Wednesday, May 24, 2017

The DB2 12 for z/OS Blog Series - Part 10: Improved EDM Memory Management

EDM pool management is improved in DB2 12 for z/OS, which is especially beneficial to organizations running many concurrent threads with with large EDM pools specified.

Prior to DB2 12, the EDMDBDC, EDMSTMTC and EDM_SKELETON_POOL DSNZPARM values were used to allocate DBD cache, dynamic statement cache and EDM skeleton pool memory and the values could not be lowered past the specified installation vales.

With DB2 12 this bahvior is modified. No storage is initially allocated for these 3 EDM structures. Instead, storage is allocated by DB2 as it is needed while being used. If more stroage is required When the specified DSNZPARM values are reached then structures that are not currently in use are removed to tkeep the storatge that is in use below the specified values.

This should result in more effective and efficient EDM storage usage and allocation. Some larger shops may see higher real storage usage by DB2.

Friday, April 21, 2017

Hope to See You in Anaheim for the IDUG DB2 Tech Conference!


This year the IDUG North American DB2 Tech Conference is being held in Anaheim, CA from April 30th through May 4th. That means we'll be near Disneyland, so you can plan for a great week of DB2 and analytics education... and then follow it up with a visit to Mickey. 

Whether or not you care about Disneyland is irrelevant, though, because a week at an IDUG event is always an educational and enjoyable time. If you’ve ever attended an IDUG conference before then you know all about the fantastic educational and entertainment opportunities that IDUG offers. Of course there will be a ton of informative technical sessions on all of the latest and greatest DB2 technologies and features. 

There are a couple of great keynote sessions scheduled this year. Mike Gualtieri, an analyst with Forrester Research, will deliver Forrester's view on Big Data, Analytics, and Open Source. And then IBM's Daniel Hernandez will talk about machine learning in another keynote session. I'm looking forward to both of them!

And this year the Data Tech Summit is being held in conjunction with the typical, informative DB2 sessions. The Data Tech Summit offers up content for data architects and data scientists on topics like big data, cognitive computing, Spark, R and analytics. So if you are looking for a little bit more than just DB2 stuff, you can check out the agenda for the Data Tech Summit at this link.

As usual, I will be busy this year at IDUG. I have a session on Thursday (Session A14, 8:00 AM) titled Prest-O Change-O where I will discuss the ins and outs of DB2 for z/OS database change management. Change is a constant and once you create your DB2 environment it is guaranteed that at some point, something will need to be modified. This session will go over the different types of changes, the complexity of some types of changes, and trends and issues impacting change management including DevOps, regulatory compliance and data growth/Big Data. Hope you can join me!

I will also be delivering a vendor-sponsored presentation for LogOn Software with intriguing title of How to Accelerate DB2 SQL Workloads... Without DB2. Whatever could that mean? You'll have to join me on Wednesday at 10:30 AM to find out!

Let's not forget the exhibit hall (aka Solutions Center) where vendors present and demo their products that can help you manage DB2 better. It is a good place to learn about new technology solutions for DB2, but also to hang out and meet with IBMers, consultants, and peers. 

This year I'll be in the CorreLog booth (#107) in the Solutions Center on Tuesday. Be sure to stop by and say hello, take a look at CorreLog's great solution for auditing DB2 for z/OS, and register to win one of my books!

Already that is a lot for one week, but there is more. You can go to full-day education sessions on Sunday (at an additional cost), attend Special Interest Groups (where you can discuss the latest industry trends and topics with other interested technicians), attend Hands-On Labs (delivering working training led by IBM), and even take complementary IBM certification exams

And don't forget to download the mobile app for the conference to help you navigate all the opportunities available to you!


The IDUG DB2 Tech Conference is the place to be to learn all about DB2 from IBMers, gold consultants, IBM champions, end users, and more. With all of this great stuff going on why wouldn't you want to be there!?!?

Monday, April 17, 2017

The DB2 12 for z/OS Blog Series - Part 9: Piece-wise Deletion

Adding the FETCH FIRST clause to the DELETE statement at first appears to be a very simple enhancement, but upon closer examination it is really quite powerful.

