Patent Publication Number: US-7584418-B2

Title: Methods, systems, and articles of manufacture for prefabricating an information page

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to the field of computer systems. More particularly, the invention relates to a method and system for prefabricating information in a computer system. 
     Many computer applications obtain and display information to users. For example, a web browser is a specially configured application for retrieving and displaying web pages. When the user of a web browser indicates a desire to view a particular page of information, the browser or its supporting hardware/software components on the user station performs actions to create and send an information request to the location of the information. The information request is sent across the network to the location of the information, is serviced at the remote location to create/send the requested information, which is then returned to the local user station for viewing. In a multi-tier architecture, the information request may be directed to a middle tier web server, which in turn handles the requesting, retrieval, and packaging of information from one or more back-end data servers. Such information retrieval and display actions are relevant to many networked computer applications, such as distributed database applications. 
     To illustrate, consider a typical user&#39;s home page that is established on a web portal site. A portion of the home page may be configured to display the latest prices for stocks owned by the user and a summary of the value of the user&#39;s stock portfolio. Other portions of the home page can be configured to display other types of information, such as news, weather, etc. When the user&#39;s browser requests the home page, a page request is sent to a web server having the responsibility for retrieving relevant items of information on the home page from one or more back-end data servers (e.g., stock price information from a database server), processing the data if necessary (e.g., to calculate stock portfolio values for the user), and packaging the page information into a designated page format for display. 
     In conventional computer systems, there is always an inherent delay associated with this process of “fabricating” a page of information. Each information request could involve multiple network roundtrips that consume a given quantity of time. Substantial delays may also occur because of large information items that must be retrieved or downloaded across the network. The information request may involve database processing at a back-end data server, causing more delays. In addition, once all the information is collected, it may have to be rendered or packaged into a specific format, causing yet more delays. These delays could significantly affect the performance or usability of a computer application. In modern business environments, such delays could contribute to unacceptable productivity losses for computer users. 
     Therefore, it is an object of the invention to provide a method and system for increasing response speeds and reducing response times to user requests for information. 
     The present invention provides a method and system for prefabricating information, in which the necessary steps to retrieve and package information requested by a user are preemptively performed by the computer system. When the user later makes an explicit request for information, the desired information can be immediately displayed to the user without the delays associated with contemporaneous retrieval and packaging of the information. 
     In one embodiment, the invention comprises a prefabricator that generates prefabrication requests. The prefabrication requests are processed to create and store prefabricated information. An interceptor receives information requests from users, and provides the prefabricated information in response to the information requests. The prefabrication components of the invention can be non-intrusively used with any existing computer application and without requiring installation of any additional hardware components. 
     The prefabrication system of the invention can be configured to automatically tune its processing to the changing conditions that exist in the computer system. This permits the prefabrication process to take full advantage of any excess resources available in the system during periods of low resource usage, by automatically increasing the prefabrication workload. During periods of high resource usage, the prefabrication workload is automatically lowered to minimize any harmful effects upon other run-time work being performed by the system. 
     The present invention can be scalably deployed to perform coordinated prefabrication services on multiple, distributed computing nodes. According to an embodiment of the invention in a multi-node environment, any number of prefabricator instances can be configured to perform prefabrication functions on separate network nodes. Each prefabricator instance handles its allocated portion of the prefabricated information, and stores the prefabricated information in a network accessible storage device. When a user makes an information request, any of the nodes within the prefabrication framework can determine if the requested information has been prefabricated, and retrieve the prefabricated information for the user. By intelligently distributing the workload across multiple nodes, the system resources in all prefabricator nodes can be optimally harnessed and dynamically tuned. Regardless of the quantity of prefabrication workload that is assigned to a given node, all nodes equally participate in the benefits of prefabricated information, since all prefabricated information, even information prefabricated by other nodes, are universally accessible from networked storage devices. 
     An embodiment of the invention provides a method to manage session security for prefabrication services. The interceptor in this embodiment is configured to verify the validity of session ID values for users. If the user makes an information request that can be satisfied with prefabricated information, then the interceptor provides the prefabricated information with the valid session ID for the user attached to the information. 
     Further details of aspects, objects, and advantages of the invention are described below in the detailed description, drawings, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention and, together with the Detailed Description, serve to explain the principles of the invention. 
         FIG. 1  depicts prefabrication components according to an embodiment of the invention. 
         FIG. 2  shows a flowchart of a prefabrication method according to an embodiment of the invention. 
         FIG. 3  illustrates a prefabrication system according to an embodiment of the invention. 
         FIG. 4  shows a prefabrication service module according to an embodiment of the invention. 
         FIG. 5  illustrates an alternate prefabrication system according to an embodiment of the invention. 
         FIG. 6  shows an n-node prefabrication system according to an embodiment of the invention. 
         FIG. 7  shows prefabrication components for an n-node prefabrication system according to an embodiment of the invention. 
         FIG. 8  shows a PRB schema according to an embodiment of the invention. 
         FIG. 9  shows prefabrication policy schemas according to an embodiment of the invention. 
         FIG. 10  identifies example indexes to user page tables. 
         FIG. 11  shows a process flow for a start loader according to an embodiment of the invention. 
         FIG. 12  depicts a flowchart of a process for constructing PRBs according to an embodiment of the invention. 
         FIGS. 13 and 14  are diagrams of system architectures with which the present invention may be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention takes the form of a method and system for prefabricating information, in which the necessary steps to retrieve and package information requested by a user are preemptively performed by the computer system—before the user makes an explicit information request. Instead, an embodiment of the invention predictively identifies and prefabricates information that may be displayed to the user in the future. When the user later makes a request for information, the desired information can be immediately displayed to the user without the delays associated with contemporaneous retrieval and packaging of the information. For the purposes of illustration, and not by way of limitation, the present explanation is made with respect to “pages” of information that are displayed to a user. It is noted, however, that other granularities of information may be prefabricated within the scope of the invention. 
     According to an embodiment, a set of prefabrication system components is deployed to prefabricate pages for a computer application. Referring to  FIG. 1 , shown is a computer application  104  that generally produces or processes information for display to users. Computer application  104  could be any application that displays information to users, such as, for example, a database application. Information pages from the computer application  104  are displayed to users via a user interface  102 , which may be, for example, a conventional web browser. User interface  102  responds to user commands to generate page requests for information pages requested by the user. 
     An interceptor  108  is logically interposed between the user interface  102  and the computer application  104 . When a page request is sent from user interface  102  to computer application  104 , the interceptor  108  intercepts the page request to determine if a valid, prefabricated page exists that is responsive to the request. This determination is made by identifying whether the requested page had already been prefabricated and cached/stored in a storage device  112 . Storage device  112  could be any device usable to store an accessible copy of the prefabricated page, such as a memory cache, a local disk drive, or a network file system (“NFS”) device. 
     If the requested page has already been prefabricated, then the page request is immediately fulfilled by retrieving the prefabricated page from the storage device  112  for display at the user interface  102 . If the requested page has not already been prefabricated, then the page request is sent to the computer application  104  to be fulfilled by dynamically fabricating the requested page. 
     A prefabricator  110  identifies information pages to prefabricate. Configuration settings and/or heuristics may be employed to predictively determine which information pages should be prefabricated. For each of these identified pages, a page request is sent from the prefabricator service module  110  to the interceptor  108 . The interceptor  108  sends these page requests to the computer application  104 . Each of these page requests from the prefabricator  110  is processed by the computer application  104  to fabricate a requested information page. The process at the computer application  104  to respond to a page request could be the same, regardless of whether the page request originates from the prefabricator service module  110  or the user interface  102 . However, information pages generated in response to prefabricated page requests from the prefabricator  110  are cached by the interceptor  108 , e.g., at a storage device  112 . In contrast, information pages dynamically fabricated in response to a current page request from the user interface  102  are immediately sent to the user interface  102  for display. These contemporaneously fabricated pages may also be cached by the interceptor  108  for later access. 
     The prefabrication components of the invention may be installed at any physical or logical location in the computer system. Physically, the interceptor and prefabricator components may be located, for example, at the physical locations of the user interface, the computer application, or at other network locations such as a middle-tier web server computer. Logically, the interceptor and prefabricator components can be installed anywhere in the computer system, and/or integrated into other system components. In an embodiment, the interceptor  108  is integrated into a middle-tier web server or is logically located before it to intercept all communications between a user interface/browser and any applications accessed by the user running on a back-end data server. 
     It is noted that the format of page requests made to the computer application  104  could remain the same, regardless of whether prefabrication is being performed in the system. The interceptor component is configured to distinguish between ordinary page requests from the user interface and page requests from the prefabricator component, and to route the fabricated page from the computer application accordingly. Thus, introducing prefabrication components into a computer system need not result in modifications to a computer application. Instead, the present invention may be employed to non-intrusively prefabricate pages for any computer application, without requiring any or significant modifications to the computer application, merely by interposing the interceptor component in the communications path (e.g., at a web server) between the computer application and its corresponding user interfaces. 
       FIG. 2  depicts a flowchart of a method for performing page prefabrication according to an embodiment of the invention. Step  202  of the method is directed to configuring one or more prefabrication policies for the system. A prefabrication policy is a set of configuration parameters that governs the manner in which prefabrication is performed. According to an embodiment of the invention, a prefabrication policy identifies some or all of the following: (1) the computer application that the policy applies to; (2) the users that the policy applies to; (3) the information pages to be prefabricated; (4) prefabrication scheduling and refresh interval(s); (5) responsibilities to prefabricate; and (6) prefabrication priorities. 
     To illustrate, the following sets forth an example of a set of prefabrication policy parameters for a computer application:
         1. Policy Name: Guest User Policy   2. Application Name: Foo   3. Applies to: All users of Foo application with Guest responsibility   4. Time and Periodicity for Prefabrication: 2:00 A.M.—refresh daily   5. Depth of Prefabrication: all start pages and menu pages for identified users
 
