|By Patrick Yeh||
|April 12, 2007 03:00 PM EDT||
Thread pooling is a common technique that modern application servers adopted to run Java applications efficiently. Even application servers not implemented by Java share the concept of using system resources more compactly to maximize overall throughput. Besides the underlying programming mystery of native OS threads, a Java thread object encapsulates some hurdles to easy-to-use and flexible synchronization at the programming level. JDK 5.0 has built-in thread pooling classes in its 'java.util.concurrent' package to facilitate programming the thread pool quickly. If we're using a J2EE application server, the container inherently enforces thread synchronization from its runtime nature. That means we don't have to fight difficult threading issues day and night, but it doesn't mean we can dismiss them. Instead, we should attend to the thread issues inside the code and the architecture. If we don't, system performance will degrade. A once well-running system will gradually become slower and slower, then application throughput will be blocked and external requests start to queue up. There's some degree of denial of service. In most commercial production environments like telecom, e-commerce and banking, this situation impacts the business and can create unplanned system outages.
While the server operator calls for help, an experienced engineer often asks something outstanding of the application environment. During the incident, we may see either ultra-high or ultra-low CPU usage at the OS level along with applications hanging and threads sticking at the JVM level from a three-dimensional viewpoint. How does one disclose the bottleneck and abnormality at the JVM level? The answer is: When the problem is reproducible then a commercial productive profiling tool or remotely debugging the JVM is an option. But taking copies of the thread dumps is widely used because it's straightforward and instantaneous. And it involves the least overhead.
Thread dumps provide a snapshot of the JVM internals at a special point at a minimal cost. We may give the JVM hosting the applications a signal SIG-QUIT with the JVM process ID (PID) on a Unix-like system (e.g., kill -3 xxxxxx; where 'xxxxxx' is the JVM PID) or have a control-break on the Windows Java console ask the JVM to output its thread information in detail to a standard output when the JVM didn't start in company with a '-Xrs' option before. Due to the importance of the thread dump, it's best to redirect the standard output to a file or pipe the information to a utility that can store and rotate the standard output to log files (see Figure1).
A JVM has a complementary function that enables it to get the thread dump at the undocumented C API level. (We can look at the Java source code that Sun released recently under the GPL to see this feature.) We may utilize this API for a simple debugging framework to address many common issues inside the application. But it requires a JNI implementation in C because there's no pure Java API to force the JVM to generate the thread dump, though we may get similar thread stack traces in JDK 5.0 via the 'getAllStackTraces()' API. Despite this tricky function, we're interested in a snapshot of the thread dump while we have identified the stuck threads (see Figure 2).
With copies of the thread dump collected at intervals of seconds, we may identify the stuck threads from the running state of each thread in the thread pool. Fortunately, some application servers do an automatic health check on the application thread pools. In fact, it acts like a watchdog that periodically check the last running statistics on the threads in the thread pools. Once the threads have run for fixed long-running seconds, it will print out the execution information on the stuck threads either in standard output or log files. Second, some platform JDK vendors have out their diagnostic utilities in the public domain to aid us in detecting stuck threads (e.g., HP's JMeter and IBM's thread analyzer). However, once we isolate the stuck threads, we'll have to figure out why they got stuck from the information (i.e., the stack traces of these stuck threads) about what they were doing when they got stuck. This way we can improve code quality and tier architecture in the next iteration (see Figure 3).
A stuck thread means a thread is blocked and can't return to the thread pool smoothly in a given period of time. When an application thread is blocked unintentionally, it means it can't quickly complete its dispatch and be reused. In most of production situations, the root cause of these stuck threads is also the root cause of bad system performance because it interferes with regular task execution. [It's also a performance issue for producers and healthy consumers. < 1 ] (request frequency) < (healthy thread count for request execution/average measured request execution time per healthy thread.]