Prior to DB2 12 for z/OS, the FETCH FIRST n ROWS ONLY clause could be specified on a SELECT statement. The clause had two impacts:
  1. the number specified for n is used by the optimizer to formulate an access path
  2. the result set of the SELECT is limited to no more than n rows
With the advent of FETCH FIRST being allowed in a DELETE statement, the number n limits the number of rows that will be deleted in a single DELETE statement. So let's assume that there are 1000 rows for employees in department 200. When we issue this DELETE statement

DELETE FROM EMP
WHERE  EMPDEPT = '200';

All 1000 rows will be deleted. However, if we issue this version of the same statement

DELETE FROM EMP
WHERE  EMPDEPT = '200'
FETCH FIRST 500 ROWS ONLY;

Only 500 rows will be deleted... you could then run it again to delete the remaining 500 rows.

So why would you want to do this? Well, our little example here is not really a good case for using FETCH FIRST on DELETE . Instead, it is primarily designed for situations where a large number of rows would be impacted. For example, assume that instead of 1000 rows there were 2 millions rows. Using FETCH FIRST  to DELETE the rows in batches, instead of 2 million all at once, can make an impossible task possible. The lock management when deleting 2 million rows can render a big, bulk deletion unwieldy as it impacts concurrent access of the data on the same pages where rows are being deleted.

So keep FETCH FIRST  in your arsenal of DB2 12 SQL tools that can help when you need to DELETE  a large number of rows.

Tuesday, April 04, 2017

The DB2 12 for z/OS Blog Series – Part 8: Index FTBs

IBM has delivered many new in-memory processing capabilities in DB2 12 for z/OS, so much so that Gartner has dubbed DB2 12 for z/OS an in-memory DBMS. This is good news for those of us in the mainframe world looking to utilize memory to improve the performance of our database applications.

Perhaps the most interesting of the new in-memory features is the new Fast Traversal Blocks, or FTBs. An FTB is an in-memory structure that can be used with unique indexes. DB2 detects which indexes are frequently used for traversals, and when a threshold is hit DB2 will build an FTB for the index in a storage area outside the buffer pool. This causes the top levels of the index to be cached thereby making it efficient to perform very fast traversals through the cached levels of the index.

FTBs are either on or off for the entire DB2 subsystem. This is managed using the new DSNZPARM named INDEX_MEMORY_CONTROL. Setting this zparm to AUTO, which is the default, indicates that 500 MB or 20 percent of the buffer pool will be used for FTBs (whichever is larger). Alternatively, you can set the upper limit to a number between 10MB and 200 GB, or you can DISABLE the feature altogether.

It may be confusing to specify a percentage of the buffer pool for caching FTBs, especially so because FTBs are stored outside of DB2’s buffer pools – that means you will not be consuming valuable buffer pool space with FTBs because the FTBs are stored in their own area of memory.

FTBs are most likely to be used by DB2 shops that run many applications performing frequent lookups where the unique index is used predominantly for reads. In those scenarios FTBs may be able to deliver a significant performance improvement.

There are two new DB2 IFCID trace records that report on index FTB usage in DB2 12 for z/OS: IFCID 389 and 477. IFCID 389 traces indexes with FTB structures and IFCID 477 traces allocation and deallocation of FTB structures.


The type of information tracked by these ICFIDs includes the number of indexes with FTBs along with number of levels in the FTB and the size of the structure. Such details will be important for DBAs looking to manage and support index FTBs in DB2 12.

Monday, March 20, 2017

The DB2 12 for z/OS Blog Series – Part 7: Relative Page Number Table Spaces

One of the most significant new features for supporting big data in a DB2 12 environment is relative page numbering (or RPN) for range-partitioned table spaces. You can either create a new RPN range-partitioned table space, or an existing range-partitioned table space can be changed to RPN via an ALTER TABLESPACE with PAGENUM RELATIVE, followed by an online REORG of the entire table space.