This is an application level policy that defines the prefabrication policies for users having “Guest” responsibility for the “Foo” computer application. In particular, this set of policies (entitled “Guest User Policy”) states that the “start page” and menu pages for every such user of the Foo application will be prefabricated and stored every day at 2:00 A.M. According to an embodiment of the invention, a start page is an initial page displayed to a user. The start page could be the application&#39;s initially displayed page, an organization&#39;s home page, a user home page, or any other page designated as an entry page to be displayed to a user. The start page often contains hyperlinks or user selectable controls to view other displayable information pages. A “menu page” can be a tabbed, menu page that is hyperlinked from the start page.
       

     Referring back to  FIG. 2 , the method thereafter prefabricates pages according to the defined prefabrication policy(s) ( 204 ). The exact steps to prefabricate a page depend in large part upon the specific contents of a page and the location of information in the page. In one embodiment, the same steps used to dynamically fabricate a page in response to a current user page request are also used to prefabricate a page in response to a prefabrication request. For an application that accesses data in a database, prefabrication may involve the steps of querying a database, processing data that is retrieved from the database, and packaging/rendering the resulting information in a specific format to be displayed to a user. The goal of the prefabrication process is to prefabricate a page as closely as possible to the page that the user would later “normally” retrieve without prefabrication. The prefabricated page would then be cached/stored for later access. 
     In operation, the prefabrication-enabled computer system filters page requests to intercept any page request that corresponds to a prefabricated page ( 208 ). If a pre-existing, valid prefabricated page responsive to the page request exists, then it is sent to the user for display ( 210 ). If the requested page does not exist or if the prefabricated page responsive to the page request is not valid, then the page request is sent to the computer application for contemporaneous fabrication ( 212 ). It is noted that prefabricated pages may be marked as being invalid under certain circumstances, e.g., if it becomes stale. The term “stale” refers to a prefabricated page in which the entire prefabricated page, or items of information located on the prefabricated page, is no longer considered to be valid. In one embodiment, staleness is based upon whether the creation/update time for a prefabricated page is within a threshold time period. A parameter can be established to determine the periodicity at which prefabricated pages should be created or updated to avoid staleness. Other approaches can also be used to establish staleness. For example, an alternate approach is based upon whether some or all of the information on the prefabricated page has been changed in a way that is relevant. Messaging can be used to determine whether some or all of the information on a prefabricated page has changed. The back-end database can send a message to the manager or location of the prefabricated page to indicate staleness. Alternatively, the cache server/prefabricator components can itself send a message to the back-end server to determine whether a prefabricated page is stale. 
     Illustrative Embodiments 
       FIG. 3  depicts an architecture  300  for page prefabrication according to an embodiment of the invention, in which an interceptor service module  304  is integrated with a web server  306 . By way of example, web server  306  may be implemented as an Apache web server (available from www.apache.org) having server-side Java servlet functionality using the Apache Jserv module. The interceptor service module  304  can be implemented as a c-based extension that is compiled into the Apache web server code base. User page requests originate from a browser  302 . Prefabricator page requests are generated by a prefabricator service module  310 . The prefabricator service module may be located at either the same hardware location as the web server  306 , or at any other machine location in the computer system. By way of example, the prefabricator service module may be implemented as a Java program co-located with the web server  306 . 
     Page requests are sent to the interceptor service module  304  as Uniform Resource Locator (URL) requests. For user page requests, the interceptor service module  304  determines if the HTTP response for the requested URL has already been prefabricated and stored. The prefabricated HTTP responses are stored in a storage device  308 . 
     If a valid, prefabricated HTTP response to the user requested URL is not available, then the URL request is dynamically processed by a Java servlet  316  to produce the desired HTTP response. The Java servlet  316  may access a database  312  to retrieve or process information associated with the URL. The HTTP response produced by the Java servlet  316  is routed to the browser  302  by the interceptor service module  304 . 
     The prefabricator service module  310  accesses a set of prefabrication policies  314  to identify URLs that should be prefabricated. Prefabrication policies  314  can be stored at the database  312 . Each URL identified to be prefabricated is sent as a prefabrication page request to the interceptor service module  304 . The prefabricator URL requests are processed by one or more Java servlets  316  to produce the desired HTTP responses. The interceptor service module  304  distinguishes between HTTP responses from user page requests and HTTP responses from prefabricator page requests. The HTTP responses to prefabricator page requests produced by the Java servlet(s)  316  are stored in the storage device  308 , before they are sent back to the prefabricator service module  310 . 
       FIG. 4  shows components of an embodiment of the prefabricator service module  310 . The start loader  404  performs the initial bootstrapping for the prefabricator service module  310 . The start loader  404  accesses the defined prefabrication policies  402  for the system to determine an initial set of pages to prefabricate. Each identified page that is a candidate for prefabrication is represented as a formatted page request, referred to herein as a page request block (PRB). As described in more detail below, the initial set of identified pages may further identify links to other candidate pages that should be prefabricated. 
     One or more PRBs are sent from the start loader  404  to the benefit analyzer  406 , with each PRB corresponding to a separate page to prefabricate. The benefit analyzer  406  prioritizes the list of PRBs based upon prioritization parameters established in the prefabrication policies  402 . Examples of prioritization parameters include available system resources, page fabrication times, user access patterns, and the page depth of a PRB page. The benefit analyzer also determines a preferred batch size to process the PRBs. Once the benefit analyzer has prioritized and generated a batched set of PRBs to process, the set of PRBs is sent to the page request feeder  408 . 
     The page request feeder  408  receives PRBs from the Benefit Analyzer  406  and issues HTTP requests based upon the received PRBs. The HTTP requests for the PRBs are sent to the interceptor service module for processing by the web server. The HTTP responses are sent from the interceptor service module/web server to the page request feeder  408 . Each PRB, along with its associated HTTP response, is sent to the URL collector  412 . 
     The page request feeder  408  is configured to concurrently handle multiple HTTP requests, by assigning PRBs to one or more processing entities (e.g., threads) that execute in parallel. The number of PRBs that is concurrently processed depends upon the level of available resources in the system. The greater the level of available system resources, the greater the number of PRBs that may be concurrently processed in the system. The prefabrication policies  402  may include parameters governing the level of system resources at which prefabrication procedures may execute or limit the quantity of system resources that may be consumed by the prefabrication policy. 
     The resource manager  410  monitors system resource usage, such as CPU and memory usage, both at the prefabricator location as well as the web server location(s), and indicates the level of system resources available to the prefabricator service module. The resource manager  410  provides system resource information used by the page request feeder  408  to throttle the rate in which HTTP requests are sent to the interceptor/web servers. The resource manager  410  can also be configured to provide information used by the page request feeder  408  to identify which web server or load balancer at which HTTP requests should be directed. 
     In this manner, the prefabrication system automatically adapts or “tunes” its processing to the changing conditions that exist in the system. This permits the prefabrication process to take full advantage of excess resources available in the system during periods of low resource usage, by automatically increasing the prefabrication workload. During periods of high resource usage, the prefabrication workload can be automatically lowered to minimize resource drains from other run-time work being performed by the system. 
     Each processed PRB and its associated HTTP response from the interceptor/web server are sent from the page request feeder  408  to the URL collector  412 . The URL collector  412  crawls through the HTTP responses to identify new URLs that should be prefabricated. The new URLs form additional PRBs that are sent to the benefit analyzer  406  for prioritization and further processing. The prefabrication policies  402  define parameters used by the URL collector  412  to identify additional URLs that should be prefabricated. In one embodiment, the pages dynamically fabricated in response to an immediate user request can also be sent to the URL collector  412  to be crawled for pages that should be prefabricated. 
     To illustrate the operations of prefabricator service module  310 , consider again the example prefabrication policy, described above, having the following policy parameters:
         1. Policy Name: Guest User Policy   2. Application Name: Foo   3. Applies to: All users of Foo application with Guest responsibility   4. Time and Periodicity for Prefabrication: 2:00 A.M.—refresh daily   5. Depth of Prefabrication: all start pages and menu pages for identified users
 
