|By Catherine Diep, Gennaro Cuomo||
|February 3, 2003 12:00 AM EST||
Server-side caching techniques have long been used to improve Internet performance of Web applications. In general, caching improves response time and reduces system load. Most techniques cache static content, which is data that changes rarely, if at all, such as graphics and text files. While the solutions for caching static content have resulted in excellent performance for some Web applications, they have little or no value in enhancing the performance of Web applications with dynamically generated pages.
For years, IBM Research has developed and refined technologies that enable the caching of dynamic content. These technologies were implemented, deployed, and verified at various high-volume sporting event sites such as the 1998 Winter Olympic Games in Nagano. The success of the sports sites demonstrated the feasibility and significance of caching dynamic content and confirmed the scalability and reliability of the caching technologies. Based on these proven and scalable caching technologies, IBM developed a dynamic content caching solution for Java 2 Enterprise Edition (J2EE) applications running on WebSphere Application Server Version 5.0. In this article we introduce WebSphere dynamic caching services.
WebSphere Application Server (WAS) offers a built-in dynamic caching service for serving dynamic content and caching data. The WebSphere development team often refers to this service simply as dynacache. There is no time-consuming installation and integration work needed to activate dynacache. The cache is enabled/disabled declaratively using simple XML configuration files or using the WAS Administrative User Interface; these methods not only allow caching to be brought up quickly and easily, but also provide great flexibility and control at runtime. Also, you can define your existing caches, such as the caching component of WebSphere Edge Server or IBM HTTP Server, as external caches and use them in conjunction with dynacache.
This article introduces the presentation-level caching features of dynacache. These features are:
Caching Dynamic Content
The key issues for caching dynamic content involve determining what should be cached, where caching should take place, and how to invalidate cached data.
What Should Be Cached?
Content or data that is changing and that at the same time must be stable over a long enough time for meaningful reuse to occur is a candidate for dynamic content caching . If access is frequent, such as with pricing information of a popular stock, then even a short period of stability may be of enough benefit to warrant the caching of dynamic content.
All dynamic Web pages consist of smaller and simpler page fragments. Some fragments are static (such as headers and footers), while others are dynamic (such as fragments containing stock quotes or sports scores). Breaking a page into fragments or components makes effective caching possible for any page, even a highly dynamic page. The goal of creating fragments or components is to maximize fragment reusability and cache utilization.
For example, Figure 1 shows that a page can be broken down into fragments based on reusability and cacheability. Some fragments - headers, footers, and navigation bars, for example - are reusable by all users who visit this site. Other fragments, such as watch lists and news, are not typically cacheable at the presentation level because of the personalized content being displayed. While some presentation fragments may not be reusable across a large set of users, the raw data contained within may very well be cacheable.
Caching can involve a final formatted whole page (such as HTML or XML), a final formatted fragment, or a piece of unformatted raw data. Each, in its own way, contributes to the ultimate benefit of caching dynamic content. Dynacache offers features that enable dynamic content to be cached at various granularities, namely whole pages, fragments, and raw data.
Where Should Caching Take Place?
Theoretically, caching of dynamic content should take place as close to the user as possible. In reality, other factors such as security and user-specific data may influence the choice for the best place to cache dynamic content.
Web application design can play an important role in determining where dynamic data is cached. One example is personalized pages. Although personalized, these pages may contain user-specific, nonuser-specific, locale-sensitive, secure, or nonsecurity-sensitive dynamic data. To maximize the benefit of caching dynamic content, these types of data should be fragmented as finely as possible so they can be cached independently at different locations. For example, the nonuser-specific, nonsecurity-sensitive fragments or components are generally useful to many users, and thus can be cached in a more public space and closer to users. The security-sensitive data should be cached behind the enterprise firewall.
In a multitier e-business environment, dynacache can be activated at the business logic and/or presentation layer. It can also control external caches on servers, such as IBM WebSphere Edge Server and IBM HTTP Server. When external caching is enabled, the cache matches pages with their universal resource identifiers (URIs) and exports matching pages to the external cache. The contents can then be served from the external cache instead of the application server, which saves resources and improves performance. Additionally, dynacache's replication and invalidation support extends the cost-effectiveness of caching dynamic content by enabling cache sharing and cache replication in an environment containing multiple tiers and servers. Finally, WAS's edge of network caching support expands the application caches into the network.
How Are Caches Invalidated?
The biggest challenge when caching dynamic content is to guarantee the freshness, consistency, and accuracy of the content. This requires efficient and comprehensive mechanisms for identifying and updating pages/fragments/data that are no longer valid, a process called invalidation.
