Welcome!

Weblogic Authors: Yeshim Deniz, Elizabeth White, Michael Meiner, Michael Bushong, Avi Rosenthal

Related Topics: Weblogic

Weblogic: Article

Transactions, Suspension, and the Ticking Clock

Keep it short - and don't time out

This month's article is again inspired by a posting on the weblogic.developer.interest.transaction newsgroup. The question (excerpted from the posting) was:

Does the <trans-timeout-seconds>10</trans-timeout-seconds> in weblogic-ejb-jar.xml apply to transactions that are in a suspended state? I have EJB1 (Container Managed/Required) that starts transaction T1 and does some work, then calls another EJB, EJB2 (Container Managed/NotSupported), which makes an interdomain T3 call. Since EJB2 is configured with NotSupported transaction attribute, transaction T1 is suspended for the time being while the business method of EJB2 is executing. The question is, if I set <trans-timeout-seconds>10</trans-timeout-seconds> for transactions started by EJB1, will it work?

The answer is yes. End of article.

Only joking! The subject of transaction timeouts and their relationship to the flow of control through an application's logic is one that often comes up, and is frequently misunderstood, so here goes another journey through "how the bits fit together."

First, a step back. As you will know if you have read my previous articles (or any other sources of information about distributed transactions), long-running XA transactions are a bad thing. Database (and potentially other) locks are held from the moment that a transaction touches the data until the point that it commits or aborts. Lots of locked data can quickly become a performance problem for any application, resulting ultimately in your whole database being locked. This is bad. The moral of that story is, keep your XA transactions as short as you possibly can to allow locks to be recycled as fast as possible.

In this context, the transaction timeout is your friend. You can set a timeout in a deployment descriptor, programmatically in your code, or via the JTA page in the BEA WebLogic console and the transaction manager will respect this timeout on your behalf. If a transaction lasts longer than the timeout permits, WebLogic's transaction manager will automatically go about rolling it back for you. The assumption is that some kind of application error (anything from a logic error to the hardware being temporarily overloaded, causing the application to run slowly) is causing the timeout to be exceeded, and that cleaning up the transaction (and thus freeing the associated locks) will help the overall health and well-being of the system.

So that's fine. That's what the transaction timeout is, and that's what it's for. Generally, tuning transaction timeout values such that transactions in a smoothly running system will never time out (by a small margin of safety) offers you a degree of protection from spikes in load and errors in logic that can turn little localized dramas into big, scary catastrophes.

As Usual, the Transaction Manager Is Your Friend
So far so clear. The confusion tends to lie with how the transaction timeout relates to other behaviors of the application server. The behaviors in question are how the timeout mechanism behaves with respect to a suspended transaction (the basis of the posting I opened with) and what happens to threads executing code on behalf of transactions that time out?

So what is suspension of a transaction? Recall that transactions have two halves. The synchronous runtime part keeps track of what application actions should be logically grouped into a transaction (controlled, by calls to begin, commit, etc.) and the asynchronous part whose obvious function is to take the list of resources collected by the runtime part and process the two-phase commit asynchronously with respect to the application flow. What the calls to UserTransaction.begin do is associate a transaction object with the current thread of execution. The fact that a transaction is associated with a thread of execution tells the application-server infrastructure to propagate the transaction along with any calls or data accesses the thread makes. A call to UserTransaction.commit disassociates the transaction object and the current thread and kicks off the two-phase commit of the (now-completed) transaction. What suspending a transaction does is simply break the association between a thread of execution and a transaction. Resuming it rebuilds the association. Thus, if you need to work outside of an active transaction, you suspend it, do the work, and then resume it when you're done.

There is one more necessary detail here: the life cycles of the synchronous and asynchronous components do not follow each other serially. Both begin concurrently when the UserTransaction.begin call is made. The synchronous part clearly ends before the asynchronous part, since the two-phase commit processing that is the latter's primary responsibility cannot begin until the synchronous piece has completed - completion signalled by calling commit.

Given the rationale I have laid out for the timeout's existence, it should be clear that the other duty performed by the asynchronous component of the transaction is timeout processing. From the moment the begin call is made, the timer starts ticking independently of the flow of your processing. When the timeout expires, the Transaction Manager will roll the transaction back. The first you hear of that happening may be when calls you make in the thread associated with the transaction start to throw exceptions, since it is not possible to propagate a rolled-back transaction (what would be the point, the results of the call will not persist under any circumstances?).

After all that, the direct answer to the question we started with is that suspending a transaction has no impact whatsoever on its timeout; it simply breaks the association between transaction and thread. If your code suspends a transaction and then goes to sleep for a week, it should expect to find that the transaction has timed out while it slept.

