Abstract:
A method of analyzing a resource leak on a first web server uses a second web server. A first HTTP request message is received from a client at a first Web server and includes an identifier of an information component stored on the first Web server which generates a reply to the first HTTP request message including the information component, and sends the reply to the client. Multiple duplicate HTTP request messages for the information component are generated at the first Web server in response to the receiving of the first request, for analyzing a resource leak on the first Web server. Each of the duplicate HTTP request messages includes the identifier of the information component. The duplicate HTTP request are transmitted to a second Web server and multiply any existing resource leak, thereby facilitating detection, diagnosis and/or analysis. The transmitting to the second Web server maintains the first Web server free from receiving the multiple HTTP request messages.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a Continuation of U.S. patent application Ser. No. 10/414,813 filed Apr. 16, 2003 which claims the benefit of U.S. Provisional Application No. 60/429,826 filed Nov. 22, 2002, each of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND  
       [0002]     The present invention relates generally to Web servers, and particularly to solving resource leaks in Web servers.  
         [0003]     The recent rapid increase in the demand for network services has caused a similar increase in the number and complexity of Web servers produced to serve that demand. Due to this complexity Web servers are exhaustively tested in development before being taken into production, where they serve customers in real time. But once in production, Web servers can be difficult to test, and the problems revealed can be difficult to solve. One common problem is the resource leak, where some resource, such as memory, is gradually consumed in a manner that is detrimental to the stability or performance of the Web server. One common resource leak is the memory leak.  
         [0004]     Web servers provide information components, such as Web pages, word processing documents, spreadsheets, images, movies, and the like, to customers. Some of these information components are static, and therefore can be provided without further processing. Other information components are dynamic, and must be generated by an information component generation process before delivery to a customer. A resource leak is caused when the resource is marked as “in use” while the information component generation process is working, but is not released when the process no longer needs that resource. The resource may be memory, synchronization objects, communication ports, or other finite computer resources. Because the resource is never released, it is not available for use by the same or other processes. Over time, such resource leaks can cause the process or whole operating system to malfunction.  
         [0005]     Resource leaks in production Web servers are typically very time consuming and difficult to diagnose and correct.  
         [0006]     First, resource leaks often happen very slowly, so days or weeks are spent collecting data to evaluate the effectiveness of each proposed solution. If many solutions must be tried, this process can consume months or more.  
         [0007]     Second, resource leaks often happen on production Web servers. Because these Web servers must be highly reliable, personnel diagnosing the resource leak may not be allowed to significantly modify the system. One common way of diagnosing a resource leak is to disable a part of the leaking process. Parts are individually disabled and enabled. When the resource leak is seen to disappear, the parts that are disabled are usually responsible for the leak. This strategy is generally disallowed on production Web servers, since the loss of functionality associated with disabling components is unacceptable. Other diagnostic software components are often used to detect and diagnose resource leaks. Tools such as leak detectors can be very valuable when finding small leaks, but the use of these tools on production servers is often forbidden. Administrators responsible for the stability of production Web servers do not want to put that stability in jeopardy by running additional diagnostic and debugging software on the Web server.  
         [0008]     Third, resource leaks are often associated with unusual or unexpected circumstances. Most software systems used on production Web servers have undergone significant testing before being deployed. Therefore, leaks associated with commonly used features of the Web server are unusual. Those leaks are typically found and corrected before deploying the software. When a leak is found on a production Web server, it is frequently associated with a feature that was not heavily tested, perhaps because it didn&#39;t seem important, or because the particular sequence of user actions was not predicted. Identifying a resource leak on a production Web server is generally pretty easy. The resource is observed to be exhausted. Identifying the cause of the resource leak is much harder, since it&#39;s typically NOT associated with any common functionality. Typically, when a flaw or bug is found in software, the circumstances that lead to the display of the flaw are reproduced in a laboratory. Once a fix has been proposed, that fix is implemented and tested in the laboratory. This model doesn&#39;t work well for leaks detected on a production system, since reproducing the circumstances of the production system in a laboratory is difficult. The usage characteristics of a production system are complicated and difficult to characterize.  
       SUMMARY  
       [0009]     The invention is known as a Web Hit Multiplier and Web Hit Redirector, and features a method, apparatus, and computer-readable media. The invention intercepts hyper-text transfer protocol (HTTP) requests intended for a Web server, copies and processes those requests, then forwards the requests to the relevant Web server. It is conceptually similar to a proxy server in that it is a layer between Web clients (such as Browsers) and the Web server, though it is most easily implemented as a plug-in to the Web server to be tested. Web clients attach to the Web Hit Multiplier and Web Hit Redirector as though it were a Web server, while Web servers receive requests from the Web Hit Multiplier and Web Hit Redirector as though it were a Browser. It involves two aspects.  
         [0000]     Web Hit Multiplier  
         [0010]     The first aspect is a Web Hit Multiplier, which increases the number of HTTP requests processed by the Web server, thereby increasing the size of any existing resource leak. This makes the leak easier to detect and diagnose. The increase in requests is accomplished by multiplying existing incoming requests. Each incoming request is recorded and transmitted to the Web server multiple times. The first copy of the request can be thought of as the primary request, and additional copies can be thought of as secondary requests.  
         [0011]     Part of the Web Hit Multiplier is most easily implemented as a plug-in to the Web server in question. When the Web Hit Multiplier receives an HTTP request from a Browser (or other HTTP client), the plug-in records the request, and allows it to pass through to the Web server unmodified. It then forwards the request to a second component, which copies the request a number of times, and sends each request to the Web server being tested. When the Web server replies with an HTTP response to the primary request, the HTTP response is returned to the Browser. The Web Hit Multiplier should not return the responses to the secondary requests to the Browser, since the Browser did not make those requests (they were made by the Web Hit Multiplier.)  