As previously noted, this is an application level policy that defines the prefabrication policies for users having “Guest” responsibility for the “Foo” computer application, where the “start page” and “menu page” for every such user of the Foo application will be prefabricated and stored every day at 2:00 A.M.
       

     When this prefabrication policy is executed, the start loader  404  in the prefabricator service module  310  performs the action of identifying the URLs of the start pages for all relevant users (i.e., “Guest” users) of the Foo computer application. In some circumstances, the start loader  404  may also identify some or all of the URLs for the menu pages for the relevant users. PRBs corresponding to the identified URLs are sent to the benefit analyzer  406 . 
     The benefit analyzer  406  prioritizes the PRBs and sends a series of PRB batches to the page request feeder  408 . Various prioritization procedures may be employed. In this example, an applicable prioritization procedure is to give higher priority to start page URLs and lower priority to other URLs having higher depths in the page hierarchy, i.e., menu page URLs. Thus, the initial batch of PRBs identified by the benefit analyzer  406  should be directed to higher priority URLs. 
     The page request feeder receives system resource information from the resource manager  410 . Based upon this system resource information, the page request feeder  408  determines the number of PRBs that may be concurrently processed at any moment in time. The PRBs are assigned to the processing entities that work for the page request feeder  408 . HTTP requests are sent by the processing entities to the interceptor/web server. HTTP responses to the HTTP requests are returned from the interceptor/web server, and are attached or logically associated with the original PRBs. 
     The PRBs and the associated HTTP responses are sent to the URL collector  412 . The URL collector  412  attempts to identify additional URLs that should be prefabricated. In this example, the prefabrication policies indicate that both start pages as well as menu pages should be prefabricated. Thus, the URL collector  412  crawls through the HTTP response for each start page to attempt to identify URLs for additional menu pages. The URLs for the identified menu pages are packaged as new PRBs that are sent to the benefit analyzer  406 . 
     The benefit analyzer  406  reprioritizes the set of pending PRBs based upon the new PRBs received from the URL collector  412 , and sends another batch of PRBs to the page request feeder  408 . The above process continues until all the PRBs have been processed or until the processing time period for the policy expires. 
     A scheduler (not shown) coordinates the activities of the components within the prefabricator service module  310 . In one embodiment, the scheduler is a thread that monitors the prefabrication policies, and determines which policies become active and which policies are scheduled to end. 
       FIG. 5  depicts an alternate embodiment of the invention, in which the interceptor service module  502  is integrated with a cache server  504 . The cache server  504  is interposed between users and the web server  506 . In this approach, the cache server  504  manages the storage and retrieval of prefabricated pages. This is in contrast to the approach of  FIG. 3 , in which the prefabricator system components are responsible for storing and retrieving cached prefabricated pages. An exemplary cache server  504  usable with the invention is described in more detail in co-pending U.S. patent application Ser. Nos. 09/650,498 and 09/649,850, entitled “Multi-Tier Caching System” and “Performance-Based Caching”, respectively, both filed on Aug. 29, 2000, which are hereby incorporated by reference in their entirety. 
     Multi-Node Prefabrication System 
     The present invention can be scalably deployed to perform coordinated prefabrication services on multiple, distributed computing nodes. By way of example, if embodiments of the invention are employed in a system configuration having multiple middle-tier machines, then the prefabricator service can be started on some or all of the middle-tier machines to share the prefabrication workload. Each prefabricator instance produces its allocated portion of the prefabricated pages, and stores the prefabricated pages in a network accessible storage device. When a user requests an information page, any of the web servers operating within the prefabrication system can determine if the requested page has been prefabricated. If so, then the web server retrieves the prefabricated page from the particular network accessible device upon which the prefabricated page was stored. 
       FIG. 6  depicts one embodiment of the invention for an “n-node” architecture, in which multiple middle-tier machines exist in the distributed computer system. Shown in  FIG. 6  is a first middle-tier node  606   a  and a second middle-tier node  606   b . Each node  606   a  and  606   b  can access the same computer applications, e.g., database application  610 , to generate a requested information page. Each middle-tier node  606   a  and  606   b  includes prefabricator components, such as an interceptor  616   a  and prefabricator  626   a  on node  606   a , and an interceptor  616   b  and prefabricator  626   b  on node  606   b . Node  606   a  stores prefabricated pages in a storage device  636   a , while node  606   b  stores prefabricated pages into a storage device  636   b . In an embodiment, storage devices  636   a  and  636   b  are both NFS-compatible storage devices accessible from other network nodes. 
     When a user page request is sent from browser  602 , the page request is routed to one of the middle-tier nodes  606   a  or  606   b  by router/load balancer  604 . The node presently handling the page request determines if a valid, prefabricated version of the requested page exists somewhere in the system. If so, then the node retrieves the prefabricated page. If the page was not locally prefabricated, and the prefabricated page is stored in a network accessible file system like a remotely produced prefabricated page, then the node retrieves the page from the network accessible file system. If the locally produced prefabricated pages are stored in a local cache or storage device, then a local request for that page would result in retrieval from the local cache or storage device. If the page was prefabricated at another network node, then the prefabricated page is retrieved from the network accessible storage device, and sent to the browser  602  for display. 
     To describe how prefabricator workload is distributed among multiple nodes, shown in  FIG. 7  are prefabricator components for an n-node prefabricator system according to an embodiment of the invention. The n-node prefabricator system includes a load distributor  702  that is responsible for distributing the page prefabrication workload. The load distributor  702  divides a given prefabricator workload among multiple prefabricator nodes. Each prefabricator node includes a prefabricator service instance  704 . While only a single prefabricator service instance  704  is shown in  FIG. 7 , it is noted that multiple such prefabricator service instances may exist in the distributed system. In one embodiment, the load distributor  702  is located at the same machine as one of the prefabricator service instances  704 . In an alternate embodiment, the load distributor  702  is located on a separate machine. 
     The load distributor  702  accesses all prefabrication policies to determine the current prefabrication workload for the distributed system. Based upon the prefabrication policies, the load distributor  702  identifies the pages to prefabricate. For each identified page, a page request PRB is created. 
     The load distributor  702  divides the set of PRBs across the fabricator nodes in the system. In an embodiment, workload distribution is based upon the resource usage and availability levels of each prefabricator node. Prefabricator nodes having higher resource availability levels are assigned more work while prefabricator nodes having lower resource availability levels are assigned less work. Examples of resource usage parameters that may factor into the workload distribution decision are CPU, memory, and current prefabrication request levels at each prefabricator node. For this reason, the resource manager  706  at each prefabricator service instance  704  preferably communicates resource usage information to the load distributor  702 . 