But why would you want RPN table spaces instead of the already-existing table spaces types in DB2? The simple answer is the ability to grow the amount of data you store. RPN table spaces enable you to store large amounts of data. The DSSIZE can grow up to 1 TB for a partition. And the maximum table size increases to 4 PB with up to 256 trillion rows per table. That is a lot of data that can be stored! Think about it this way: if you were to insert 1000 rows per second it would take more than 8000 years to fill the table to capacity!

With RPN table spaces you get the ability to create larger partition sizes. The maximum partition size is now 1 TB (it used to be 256 GB). So if you are reaching the capacity size of existing table space options, RPN table spaces will allow you to store a LOT more data. Of course, this requires an expanded RID, which increases from 5 bytes to 7 bytes. So that will impact the DDL for the mapping table for your online REORG utilities.

But size is not the only issue. RPN table spaces improve availability, too. You can specify DSSIZE at the partition level for RPN table spaces. So each partition can have its own, different DSSIZE specification. Furthermore, the allowable DSSIZE value is no longer dependent on the page size and number of table space partitions. The DSSIZE change can be an immediate change (no online REORG required to take effect) as long as the change does not decrease the DSSIZE value.

As you move your DB2 subsystems to Version 12, consider migrating your larger range-partitioned table spaces to RPN to take advantage of these new capabilities.


Thursday, March 02, 2017

The DB2 12 for z/OS Blog Series – Part 6: Transferring Ownership of Database Objects

When a database object is created it is given a qualified two-part name. This applies to tables, indexes, table spaces, distinct types, functions, stored procedures, and triggers. The first part is the schema name (or the qualifier), which is either implicitly or explicitly specified. The default schema is the authorization ID of the owner of the plan or package. The second part is the name of the object. 

But things can get confusing. When an object is created, an authorization ID is assigned as the owner of the object. This may, or may not, be used as the schema qualifier for the object. The object owner implicitly inherits privileges to reference, maintain and grant privileges to the object. 

Changing the owner of a database object used to be a difficult process. But DB2 12 for z/OS delivers a simple method of transferring the ownership of your database objects: the TRANSFER OWNERSHIP SQL statement. 

The primary purpose for this new feature is to make it easier to manage database objects that are owned by an employee who no longer works for your company. You can use TRANSFER OWNERSHIP to simply switch the ownership of the database objects to another employee. The new owner can be an authorization ID or a role. You can issue the statement interactively, or embed it in an application program. 

The TRANSFER OWNERSHIP statement does not change the schema of the transferred database object. 

In order to transfer ownership of a database object, you must either be the owner of the object or have SECADM authority. The basic syntax of the statement is as follows: 

TRANSFER OWNERSHIP OF object-name
 TO {USER authorization-name | 
     SESSION_USER | 
     ROLE role-name} 
 REVOKE PRIVILEGES 

Be careful if a package depends on the current owner's privileges. The dependent package will be invalidated unless the current owner is already explicitly granted those privileges from another source prior to the object ownership transfer. For example, after the ownership of a table is transferred and if a dependent package requires the SELECT privilege on that table by the current owner, the dependent package is invalidated unless the current owner has already been explicitly granted the SELECT privilege for that table before its ownership transfer. 

Here is a quick example transferring the ownership of a specific index to a different user, in this case, JOHNDOE. 

TRANSFER OWNERSHIP OF INDEX TR_P.XHIST02
 TO USER JOHNDOE 
REVOKE PRIVILEGES;

Friday, February 24, 2017

The DB2 12 for z/OS Blog Series - Part 5: Enhancements for Managing Dynamic and Static SQL

Most modern application development is done using dynamic SQL. But some features work only with static SQL and others only with dynamic SQL. DB2 12 for z/OS delivers functionality that minimizes the difference between static and dynamic SQL.

Dynamic plan stability brings the plan stability feature of static SQL to dynamic SQL. With plan stability for static SQL, you can use the PLANMGMT parameter of REBIND to save off old access paths that can be switched back to active if the new access paths are inefficient for any reason.