Blocking without specifying a network connect or read timeout is the most frequent reason we have seen. When we don't manually configure a timeout for each method call involving networking, it will have a potential blocking behavior by the underlying physical socket read/connect characteristic. While waiting infinitely for the response from the other side, the native OS networking layer probably throws an I/O exception. By default this behavior takes an unexpectedly long time (e.g., 240 seconds). Modern distributed systems need to factor in this situation (especially, Web Services invocations). Though we may set timeouts for well-known protocols via some system properties (e.g., sun.net.client.defaultConnectTimeout and sun.net.client.defaultReadTimeout), the newer version of JDK might provide a generic mechanism to explicitly configure each default timeout value for those whose methods call socket connect/read as a security policy file. For example, com.sun.jndi.ldap.read.timeout (http://java.sun.com/docs/books/tutorial/jndi/newstuff/readtimeout.html) wasn't available prior to JDK 6.0 for LDAP service provider read timeout. Otherwise, when the problematic code isn't under the control of end users, it usually needs to restart the application to temporarily reset the abnormal phenomenon propagated from the other side. In addition, we should take into account whether the service we called is idempotent while analyzing this kind of issue in the design phase because we don't know whether the service at the other end keeps executing when the thread has ended its invocation after a timeout (see Figure 4).
The unexpectedly long execution time of a SQL statement is a common condition that causes a stuck thread. In the thread dump we collected, we can see that the stuck thread was running a network socket read for a long time without changes and the thread's stack trace contains many JDBC driver classes. Under these conditions, we can also check the status of the database it connected with and set the query timeout for all application code using a JDBC statement setQueryTimeout method. (Most JDBC drivers support this feature but we'd have to read the JDBC driver's release note first.) According to the different nature of every SQL query, it would be better to segregate the programs that have a longer execution time in another thread pool and tune the database table with indices for faster access. We would also need to check whether the JDBC driver is certified with the connected database. A sub-issue is the accessed table locked by other processes so the threads for the JDBC query couldn't continue because of table locking.
Resource contention is an issue that's hard to find if we don't get the entire thread dump to analyze. Basically, it's an issue of producers and consumers. Any limited resources on the system (JDBC connections, socket connections, etc.) will impact this issue. The best thing to do is look at the thread dump, get the stuck thread name from the log, and find the bottleneck that's causing the stuck thread.
File descriptor leaking is an issue that causes this phenomenon (Note that a Unix socket implementation requires a file descriptor). So the JVM should have enough file descriptor numbers to host our applications. Generally, we can adjust the open file limit with the Unix shell 'ulimit' command for the current shell. And we can list the open files with the public domain 'lsof' tool. It's intensely interesting that many developers don't explicitly use the 'close()' method in the final block when an object inherently provides a 'close()' method and want JVM to release these unclosed objects when garbage is collected. We should keep firmly in mind that that act is bad without closing the system resource after use. A special case is when the socket connections in the application don't close properly while still being underdeployed and then the application begins to throw an IOException with a 'Too many open files' message after repeated application redeployment.
|Patrick 08/03/07 04:21:08 AM EDT|
|Omar 04/09/07 04:10:36 PM EDT|
First of all, excellent article!! Very informative and practical.
You make reference of a utility to monitor stack threads. Where can I download this utility? There seems to be a .jar file an a shared library.
Thanking you in advance,
SYS-CON Events announced today that Cisco, the worldwide leader in IT that transforms how people connect, communicate and collaborate, has been named “Gold Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Cisco makes amazing things happen by connecting the unconnected. Cisco has shaped the future of the Internet by becoming the worldwide leader in transforming how people connect, communicate and collaborate. Cisco and our partners are building the platform for the Internet of Everything by connecting the...
Mar. 29, 2015 07:00 PM EDT Reads: 5,202
SYS-CON Events announced today that robomq.io will exhibit at SYS-CON's @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. robomq.io is an interoperable and composable platform that connects any device to any application. It helps systems integrators and the solution providers build new and innovative products and service for industries requiring monitoring or intelligence from devices and sensors.