     A first approach to assigning work to prefabricator nodes involves looking at resource utilization levels in a global way, where the entirety of the workload is distributed across all the participating nodes to balance resource usage across the entire system. The total resource “headroom” for each node is identified to make the workload allocation. A second approach to assigning work involves looking at each prefabrication node on an individual basis, and assigning work to a node only within the exact resource utilization constraints that have been imposed for that node. 
     The load distributor  702  maintains a PRB data structure that lists all PRBs to prefabricate as well as the identity of the specific prefabricator node assigned to each PRB. The PRB data structure can be stored as a table in a database  708 . The start loader  710  at each prefabricator service instance  704  scans the PRB data structure to identify the PRBs assigned to that instance. The assigned PRBs for the prefabricator service instance  704  are sent to the benefit analyzer  712  for that instance  704  for prioritization and further processing. The processing of the PRBs thereafter is substantially identical to the processing of PRBs as described with reference to  FIG. 4 , with the exception that the HTTP response is stored in a network accessible network storage device. In addition, the completed PRBs are identified as such in the PRB data structure. In an embodiment, the PRB data structure is the same as the user page table, described in more detail below. 
     The load distributor  702  can be configured to distribute the prefabrication workload at a number of occasions. For example, the load distributor  702  may redistribute the workload at prefabrication system startup time, at predefined intervals, or when a “redistribute workload” command is explicitly issued. Each prefabricator instance can be configured to periodically log a set of statistics or status messages in a database. These statistics can be used to identify load imbalances across the system that can be corrected by redistributing the workload. In addition, the periodic reports can be used to identify error conditions at the distributed nodes. For fault tolerance purposes, load redistribution may also occur based upon identifying an error or problem at one of the prefabrication nodes. 
     The present invention can therefore be effectively scaled over any number of prefabricator nodes, merely by distributing the prefabrication workload over the prefabrication nodes in the system. The excess resources in all prefabricator middle-tier nodes can be harnessed by appropriate distribution or redistribution of additional workloads to those nodes having excess resource availability levels. On the other hand, those nodes having lower available resources are assigned smaller portions of the prefabrication workload. Regardless of the quantity of prefabrication workload that is assigned to a given node, all nodes equally participate in the benefits of prefabricated pages, since all prefabricated pages, even pages prefabricated by other nodes, are universally accessible from networked storage devices. 
     PRB—Page Request Block 
     According to an embodiment, information pages that are candidates for prefabrication are internally represented as formatted page requests or PRBs.  FIG. 8  shows a PRB structure according to one embodiment of the invention. Attribute  802  identifies the specific uniform resource identifier (URI), e.g., URL+cookie information, associated with a PRB. Attribute  804  identifies the user identifier of the user associated with the PRB request. Attribute  806  sets forth the application identifier associated with the PRB. Attribute  808  sets forth the responsibility identifier for the PRB. Attribute  810  defines the page depth for the PRB request. If the start page or home page is considered depth “0”, the next additional navigational level from that start/home page is considered depth “1”, the next immediate navigational level from level “1” is considered depth level “2”, etc. The depth attribute  810  identifies the depth level of the URI associated with the PRB. The weight attribute  812  identifies the prioritization weight associated with the PRB, which is computed and used by the benefit analyzer component to sort the list of pending PRBs. Attribute  818  identifies an average page generation time. The average generation time is set by the Page Request Feeder component once a PRB has been fabricated. 
     An inherent hierarchy exists between many PRBs within the system. A PRB (A) that is created by identifying URIs in the page represented by another PRB (B) is referred to as a child of PRB (B). Any PRB can have zero or more child PRBs. The child PRBs are considered to be at a depth of one more than the depth of the parent PRB. Attribute  814  identifies the entry page for this application of the present PRB. Attribute  816  identifies the child PRBs for the present PRB. Attribute  820  identifies the number of child PRBs to the present PRB. 
     In an embodiment, PRBs being processed by the system are stored in-memory in a UserPageTable, which is described in more detail below. This table preferably persists in a database. A history table is maintained in one embodiment to track all PRBs processed by the system for a given application. Statistics, such as the frequency or rate of change for a PRB, are maintained in the history table. These statistics can be used to modify or update weighting algorithms for PRBs. PRBs that are very old and which are not recently or frequently accessed can be expunged from the history table. 
     Prefabrication Policy 
     This section describes the structure of prefabrication policies according to an embodiment of the invention. According to an embodiment, the prefabrication policy contains configuration information used to bootstrap and tune the prefabricator. The prefabrication policies are preferably striped by application and are stored as persistent information in a database. The prefabrication policy identifies some or all of the following: (1) the computer application that the policy applies to; (2) the users that the policy applies to; (3) the information pages to be prefabricated; (4) prefabrication scheduling and refresh interval(s); (5) responsibilities that the policy applies to; and (6) prefabrication priorities. A hierarchy of different categories of policies can be used in the invention, such as the following categories:
         System Resource Policies: This type of policy applies at a system-wide level, and establishes system resource conditions under which the prefabrication process is permitted to operate. Examples of this policy type would include policies that specify a CPU consumption limit, available memory, or disk space limitations.   Application Level Policies: This set of policies applies at an application-wide level, and establishes prefabrication parameters for specific computer applications in the system. For a given application, this set of policies can be used to establish, for example, the time of day at which the prefabrication process is performed, the periodicity with which pages are prefabricated (to prevent staleness), and the identity, type, and/or quantity of pages that should be prefabricated. One or more application level policies may be established for a given application.   Responsibility and User level Policies: These sets of policies applies to specific responsibilities and users within an application. In an embodiment, these policies are a subset of the application level policies, and will override any setting at the application level. Each application may correspond to multiple responsibility and user level policies.   Transient policies: These are run-time policies that the prefabricator service auto-tunes as it runs. In one embodiment, this type of policy is calculated at run-time and is based upon the availability of resources and current state of the system. An example includes a policy that tunes the number of PRBs concurrently processed by the request feeder. The parameters of the system resource policies can be used to implement transient policies. In an embodiment, these policies are not persisted in the database.       