DB2 12 introduces dynamic plan stability, which is a little different but should prove to be quite useful. You can choose to stabilize dynamic SQL access paths by storing them in the DB2 system catalog. DB2 will not just automatically start to capture all dynamic access paths. There are options for selecting which queries to stabilize, so you do not have to store all dynamic SQL. This is controlled by the command:

 -START DYNQUERYCAPTURE

When a dynamic statement is run, DB2 will look in the dynamic statement cache first. If it is not found there, DB2 will look in the system catalog before resorting to a full prepare. This is particularly useful when statements are flushed from the DSC and a prepare would otherwise be required.

You can label a set of stabilized SQL statements into a group known as a stabilization group. This makes it easier for DBAs to track and manage stabilized queries.

Click here for more details on Dynamic Plan Stability.

So dynamic plan stability can make your dynamic SQL more static. But there is another new DB2 12 capability that can make your static SQL more dynamic: static Resource Limit Facility (RLF). The RLF, heretofore, could only be used to govern dynamic SQL statements. RLF tables, manipulated by DBAs, contain limits that make sure that dynamic SQL statements do not consume too many resources such as CPU, I/O, locks, etc. This enables improperly tested SQL or poor resource planning from disrupting performance.

But dynamic SQL is not the only type of SQL that could cause performance issues; static SQL transactions can benefit from the same controls. DB2 12 extends the RLF to support static SQL statements thereby improving the ability to avoid problem applications from dominating your system’s resource consumption.

Specifically, you can set up reactive governing for static SQL statements by adding new rows in resource limit facility tables. Static SQL statements will be governed by rows where RLFFUNC='A' (for DSNRLSTxx tables) and RLFFUNC='B' (for DSNRLMTxx tables).

You can control whether resource limits apply to dynamic only, static only or all SQL statements using the DSNZPARM RLFENABLE. Acceptable values are DYNAMIC, STATIC, or ALL and the default is DYNAMIC. Furthermore, you can specify the default resource limit actions for static SQL statements by setting two DSNZPARMS:
  • RLFERRSTC for local statements
  • RLFERRDSTC for remote statements


In each case, the acceptable values are NOLIMIT, NORUN, or a number between 1 and 500000. You use NOLIMIT to let any static SQL statement that does not correspond to a row in the resource limit table run freely. Alternately, NORUN indicates that any static SQL statement that does not correspond to a row in the resource limit table is prevented from running. Finally, if you specify a number between 1 and 500000, that will be the number of service units to use as the default resource limit. If the limit is exceeded, the SQL statement is terminated.

If you need more details on setting up resource limits in general, you can find that information in the IBM manuals and online here.

But the bottom line is that DB2 12 gives users more and better options for managing both their dynamic and static SQL performance.  And that is definitely a good thing!

Monday, February 13, 2017

The DB2 12 for z/OS Blog Series - Part 4: Real Time Statistics History

For those uninitiated to what RTS are, they are a series of statistics that are automatically maintained by DB2 and can be used by DBAs (and tools) to schedule maintenance tasks like REORG and COPY.

Prior to the introduction of RTS, the only way to gather statistics about DB2 database structures was by running the RUNSTATS utility. RUNSTATS collects statistical information about DB2 database objects and stores this data in the DB2 Catalog. There are two types of statistics collected by RUNSTATS: data used by the optimizer to formulate efficient access paths and data used by DBAs to determine when maintenance tasks should be run. The optimization statistics are still required, and therefore, so is RUNSTATS. The maintenance statistics, on the other hand, can be ignored and replaced by RTS.

RTS runs in the background and automatically updates statistics in two system catalog tables (one for table space data and one for index data) as your DB2 data is modified. This differs from RUNSTATS, which is a hands-on administrative process. RTS is hands-off.
So what is new with RTS in DB2 12 for z/OS?

The most significant enhancement is the ability to maintain RTS history using DB2’s system-time temporal capabilities. When history is enabled, both SYSIBM.SYSINDEXSPACESTATS and SYSIBM.SYSTABLESPACESTATS will have a table with "_H" on the end that have the same columns, with the same data types. But the temporal relationship is not automatically enabled, you have to choose to do so.

