The DB2 12 for z/OS Blog Series - Part 11: Enhanced Support for Arrays

The ARRAY data type was added to DB2 in the last release (Version 11) with the ability to define both ordinary arrays or associative arrays. An ordinary array has a user-defined number of elements that are referenced by their ordinal position in the array. An associative array has no user-defined number of elements that are referenced by the array index value. An associative array’s index values do not have to be contiguous but they are unique. SQL PL variables and parameters for SQL PL routines could be defined as arrays. 

Support for global variables was also added to DB2 11 for z/OS, but they could not be defined as an ARRAY. With DB2 12 for z/OS you can create global variables with an array data type. So the following is now legal as long as you are on V12 or higher:

  CREATE TYPE IntgrArray AS INTEGER ARRAY[5]
  ...
  CREATE VARIABLE IntgrArrayGV IntgrArray

A data type is defined as an integer array and a global variable is created using that data type.

Additional enhancements for array handling added to DB2 12 include the ability to use the ARRAY_AGG aggregate function to create an associative array... and  you can specify the ORDER BY clause on the ARRAY_AGG aggregate function (as an option). The ARRAY_AGG function enables your programs to utilize arrays without having to code SQL PL in stored procedures or triggers.

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.

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!?!?

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.

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.