|By Wes Hewatt||
|April 9, 2004 12:00 AM EDT||
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.
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.
|Thomas 09/27/07 09:44:01 AM EDT|
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?
Gian Luca Paloni
Pulzze Systems was happy to participate in such a premier event and thankful to be receiving the winning investment and global network support from G-Startup Worldwide. It is an exciting time for Pulzze to showcase the effectiveness of innovative technologies and enable them to make the world smarter and better. The reputable contest is held to identify promising startups around the globe that are assured to change the world through their innovative products and disruptive technologies. There w...
Aug. 27, 2016 07:45 AM EDT Reads: 645
DevOps at Cloud Expo, taking place Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long dev...
Aug. 27, 2016 06:15 AM EDT Reads: 2,333
Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...
Aug. 27, 2016 03:15 AM EDT Reads: 1,766
Personalization has long been the holy grail of marketing. Simply stated, communicate the most relevant offer to the right person and you will increase sales. To achieve this, you must understand the individual. Consequently, digital marketers developed many ways to gather and leverage customer information to deliver targeted experiences. In his session at @ThingsExpo, Lou Casal, Founder and Principal Consultant at Practicala, discussed how the Internet of Things (IoT) has accelerated our abil...
Aug. 27, 2016 02:30 AM EDT Reads: 2,001
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
Aug. 27, 2016 01:45 AM EDT Reads: 1,731
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions wi...
Aug. 27, 2016 01:15 AM EDT Reads: 2,014
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
Aug. 27, 2016 12:45 AM EDT Reads: 2,935
SYS-CON Events announced today that 910Telecom will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
Aug. 26, 2016 10:00 PM EDT Reads: 1,859
SYS-CON Events announced today Telecom Reseller has been named “Media Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. 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.
Aug. 26, 2016 07:00 PM EDT Reads: 684
Smart Cities are here to stay, but for their promise to be delivered, the data they produce must not be put in new siloes. In his session at @ThingsExpo, Mathias Herberts, Co-founder and CTO of Cityzen Data, will deep dive into best practices that will ensure a successful smart city journey.
Aug. 26, 2016 04:45 PM EDT Reads: 1,549
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportuni...
Aug. 26, 2016 04:00 PM EDT Reads: 3,951
There is growing need for data-driven applications and the need for digital platforms to build these apps. In his session at 19th Cloud Expo, Muddu Sudhakar, VP and GM of Security & IoT at Splunk, will cover different PaaS solutions and Big Data platforms that are available to build applications. In addition, AI and machine learning are creating new requirements that developers need in the building of next-gen apps. The next-generation digital platforms have some of the past platform needs a...
Aug. 26, 2016 03:15 PM EDT Reads: 501
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
Aug. 26, 2016 10:15 AM EDT Reads: 3,598
Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, will discuss the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
Aug. 26, 2016 09:45 AM EDT Reads: 1,872
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, 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 enterpri...
Aug. 26, 2016 05:00 AM EDT Reads: 3,063
I wanted to gather all of my Internet of Things (IOT) blogs into a single blog (that I could later use with my University of San Francisco (USF) Big Data “MBA” course). However as I started to pull these blogs together, I realized that my IOT discussion lacked a vision; it lacked an end point towards which an organization could drive their IOT envisioning, proof of value, app dev, data engineering and data science efforts. And I think that the IOT end point is really quite simple…
Aug. 25, 2016 11:45 PM EDT Reads: 2,323
Identity is in everything and customers are looking to their providers to ensure the security of their identities, transactions and data. With the increased reliance on cloud-based services, service providers must build security and trust into their offerings, adding value to customers and improving the user experience. Making identity, security and privacy easy for customers provides a unique advantage over the competition.
Aug. 25, 2016 09:15 PM EDT Reads: 2,247
Is the ongoing quest for agility in the data center forcing you to evaluate how to be a part of infrastructure automation efforts? As organizations evolve toward bimodal IT operations, they are embracing new service delivery models and leveraging virtualization to increase infrastructure agility. Therefore, the network must evolve in parallel to become equally agile. Read this essential piece of Gartner research for recommendations on achieving greater agility.
Aug. 25, 2016 05:15 PM EDT Reads: 795
SYS-CON Events announced today that Venafi, the Immune System for the Internet™ and the leading provider of Next Generation Trust Protection, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Venafi is the Immune System for the Internet™ that protects the foundation of all cybersecurity – cryptographic keys and digital certificates – so they can’t be misused by bad guys in attacks...
Aug. 25, 2016 01:00 PM EDT Reads: 2,640
For basic one-to-one voice or video calling solutions, WebRTC has proven to be a very powerful technology. Although WebRTC’s core functionality is to provide secure, real-time p2p media streaming, leveraging native platform features and server-side components brings up new communication capabilities for web and native mobile applications, allowing for advanced multi-user use cases such as video broadcasting, conferencing, and media recording.
Aug. 25, 2016 08:45 AM EDT Reads: 2,166