Welcome!

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

Related Topics: Weblogic

Weblogic: Article

XA Transactions

Needed More Often Than You Think

Most developers have at least heard of XA, which describes the standard protocol that allows coordination, commitment, and recovery between transaction managers and resource managers.

Products such as CICS, Tuxedo, and even BEA WebLogic Server act as transaction managers, coordinating transactions across different resource managers. Typical XA resources are databases, messaging queuing products such as JMS or WebSphere MQ, mainframe applications, ERP packages, or anything else that can be coordinated with the transaction manager. XA is used to coordinate what is commonly called a two-phase commit (2PC) transaction. The classic example of a 2PC transaction is when two different databases need to be updated atomically. Most people think of something like a bank that has one database for savings accounts and a different one for checking accounts. If a customer wants to transfer money between his checking and savings accounts, both databases have to participate in the transaction or the bank risks losing track of some money.

The problem is that most developers think, "Well, my application uses only one database, so I don't need to use XA on that database." This may not be true. The question that should be asked is, "Does the application require shared access to multiple resources that need to ensure the integrity of the transaction being performed?" For instance, does the application use Java 2 Connector Architecture adapters, the BEA WebLogic Server Messaging Bridge, or the Java Message Service (JMS)? If the application needs to update the database and any of these other resources in the same transaction, then both the database and the other resource need to be treated as XA resources.

In addition to Web or EJB applications that may touch different resources, XA is often needed when building Web services or BEA WebLogic Integration applications. Integration applications often span disparate resources and involve asynchronous interfaces. As a result, they frequently require 2PC. An extremely common use case for WebLogic Integration that calls for XA is to pull a message from WebSphere MQ, do some business processing with the message, make updates to a database, and then place another message back on MQ. Usually this whole process has to occur in a guaranteed and transactional manner. There is a tendency to shy away from XA because of the performance penalty it imposes. Still, if transaction coordination across multiple resources is needed, there is no way to avoid XA. If the requirements for an application include phrases such as "persistent messaging with guaranteed once and only once message delivery," then XA is probably needed.

Figure 1 shows a common, though extremely simplified, BEA WebLogic Integration process definition that needs to use XA. A JMS message is received to start the process. Assume the message is a customer order. The order then has to be placed in the order shipment database and placed on another message queue for further processing by a legacy billing application. Unless XA is used to coordinate the transaction between the database and JMS, we risk updating the shipment database without updating the billing application. This could result in the order being shipped, but the customer might never be billed.

Once you've determined that your application does in fact need to use XA, how do we make sure it is used correctly? Fortunately, J2EE and the Java Transaction API (JTA) hide the implementation details of XA. Coding changes are not required to enable XA for your application. Using XA properly is a matter of configuring the resources that need to be enrolled in the same transaction. Depending on the application, the BEA WebLogic Server resources that most often need to be configured for XA are connection pools, data sources, JMS Servers, JMS connection factories, and messaging bridges. Fortunately, the entire configuration needed on the WebLogic side can be done from the WebLogic Server Console.

Before worrying about the WebLogic configuration for XA, we have to ensure that the resources we want to access are XA enabled. Check with the database administrator, the WebSphere MQ administrator, or whoever is in charge of the resources that are outside WebLogic. These resources do not always enable XA by default, nor do all resources support the X/Open XA interface, which is required to truly do XA transactions. For example, some databases require that additional scripts be run in order to enable XA.

For those resources that do not support XA at all, some transaction managers allow for a "one-phase" optimization. In a one-phase optimization, the transaction manager issues a "prepare to commit" command to all of the XA resources. If all of the XA resources respond affirmatively, the transaction manager will commit the non-XA resource. The transaction manager will then commit all of the XA resources. This allows the transaction manager to work with a non-XA resource, but normally only one XA resource per transaction is allowed. There is a small chance that something will go wrong after committing the non-XA resource and before the XA resources all commit, but this is the best alternative if a resource just doesn't support XA.

Connection pools are where most people start configuring WebLogic for XA. The connection pool needs to use an XA driver. Most database vendors provide XA drivers for their databases. BEA WebLogic Server 8.1 SP2 ships with a number of XA drivers for Oracle, DB2, Informix, SQL Server, and Sybase. We need to ensure that the Driver classname on the connection pool page of the BEA WebLogic Console is in fact an XA driver. When using the configuration wizards in BEA WebLogic Server 8.1, the wizards always note which drivers are XA enabled.