Dynacache provides invalidation techniques that are rules-based, time-based, group-based, and programmatic. It can also invalidate the remote caches that were configured as its external caches. Dynacache uses a facility called the Data Replication Service, which is a JMS-based facility, to replicate cached data and propagate invalidate events within a WebSphere cluster.
Dynamic Cache Service Architecture
Figure 2 illustrates the architecture of dynacache. Dynacache operates within WebSphere's JVM to provide generalized Java object caching for use by various consumers. In order to minimize memory consumption, the caching service utilizes a modified LRU (least recently used) eviction policy for cached entries. As a service, dynacache can be configured, tuned, and monitored through WebSphere's systems management interfaces.
In its simplest form, dynacache can be thought of as a highly functional Hashtable. One of its primary purposes is to store (put) and retrieve (get) Java objects from memory. As the various caching entry-points interact with the object store, dynacache manages the entries by controlling growth by running replacement or eviction algorithms. Entries in the cache are managed by a policy based on the class of entry (e.g., servlet/JSP, EJB, command, etc.). The policy is expressed as an XML file called cachespec.xml. The policy defines both global and class-specific characteristics of the cache. For example, cache size, replication policy, and disk offload configurations are globally defined for an instance of dynacache. However, much of the policy data is class specific, describing the rules by which Cache IDs are generated. Cache policies can be written to control servlet/JSP, command bean, and Web services response caching.
Dynacache provides a disk overflow capability, known as Hash Table on Disk (HTOD), that is an optimized file store for serialized Java objects. The HTOD takes the form of a single logical disk file (which can expand to multiple physical 1GB files). Leveraging dynacache and HTOD allows for robust and centralized memory management and provides the potential to leverage networked file systems via NAS (network attached storage) and SANs (storage area networks) for high availability.
To support caching done outside of the J2EE application space, the caching service can cooperate with external caches through its external cache adapter to actively trigger invalidations of cached Web content to registered adapters, which include the WebSphere HTTP Plugin, IBM HTTP Server, and its FRCA (Fast Response Cache Accelerator) cache, and the WebSphere Edge Server now shipped as part of WebSphere Application Server Network Deployment.
Servlet/JSP Result Cache
The servlet/JSP result cache intercepts calls to a servlet's service method, and checks whether the invocation can be served from a cache. If the servlet cannot be served from cache, it is invoked to generate the output that will be cached. The resulting cache entry contains the output; the side effects of the invocation, for example, calls to other servlets or JSP files; and the metadata about the entry, including timeout and entry priority information
Servlet/JSP result cache caching can be based on:
- Request parameters and attributes
- The URI used to invoke the servlet or JSP
- Session information
- Other options, including cookies
Alternatively, the cache entries generated by the servlet/JSP result cache can be pushed to external caches, such as the cache component of WebSphere Edge Server or IBM HTTP Server. For J2EE applications that have high read/write ratios, the servlet/JSP result cache creates an opportunity for significant gains in server response time, throughput, and scalability. Moreover, since the servlet/JSP result cache is nonintrusive and is enabled declaratively, currently deployed and running servlets/JSPs can be configured to take advantage of dynamic content caching without changing any code.
The Command Cache
The command cache is used to cache dynamic data that requires back-end data retrieval, such as back-end database JDBC calls. The command cache forms a good synergy with the servlet/JSP result cache because in some cases even caching the most granular, final-formatted fragment is not sufficient. For example, a personalized page may contain a stock watch-list fragment (see Figure 4). This fragment consists of two sets of information: the watch list, which is highly personalized, and the corresponding stock symbol pricing information, which is generalized information and usable by many users.
Suppose the stock list is the customer's stock portfolio, which is highly sensitive and is stored at the back-end server. In this case it is not effective to cache the final formatted fragment. Since the stock quotes are highly volatile, this fragment will be regenerated repeatedly. The net result is that every time this fragment is reconstructed, it is necessary to retrieve the stock list from the source. A better approach is to use the command cache to cache the stock list and avoid fetching the list continually from the back-end database.
To use the command cache, user applications need to write to the WebSphere Command Framework API. The WebSphere Command Framework is based on the Command Design Pattern widely used in Java programming paradigms. Typically, these applications use "setters" to set the command's input states, one or more "execute" methods, and "getters" to retrieve the results. The results can be either formatted or raw data.