     At the java-layer or middle-tier, policies can be represented as object instances of a Policy class. Some of the properties in the Policy object are persistent while others are transient. The following is a list of properties for the Policy class that may be employed in one embodiment of the invention:
         applicationID): the unique ID associated with an application. (persistent)   isEnabled: determines if prefabricator is enabled or disabled for the application corresponding to the applicationID. (persistent)   startTime: the time at which the prefabricator service should be started for this policy. In one embodiment, this property cannot be modified at the responsibility or user level. (persistent)   endTime: the time (if any) at which the prefabricator service should be stopped for the policy. In one embodiment, this property can be modified at the responsibility or user level. (persistent)   interval: the periodicity with which the prefabricator service should regenerate pages. This property represents a “staleness” threshold for prefabricated pages. In one embodiment, this property can be modified at the responsibility or user level. (persistent)   depth: this represents the desired depth for which pages are prefabricated. By way of example, this property represents whether only home/start pages, all pages, or a defined depth x of pages of the application should be prefabricated. In one embodiment, this property can be modified at the responsibility or user level. (persistent)   currentDepth: this property represents the actual depth the prefabricator service auto-tunes to prefabricate based on availability of system resources and other heuristics. For example, if the “depth” parameter for the policy indicates that 4 levels of pages should be prefabricated, but system resource levels only allow 1 level of pages to be prefabricated, then the “currentDepth” parameter is set to “1”.   currentBatchSize: this represents is the number of concurrent requests that the page request feeder sends to the web server based on availability of system resources and other heuristics.   cpuConsumptionLimit: this property identifies an upper limit on the maximum percentage of the CPU the system should utilize. In one embodiment, this is a system wide parameter. (persistent)   memoryConsumptionLimit: this property identifies a lower limit on the amount free memory that should exist in the system. In one embodiment, this is a system wide parameter. (persistent)   diskSpace: this property indicates the amount of disk space that is available to store the prefabricated pages. In one embodiment, this is a system-wide parameter. (persistent)   isAllResp: this property determines whether policy should run for all responsibilities of the application. (persistent)   isAllUser: this property determines whether policy should run for all users. (persistent)       

       FIG. 9  shows a schema for persisting policies according to an embodiment of the invention. For every application, there is one row in a prefabrication application policy table  902  that persists application-level policies. Based on whether any responsibility or user-level policies are configured, there are zero or more corresponding rows in a prefabrication user policy table  904 . Table accessor methods are implemented in a procedural query language, e.g., PL/SQL, and invoked from the Java layer, e.g., using JDBC. 
     As a security measure, policy information is preferably maintained or modified only by appropriately authorized administrators. When an administrator changes a policy, it is preferably immediately updated and propagated, e.g., to the relevant database tables at which the policies are stored. 
     In an embodiment of the invention, for every application the prefabricator services is processing, a Policy object is instantiated on the prefabricator service side. A policy thread/process is configured to periodically refreshes the persistent properties of the Policy objects. In an embodiment, each prefabricator service is dedicated to only one application, i.e., if there are three applications to be prefabricated, then three instances of the prefabricator service are started. In this approach, a prefabricator service instance corresponds to only Policy object instances for this application and the policy thread/process will refresh only the policies for this application. In an alternate embodiment, a prefabricator service is configured to support multiple applications. In this alternate approach, multiple policy objects belonging to multiple applications are associated with a prefabricator service instance. 
     Different components in the prefabricator service access the policy object. For example, the start loader component accesses the policy object to identify the users and responsibilities configured for a given application, and to generate the initial workload. The benefit analyzer accesses the policy object to identify system configurations and refresh intervals. The benefit analyzer also updates the currentDepth property in the policy object. The page request feeder sets up the currentBatchSize property based upon the number of concurrent requests that can be handled. The URL collector reads the currentDepth property information to decide whether to crawl a prefabricated page. 
     User Page Table 
     An in-memory data structure, referred to herein as the User Page Table, keeps track of all the PRBs that the prefabricator service is processing in an embodiment of the invention. The contents of the User Page Table represent the entire set of PRBs that have been identified for prefabrication. The User Page Table includes both PRBs that have been prefabricated as well as those not yet prefabricated, and includes data indicating which PRBs have been prefabricated. 
     In an embodiment, the User Page Table is frequently accessed, queried, and updated by the Benefit Analyzer component. Indexes can be built that allow querying of the user page table using some of the PRB attributes. The index tables are constructed as Hashtables, with the key being the PRB property and the value being a Vector of PRBs that have the same key-property value. The User Page Table can itself be implemented as a Vector of PRBs.  FIG. 10  provides a list of index tables built for fast access of the user page table elements according to one embodiment of the invention. 
     In an embodiment, the Benefit Analyzer is the only component in the prefabricator service module that directly invokes changes to User Page Table. The Benefit Analyzer can be configured to ensure that no duplicate PRBs (i.e, two PRBs with the same URI) are added to the table. 
     Start Loader 
     This section describes a start loader according one embodiment of the invention. The start loader generates the initial set of PRBs to be processed by the prefabricator service. A default implementation of the start loader provides a mechanism to generate all possible URIs for user start/home/entry pages, based on the applications, responsibilities and users configured in the Prefabricator Policy. In an embodiment, applications can override this default implementation to provide application specific logic for determining the entry page URIs for users. Every URI generated by the start loader is represented as a PRB and passed on to the Benefit Analyzer component. It is noted that other mechanisms, in addition to the start loader, may also be employed to generate the initial workload for the prefabricator service. For example, the set of PRBs created in a prior prefabrication session, including PRBs previously generated from the URL collector, can be used as the initial workload for a present prefabrication session. This alternate approach is useful for pages that tend to remain static over time. 
     Referring to  FIG. 11 , shown is a start loader process flow according to one embodiment of the invention. The Start Loader is instantiated as a thread and the constructor takes in an application ID as an input. The application ID is used to retrieve the appropriate prefabricator policy. From the prefabrication policy, a determination is made of the appropriate set of responsibilities and userIDs for which the workload needs to be generated. The Start Loader thread regenerates the initial workload periodically, e.g., twice a day or every time the prefabricator is started. This ensures that any new users registered in the system and other such changes are captured by the initial workload. 
       FIG. 12  shows a flowchart processing logic for generating PRBs for the appropriate entry-level pages resides in the implementor of the URLParameterInterface, according to an embodiment of the invention. At  1202 , the implementor loads the prefabricator policy object associated with the application ID. 
     Using the Policy object, the method identifies the special responsibilities and user ID configured for the policy ( 1204 ). If no special responsibilities are configured, then it is assumed that all responsibilities within the application need to be prefabricated. Else, only the configured set of responsibilities are used. In addition, the process ensures that all configured userIDs are generated in the initial workload. Unlike responsibilities, this set of users may not be the only users for which prefabrication is turned on. A determination is made regarding a valid set of userIDs that match the configured set of responsibilities. In addition, a determination is made regarding the responsibility identifiers for the userIDs configured. User ID and responsibility tables can be maintained and queried to perform these determinations. The prefabricator logs into the system as a trusted user, and then switches identity to a specific user when it is prefabricating a page for that user. 
     The method determines the entry page URI for every applicable user ID ( 1206 ). Using application specific logic and data, the component that generates the initial workload generates URL values for all users it is prefabricating for ( 1208 ). These URL representations are appended to the previously obtained URI. The method thereafter constructs a PRB for each generated URI ( 1210 ). The constructed PRBs are sent to the benefit analyzer for further processing and prefabrication. 
     Benefit Analyzer 
     This section describes an embodiment of the benefit analyzer. At any given point of time and state of the prefabricator system, the benefit analyzer determines the next set of pages to prefabricate. In one approach, the benefit analyzer is executed as a single thread. 
     The benefit analyzer maintains an in-queue of pending PRBs. The in-queue contains all the PRBs to be processed once at any point in time. The in-queue is populated by PRBs from either the start loader or the URL collector. As noted above, the start loader produces the initial bootstrapping workload. The URLCollector produces new PRBs for the benefit analyzer by crawling previously processed PRB outputs. The benefit analyzer also uses the User Page Table to identify the workload of PRBs to process. The benefit analyzer maintains an out-queue of PRBs to send to the page request feeder. 
     The benefit analyzer uses a weighting algorithm to prioritize the queue of pending PRBs and to associate a weight with every PRB in the system. In one embodiment, the weight (w) is related to the following:
         w∝ 1/depth (where home page is at depth  0 , menu-pages are at depth  1 , submenus at depth  2 , etc.)   ∝ time to process PRB (in one approach, a slower PRB is better candidate for prefabrication than an already fast PRB)   ∝ parameter-relevance (e.g., userID&#39;s configured in policy may have higher weight than others)   ∝ user-hit ratio (highly accessed PRBs are more important than others)
 
