i Can ... Work With Your JVMs

This week's post was written by Arv Fisher. Arv is the team leader of the Java development team in the IBM i development lab. Thanks, Arv!

Have you ever wanted to check the current garbage collection (GC) heap size, check GC performance or display the parameters the JVM was started with? If you have environments that use Java, these questions as well as many others probably come to mind.

The IBM i 6.1 release has three new commands to assist in answering your JVM environment and performance questions:

• Work With JVM Jobs (WRKJVMJOB)
• Print JVM Job (PRTJVMJOB)
• Generate JVM Dump (GENJVMDMP)

The new commands can be used on any job where an IBM Technology for Java (IT4J) VM is currently running.

By default WRKJVMJOB will list all the currently active JVMs regardless of how they were started. GC information, JVM arguments, environment variables, thread information including Java thread names, the capability to see the Java stack frames, native heap sizes and more are available using WRKJVMJOB. (One thing that's really cool here is the environment variables for the job-until WRKJVMJOB, there was no interface to easily display the environment variables of a job other than your own! So WRKJVMJOB has some interesting function beyond just working with JVMs!)

When JVM performance is being investigated, GC information is a requirement. Most will validly choose not to run with verbose GC enabled all the time, and having to restart the JVM just to enable verbose GC isn't always an option. IBM i always keeps track of the last 300 GC cycles for each IT4J JVM. Just use WRKJVMJOB to print the GC Cycle Table to a spool file. The GC information in the spool file is in a somewhat readable form or IBM Support Assistant (ISA) Version 4 can access IBM Monitoring and Diagnostic Tools for Java -- Garbage Collection and Memory Visualizer (GCMV) -- to analyze the GC information. If you have your own favorite tool that analyzes the traditional verbose GC information you can specify -verbosegc on the Java command line or just use WRKJVMJOB to enable or disable verbose GC at any time. On IBM i, we allow you to collect GC information even when the JVM was not started with verbose GC enabled.

Interested in performing an analysis of the Java objects that exist in the GC heap? Use WRKJVMJOB to simplify the task. To perform an in-depth heap analysis, you need to generate a heap dump. In the past on IBM i and on other platforms, you had to start the JVM with some special Xdump options, find the process identifier of the JVM and then issue a command that looked like "kill -QUIT 5342". I know you were thinking the first time you issued the command and probably still do today, "What were they thinking?". On IBM i, we agreed and thought we can help. Without starting up the JVM with any special options, use WRKJVMJOB to request any IT4J JVM to generate a heap dump. We also have the capability to generate a Java or System dump if you run into a situation where it's necessary. Once you have your heap dump, you can use ISA Version 4 to get access to the tool Memory Dump Diagnostic for Java (MDD4J) to analyze the GC heap. There are times when the special Xdump options may be necessary. They still can be specified on the Java command line as you would have done in the past. We have also provided an option in WRKJVMJOB on the Work With JVM Jobs panel (12=Dump) to generate a dump using the options specified on the Java command line.

WRKJOB also has a new option, 45, to invoke WRKJVMJOB if that job has an active JVM. Experiment with WRKJVMJOB; you'll probably find information that can be helpful and is readily available. Be sure to load the latest Java Group PTF to get the most current version of the commands.

The new commands don't support the Classic JVM. IT4J will be the only JVM supported in the follow-on release to 6.1. See the Upgrade Planning Statement for the Java Developer Kit for additional information. 

The complete list of options for WRKJVMJOB is available at the Information Center.

PRTJVMJOB allows you to target a specific JVM and lets you directly print the information you can display under WRKJVMJOB. The complete list of options for PRTJVMJOB is available at the Information Center.

GENJVMDMP allows you to target a specific JVM and request it to generate a Java, System or Heap dump. The dump options are also available under WRKJVMJOB. The complete list of GENJVMDMP options is available at the Info Center.

Additional information on ISA version 4 can be found at the IBM Education Assistant Web site. 