To enable the temporal relationship between a history table and its associated catalog table you must issue an ALTER statement to “hook up” the relationship. Here are the DDL statement for each of the RTS tables:

  ALTER TABLE SYSIBM.SYSINDEXSPACESTATS
  ADD VERSIONING
  USE HISTORY TABLE SYSIBM.SYSIXSPACESTATS_H;

  ALTER TABLE SYSIBM.SYSTABLESPACESTATS
  ADD VERSIONING
  USE HISTORY TABLE SYSIBM.SYSTABSPACESTATS_H;

Before turning on RTS history you should take care to build a process for maintaining, consolidating and purging historical information. Remember, that each time the STATSINT interval is reached, new RTS data will be written, causing the old information to be written to the system time temporal table. That history table will grow over time. You will want to have a plan for how to manage that growth. Perhaps you will want to aggregate the data daily, or weekly, or monthly. Or maybe you will just want to purge the data after a period of time. At any rate, your strategy for managing this data should be worked out before you decide to start collecting RTS history.

Why would you want to record historical RTS information? Well, such details can be useful for analyzing activity and predicting future requirements. With historical RTS you can see trends and might be able to improve performance, maintenance tasks, and service to your end users. And, of course, this means that you can write SQL time travel queries against the RTS system catalog tables.

You can always turn off historical RTS collection by severing the temporal relationship. This is accomplished by issuing ALTER TABLE specifying the DROP VERSIONING clause on the appropriate table. For example:

  ALTER TABLE SYSIBM.SYSTABLESPACESTATS
  DROP VERSIONING;

At any rate, the ability to take advantage of DB2’s temporal capabilities to capture RTS history is a powerful new feature of DB2 12 for z/OS that DBAs and performance analysts will want to take advantage of.


One other DB2 12 change to RTS worth noting, is the addition of the GETPAGES column to both table space and index space stats. This column is used to record the number of GETPAGE requests for the table space since the last time REORG was run (or since the object was created).

Tuesday, February 07, 2017

The DB2 12 for z/OS Blog Series - Part 3: Temporal Improvements

Temporal tables and time-travel query support was added in DB2 10 for z/OS. With temporal tables a time period is attached to the data to indicate when it was valid or changed in the database. A traditional database stores data implied to be valid at the current point-in-time; it does not track the past or future states of the data. Temporal support makes it possible to store different database states and to query the data as of those different states. That means different DDL to support temporal data, as well as different SQL syntax to query it.

Using built-in DB2 temporal capabilities is much easier than coding for it yourself, but as with most new features there were some additional tweaks that customers asked for. DB2 12 for z/OS delivers on making it easier for organizations to adopt and use temporal DB2 data and queries by supporting:
  • temporal referential constraints, 
  • more flexible time periods, and 
  • logical transactions.


Let’s examine each of these areas in a bit more depth. First up, let’s take a look at temporal referential constraints. Prior to DB2 12, temporal referential integrity required triggers or stored procedures to implement. But with DB2 12, you can define a temporal referential constraint for a temporal table that contains a BUSINESS_TIME period by specifying the PERIOD BUSINESS_TIME clause in the definition of the constraint. This should improve data integrity for temporal tables and increase temporal uptake for DB2 customers.

The second new temporal feature is improved flexibility for defining the application period in temporal tables. The application period is defined with two date/time columns, one specifying the beginning of the period and the other specifying the end of the period. Prior to DB2 12, the beginning value of a period had to be inclusive, and the end value had to be exclusive. So for a period beginning at 2017-01-01 and ending 2019-10-01, 2017-01-01 is part of the period but 2019-10-01 is not part of the period. This type of period is called an inclusive-exclusive period.

In DB2 12, you can create an application-period temporal table with a BUSINESS_TIME period that is inclusive-inclusive. That means that the end value is considered to be part of the period, instead of outside the period definition.

Generally speaking, the inclusive-exclusive definition is preferred (and is the default) because it complies with the SQL standard. However, if your data already exists as inclusive-inclusive, or it makes more sense to your business users, then DB2 12 support for inclusive-inclusive will make it easier for your organization to use DB2 temporal tables and time travel queries.