When more than one XA driver is available for the database involved, be sure to run some benchmarks to determine which driver gives the best performance. Sometimes different drivers for the same database implement XA in completely different ways. This leads to wide variances in performance. For example, the Oracle 9.2 OCI Driver implements XA natively, while the Oracle 9.2 Thin Driver relies on stored procedures in the database to implement XA. As a result, the Oracle 9.2 OCI driver generally performs XA transactions much faster than the Thin driver. Oracle's newest Type 4 driver, the 10g Thin Driver, also implements XA natively and is backwards compatible with some previous versions of the Oracle database. Taking the time to fully evaluate alternative drivers can lead to significant performance improvements.

If only some of the database access needs to be done under XA, create two connection pools for the same database. Use an XA driver on one of the connection pools and a non-XA driver on the other. This will avoid the performance overhead of XA transactions for database calls that don't need 2PC.

Closely related to the connection pools are the data sources. In order to use XA, a data source must have the value "Honor Global Transactions" set to true. Prior to BEA WebLogic Server 8.1, these data sources appeared in the Console under the heading "Tx Data Sources". In 8.1, all data sources are under the same heading. Turning this flag on means that BEA WebLogic Server will be able to correctly handle transactions in a number of different scenarios. Setting this flag will ensure that WebLogic Server's JTA implementation will automatically enroll the data source in an XA transaction if it is required. There are also situations where this flag should be set even if your application does not use XA. The "Honor Global Transactions" flag should also be enabled if your application makes any explicit JTA calls, uses container-managed transactions with EJBs, or issues multiple SQL statements within the same transaction. In these non-XA situations, BEA WebLogic Server will ensure that the application retains the proper database connection from the connection pool to ensure transactional integrity.

A second flag on the data source page that is occasionally used is the "Emulate Two-Phase Commit for Non-XA Driver" setting. This flag should only be used if an XA driver cannot be obtained for the database. When this flag is on, a one-phase optimization is used. BEA WebLogic Server will first issue the "prepare to commit" command to the XA resources, commit the database that has emulation enabled, and then commit the resources in the transaction that are XA enabled. As long as nothing goes wrong, the data will still be consistent.

There is a potential that WebLogic Server will commit the non-XA transaction, only to have the transaction on the XA resource fail. WebLogic Server allows only one data source using emulation per transaction. Given the availability of XA drivers for most databases and the potential for inconsistent data, this setting should rarely be used. Figure 2 shows a data source properly configured for XA.

Within BEA WebLogic Server, JMS Servers themselves are XA resources. There is nothing special that needs to be configured to XA enable a JMS Server, but there is one configuration item that seems counter-intuitive. When using a JDBC store for the JMS Server, you might think that the connection pool used by the JDBC store needs to use an XA driver. In fact, the exact opposite is true. The connection pool for the JDBC store should not use an XA driver. In this case, the XA resource is the JMS Server, not the database. For this reason, a JMS Server that uses a file store is still capable of participating in an XA transaction. The decision about whether to use a file store or a JDBC store for a JMS Server should not be based on whether or not an application will need to use XA.

The next step to ensure that you are using XA with your JMS-based application is to use an XA connection factory. Again, the application code does not change, but a configuration setting in the BEA WebLogic console needs to be checked. After creating a new connection factory, you need to go to the "Transactions" tab and check "XA Connection Factory Enabled". Changing this value will require a server restart. If only some of the application's work with JMS needs to use XA, you may want to create another connection factory that does not use XA. Figure 3 shows a JMS connection factory configured for XA transactions.

The last resource that deserves mention is the messaging bridge, which was introduced originally for BEA WebLogic Server 7.0 and is intended to make it easier to integrate WebLogic JMS with foreign JMS providers. The messaging bridge acts as a bidirectional store-and-forward mechanism to transfer messages back and forth between WebLogic JMS and another messaging product, such as WebSphere MQ. WebLogic applications do not interact directly with the messaging bridge. Instead, they interact in a normal manner with the local WebLogic JMS queues or topics. The local queue or topic is then bridged to the foreign JMS provider. However, there are several configuration settings for the messaging bridge that need to be set correctly to ensure "guaranteed once and only once" delivery between WebLogic and the other product. Some of the settings are on the JMS Bridge Destination and some of the settings are on the bridge itself. These settings affect whether or not BEA WebLogic Server will use XA transactions when it transfers messages.

When configuring a Bridge Destination, there are three settings that control whether or not WebLogic Server will treat the destination as an XA resource: the adapter, the Adapter JNDI Name, and the Connection Factory JNDI Name. BEA WebLogic Server uses J2EE Connector Architecture adapters to communicate with the Bridge Destinations. The adapter that is used must support XA. BEA WebLogic Server provides a generic XA adapter named jms-xa-adp.rar. The Adapter JNDI Name for this is eis.jms.WLSConnectionFactoryJNDIXA. Finally, the foreign JMS Server must have an XA-enabled connection factory, and the name of this connection factory is placed in the Connection Factory JNDI Name field.

