribution for the IBM mainframe z/OS environment. The entire collection of free software can be downloaded at the site as well as freeware for JES2, JES3, and other related S/390 material. A large repository of links to S/390 related sites on the Internet and archives of older material are also features.

How to load LOB tablespaces using DSN1COPY?

In the past, I've tried to load tablespaces with LOB columns using the regular IBM Load, BMC Load Plus & CA Fast Load. None of these tools support LOB tablespaces. You get into a series of errors.

The only utility that has ever worked for me is DSN1COPY. It's a pain to use DSN1COPY though. You need several things to go right for this to work. Let me try to explain as simple as possible.

In this example, I'm copying data from an imagecopy dataset into a table in a TEST subsystem. The first thing you need to remember is that, you need to know the DBID of the database, PSID of the tablespace and OBID of the table for both the source and target subsystems.

These are the steps:

1. STOP the base and LOB tablespaces and indexes for the LOB table on the target subsystem

2. Run DSN1COPY with the right parameters. I use PARM='PAGESIZE(32K),LOB,FULLCOPY,OBIDXLAT,RESET'. Supply the imagecopy dataset of the table on the source subsystem for SYSUT1 and supply the DSNDBC linear dataset of the table on the target subsystem for SYSUT2.

3. START the base and LOB tablespaces and indexes for the LOB table on the target subsystem

4. Rebuild the indexes

5. Run runstats

If the DSN1COPY step abends with "DSN1992I VSAM PUT ERROR, RPLERREG = 008, RPLERRCD = 028", check JESMSGLG. If you see a message like this "IEC070I 204-220,jobname,stepname,SYSUT2,6BF7,DBD115& IEC070I DB2CATx.DSNDBC.dbname.tsname.I0001.A001", it means you do not have enough space in that dataset. Make sure, you assign multiple datasets with suffix A001, A002, etc. in the target subsystem, it needs to accommodate all data from the source.

If you see a message like this "IEC070I 209-220,jobname,stepname,SYSUT2,89B5,DBD235,& IEC070I DB2CATx.DSNDBC.dbname.tsname.I0001.A001,", that means no space is available in the DASD volume. To fix this problem, make the dataset multi volume so that it can extend space into multiple volumes.

HTH !!

Date of a particular day

A developer asked me, how do I find the date for last Sunday. It was a Wednesday when he asked. After some thinking, this is what I gave him as solution. This works in DB2, not sure about other databases. 

SELECT CURRENT DATE - (DAYOFWEEK(CURRENT DATE) - 1) DAYS 
  FROM SYSIBM.SYSDUMMY1                                 

This solution works only for Sunday. For Monday, change 1 to 2, for Tuesday 3 and so on.

I've not done an extensive testing, so take it with a grain of salt :)

REXX to calculate holiday dates in US

What are all the government/bank holiday dates in the US in 2012? You can tell this by grabbing a calendar or doing a search on the net. What if you need this information in a program? What if you need this information for year 2013, 2014 etc.? Mr Martin Dunkel has written a REXX and he has graciously agreed to share his code with us all. The code is available in the link below. Please feel free to make a copy of it and change as needed. I've tested this code as it is. His contact info is available in the REXX, in case you have any questions that I cannot answer.

All credit goes to Mr Martin Dunkel !! Thank You Mr Dunkel.

Here is the code: https://docs.google.com/open?id=0B4whLShAZsgERW1vZmlVSDQ0WXc

DB2 for zOS Index on Expression

DB2 for z/OS version 9 brought in a new feature called "Index on Expression". Yes, you can create indexes on frequently used expressions in your queries. For example, if you often do a SELECT FIRST_NAME WHERE UPPER(LAST_NAME) = 'SMITH', then creating an index on UPPER(LAST_NAME) will be useful.

Until V8, you can create index on just columns, not on expressions/functions etc. So, you would have created an index on LAST_NAME, but DB2 would have ignored it because when you use a function on a column, DB2 ignores index access. But starting in V9, you can create an index on UPPER(LAST_NAME) and DB2 will use this index.

Now, to the tricky part ...

I tried to create an index on UPPER(LAST_NAME), DB2 complained that I need to specify 'locale' name. After reading a little bit about 'locale names', I specified UPPER(LAST_NAME, 'En_US') and DB2 happily created the index. I also ran runstats on the table. However, when I did an explain on the query SELECT FIRST_NAME WHERE UPPER(LAST_NAME) = 'SMITH', DB2 didn't seem to pick up the newly created index. That puzzled me.