The command cache intercepts the "execute" method call of a command written for the command cache and checks whether the command object can be served from the cache. If the command object does not exist in the cache, the logic in the execute method is performed and the resulting object is cached.
The caching behavior of the command cache is defined declaratively with the XML cache policy file, which describes whether and how a command should be cached. The command cache can be used at the presentation and/or business logic layer in multitier environments.
The command cache is easy to use. For existing applications that follow a Model-View-Control (MVC) design pattern, the command cache can be implemented with minimal impact to existing code.
Replication support further extends the value of caching in an e-business application. With this support, caches can be shared (central cache) or replicated (local cache) among servers. Replication can be enabled and configured declaratively with XML cache policy files. Cache policy also defines the cache entries or groups that should be shared or replicated.
Replication support uses a built-in high-performance standards-based JMS messaging system as its underlying engine for data replication.
Figure 5 shows an example of three servers configured to have their local caches replicated with each other. The messaging broker can be the built-in JMS broker belonging to one of the three servers. In this case, the broker is the built-in JMS broker at server one. A request for data (1) hits server one (or any of the three servers). If the requested data is not in the cache, the data is fetched from the back-end server (2). Resulting data from the back-end server (3) is cached at server one and then returned to the requester (4). When the cache of server one detects the cache update request, it publishes a message (a) regarding the change to the messaging broker. Whatever change occurred at server one is automatically replicated to server two (b) and server three (c).
The difference between caching static and dynamic content is the requirement for proactive and effective invalidation mechanisms, such as event-based invalidation, to ensure the freshness of content. Time-based invalidation alone is no longer adequate for dynamic cache invalidation.
Dynacache provides rules-based, time-based, and group-based invalidation techniques. The WebSphere Application Server Enterprise Edition, version 5, offers access to programmatic cache and invalidation techniques. Invalidation policies can be defined with XML cache policy files. Invalidation policies allow triggering events to invalidate cache entries without the need to write explicit code. More complex invalidation scenarios may require code that invokes the invalidation API.
The responsibility for synchronizing the dynamic cache of external caches with the application server is shared by both systems. For example, a public Web page dynamically created and cached at the application server using the servlet/JSP result cache can be exported by the application server and cached by the edge server's Caching Proxy. The Caching Proxy can then serve the application's execution results repeatedly to many different users until notified that the page is invalid. Content in the Caching Proxy's servlet response cache is valid until the proxy server removes an entry because the cache is congested, the default timeout set by the Caching Proxy's configuration file expires, or the Caching Proxy receives an invalidate message directing it to purge the content from its cache. Invalidate messages originate at the application server that owns the content and are propagated to each configured Caching Proxy.
Edge of Network Caching Support
Dynacache can use IBM HTTP Server's high-speed cache, referred to as the Fast Response Cache Accelerator, as its external cache, to cache whole pages and fragments.
The Edge Components of WebSphere Application Server Network Deployment v5.0 can also be configured as the application server's external cache for whole-page caching. In such cases, dynacache can be enabled to match pages with their universal resource identifiers (URIs) and export matching pages to the external cache. The contents can then be served from the external cache instead of the application server to significantly save resources and improve performance.
Figure 6 shows an example of exporting a dynamically cached page from the application server to the cache component of the edge server. More information about caching dynamic content at the edge of the network can be found in the white paper, "WebSphere Edge Services Architecture Guide to Edge Applications" (www-3.ibm.com/software/webservers/ edgeserver/doc/Guide_to_Edge_Apps_2.pdf).
With dynacache's external cache control, distributed-fragment caching, and assembly support, dynamic content can be exported, cached, and assembled at the most optimal location, closer to the end user. More important, the WebSphere Application Server can maintain control of the external cache through its invalidation support to ensure the freshness of cached content. As a result, WebSphere Application Server is equipped to create and serve highly dynamic Web pages without jeopardizing page performance and user experiences.
In Table 1, you can see which caching technique and cache distribution technique are most useful for each type of Web content.
WebSphere Application Server provides a variety of graphical user interface tools to help configure and monitor the dynamic content cache.
Application Assembly Tool
The Application Assembly Tool (AAT) is used to package application code components into the needed modules, which comply with the J2EE specification for deployment onto the application server. AAT can also be used to configure the cache policy associated with the application for caching.
Cache Monitor Servlet
The Cache Monitor Servlet is provided as an installable Enterprise Archive file that can be installed and used for monitoring cache statistics.