The messaging bridge itself has different qualities of service available: Exactly-Once, Atmost-once, and Duplicate-okay. If "guaranteed once and only once" delivery is a requirement for the application, then the only acceptable setting for Quality of Service on the messaging bridge configuration page is "Exactly-Once". The QoS Degradation Allowed flag should also be unchecked. Checking this box allows BEA WebLogic Server to default to a lower quality of service if it is unable to get an XA connection to the foreign provider. This is usually a very bad idea. Qualities of service should be dictated by the business requirements. Business requirements are rarely flexible enough to switch back and forth between "Exactly-Once" and other service levels. Using the QOS Degradation Allowed flag means that no one can predict which quality of service WebLogic Server will be using at runtime.

Once you've configured XA for the resources involved in an application, how can you determine that everything is working properly? Under normal conditions, where all resources are available and operating correctly, a non-XA–enabled application will behave exactly the same as an XA-enabled one. XA proves its value when an application encounters unexpected situations. The test plan for an application should include scenarios where each resource is unavailable. Testing should also evaluate what happens when a resource becomes unavailable in the middle of processing transactions. Intentionally killing a BEA WebLogic Server instance, causing a duplicate key error, or restarting a database simulates situations that can happen in production. If XA has been properly configured, all resources should complete or roll back the same transactions.

Conclusion
By now two things should be clear. XA transactions are needed more often than most developers realize, and XA is very easy to configure within BEA WebLogic Server. Always evaluate the configuration based on the application's business requirements and then choose the appropriate settings to make sure that transactions behave in the way they should.

More Stories By Wes Hewatt

Wes Hewatt has over fourteen years of experience designing and deploying mission critical applications for Fortune 1000 companies. As a Senior Systems Engineer for BEA Systems, Mr. Hewatt works with BEA's customers to develop J2EE applications for the WebLogic Platform. He specializes in web services and integration technologies.

Comments (4) 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
Thomas 09/27/07 09:44:01 AM EDT

Hi,

I am pretty new on this subject, but I don't get this sentence:

"This allows the transaction manager to work with a non-XA resource, but normally only one XA resource per transaction is allowed."

Shouldn't this be "but normally only one non-XA resource per transaction is allowed"?

Otherwise the "one-phase-commit" optimization would only be applicable for the case, that you have two resources, one XA and one non-XA. But there is no problem to expand the XA resources to as many as possible, because they all support the two-phase-commit, and I think this is done with the XA resources also in the one-phase-commit, because they respond to the commit-request of the transaction manager. The only thing that's different from a "real" two-phase-commit is the non-XA resource, which "prepared to commit" like the other XA resources. Is this correct?

Steve Kaminski 07/17/07 09:14:10 PM EDT

Hi, I am told that if you have a single XA datasource (using an XA driver) and you initiate a transaction on that datasource that involves only 1 resource WLS JTA will perform the transaction as a local transaction and as such avoid the overhead involved in an XA (global) transaction. Is this true? and if so why would you ever need one data source for non-XA and another for XA transactions as you suggest in this article?

Very good article by the way, well done on a difficult subject. You have a skill.

Sudheer Bandaru 05/14/04 12:04:56 PM EDT

The article was excellent and well designed which even covers many points that might be helpful to solve the errors and warnings when using an application.Also explains clearly when and how to use XA drivers to a new user.

Gian Luca 05/12/04 06:26:52 AM EDT

The article is well done! But we were interested more specifically in what happens in case of system crashes or DataBase failure... We encoutered problems of in-doubt transactions (Oracle 8/9) not recovered by the BEA''s Transaction recovery System !! Have you got informations at regards?
Thanks,