After reading a little further, I found that I need to specify the same 'locale' in the query too. After specifying the 'locale', I did an explain and DB2 picked up the index. This is the modified query:

SELECT FIRST_NAME WHERE UPPER(LAST_NAME, 'EN_US') = 'SMITH'

Keywords: DB2, z/OS, Index, Expression, Upper, Locale, function

How to find the RSU or PUT level maintenance through SMP/E?

Usually, if you are working on a mainframe issue (DB2 or CICS or MQ or any mainframe stuff), and if you are dealing with a 3rd party vendor, they would ask the maintenance level or patch level or PUT level or RSU level of your system or product. How do you find the RSU/PUT level?


If you install your products through SMP/E, this is how you find this information.
Go to SMP/E panel, and enter SMCSI dataset (global zone data set) and select option 3 and hit enter.

Select option 3 from this screen and hit enter.

Just hit enter again (no input for ZONE NAME).

Now select the region you are interested in. GLOBAL zone will show all the RSU that has been RECEIVED (it may or may not be APPLYed already). TARGET zone will show all the RSU that has been APPLYed.


e.g., this screen shows the last maintenance applied (RSU1103), along with the previous maintenance:

DB2 V9 for z/OS - New ZPARM EDM_SKELETON_POOL

I'm working on upgrading DB2 for zOS from V8 to V9. I completed upgrading it to V9 CM (Compatibility/Conversion Mode) in one of our PROD subsystems about 2 weeks ago and the next business day was horrible. The performance was bad for the entire subsystem. The LPAR CPU peaked to 98% of the total MIPS capacity.

The activity rate against the SPT01 tablespace jumped several times and the CICS regions started sucking 20% more CPU. We noticed a few bad queries through Omegamon and we fixed them by either tweaking the stats or putting some new indexes. But that didn't bring down the CPU consumption much. The interesting part was, our zIIP engine started to peak at 100%, which usually stays at 40%. We found one query that had done a bunch of updates and got stuck - it was using a lot of CPU but was not doing any productive work. We cancelled this thread, but it wouldn't go away and the zIIP engine was still at 100%. Many more transactions/threads started to back log because of lack of CPU availability. The cancelled thread didn't die and still was burning CPU. We ended up cycling DB2 with a MODE(FORCE) command. Still, when DB2 came back, it started recovery of the cancelled thread, so we had to force kill it.

When that thread was at last gone, we looked at the CPU rate, and it was right back at the 98% with the only exception that zIIP processor was at 75% level.

We opened a Sev 1 PMR with IBM. As usual, they asked for dumps, SMF, RMF records etc. [Rant On] I would have thought IBM provided a solution to try for a problem with such a mature product. But instead they were waiting on us to provide docs. [Rant Off]


Anyway, we did some more research and found that, in DB2 V9, copies of packages and plans have been moved from below the 2GB bar to above the bar. This is done through a new zparm called EDM_SKELETON_POOL. The default value for this zparm is too low. So we increased it by 20 times. The system is in a much better shape now.

This is from Omegamon for DB2:
Package Table (PT) Reqs         1005483K 
PT Loads                        80073250 
% of PT Loads from DASD             7.96%


The "% of PT Loads from DASD" should be less than 10% for a healthy system. It was about 55% in our system before increasing the value of EDM_SKELETON_POOL. With any other virtual memory, make sure that there is enough physical memory to support this increase.


After this fix, the CPU looks much better but we are still seeing some runaway transactions or changed accesspath (which are not good in many cases). We're fixing them by rewriting the queries in most cases.

Accessing DB2 LUW table through a COBOL program on mainframe

If you are planning to write a COBOL program to access data from a table on DB2 LUW, you need to do the right setup first. I've described them here as much as I remember. If you get into any trouble, let me know, we can try to resolve it together.

Things to do on Mainframe DB2

Insert row in SYSIBM.LOCATIONS with these values

• LOCATION - dbname <-- This is the DB2 LUW database name

• LINKNAME - linkname <-- This is parent of a row in SYSIBM.IPNAMES or SYSIBM.LUNAMES (For this to work it needs to be the name of the DB on the UDB box, because this is how it determines which DB to connect to if that DB2 instance has more than one DB under it.)

• IBMREQD - N

• PORT - portnum <-- This is the connection port on the UDB box. To find this on AIX do: "cat /etc/services". The end of the file will have the connection port for the DB2 instance. On NT it will be 50000.