As more e-business sites seek to retain customers by serving personalized content, they face potential server-side bottlenecks, slow response time, and increasing infrastructure costs. The dynacache service employed by WebSphere can solve these critical challenges. Caching dynamic content that requires back-end requests or CPU-intensive computations can reduce server-side bottlenecks and maximize system resources, thus boosting performance and reducing infrastructure cost.
Dynacache users can benefit from using the available comprehensive functions to cache their dynamic content. The servlet/JSP result cache and the command cache make possible the caching of dynamic content at various levels of granularity for the highest possible number of cache hits. The replication and invalidation support facilitates caches to be shared, replicated, and synchronized in multitier or multiserver environments. The edge of network caching support, with its external caches and fragment support, generates a virtual extension of application server caches into the network.
Using dynacache can improve throughput and performance. As expected, improvements vary depending on how dynamic the data is, how well the pages are designed (fragmented) for maximum cache hits, and how costly it is to fetch and construct the content. Nevertheless, considerable benefits can be realized. Furthermore, the success of the IBM sports sites confirms the scalability and reliability of these underlying technologies in a truly high-volume environment.
|wesnur 11/25/09 05:10:00 AM EST|
Hi Catherine , Gennaro
I have read your article thoroughly; it is in deed very informative one. There is no second thought that Dynamic Caching is the ultimate solution of the issues like Scalability, Reliability and Performance. But you haven’t talked about the topologies which can be used for dynamic caching. I wanted to request if you could please read this article and give you opinion about the topologies as well Benefits of using NCache Dynamic Clustering Capabilities.
The Internet of Everything (IoE) brings together people, process, data and things to make networked connections more relevant and valuable than ever before – transforming information into knowledge and knowledge into wisdom. IoE creates new capabilities, richer experiences, and unprecedented opportunities to improve business and government operations, decision making and mission support capabilities.
Jul. 30, 2015 09:00 AM EDT Reads: 245
In his keynote at 16th Cloud Expo, Rodney Rogers, CEO of Virtustream, discussed the evolution of the company from inception to its recent acquisition by EMC – including personal insights, lessons learned (and some WTF moments) along the way. Learn how Virtustream’s unique approach of combining the economics and elasticity of the consumer cloud model with proper performance, application automation and security into a platform became a breakout success with enterprise customers and a natural fit for the EMC Federation.
Jul. 30, 2015 09:00 AM EDT Reads: 2,145
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists addressed this very serious issue of profound change in the industry.
Jul. 29, 2015 03:00 PM EDT Reads: 1,259
Discussions about cloud computing are evolving into discussions about enterprise IT in general. As enterprises increasingly migrate toward their own unique clouds, new issues such as the use of containers and microservices emerge to keep things interesting. In this Power Panel at 16th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the state of cloud computing today, and what enterprise IT professionals need to know about how the latest topics and trends affect their organization.
Jul. 29, 2015 02:00 PM EDT Reads: 1,174
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Jul. 29, 2015 01:45 PM EDT Reads: 427
For IoT to grow as quickly as analyst firms’ project, a lot is going to fall on developers to quickly bring applications to market. But the lack of a standard development platform threatens to slow growth and make application development more time consuming and costly, much like we’ve seen in the mobile space. In his session at @ThingsExpo, Mike Weiner, Product Manager of the Omega DevCloud with KORE Telematics Inc., discussed the evolving requirements for developers as IoT matures and conducted a live demonstration of how quickly application development can happen when the need to comply wit...
Jul. 29, 2015 07:30 AM EDT Reads: 280
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Architect for the Internet of Things and Intelligent Systems, described how to revolutionize your archit...
Jul. 28, 2015 06:30 PM EDT Reads: 1,378
It is one thing to build single industrial IoT applications, but what will it take to build the Smart Cities and truly society-changing applications of the future? The technology won’t be the problem, it will be the number of parties that need to work together and be aligned in their motivation to succeed. In his session at @ThingsExpo, Jason Mondanaro, Director, Product Management at Metanga, discussed how you can plan to cooperate, partner, and form lasting all-star teams to change the world and it starts with business models and monetization strategies.
Jul. 28, 2015 04:30 PM EDT Reads: 1,756
Converging digital disruptions is creating a major sea change - Cisco calls this the Internet of Everything (IoE). IoE is the network connection of People, Process, Data and Things, fueled by Cloud, Mobile, Social, Analytics and Security, and it represents a $19Trillion value-at-stake over the next 10 years. In her keynote at @ThingsExpo, Manjula Talreja, VP of Cisco Consulting Services, discussed IoE and the enormous opportunities it provides to public and private firms alike. She will share what businesses must do to thrive in the IoE economy, citing examples from several industry sectors.
