A Condensed 35-Year History of DB2 for z/OS (...and Db2 for z/OS)

Let's go back in time... over three decades ago... back to the wild and woolly 1980s! And watch our favorite DBMS, DB2, grow up over time.

DB2 Version 1 Release 1 was announced on June 7, 1983, and it became generally available on Tuesday, April 2, 1985. I wonder if it was ready on April 1st but not released because of April Fool’s Day? Initial DB2 development focused on the basics of making a relational DBMS work. Early releases of DB2 were viewed by many as an “information center” DBMS, not for production workloads, like IMS was.

Version 1 Release 2 was announced on February 4, 1986 and was released for general availability a month later on March 7, 1986. Can you imagine waiting only a month for a new release of DB2 these days? But that is how it happened back then. Same thing for Version 1 Release 3, which was announced on May 19, 1987 and became GA on June 26, 1987. DB2 V1R3 saw the introduction of DATE data types.

You might notice that IBM delivered “releases” of DB2 back in the 1980s, whereas today (and ever since V3) there have only been versions. Versions are major changes, whereas releases are not quite as significant as a version.

Version 2 Release 1 was announced in April 1988 and delivered in September 1988. Here we start to see the gap widening again between announcement and delivery. V2R1 was a significant release in the history of DB2, a bellwether of sorts for when DB2 began to be viewed as capable of supporting mission-critical, transaction processing workloads. Not only did V2R1 provide significant performance enhancements but it also signaled the introduction of declarative Referential Integrity (RI) constraints.

No sooner than V2R1 became GA than IBM announced Version 2 Release 2 on October 4, 1988. But it was not until a year later that it became generally available on September 23, 1988. DB2 V2R2 again bolstered performance in many ways. It also saw the introduction of distributed database support (private protocol) across MVS systems.

Version 2 Release 3 was announced on September 5, 1990, and became generally available on October 25, 1991. Two very significant features were added in V2R3: segmented table spaces and packages. Segmented table spaces quickly became a de facto standard and packages made DB2 application programs easier to support. DB2 V2R3 is also the version that beefed up distributed support with Distributed Relational Database Architecture (DRDA).

Along comes DB2 Version 3, announced in November 1993 and GA in December 1993. Now it may look like things sped up again here, but not really. This is when the early support program for DB2 started. Early support was announced in March 1993 and delivered to customers in June 1993. V3 greatly expanded the number of buffer pool options available (from 5 pools to 80), and many advances were made for DB2 to take better advantage of the System 390 environment, including support for hardware-assisted compression and hiperpools. It was also V3 that introduced I/O parallelism for the first time.

Version 4 signaled another significant milestone in the history of DB2. It was highlighted by the introduction of Type 2 indexes, which removed the need to lock index pages (or subpages, now obsolete). Prior to V4, index locking was a particularly thorny performance problem that vexed many shops. Data Sharing made its debut in V4, too, and with it, DB2 achieved new heights of scalability and availability allowing users to upgrade without an outage and to add new subsystems to a group “on the fly.” DB2 V4 also introduced stored procedures, as well as CP parallelism.

In June 1997 DB2 Version 5 became generally available. It was the first DB2 version to be referred to as DB2 for OS/390 (previously it was DB2 for MVS). Not as significant as V4, we see the trend of even-numbered releases being bigger and more significant than odd-numbered releases (of course, that is just my opinion). V5 was touted by IBM as the e-business and BI version. It included Sysplex parallelism, prepared statement caching, reoptimization, online REORG, and conformance to the SQL-92 standard.

Version 6 brings us to 1999 and the introduction of the Universal Database term to the DB2 moniker. The “official” name of the product became DB2 Universal Database for OS/390. And the Release Guide swelled to over 600 pages! Six categories of improvements were introduced with V6 spanning object-relational extensions, network computing, performance and availability, capacity improvements, data sharing enhancements, and user productivity. The biggest of the new features were SQLJ, inline statistics, triggers, large objects (LOBs), user-defined functions, and distinct types.

Version 6 is also somewhat unique in that there was this “thing” typically referred to as the V6 refresh. It added functionality to DB2 without there being a new release or version. The new functionality in the refresh included SAVEPOINTs, identity columns, declared temporary tables, and performance enhancements (including star join).

March 2001 brings us to DB2 Version 7, another “smaller” version of DB2. Developed and released around the time of the Year 2000 hubbub, it offered much-improved utilities and some nice new SQL functionality including scrollable cursors, limited FETCH, and row expressions. Unicode support was also introduced in Db2 V7.