Mar. 29, 2015 06:00 PM EDT Reads: 1,469
The WebRTC Summit 2014 New York, to be held June 9-11, 2015, at the Javits Center in New York, NY, announces that its Call for Papers is open. Topics include all aspects of improving IT delivery by eliminating waste through automated business models leveraging cloud technologies. WebRTC Summit is co-located with 16th International Cloud Expo, @ThingsExpo, Big Data Expo, and DevOps Summit.
Mar. 29, 2015 06:00 PM EDT Reads: 1,581
Temasys has announced senior management additions to its team. Joining are David Holloway as Vice President of Commercial and Nadine Yap as Vice President of Product. Over the past 12 months Temasys has doubled in size as it adds new customers and expands the development of its Skylink platform. Skylink leads the charge to move WebRTC, traditionally seen as a desktop, browser based technology, to become a ubiquitous web communications technology on web and mobile, as well as Internet of Things compatible devices.
Mar. 29, 2015 06:00 PM EDT Reads: 1,839
Docker is an excellent platform for organizations interested in running microservices. It offers portability and consistency between development and production environments, quick provisioning times, and a simple way to isolate services. In his session at DevOps Summit at 16th Cloud Expo, Shannon Williams, co-founder of Rancher Labs, will walk through these and other benefits of using Docker to run microservices, and provide an overview of RancherOS, a minimalist distribution of Linux designed expressly to run Docker. He will also discuss Rancher, an orchestration and service discovery platf...
Mar. 29, 2015 04:15 PM EDT Reads: 2,428
Wearable technology was dominant at this year’s International Consumer Electronics Show (CES) , and MWC was no exception to this trend. New versions of favorites, such as the Samsung Gear (three new products were released: the Gear 2, the Gear 2 Neo and the Gear Fit), shared the limelight with new wearables like Pebble Time Steel (the new premium version of the company’s previously released smartwatch) and the LG Watch Urbane. The most dramatic difference at MWC was an emphasis on presenting wearables as fashion accessories and moving away from the original clunky technology associated with t...
Mar. 29, 2015 04:00 PM EDT Reads: 1,409
SYS-CON Events announced today that Vitria Technology, Inc. will exhibit at SYS-CON’s @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Vitria will showcase the company’s new IoT Analytics Platform through live demonstrations at booth #330. Vitria’s IoT Analytics Platform, fully integrated and powered by an operational intelligence engine, enables customers to rapidly build and operationalize advanced analytics to deliver timely business outcomes for use cases across the industrial, enterprise, and consumer segments.
Mar. 29, 2015 03:30 PM EDT Reads: 2,165
SYS-CON Events announced today that Solgenia will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Solgenia is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between Personal and Professional Social, Mobile and Cloud user experiences, our solutions help large and medium-sized organizations dr...
Mar. 29, 2015 03:00 PM EDT Reads: 2,839
SYS-CON Events announced today that Liaison Technologies, a leading provider of data management and integration cloud services and solutions, has been named "Silver Sponsor" of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York, NY. Liaison Technologies is a recognized market leader in providing cloud-enabled data integration and data management solutions to break down complex information barriers, enabling enterprises to make smarter decisions, faster.
Mar. 29, 2015 03:00 PM EDT Reads: 3,449
@ThingsExpo has been named the Top 5 Most Influential M2M Brand by Onalytica in the ‘Machine to Machine: Top 100 Influencers and Brands.' Onalytica analyzed the online debate on M2M by looking at over 85,000 tweets to provide the most influential individuals and brands that drive the discussion. According to Onalytica the "analysis showed a very engaged community with a lot of interactive tweets. The M2M discussion seems to be more fragmented and driven by some of the major brands present in the M2M space. This really allows some room for influential individuals to create more high value inter...
Mar. 29, 2015 01:45 PM EDT Reads: 4,660
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on Twitter at @MicroservicesE
Mar. 29, 2015 12:00 PM EDT Reads: 1,445
After making a doctor’s appointment via your mobile device, you receive a calendar invite. The day of your appointment, you get a reminder with the doctor’s location and contact information. As you enter the doctor’s exam room, the medical team is equipped with the latest tablet containing your medical history – he or she makes real time updates to your medical file. At the end of your visit, you receive an electronic prescription to your preferred pharmacy and can schedule your next appointment.