Tell Time in Your Time Zone

Since V5R3, IBM has been working on updating the time support within the i operating system. You can see evidence of this with the time zone descriptions, which were introduced in V5R3. By using time-zone descriptions, you can allow the system to automatically adjust the system time for Daylight Saving Time (DST). But beyond the addition of time-zone descriptions and time adjustment, you haven't seen other time-related changes in subsequent releases. However, much work has been done internally within the operating system to move to a Coordinated Universal Time (UTC)-based time system; in a UTC-based system, the date and time values are stored in UTC and converted to and from a job's own time zone when displayed or changed by the user. This would ultimately allow different users in different time zones to work in their own local time.

As of the 6.1 release, IBM i doesn't have the capability to support multiple time zones within a single LPAR. However, we do get a fair number of inquiries about supporting multiple time zones. Because of these requests, we determined that we needed to provide a solution that was "good enough" for the majority of the requests we received.

So with the 6.1 release, we worked with some tool partners to provide time simulation tools. These tools have existed on prior releases, but no longer worked on 6.1. And on the prior releases, the implementation approach was not one that IBM would support. However, in 6.1 these partners can now provide the time override capabilities in a manner that's supported by IBM.

These time-simulation tools operate by overriding the date and time at the job level. These tools don't provide job-level time zone support in every environment, but they do override the date and time in RPG, COBOL, DDS and most system display screens, APIs, etc. Functions that use cached timestamps or materialize timestamps directly don't have the capability to be overridden and would continue to use the system time, or in the case of C and Java, use the time zone from the locale, if specified. As such, there are some limitations to these tools, which is why I said earlier that we worked to provide a solution that was "good enough" for many, and we do have customers using these tools successfully.

You can find additional information about these time simulation tools at the following links:

    AnyDate 

    TimeZoNe/400 

I'd like to thank Angela Newton for assisting with this blog post; Angela is the lead of the work management team and has been the key developer involved to provide the IBM i enablement in 6.1 for these time-simulation tools.

Navigating IBM i's Documentation Web

I thought it’d be good to start by reviewing the IBM i documentation and online resources available. Most of the technical topics that I'll be sharing via this blog are already documented in some manner – the issue is knowing where to find the documentation and then finding the time to read all it all!

IBM i Information Center

This is the formal documentation repository for each release. The Information Center has a tremendous amount of documentation but built-in search capabilities do leave a little to be desired. The English version of the Information Center is updated periodically; national language translated versions are not.

IBM Systems Hardware Information Center

This is where the hardware information is documented. Depending upon where you navigate to, you may end up taking links that lead you back to the IBM i Information Center.

IBM i Web presence 

This is the IBM Web site for IBM i marketing information. It's mostly overview information that reviews the key features and benefits. These Web pages generally link to the IBM i Information Center for technical documentation. There’s an amazing amount of information within the IBM i Web presence - but once again, finding it is the challenge! However, the Web pages do have a method to the madness. Each major topic area follows the same standards for organization, high-level content and layout.

I've solicited favorite links from my peers in the lab to build the following list:

• Performance Management Web page
• iDoctor for IBM i
• Systems Management 
• IBM i Access
• Security
• Availability
• TCP/IP
• HTTP Server
• BRMS
• IBM Integrated Web Application Server
• Integrated Web Services for i
• DB2 for i main page
• DB2 Web Query
• DB2 Web Query community page
• Virtualization with IBM i, PowerVM and Power Systems
• IBM i on a Power Blade Read-me First
• IBM i on POWER Blades Supported Environments
• IBM i integration with BladeCenter and System x

Redbooks 

Redbooks, Redpapers and Technotes are great technical resources. They’re generally focused on a specific topic and cover conceptual as well as task-oriented documentation. That is, Redbooks not only tell you how to do something, but also describe why you want to do something. Redbooks are produced only for a small set of topics that IBM i supports. Within the Redbooks Web site, you’ll find a specific section for "System i" Redbooks; note that "System i" is really a legacy name since the Redbooks included in this section include Redbooks for IBM i software topics as well.

AS/400 Online Library 

I don't use this site a lot, but I really like it when I need it! Given that a lot of the software on i has been there for a long time, some of the "legacy" functions haven’t been documented in the IBM i Information Center. The Information Center does contain links to the older books that are still applicable, but you have to know how to find those links! This online library Web site is how I find the older documentation more easily.