The weight (w) of a PRB can be defined as:
 
 w=k* 1/depth+ p*t   processPRB   +q+r *hit-count
 
where, k, p, q, and r are selected constant-values. For the hit-count, a feedback mechanism is implemented from the web-server to the prefabrication service. If this mechanism does not exist, then constant “r” can be set to 0. In a preferred embodiment, the depth factor is the most important factor. Hence, constant “k” is set to a higher value than “p” and “q.” The exact weighting formula and weighting constants is a design choice based upon the exact application and set of performance requirements to which the invention is directed. The in-queue of the benefit analyzer is prioritized based on PRB weights. The benefit analyzer thereafter passes the next, prioritized PRB to be processed to the page request feeder, on demand.
       

     In one embodiment, the applicable policies may also be prioritized by the benefit analyzer. The requirements of first policy could be given higher priority than the requirements of a second policy. For example, if a first policy has a higher priority than a second policy, then the set of PRBs produced in response to the first policy is given greater weight than the set of PRBs produced in response to the second policy. 
     In one embodiment, the Benefit Analyzer is configured to generate, track, or maintain the following statistics: (1) Number of PRB generated; (2) Average refresh rate; (3) Total number of PRBs in the system—user page table size; (4) Optimal batch size; (5) Current depth; (6) start time of policies; (7) end time of policies; (8) duration of run; and, (9) hit ratio=(number of prefabricated URIs accessed)/(total number of URIs user requested). 
     Page Request Feeder 
     This section describes an embodiment of the page request feeder. The page request feeder initiates page generation from the PRBs. Based on the current system snapshot, the page request feeder sets the number of concurrent requests to send to the web-server, receives the responses back, and passes the page response to the URL Collector. The Page Request Feeder receives PRBs to be processed as input from the BenefitAnalyzer. The page request feeder also uses the optimal batch size value and maximum CPU consumption limit value from the Policy object. 
     The Page Request Feeder includes a “monitor” processing component (e.g., monitor thread) and a changing number of “worker” components (e.g., worker threads). The monitor thread is responsible for dynamically changing the number of concurrent requests to send to the web server based on the current system snapshot. The monitor thread uses the following steps to dynamically adjust the number of requests: (1) The monitor thread checks if the current CPU utilization in the system is less than the maximum CPU value configured in the policy object; (2) the number of outstanding page requests is checked to determine if it is less than the optimal value listed in the prefabrication policy; and, (3) if both of the above conditions are met, then one or more PRBs are retrieved from the benefit analyzer and passed to a free worker thread, or to a new, created worker thread if none is presently available. 
     Each worker thread is responsible for performing the following steps: (1) taking a PRB from the request feeder&#39;s in-queue; (2) sending a HTTP Request to process the URI in the PRB; (3) appending the HTTP Response to the PRB; and (4) passing the PRB to the URL collector. 
     In one embodiment of the invention, the page request feeder&#39;s concurrency level, or number of outstanding requests, is controlled by the benefit analyzer. However, this approach may cause a delay in the prefabricator system adapting to changes in the middle-tier or database workload. Thus, in an alternate embodiment, the benefit analyzer determines the optimal concurrency, but the request feeder calculates the adaptive or current concurrency it should support. This provides better reaction time to bursty traffic on the webserver, or sudden changes in the system load. 
     URL Collector 
     This section describes an embodiment of the URL collector. The URL Collector obtains PRBs as inputs from an in-queue from the Page Request Feeder. Each PRB includes an HTTP response stream that was produced and sent by the web server in response to the HTTP request of the PRB. The URL Collector crawls through the HTTP response stream to gather new URIs to prefabricate. In an embodiment, the URL collector functions as a web crawler, and crawls through a response stream based upon the current prefabrication policy. The prefabrication policy determines which pages should be crawled by the URL collector. For example, the currentDepth parameter in the Policy object can be used to establish whether a particular page should be crawled. 
     In an embodiment, the URL collector executes as a single thread. For every relevant PRB in the URL collector&#39;s in-queue, it parses the response stream string buffer, looking for all the &lt;href&gt; references. For each relevant &lt;href&gt;, the URL collector constructs a PRB and sends it to the Benefit Analyzer. The Benefit Analyzer ensures no duplicate URIs are added to the PRB list. 
     The URL collector is configured to only crawl pages that have not already been crawled, or that has changed since the last time it was crawled. To accomplish this, the URL Collector checks whether the response stream buffer size is the same as last time it was crawled. A checksum or hashID routine can be executed to additionally determine if a page has sufficiently changed as to require being crawled. Any response streams forming an error page, e.g., which have compilation or other JSP exceptions, are not crawled. 
     Resource Manager 
     This section describes an embodiment of the resource manager usable in the invention. The resource manager monitors system resource usage, such as CPU and memory usage, on the machine where the prefabricator service is executing. The resource manager is also the component responsible for monitoring the load of the middle-tier system, by monitoring the number of concurrent requests of the Apache servers that the prefabricator service is interested in. This monitoring can be performed by sending URL requests to the mod-status Apache modules. 
     Based on the current system usage and predefined system resource limits, the resource manager provides information to other prefabricator components, such as the page request feeder, regarding whether the preset system resource limits have been exceeded, and how many page prefabrication requests that the prefabricator service can send to the Apache servers. 
     The Resource Manager uses the following system resource limits and information from the System Policy object, which in one embodiment, is stored in the database: (1) a list of all Apache servers and their port numbers in the middle-tier system; (2) whether a load balancer should be used, and if so, the host name and port number of the load balancer; (3) memory usage limit; (4) CPU usage limit; and, (5) maximum number of concurrent requests that the middle-tier system should be able to handle without significant impact on system response time. 
     The Resource Manager accesses the configuration information to determine which web server or load balancer the page prefabricator requests should be sent to. In an embodiment, if a load balancer is being used (e.g., for an n-node architecture), all page prefabrication requests should be sent to the load balancer. If no load balancer is available, page prefabrication requests are sent to the local web server, i.e., the web server residing on the same machine as the prefabricator service. If there are more than one web server running on such machine, an equal number of page prefabrication requests are sent to each web server. 
     The resource manager also determines the number of concurrent page prefabrication HTTP requests that the Page Request Feeder can send. In an embodiment, the following configured values are used in the calculation of the number of concurrent request that a prefabricator service instance should be sent to the web server:
         Rmax is the maximum number of concurrent requests that the middle-tier system can handle without a significant degradation of response time   W is the relative weight of the machine where the prefabricator service instance is running in.   Wtotal is the total relative weight of all configured machines.       