The Transaction Has Timed Out While It Slept
Finally, to the second relationship I mentioned - that between the timed-out transaction and the thread currently executing work on the transaction's behalf. Some people hope that if they set a transaction timeout on an operation, when the timeout is exceeded all work on behalf of the transaction will instantly stop. In an ideal world, that would happen (and WebLogic does all it can to try and stop you wasting cycles by refusing to propagate a timed-out transaction), but the world (and the world I am referring to here is the general world of java) is not ideal. So the transaction times out, and WebLogic wants to stop your thread. What can it do? Looking at the java.lang.Thread class, we quickly conclude that it can't do a whole lot. It could call Thread.interrupt, but then code inside the thread would have to catch the Interrupt and clean up - so this requires cooperation for the application code. It could call Thread.destroy, but according to the Javadoc this is not implemented (and if it was, would leave no way to clean up resources). Or it could call Thread.stop() except that that's deprecated with a mile-long health warning that talks about how stopping a thread with no controlled cleanup could lead to all sorts of inconsistent data being left around.

There is no easy answer - there isn't really a facility in J2SE or J2EE as they stand today to allow a thread to be safely and asynchronously terminated. WebLogic does what it can - the node manager will try and detect "stuck" threads to warn operators about them; the runtime will try and prevent work continuing on behalf of rolled-back transactions by throwing exceptions rather than propagating them. And, it does all it can at the JDBC level (such as calling Statement.cancel for statements running on behalf of rolling back transactions where possible) but at the end of the day - until the thread returns control to the container - there isn't much more WebLogic can do than wait.

In summary, the transaction timeout impacts the asynchronous behavior of the transaction manager only - it has no direct impact whatsoever on the flow of control within the application logic.

I have timed out again for another month. Roll back and read more next time!

More Stories By Peter Holditch

Peter Holditch is a senior presales engineer in the UK for Azul Systems. Prior to joining Azul he spent nine years at BEA systems, going from being one of their first Professional Services consultants in Europe and finishing up as a principal presales engineer. He has an R&D background (originally having worked on BEA's Tuxedo product) and his technical interests are in high-throughput transaction systems. "Of the pitch" Peter likes to brew beer, build furniture, and undertake other ludicrously ambitious projects - but (generally) not all at the same time!

Comments (1) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
Dhilip Krishnan 04/14/04 04:57:01 PM EDT

Hi Peter,

I am glad to read your article on transaction timeout and suspended transactions. The insight you provided is very useful. Its me who posted the question with bea earlier.

Espically the section "The Transaction Has Timed Out While It Slept", provides useful insight into how transaction manager handles timedout transactions.

The biggest lesson I learned while investigating this issue was not to mix up transaction attributes amoung resources while using multiple resources in a single transaction. If you have three ejbs invoking one after the other in a chain, your are better off setting all of the ejb''s transaction attributes to either "Required" or "Not Required".

@ThingsExpo Stories
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
"Akvelon is a software development company and we also provide consultancy services to folks who are looking to scale or accelerate their engineering roadmaps," explained Jeremiah Mothersell, Marketing Manager at Akvelon, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
It is of utmost importance for the future success of WebRTC to ensure that interoperability is operational between web browsers and any WebRTC-compliant client. To be guaranteed as operational and effective, interoperability must be tested extensively by establishing WebRTC data and media connections between different web browsers running on different devices and operating systems. In his session at WebRTC Summit at @ThingsExpo, Dr. Alex Gouaillard, CEO and Founder of CoSMo Software, presented ...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
WebRTC is great technology to build your own communication tools. It will be even more exciting experience it with advanced devices, such as a 360 Camera, 360 microphone, and a depth sensor camera. In his session at @ThingsExpo, Masashi Ganeko, a manager at INFOCOM Corporation, introduced two experimental projects from his team and what they learned from them. "Shotoku Tamago" uses the robot audition software HARK to track speakers in 360 video of a remote party. "Virtual Teleport" uses a multip...
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
SYS-CON Events announced today that Evatronix will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Evatronix SA offers comprehensive solutions in the design and implementation of electronic systems, in CAD / CAM deployment, and also is a designer and manufacturer of advanced 3D scanners for professional applications.
Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
An increasing number of companies are creating products that combine data with analytical capabilities. Running interactive queries on Big Data requires complex architectures to store and query data effectively, typically involving data streams, an choosing efficient file format/database and multiple independent systems that are tied together through custom-engineered pipelines. In his session at @BigDataExpo at @ThingsExpo, Tomer Levi, a senior software engineer at Intel’s Advanced Analytics gr...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things’). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing? IoT is not about the devices, it’s about the data consumed and generated. The devices are tools, mechanisms, conduits. In his session at Internet of Things at Cloud Expo | DXWor...
Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution. In his session at @ThingsExpo, Akvelon expert and IoT industry leader Sergey Grebnov provided an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.