Support for IBM i Web site

The link I have provided is the System i support link - not the Power Systems support link. The Power Systems support page doesn't have all the popular links that the System i support page has - and I think those popular links are pretty good. In addition, through this Web interface you can "Search Support," which includes more documents when going through the System i support page. Searching through the support site has the really nice feature of searching through multiple repositories - Redbooks, Software Knowledge Base, Hardware and Software Information Centers, educational information, PTFs and APARs, and more. While on the topic of the support Web site, I want to specifically discuss the Software Knowledge Base.

Software Knowledge Base

The software knowledge base is a collection of articles written by IBM support representatives to describe or document common situations, scenarios or problems seen by the support center representatives. Some of the articles are available to everyone for free, and some are only available if you have software support. But these articles can provide some really helpful information. Perhaps in future blogs, I'll point out a few that I find particularly helpful.

Within the IBM i Support site, I want to highlight a couple Web pages.

• IBM Disk Sanitizer is a cool new function to securely erase IBM i disks units that I'm sure will make a future blog.
• Future software upgrade planning information is the Web site where IBM makes our future planning statements so you can be aware of potential future changes and plan for them.

No wonder we have a hard time knowing all that's available! Just trying to summarize the main Web information turned out to be surprising difficult; but what's really amazing is that I've just scratched the surface in this brief review of IBM i online information. Each and every one of these links is just the starting point for a wealth of information, not to mention the fact that I've only identified a subset of the topics that we document on the Web. This just confirms why it’s so hard to know about all the capabilities of i and why we need this blog!

Next week's blog will be on to the technical topics. Stay tuned. 

Why i Can

IBM i, being an integrated operating environment, has tremendous capabilities. A few of us in the development lab in Rochester have wanted to find a more direct way to share all of the great things done to improve and enhance IBM i. We document the enhancements in the IBM i Information Center, but outside of our marketing information, it's hard to find a nice summary of "What's new in IBM i 6.1" (or whatever release you’re interested in.) You have to scour the IBM i Information Center for the "What's New" topics scattered throughout the documentation, or look through the information and see what has been identified as being changed. And even then, not everything may be there. Many enhancements have been delivered via PTFs for current releases and the documentation is generally in the PTF cover letter --and I suspect most of you don’t read all the PTF cover letters! Plus there are no change flags on command documentation, so you have to manually compare to figure what, if anything, has changed. The documentation provided by IBM also tends to be very task oriented -- it tells you how to do something, but it may not tell you why you care. In fact, the same concern was raised in the blog by Susan Gantner and Jon Paris a while back, and it pointed out to us that there was a need for a more interactive, direct method of spreading the word about the capabilities of IBM i.

The intent of this new blog is to share the “hidden gems” within IBM i. The name “i Can” is to convey the fact that IBM i can do even more than most realize. The updates to this blog will generally be information about the latest features in the most current releases of 5.4 and 6.1. I hope to also provide some insight into why you may actually be interested in something you didn't realize you should know about.

As I’ve been planning what I'll be writing about, I discovered something -- there are a lot of enhancements and features that even the leading experts within the development lab weren’t aware of. If we within the development lab have a hard time knowing the full capabilities of our beloved operating system, how much more challenging it must be for those of you who are users of it!

And who am I? I've been working on the IBM i and its predecessors my whole career, all of which has been at IBM in Rochester. I’ve generally been part of the team that works on the “little things” that provide good value for our customers and rarely been part of major announcements within a release. Thus, sharing information about the hidden gems has always been something I thought we could do better, and now the opportunity to do just that is here. I have technical leadership responsibilities on IBM i in what I call the “core” technologies - work management, messaging, output and print management, security, networking, performance and diagnostic tools, install/upgrade, etc... -- most of the things that we've had on i forever; those things that are central to the integrated value of what i provides.

I'm thrilled to have this opportunity to share information via this blog. But this blog won't be written by me alone; we'll have developers from the lab share their expertise through this blog as well. In my (very biased) personal opinion, the i development lab in Rochester is second to none. I find it amazing what that team can accomplish! We just need to do a better job of getting the word out about everything that i can do. If there are topics that you want to hear more about, please let me know! And please provide your input and feedback via blog comments.