Gian Luca Paloni

@ThingsExpo Stories
The IoTs will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, will demonstrate how to move beyond today's coding paradigm and share the must-have mindsets for removing complexity from the development proc...
SYS-CON Events announced today that EastBanc Technologies will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. EastBanc Technologies has been working at the frontier of technology since 1999. Today, the firm provides full-lifecycle software development delivering flexible technology solutions that seamlessly integrate with existing systems – whether on premise or cloud. EastBanc Technologies partners with p...
SYS-CON Events announced today that MangoApps will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. MangoApps provides modern company intranets and team collaboration software, allowing workers to stay connected and productive from anywhere in the world and from any device. For more information, please visit https://www.mangoapps.com/.
SYS-CON Events announced today that Super Micro Computer, Inc., a global leader in Embedded and IoT solutions, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Supermicro (NASDAQ: SMCI), the leading innovator in high-performance, high-efficiency server technology, is a premier provider of advanced server Building Block Solutions® for Data Center, Cloud Computing, Enterprise IT, Hadoop/Big Data, HPC and ...
18th Cloud Expo, taking place June 7-9, 2016, at the Javits Center in New York City, NY, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises are using some...
SYS-CON Events announced today Object Management Group® has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that IBM Cloud Data Services has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. IBM Cloud Data Services offers a portfolio of integrated, best-of-breed cloud data services for developers focused on mobile computing and analytics use cases.
Cloud computing delivers on-demand resources that provide businesses with flexibility and cost-savings. The challenge in moving workloads to the cloud has been the cost and complexity of ensuring the initial and ongoing security and regulatory (PCI, HIPAA, FFIEC) compliance across private and public clouds. Manual security compliance is slow, prone to human error, and represents over 50% of the cost of managing cloud applications. Determining how to automate cloud security compliance is critical...
The Internet of Things (IoT) is growing rapidly by extending current technologies, products and networks. By 2020, Cisco estimates there will be 50 billion connected devices. Gartner has forecast revenues of over $300 billion, just to IoT suppliers. Now is the time to figure out how you’ll make money – not just create innovative products. With hundreds of new products and companies jumping into the IoT fray every month, there’s no shortage of innovation. Despite this, McKinsey/VisionMobile data...
"What we see what happens when you have a completely networked society and the potential to now drive the value creation and the collaboration and the ecosystems that are possible when you start to be able to connect people and industries together in ways that have never been possible before," explained Esmeralda Swartz, VP of Marketing Enterprise & Cloud at Ericsson, in this SYS-CON.tv interview at @ThingsExpo, held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA.
WebRTC is bringing significant change to the communications landscape that will bridge the worlds of web and telephony, making the Internet the new standard for communications. Cloud9 took the road less traveled and used WebRTC to create a downloadable enterprise-grade communications platform that is changing the communication dynamic in the financial sector. In his session at @ThingsExpo, Leo Papadopoulos, CTO of Cloud9, will discuss the importance of WebRTC and how it enables companies to fo...
SYS-CON Events announced today that ContentMX, the marketing technology and services company with a singular mission to increase engagement and drive more conversations for enterprise, channel and SMB technology marketers, has been named “Sponsor & Exhibitor Lounge Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York City, New York. “CloudExpo is a great opportunity to start a conversation with new prospects, but what happens after the...
The IoT is changing the way enterprises conduct business. In his session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, discuss how businesses can gain an edge over competitors by empowering consumers to take control through IoT. We'll cite examples such as a Washington, D.C.-based sports club that leveraged IoT and the cloud to develop a comprehensive booking system. He'll also highlight how IoT can revitalize and restore outdated business models, making them profitable...
Customer experience has become a competitive differentiator for companies, and it’s imperative that brands seamlessly connect the customer journey across all platforms. With the continued explosion of IoT, join us for a look at how to build a winning digital foundation in the connected era – today and in the future. In his session at @ThingsExpo, Chris Nguyen, Group Product Marketing Manager at Adobe, will discuss how to successfully leverage mobile, rapidly deploy content, capture real-time d...
What a difference a year makes. Organizations aren’t just talking about IoT possibilities, it is now baked into their core business strategy. With IoT, billions of devices generating data from different companies on different networks around the globe need to interact. From efficiency to better customer insights to completely new business models, IoT will turn traditional business models upside down. In the new customer-centric age, the key to success is delivering critical services and apps wit...
Join us at Cloud Expo | @ThingsExpo 2016 – June 7-9 at the Javits Center in New York City and November 1-3 at the Santa Clara Convention Center in Santa Clara, CA – and deliver your unique message in a way that is striking and unforgettable by taking advantage of SYS-CON's unmatched high-impact, result-driven event / media packages.
As cloud and storage projections continue to rise, the number of organizations moving to the cloud is escalating and it is clear cloud storage is here to stay. However, is it secure? Data is the lifeblood for government entities, countries, cloud service providers and enterprises alike and losing or exposing that data can have disastrous results. There are new concepts for data storage on the horizon that will deliver secure solutions for storing and moving sensitive data around the world. ...
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, will provide an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life ...
SYS-CON Events announced today that MobiDev will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex software systems for startups and enterprises. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobile software company with over 200 develope...
SoftLayer operates a global cloud infrastructure platform built for Internet scale. With a global footprint of data centers and network points of presence, SoftLayer provides infrastructure as a service to leading-edge customers ranging from Web startups to global enterprises. SoftLayer's modular architecture, full-featured API, and sophisticated automation provide unparalleled performance and control. Its flexible unified platform seamlessly spans physical and virtual devices linked via a world...