     If a load balancer is to be used, then the Resource Manager regularly monitors the number of concurrent requests on all the web servers configured (Rc 1 ). In an embodiment, the number of requests (R) that this prefabricator service instance can send to the load balancer is:
 
 R= ( R max− Rc 1)*( W/W total)
 
     If a load balancer is not used, and page prefabrication requests are to be sent to the local web server, then the Resource Manager regularly monitors the number of concurrent requests on the local web server(s) (Rc 2 ). In an embodiment, the number of requests (R) that this prefabricator service instance can send to the load balancer is:
 
 R= ( R max*( W/W total))− Rc 2
 
     The resource manager also monitors the CPU and Memory usage on the local system. In an embodiment, a separate thread is spawned for CPU and memory usage measurements. The measurements are taken at predefined intervals, and the resource manager uses the measured usage number and the preset resource limits to determine whether the limits have been exceeded. The resource manager produces the following outputs: (1) current CPU usage on the local machine; (2) whether the CPU usage limit been exceeded; (3) current memory usage on the local machine; (4) whether the memory usage limit been exceeded; (5) the host name and port number of the web servers where page prefabrication HTTP requests should be sent to; and, (6) the number of concurrent page prefabrication HTTP requests that this page prefabricator service instance can send to the web server(s) or load balancer. 
     Resource Optimization 
     The goal of the prefabricator service is to optimally use the available system resources to prefabricate and regenerate pages. In one approach, the prefabrication and refresh rate should be as fast as, or faster than, the refresh interval configured for a given policy. The refresh interval configured by the administrator indicates the staleness of pages that are acceptable for the specific application. 
     By way of example, the following describes a resource optimization method for a system having one or more middle-tier machines that access a back-end server (e.g., a database server). The following factors are used in this embodiment to optimize resource utilization for the prefabrication process:
         maximum percentage of system [middle-tier+prefab service] CPU that can be utilized (CPU midtier )   maximum percentage of back-end server CPU that can be utilized (CPU database )   average response time or PRB processing time (T average )
 
As the above three parameters vary, the way in which the number of concurrent PRBs are processed also varies, as shown in the table below:
       

     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                   
                 # of 
               
               
                   
                   
                   
                   
                 concurrent 
               
               
                 T average   
                 CPU middle-tier   
                 CPU database   
                 Reason 
                 requests 
               
               
                   
               
             
            
               
                 Slow 
                 high 
                 Low 
                 Jserv load is 
                 Reduce 
               
               
                   
                   
                   
                 too high 
               
               
                 Slow 
                 low/normal 
                 High 
                 DB is 
                 Reduce or 
               
               
                   
                   
                   
                 bottleneck 
                 nothing 
               
               
                 Fast 
                 high 
                 Low 
                 Jserv load is 
                 if CPU middle-   
               
               
                   
                   
                   
                 high 
                   tier  &gt; CPU max   
               
               
                   
                   
                   
                   
                 reduce 
               
               
                 Fast 
                 low/normal 
                 High 
                 DB is 
                 If 
               
               
                   
                   
                   
                 bottleneck 
                 CPU database  &gt; 
               
               
                   
                   
                   
                   
                 CPU max   
               
               
                   
                   
                   
                   
                 reduce 
               
               
                   
               
            
           
         
       
     
     Based on the above table, the number of concurrent requests can be increased from the prefabrication service to the web-server until the CPU utilization reaches the maximum level. Once this level is reached, the concurrency that provides a CPU utilization level less than the maximum response-time is chosen as the optimal concurrency. This optimal concurrency is re-calibrated periodically so as to tune to the changing system behavior. 
     An alternative approach uses a parameter setting that sets the maximum number of concurrent requests that can be handled by the web-server. This parameter setting can be provided, for example, by an authorized administrator. In this approach, the goal of the prefabricator system is not to use all the available resources, but instead to use the optimal amount of available resources to obtain the best refresh time per page. This approach uses the maximum number of concurrent requests that can be issued. The exact parameter setting for the maximum or optimal concurrency in the system is fundamental to this approach. The incoming traffic to the Jserv process should be carefully tuned to avoid overloading the user system with too many concurrent requests. An advantage of this approach is that it avoids making platform dependent system calls, distributed CPU measurements, and it can be used to specify the exact amount of CPU resource the prefabricator should use. 
     Security and Session Management 
     This section describes security management methods for prefabrication according to an embodiment of the invention. For the purposes of illustration, and not by way of limitation, the present explanation refers to a user connection as a “session” and to the identifier for the user connection as a “session ID”. An identified user session may be formed, for example, when a user establishes an authorized connection to a database server to execute a database application. The session ID is used to validate a user session and to identify user preferences. In one approach to implementing sessions, a valid session ID is issued when a user successfully logs into an application. The session ID is checked for validity before the user is permitted to access pages within the application. The session ID remains valid until the user logs out. 
     As the user moves from page to page within the session, the session ID is passed along with the viewed pages by the server. The session ID is set as a cookie value when cookies are enabled, or as an URL parameter when cookies are disabled. In the present invention, since some pages accessed by a user are prefabricated while other are contemporaneously fabricated, there may be breaks in continuity between the pages handled by the server that are sent to the user, and thus the session IDs may not be fully passed from page to page. The present invention provides additional techniques to verify the validity of a session ID associated with a user session, even when prefabricated pages are returned to the user. 
     In one embodiment of the invention, the prefabricator is configured to avoid prefabricating the log-in page for a user. Thus, the user must proceed with normal log-in procedures to establish a valid user session. Upon successfully logging in, a session ID is assigned to the user session. 
     The first time the user requests a page from the interceptor, the validity of the session ID is verified through normal verification procedures, e.g., by passing the page request to the back-end database server. From that point on, the interceptor maintains a record of the validity of the session ID. If the user request a page that is not prefabricated, then the server dynamically services the page request and places the session ID on the page response. However, if the user requests a page that has been prefabricated, the interceptor returns the prefabricated page to the user - with the valid session ID includes as part of the page. Thus, the interceptor will itself make sure that the session ID is passed along in the page returned to the user, even if a prefabricated page is returned to the user. Because the valid session ID is always returned to the user in the response page, user sessions will not change during transitions when users move between prefabricated and non-prefabricated pages. 
     In an n-node environment, it is possible that within a single session, a user will send page requests to multiple server nodes. According to one embodiment, the interceptor module that first verifies the validity of a session ID will propagate that session ID to every other node in the system. A record of that session ID will be maintained at every node as being valid. When the user issues a page request, the router or load balancer will route that page request to one of the distributed nodes. Since the local interceptor at that node will presumably already recognize the validity of the session ID for the user, that local interceptor can immediately service the page request without further verifications. If the requested page has already been prefabricated, the page response with the attached session ID, can be immediately returned to the user. 
     In an embodiment of the invention, a cookie is employed to store information about the user&#39;s preferences, application the user is logged into and the responsibility the user has. The cookie may also contain other state information, such as the selected menu page. When cookies are disabled, this information is set as an URL parameter. 
     When a user logs in with a valid user name and password, a session identifier is generated for tracking the user session. This session identifier is contained in all subsequent requests of the user, until the time the user logs out voluntarily or the session times out. The session identifiers are captured at login time and stored in a shared-memory table (so all Apache processes have access to it). Subsequent requests that are serviced from Cache are sent back only after confirming that the session identifier is present in Shared memory. If the session identifier is not present in the shared-memory, session validation and default processing to the Jserv is performed. This ensures that an invalid session identifier cannot be used to access the system. 
     The following steps are performed to set-up a user session according to an embodiment of the invention:
     a) The system authenticates the user using guest username and password;   b) A user session is created using the userID passed in by the prefabricator service;   c) The user&#39;s identity is switched to the userID passed as input. This sets the session as belonging to the relevant user; and,   d) Determine the session ID for this session.   