• TPN - Leave this empty

• Insert row in SYSIBM.IPNAMES

• LINKNAME - linkname This ties to a row in SYSIBM.LOCATIONS with column LINKNAME set to same

• SECURITY_OUT - A A means Already verified

• USERNAMES -

• IBMREQD - N

• IPADDR - nn.nn.nn.nn This is the IP address. You can find this by doing a ping command from a TSO command line or from a NT command prompt. (e.g. PING EXPLORER)

Then the DDF address space must be stopped and restarted to pick up the changes made to the SYSIBM.IPNAMES, SYSIBM.LUNAMES.


Things to do on DB2 LUW

You need to update the DataBaseManager configuration which is at the DB2 Instance level. You can display the current settings with this command from a command line on NT or AIX

DB2 GET DBM CFG | more

Part of the output will look like this:

Database manager authentication (AUTHENTICATION) = SERVER

Cataloging allowed without authority (CATALOG_NOAUTH) = NO
Trust all clients (TRUST_ALLCLNTS) = YES
Trusted client authentication (TRUST_CLNTAUTH) = CLIENT

There are 2 parms that must be changed from the default to allow connecting from the host--AUTHENTICATION and TRUST_ALLCLNTS. Use the following commands to change these. The changes don't take effect until the db2 instance is stopped and started, so you may need to coordinate cycling the instance with applications and the server owner(s).


UPDATE DBM CFG USING AUTHENTICATION CLIENT
UPDATE DBM CFG USING TRUST_ALLCLNTS DRDAONLY

To cycle the DB2 instance use DB2STOP After it stops do a DB2START. Its a good idea to do a DB2 LIST APPLICATIONS beforehand to see if there are any threads. You can use a FORCE command if you need to to kill any threads.

On top of the above things, if you are writing a COBOL program on host and trying to connect to DB2 LUW, these steps must also be followed.

1. BIND PACKAGE (luwdbname.collectionid) OWNER(CHGTMANP) ISOLATION(CS) QUALIFIER(ALIUPDP) MEMBER(programname) DYNAMICRULES(RUN) VALIDATE(BIND) SQLERROR(CONTINUE) ACTION(REPLACE)

2. Make sure the above BIND statement doesn't fail on anything other than -204 (especially look for -551s, because this could lead to -525 at run time)

3. Grant DBADM authority to the userid that is specified in the OWNER parameter of your BIND card

4. Add the new "dabase.collection.*" to PKLIST on the plan that you will use to run your cobol program
e.g.,

BIND PLAN(plan name) OWNER(owner) QUALIFIER(qualifier)+

     NODEFER(PREPARE) VALIDATE(BIND) ISOLATION(CS)+
     CACHESIZE(1024) CURRENTDATA(NO) DEGREE(1)+
     SQLRULES(DB2) ACQUIRE(USE) RELEASE(COMMIT)+
     EXPLAIN(NO) REOPT(NONE) KEEPDYNAMIC(NO)+
     IMMEDWRITE(NO) DBPROTOCOL(DRDA) ENCODING(37)+
     DISCONNECT(EXPLICIT)+
     PKLIST(collction1.*,+
            collection2.*,+
            database.collection3.*)+
     ENABLE(*)+
     ACTION(REPLACE) RETAIN

5. In the COBOL program, make sure the programmers are coding these in the right order:


SET CURRENT PACKAGESET = 'collectionname'
CONNECT TO :database-name

6. Give EXECUTE access to PUBLIC on the package on LUW for the first time it is bound. This should be done for each new package you create

DB2 UDB Partitioned Database - Unique Index

In the absence of the DBA that usually works on DB2 UDB, I tried to create an unique index on a table that is defined on a partitioned database. I realized that it's not very straight forward to do so.

From DB2 manual: "There are performance advantages to creating a table across several database partitions in a partitioned database environment. Creating a table that will be a part of several database partitions is specified when you are creating the table. There is an additional option when creating a table in a partitioned database environment: the distribution key. A distribution key is a key that is part of the definition of a table. It determines the database partition on which each row of data is stored.

You must be careful to select an appropriate distribution key because it cannot be changed later. Furthermore, any unique indexes (and therefore unique or primary keys) must be defined as a superset of the distribution key. That is, if a distribution key is defined, unique keys and primary keys must include all of the same columns as the distribution key (they might have more columns)."

This is where I got totally lost "any unique indexes (and therefore unique or primary keys) must be defined as a superset of the distribution key. That is, if a distribution key is defined, unique keys and primary keys must include all of the same columns as the distribution key (they might have more columns)". I was trying create the unique index on a column which was not the hash key and I was getting an SQL0270N Reason Code 1. After including the hash key along with the other key, it worked.