Mar. 29, 2015 12:00 PM EDT Reads: 769
The list of ‘new paradigm’ technologies that now surrounds us appears to be at an all time high. From cloud computing and Big Data analytics to Bring Your Own Device (BYOD) and the Internet of Things (IoT), today we have to deal with what the industry likes to call ‘paradigm shifts’ at every level of IT. This is disruption; of course, we understand that – change is almost always disruptive.
Mar. 29, 2015 11:45 AM EDT Reads: 1,104
SYS-CON Events announced today the IoT Bootcamp – Jumpstart Your IoT Strategy, being held June 9–10, 2015, in conjunction with 16th Cloud Expo and Internet of @ThingsExpo at the Javits Center in New York City. This is your chance to jumpstart your IoT strategy. Combined with real-world scenarios and use cases, the IoT Bootcamp is not just based on presentations but includes hands-on demos and walkthroughs. We will introduce you to a variety of Do-It-Yourself IoT platforms including Arduino, Raspberry Pi, BeagleBone, Spark and Intel Edison. You will also get an overview of cloud technologies s...
Mar. 29, 2015 11:00 AM EDT Reads: 2,091
SYS-CON Events announced today that SafeLogic has been named “Bag Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. SafeLogic provides security products for applications in mobile and server/appliance environments. SafeLogic’s flagship product CryptoComply is a FIPS 140-2 validated cryptographic engine designed to secure data on servers, workstations, appliances, mobile devices, and in the Cloud.
Mar. 29, 2015 11:00 AM EDT Reads: 1,416
SOA Software has changed its name to Akana. With roots in Web Services and SOA Governance, Akana has established itself as a leader in API Management and is expanding into cloud integration as an alternative to the traditional heavyweight enterprise service bus (ESB). The company recently announced that it achieved more than 90% year-over-year growth. As Akana, the company now addresses the evolution and diversification of SOA, unifying security, management, and DevOps across SOA, APIs, microservices, and more.
Mar. 29, 2015 08:30 AM EDT Reads: 2,048
GENBAND has announced that SageNet is leveraging the Nuvia platform to deliver Unified Communications as a Service (UCaaS) to its large base of retail and enterprise customers. Nuvia’s cloud-based solution provides SageNet’s customers with a full suite of business communications and collaboration tools. Two large national SageNet retail customers have recently signed up to deploy the Nuvia platform and the company will continue to sell the service to new and existing customers. Nuvia’s capabilities include HD voice, video, multimedia messaging, mobility, conferencing, Web collaboration, deskt...
Mar. 29, 2015 01:00 AM EDT Reads: 1,459
SYS-CON Media announced today that @WebRTCSummit Blog, the largest WebRTC resource in the world, has been launched. @WebRTCSummit Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @WebRTCSummit Blog can be bookmarked ▸ Here @WebRTCSummit conference site can be bookmarked ▸ Here
Mar. 28, 2015 08:00 PM EDT Reads: 1,800
SYS-CON Events announced today that Akana, formerly SOA Software, has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Akana’s comprehensive suite of API Management, API Security, Integrated SOA Governance, and Cloud Integration solutions helps businesses accelerate digital transformation by securely extending their reach across multiple channels – mobile, cloud and Internet of Things. Akana enables enterprises to share data as APIs, connect and integrate applications, drive part...
Mar. 28, 2015 04:15 PM EDT Reads: 1,541
Cloud is not a commodity. And no matter what you call it, computing doesn’t come out of the sky. It comes from physical hardware inside brick and mortar facilities connected by hundreds of miles of networking cable. And no two clouds are built the same way. SoftLayer gives you the highest performing cloud infrastructure available. One platform that takes data centers around the world that are full of the widest range of cloud computing options, and then integrates and automates everything. Join SoftLayer on June 9 at 16th Cloud Expo to learn about IBM Cloud's SoftLayer platform, explore se...
Mar. 28, 2015 02:00 PM EDT Reads: 1,634