Jul. 28, 2015 11:00 AM EDT Reads: 2,036
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Opening Keynote at 16th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, d...
Jul. 27, 2015 09:00 PM EDT Reads: 2,041
There will be 150 billion connected devices by 2020. New digital businesses have already disrupted value chains across every industry. APIs are at the center of the digital business. You need to understand what assets you have that can be exposed digitally, what their digital value chain is, and how to create an effective business model around that value chain to compete in this economy. No enterprise can be complacent and not engage in the digital economy. Learn how to be the disruptor and not the disruptee.
Jul. 27, 2015 10:00 AM EDT Reads: 2,023
Akana has released Envision, an enhanced API analytics platform that helps enterprises mine critical insights across their digital eco-systems, understand their customers and partners and offer value-added personalized services. “In today’s digital economy, data-driven insights are proving to be a key differentiator for businesses. Understanding the data that is being tunneled through their APIs and how it can be used to optimize their business and operations is of paramount importance,” said Alistair Farquharson, CTO of Akana.
Jul. 27, 2015 09:00 AM EDT Reads: 315
Business as usual for IT is evolving into a "Make or Buy" decision on a service-by-service conversation with input from the LOBs. How does your organization move forward with cloud? In his general session at 16th Cloud Expo, Paul Maravei, Regional Sales Manager, Hybrid Cloud and Managed Services at Cisco, discusses how Cisco and its partners offer a market-leading portfolio and ecosystem of cloud infrastructure and application services that allow you to uniquely and securely combine cloud business applications and services across multiple cloud delivery models.
Jul. 27, 2015 08:00 AM EDT Reads: 1,898
The enterprise market will drive IoT device adoption over the next five years. In his session at @ThingsExpo, John Greenough, an analyst at BI Intelligence, division of Business Insider, analyzed how companies will adopt IoT products and the associated cost of adopting those products. John Greenough is the lead analyst covering the Internet of Things for BI Intelligence- Business Insider’s paid research service. Numerous IoT companies have cited his analysis of the IoT. Prior to joining BI Intelligence, he worked analyzing bank technology for Corporate Insight and The Clearing House Payment...
Jul. 26, 2015 09:00 PM EDT Reads: 1,568
"Optimal Design is a technology integration and product development firm that specializes in connecting devices to the cloud," stated Joe Wascow, Co-Founder & CMO of Optimal Design, in this SYS-CON.tv interview at @ThingsExpo, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 25, 2015 02:00 PM EDT Reads: 382
SYS-CON Events announced today that CommVault has been named “Bronze Sponsor” of SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. A singular vision – a belief in a better way to address current and future data management needs – guides CommVault in the development of Singular Information Management® solutions for high-performance data protection, universal availability and simplified management of data on complex storage networks. CommVault's exclusive single-platform architecture gives companies unp...
Jul. 25, 2015 01:00 PM EDT Reads: 1,949
Electric Cloud and Arynga have announced a product integration partnership that will bring Continuous Delivery solutions to the automotive Internet-of-Things (IoT) market. The joint solution will help automotive manufacturers, OEMs and system integrators adopt DevOps automation and Continuous Delivery practices that reduce software build and release cycle times within the complex and specific parameters of embedded and IoT software systems.
Jul. 25, 2015 12:15 PM EDT Reads: 452
"ciqada is a combined platform of hardware modules and server products that lets people take their existing devices or new devices and lets them be accessible over the Internet for their users," noted Geoff Engelstein of ciqada, a division of Mars International, in this SYS-CON.tv interview at @ThingsExpo, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 25, 2015 12:00 PM EDT Reads: 1,528
Internet of Things is moving from being a hype to a reality. Experts estimate that internet connected cars will grow to 152 million, while over 100 million internet connected wireless light bulbs and lamps will be operational by 2020. These and many other intriguing statistics highlight the importance of Internet powered devices and how market penetration is going to multiply many times over in the next few years.
Jul. 25, 2015 09:00 AM EDT Reads: 1,482
SYS-CON Events announced today that Dyn, the worldwide leader in Internet Performance, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Dyn is a cloud-based Internet Performance company. Dyn helps companies monitor, control, and optimize online infrastructure for an exceptional end-user experience. Through a world-class network and unrivaled, objective intelligence into Internet conditions, Dyn ensures traffic gets delivered faster, safer, and more reliably than ever.
Jul. 24, 2015 11:00 PM EDT Reads: 2,053