DB2 Version 8 followed, but not immediately. IBM took advantage of Y2K and the general desire of shops to avoid change during this period to take its time and deliver the most significant and feature-laden version of DB2 ever. V8 had more new lines of code than DB2 V1R1 had total lines of code!

With DB2 9 for z/OS, we drop the “V” from the name. Is that in response to Oracle’s naming conventions? Well, we do add a space between the DB2 and the version number because we don’t want to talk about DB-twenty-nine! A lot of great new functionality comes with DB2 9 including additional database definition on demand capabilities, binary data types, and a lot of new SQL capabilities including OLAP functions and EXCEPT/INTERSECT. But probably the biggest new feature is pureXML, which allows you to store DB2 data as native XML. The XML is stored natively as a new data type that can be searched and analyzed without the need to reformat it. The approach was novel in that it  supports native XML, basically enabling dual storage engines.

And that brings us to DB2 10 for z/OS. This version of DB2 was built to take advantage of many zEnterprise (the latest new mainframe at the time) features to deliver scalability. Examples include improved compression, cache optimization, blades for running the Smart Analytics Optimizer, etc. 

Additional capabilities included many performance improvements (BIND, IN-list, utilities, etc.), hash organized table spaces, high-performance DBATs (DDF threads) forced to use RELEASE COMMIT, parallel index updating, efficient caching of dynamic SQL with literals, temporal data support, safe query optimization, improved access path hints, access to currently committed data, new TIMESTAMP precision and time zones, and buffer pool options for pinning objects in memory.

In October 2013 we got another new version, DB2 11 for z/OS. Click on that link if you want all the details, but some highlights included transparent archiving, global variables, improved SQL PL, APREUSE(WARN), significant utility improvements, DROP COLUMN support, and JSON support with IBM BigInsights.

And that brings us to the present day, with DB2 12 for z/OS as the current (and soon to be only) supported version of Db2. Released for general availability in October 2016, DB2 12 for z/OS abandons the traditional new release cycle that IBM has followed for decades, adopting a new continuous delivery model. New functionality is now delivered in Function Levels (FLs) that are easily applied and delivered much more rapidly than in the past. Indeed, the current Db2 function level is FL506, which means there have been 6 new function levels added since 2016.

Version 12 brought with it a plethora of new capabilities including virtual storage enhancements, optimization improvements, and improved control over the introduction of new SQL capabilities. DB2 12 for z/OS delivered many improvements for both application development and database administration. Examples of new application capabilities include:

• Additional support for triggers, arrays, global variables, pureXML, and JSON
• MERGE statement enhancements
• SQL pagination support
• Support for Unicode columns in an EBCDIC table
• Piece-wise deletion of data
• Support for temporal referential constraint
• More flexibility in defining application periods for temporal tables
• PERCENTILE function support
• Resource limits for static SQL statements
• Db2 REST services improve efficiency and security
• DevOps with Db2: Automated deployment of applications with IBM UrbanCode Deploy

Examples of new DBA and SYSADM capabilities include:

• Installation or migration without requiring SYSADM
• Improved availability when altering index compression
• Online schema enhancements
• Improved catalog availability
• Object ownership transfer
• Improved data validation after running DSN1COPY
• Automatic start of profiles at Db2 start
• Increased partition sizes and simplified partition management for partition-by-range table spaces with relative page numbering
• Ability to add partitions between existing logical partitions
• UNLOAD privilege for the UNLOAD utility
• Temporal versioning for Db2 catalog tables
• Statistics collection enhancements for SQL performance    

Of course, these are just some of the V12 improvements; there are many more (as well as all of the Function Level improvements)!

Then sometime in the middle of 2017, IBM decided to change the name of DB2 by making the uppercase B a lowercase b. So now the name of our beloved DBMS is Db2. Nobody has been able to explain to me what the benefit of this was, so don’t ask me!

The Bottom Line

I worked with DB2 way back in its Version 1 days, and I’ve enjoyed watching DB2 grow over its first 35 years. Of course, we did not cover every new feature and capability of each version and release, only the highlights. Perhaps this journey back through time will help you to remember when you jumped on board with Db2 and relational database technology. I am happy to have been associated with Db2 (and DB2) for its first 35 years and I look forward to many more years of working with Db2… 

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.