Finally, DB2 12 offers temporal logical transactions on system temporal tables (that is, those using SYSTEM_TIME periods). With this new feature, DB2 supports logical units of temporal work that are not determined by COMMIT and ROLLBACK. That means that values for row-begin and row-end columns are determined by applications based on a built-in global variable that you can set.


So overall, DB2 12 for z/OS makes using temporal tables easier and more flexible with these three compelling new features.

Wednesday, February 01, 2017

The DB2 12 for z/OS Blog Series - Part 2: Advanced Triggers

As we continue our series on new functionality in DB2 12 for z/OS, today we take a look at the improvements delivered for triggers.

Before we dive into the new capabilities, let's briefly review what triggers are. Triggers are event-driven specialized procedures that are stored in, and executed by, the DBMS. Each trigger is attached to a single, specified table. Triggers can be thought of as an advanced form of "rule" or "constraint" written using procedural logic. A trigger can not be directly called or executed; it is automatically executed (or "fired") by the DBMS as the result of a modification being made to the associated table. Once a trigger is created it is always executed when its "firing" event occurs (update, insert, delete, etc.). Triggers are generally used to promote data integrity and make the database self-maintaining.

So far, so good. But what does DB2 12 provide us that we did not have in prior releases?

Well, now we have a new type of trigger called an advanced trigger. All this really means is that the trigger supports new capabilities that I will outline momentarily. Triggers created before you have moved to function level 500 (this is new terminology for DB2 12 that roughly equate to NFM in earlier releases) will be referred to as basic triggers. 

So what makes a trigger advanced? Simply put, support for additional development and usability capabilities. The following features are supported only with advanced triggers:

  • You can define and reference SQL variables in the trigger
  • More types of SQL statements can be used, including dynamic SQL statements
  • SQL PL control statements can be used in the trigger
  • It is possible to reference global variables, and to assign values to global variables
  • Finally, you can explicitly specify options, including BIND options
  • Comments are supported in SQL statements
  • You can include definitions for multiple versions of the trigger

These are all good things. But there are some additional changes that you need to be aware of with advanced triggers. All transition variables are nullable in advanced triggers. And debugging options are available. Perhaps the most significant change though is the support for a more robust ALTER TRIGGER statement that can be used to change trigger options or regenerate the trigger body. Only a very rudimentary ALTER capability is available for basic triggers.

Another nice capability for advanced triggers it that CREATE TRIGGER now provides the OR REPLACE clause. This lets the developer use one CREATE statement to define a trigger or update an existing trigger depending on whether the trigger already exists. The OR
REPLACE option can also be used with a CREATE TRIGGER statement to define a
new version of a trigger, or to replace an existing version of a trigger.


A nice chart of the behavioral differences between basic and advanced triggers can be found here, if you are interested in additional details.

The bottom line is that for shop's that rely on triggers, or that are looking to use more triggers, the set of new functionality offered in DB2 12 for z/OS greatly expands the usefulness and usability for triggers.

Tuesday, January 17, 2017

The DB2 12 for z/OS Blog Series - Part 1: SQL Pagination

Today’s blog post kicks off a new series of posts that examine new features and functionality delivered with the latest and greatest new version of DB2 foir z/OS – Version 12.

We’ll begin with a nice new feature that should make it easier for programmers writing queries where the program needs to be able to deal with a subset of results. For example, to show the first 25 rows, then the next, etc. This is a frequent requirement for mobile and web applications that are common these days.

This separating of rows into piece can now be accomplished quite easily in DB2 12 with the new OFFSET syntax. OFFSET is specified as a clause of the SELECT statement and it is used to specify the number of rows in the result table that will be skipped before
any rows are retrieved.

The offset clause is simple to code. You just need to determine the number of rows that you want to skip and code that in the clause. For example, to skip 5 rows you would code OFFSET 5 ROWS. Simple, right? Well, conceptually, yes, but in practice you have to be careful.