     The created sessionID is used by the Start Loader to construct the URI for the user. Since session creation and validation may be expensive, the session ID is shared by prefabricator requests belonging to multiple users. Therefore, when a prefabricator generated HTTP request is issued, the typical validation of sessionID process is bypassed. Instead, the cookie parameters are used to obtain the user&#39;s preference settings and to set up the user context correctly. This sets up both at the middle-tier and the connection-level context of the user. 
     If cookies are turned on, then the generated URI contains all URL parameters and cookie parameters according to an embodiment. In order to support smooth transition between prefabricated and non-prefabricated pages, the interceptor uses the actual user&#39;s sessionID in the URI and not the prefabricator generated sessionID. This ensures that, regardless of which page that is being accessed, the user is always in the context of the currently logged in session. 
     Interceptor 
     This section describes an embodiment of the interceptor. The interceptor stores prefabricated versions of dynamically generated JSP (JavaServer Pages) in its cache, and attempts to service real-user requests using these static cached versions of JSPs. The Interceptor over-rides the default behavior of the Apache WebServer&#39;s mod_serv module, by first attempting to service the user requests using pre-fabricated cached page responses. The user request is mapped to a prefabricated page filename and if an exact match is found in the cache, the prefabricated response is served back to the user. If no match is found, the default dynamic page generation process occurs and the page is sent back to the user. 
     The interceptor handles a page request differently depending upon whether the page request originates from the prefabricator or from the user. In an embodiment, a parameter is defined in the page request object that identifies the originator of the page request. 
     If a user sends a page request, then the interceptor performs the following steps to process the page request according to one embodiment:
     1. Map the page request to unique identifier that can be used to look up prefabricated page, e.g., in the file system.   2. Check if the requested page exists in the cache. If the prefabricated page exists and was generated within the maximum permissible cache staleness and return the pre-fabricated page to the user.   3. If the requested page is not present in cache, perform default dynamic generation.   4. If the requested page is present in cache, but violates a maximum staleness requirement, dynamically generate the page and also refresh the Cached file with the dynamically generated page.   5. Return page response to user.   

     If the prefabricator sends the page request, then the interceptor performs the following steps to process the page request:
     1. Dynamically generate the page.   2. Map the page request to unique identifier that can be used to look up prefabricated page.   3. Store the response in the cache under the static filename generated in step 2.   4. Return page response to prefabricator.   

     SYSTEM ARCHITECTURE OVERVIEW 
     Referring to  FIG. 13 , in an embodiment, a computer system  1320  includes a host computer  1322  connected to a plurality of individual user stations  1324 . In an embodiment, the user stations  1324  each comprise suitable data terminals, for example, but not limited to, e.g., personal computers, portable laptop computers, or personal data assistants (“PDAs”), which can store and independently run one or more applications, i.e., programs. For purposes of illustration, some of the user stations  1324  are connected to the host computer  1322  via a local area network (“LAN”)  1326 . Other user stations  1324  are remotely connected to the host computer  1322  via a public telephone switched network (“PSTN”)  1328  and/or a wireless network  1330 . 
     In an embodiment, the host computer  1322  operates in conjunction with a data storage system  1331 , wherein the data storage system  1331  contains a database  1332  that is readily accessible by the host computer  1322 . Note that a multiple tier architecture can be employed to connect user stations  1324  to a database  1332 , utilizing for example, a middle application tier (not shown). In alternative embodiments, the database  1332  may be resident on the host computer, stored, e.g., in the host computer&#39;s ROM, PROM, EPROM, or any other memory chip, and/or its hard disk. In yet alternative embodiments, the database  1332  may be read by the host computer  1322  from one or more floppy disks, flexible disks, magnetic tapes, any other magnetic medium, CD-ROMs, any other optical medium, punchcards, papertape, or any other physical medium with patterns of holes, or any other medium from which a computer can read. In an alternative embodiment, the host computer  1322  can access two or more databases  1332 , stored in a variety of mediums, as previously discussed. 
     Referring to  FIG. 14 , in an embodiment, each user station  1324  and the host computer  1322 , each referred to generally as a processing unit, embodies a general architecture  1405 . A processing unit includes a bus  1406  or other communication mechanism for communicating instructions, messages and data, collectively, information, and one or more processors  1407  coupled with the bus  1406  for processing information. A processing unit also includes a main memory  1408 , such as a random access memory (RAM) or other dynamic storage device, coupled to the bus  1406  for storing dynamic data and instructions to be executed by the processor(s)  1407 . The main memory  1408  also may be used for storing temporary data, i.e., variables, or other intermediate information during execution of instructions by the processor(s)  1407 . A processing unit may further include a read only memory (ROM)  1409  or other static storage device coupled to the bus  1406  for storing static data and instructions for the processor(s)  1407 . A storage device  1410 , such as a magnetic disk or optical disk, may also be provided and coupled to the bus  1406  for storing data and instructions for the processor(s)  1407 . 
     A processing unit may be coupled via the bus  1406  to a display device  1411 , such as, but not limited to, a cathode ray tube (CRT), for displaying information to a user. An input device  1412 , including alphanumeric and other columns, is coupled to the bus  1406  for communicating information and command selections to the processor(s)  1407 . Another type of user input device may include a cursor control  1413 , such as, but not limited to, a mouse, a trackball, a fingerpad, or cursor direction columns, for communicating direction information and command selections to the processor(s)  1407  and for controlling cursor movement on the display  1411 . 
     According to one embodiment of the invention, the individual processing units perform specific operations by their respective processor(s)  1407  executing one or more sequences of one or more instructions contained in the main memory  1408 . Such instructions may be read into the main memory  1408  from another computer-usable medium, such as the ROM  1409  or the storage device  1410 . Execution of the sequences of instructions contained in the main memory  1408  causes the processor(s)  1407  to perform the processes described herein. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and/or software. 
     The term “computer-usable medium,” as used herein, refers to any medium that provides information or is usable by the processor(s)  1407 . Such a medium may take many forms, including, but not limited to, non-volatile and volatile media. Non-volatile media, i.e., media that can retain information in the absence of power, includes the ROM  1409 . Volatile media, i.e., media that can not retain information in the absence of power, includes the main memory  1408 . Additionally, transmission media can take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. 
     Common forms of computer-usable media include, for example: a floppy disk, flexible disk, hard disk, magnetic tape, any other magnetic medium, CD-ROM, any other optical medium, punchcards, papertape, any other physical medium with patterns of holes, RAM, ROM, PROM (i.e., programmable read only memory), EPROM (i.e., erasable programmable read only memory), including FLASH-EPROM, any other memory chip or cartridge, carrier waves, or any other medium from which a processor  1407  can retrieve information. Various forms of computer-usable media may be involved in providing one or more sequences of one or more instructions to the processor(s)  1407  for execution. The instructions received by the main memory  1408  may optionally be stored on the storage device  1410 , either before or after their execution by the processor(s)  1407 . 
     Each processing unit may also include a communication interface  1414  coupled to the bus  1406 . The communication interface  1414  provides two-way communication between the respective user stations  1424  and the host computer  1422 . The communication interface  1414  of a respective processing unit transmits and receives electrical, electromagnetic or optical signals that include data streams representing various types of information, including instructions, messages and data. A communication link  1415  links a respective user station  1424  and a host computer  1422 . The communication link  1415  may be a LAN  1326 , in which case the communication interface  1414  may be a LAN card. Alternatively, the communication link  1415  may be a PSTN  1328 , in which case the communication interface  1414  may be an integrated services digital network (ISDN) card or a modem. Also, as a further alternative, the communication link  1415  may be a wireless network  1330 . A processing unit may transmit and receive messages, data, and instructions, including program, i.e., application, code, through its respective communication link  1415  and communication interface  1414 . Received program code may be executed by the respective processor(s)  1407  as it is received, and/or stored in the storage device  1410 , or other associated non-volatile media, for later execution. In this manner, a processing unit may receive messages, data and/or program code in the form of a carrier wave. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions shown in the process flow diagrams described herein is merely illustrative, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.