First of all, you must know where/when you can code an OFFSET clause. OFFSET can be specified on a subselect or fullselect that is outermost fullselect in a prepared SQL statement or a DECLARE CURSOR statement. OFFSET is also permissible in a SELECT INTO statement. However, you cannot code an OFFSET clause in a view definition, an MQT, the RETURN statement of SQL table functions, in row permissions or column masks, or in the outermost fullselect for a sensitive dynamic cursor. A further restriction is that the statements that includes the OFFSET clause cannot contain an expression that is not deterministic or that has external action.

The second, and I think more interesting aspect to consider when using the OFFSET clause is that your result set must be predictable to assure that you are retrieving useful data. As we all should know, the access path chosen by the optimizer can alter the order in which rows are returned. If you want to access rows in sets of 25, for example, then you want to make sure that each successive set does not contain any rows from previous sets, and does not omit any rows in between sets.

So how do we do this? The best approach is to code up an ORDER BY clause that specifies columns that uniquely identify each row in the result table. If there are duplicates, then there is no way to verify that you are getting the data that you want. IN other words, the order of the rows is not deterministic. The data being skipped will not be predictable and it is highly likely that you will not be accessing all of the data that you want (or perhaps even accessing the same data twice).

It is also important to understand that if the OFFSET number of rows is greater than the number of rows in the intermediate result table, you will get an empty result.

So let’s look at a quick example. Suppose we are looking for employees earning more than $50000. Further, we want to skip the first 10 rows of the EMP table, and grab the next 10. This SQL should do the trick:

SELECT *
FROM EMP
WHERE SALARY > 50000.00
ORDER BY EMPNO
OFFSET 10 ROWS
FETCH FIRST 10 ROWS ONLY;

The OFFSET 10 ROWS will cause the first 10 qualifying rows to be skipped. The FETCH clause gets the next 10 qualifying rows (after skipping the first 10).

But OFFSET is not the only new feature to help developers with SQL pagination. Also available with DB2 12 is data-dependent pagination, which uses row value
expressions in a basic predicate. That sounds more complicated than it really is, so let’s look at an example:

We can code a WHERE clause like this to search more rows with a name greater than mine:

WHERE (LASTNAME, FIRSTNAME) > (′MULLINS′, ′CRAIG′)

This is easier than what we previously had to do (before DB2 12), which was breaking the WHERE up as follows:

WHERE (LASTNAME = ′MULLINS′ AND FIRSTNAME > ′CRAIG′)
OR (LASTNAME > ′MULLINS′)


The bottom line is that application coding for pagination becomes a lot easier in DB2 12 for z/OS…

Monday, January 09, 2017

The Tao of DB2 - Part 15: Putting it all together!

We rejoin our soon-to-be-retiring DBA and the intern who is tasked with replacing him as the old DBA continues to teach the young intern about Tao and DB2.

"Soon, I will be retiring, and all of this will be yours," said the expert DBA. "Are you ready?"

"I am trying my best," said the intern. "Do you have any more advice for me before you go?"

"Ahhh... you are wise to ask. Let me again reach into the Tao to deliver a lesson..."



Squinting confusedly at his mentor the intern mumbled "…but a fish has nothing to do with my job."

The Taoist DBA corrected his intern saying "There are lessons to be learned everywhere and from everything."

The lesson here is that you should not attempt to fix what isn't broken. Just like a small fish can be spoiled simply by handling it, so can a well-tuned DB2 application. Establish service level agreements and if all is running within the agreed-upon service level, leave it alone.

"Another lesson from the Tao," said the elder DBA, "is that by giving as much care to the end as to the beginning, there will be few failures."

"You have done a great job preparing me," said the intern. "I feel my confidence rising,but I am frustrated that I am not yet a master."

Taoist DBA winked and said "Then you know how it feels!"


The lesson here is that persistence is a quality that all successful DBAs possess. Perplexed by a problem, it is always that next “thing” that will solve it… and that is a good quality. Nobody can know everything, but the more you work at it, the more things will become second nature to you as a DB2 DBA. 

"As a final lesson, let me tell you that you will learn to be ‘one with DB2’ as you apply your knowledge and these lessons to the job at hand.  Don’t panic, use your training, and the Tao of DB2 will flow through you…" were the next to last words the Taoist DBA had to say to the intern.





And with that, his mentor disappeared...