         [0012]     The Web Hit Multiplier does not multiply requests that were generated by the Web Hit Multiplier itself. It can recognize its own requests via a number of methods, including client IP address, a custom header, etc.  
         [0013]     The Web Hit Multiplier includes additional features to help with diagnosis. In one embodiment, a filter selects resources for which requests should be multiplied based on predetermined criteria.  
         [0014]     First, it includes a filter that identifies the resources for which requests should be multiplied. When a leak is suspected in one component of the Web server, requests to just that component can be multiplied, while leaving requests to other components unmultiplied. Choosing to multiply (or not multiply) suspected components can help narrow down the component that is causing the leak. Since Web servers typically identify components and resources via Universal Resource Locators (URLs), the Web Hit Multiplier filters requests by URL, and only multiplies those URLs that match zero or more specified regular expressions. Additionally, the user may specify zero or more regular expressions that indicate URLs which should NOT be multiplied (i.e. the user can specify a positive condition that triggers multiplication or a negative condition that suppresses it.)  
         [0015]     Second, it includes a filter that identifies requests that are intended to change the state of the Web server, and does not multiply those requests. For example, suppose that a Web server is acting as a banking system. When a client requests a transfer of funds from one account to another through the bank Web site, the Web Hit Multiplier will NOT multiply this request. The user would NOT want the transfer to happen multiple times.  
         [0016]     Most requests to change state are handled through HTTP POST requests, as described in the HTTP specification. The Web Hit Multiplier will allow the user to specify which HTTP methods (e.g. “POST” or “GET”) should be multiplied, and which should not. URL based filtering (as described above) can also be used to filter out unwanted actions.  
         [0000]     Web Hit Redirector  
         [0017]     The second aspect is a Web Hit Redirector, which allows a secondary, test Web server to receive the same HTTP requests as a primary, production Web server. The Web Hit Redirector is very similar to the Web Hit Multiplier, except that instead of sending copies of the request to the primary Web server, the copied requests are processed and sent to the test Web server. This allows diagnosticians to modify the test Web server, and analyze the effects of the change in an environment with “real world” usage patterns. This is accomplished by copying incoming requests. Each incoming request is copied one or more times. The original copy is transmitted to the production Web server. This is known as the primary request. Other copies are transmitted to the test Web server or servers. These are known as test, or secondary, requests. In the Web Hit Redirector, the primary requests and test requests are typically NOT identical. The test requests must be “corrected” to be acceptable to the test Web server.  
         [0018]     Requests must be modified before forwarding them to the test Web server due to the way that Web servers identify the client that they are serving. HTTP is a stateless protocol, so in general the Web server does not know which client made which request. For example, if the Browser requested the “next” page of a long document, the Web server would need to know which client made the request—was it the client that is viewing page 2 (in which case it should return page 3), or was it the client that is viewing page 27 (in which case it should return page 28.) The HTTP protocol does not solve this problem, but there are standard practices to get around this limitation.  
         [0019]     Standard industry practice is to use a “cookie” to maintain state on the Web server. The cookie is a small identifier that&#39;s generated by the Web server, and is associated with the particular client. When the server responds to a request, it generates a cookie, and returns it with the response. The Browser (or other client) stores the cookie, and returns it to the Web server with any subsequent request. The Web server can use the cookie to correlate subsequent requests with the client that&#39;s making the request. This cookie is called a session cookie since it&#39;s used to establish the “session” of the current user on the Web server. For example user A might request “the next page.” The Web server would return page 1, along with the session cookie “User1”. Then user B might request “the next page”, and the Web server would again return page 1, along with the session cookie “User2.” Next, user A might request “the next page” (meaning page 2.) Along with the request, user A returns the session cookie “User1” to the Web server. The Web server remembers that the cookie “User1” is associated with a user that has already seen page 1, so it returns page 2. The Web server knows that user A should now see page 3 next, and that user B should see page 2 next, even though the Web server doesn&#39;t really know anything else about the users. All major browsers and Web servers support session cookies in this manner, even though cookies are not strictly part of the HTTP 1.0 specification.  
         [0020]     This creates a problem for the Web Hit Redirector. Since the Web server defines the format and meaning of cookies, the cookies from one Web server cannot, in general, be successfully sent to a second Web server. The second Web server will not understand the meaning of the cookie (e.g. sending the cookie “User2” to some other Web server may result in an error, since there may only be one user on the second system. Even if there are two users, the second user of the second Web server is NOT the same user as the second user of the first Web server.) Thus, when the Web Hit Redirector sends a request that was originally intended for the production Web server to the test Web server, the test Web server will not know how to interpret any cookies associated with the request.  
         [0021]     The Web Hit Redirector maps cookies on the production Web server to cookies on the test Web server. When it receives a request for a resource on the production Web server, it copies the request, and replaces any cookies that identify state on the production Web server with the corresponding cookies for the test Web server. To do so, it maintains a map of production cookies to test cookies. Before forwarding a request to the test Web server, the Web Hit Redirector modifies the request, replacing any session cookies that were intended for the production Web server with the mapped cookies that are appropriate to use with the test Web server. The Web Hit Redirector includes additional features to help with diagnosis.  
         [0022]     The Web Hit Redirector contains the same filtering features as the Web Hit Multiplier. Specifically, it has the ability to filter requests by URL, selectively allowing or disallowing those URLs that match specified regular expressions. It also has the ability to filter by HTTP method (e.g. redirecting HTTP GET requests, while ignoring HTTP POST requests.)  
         [0023]     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0024]      FIG. 1  shows a data communications system according to one embodiment.  
         [0025]      FIG. 2  depicts a process performed by the communications system of  FIG. 1  according to one embodiment.  
         [0026]      FIG. 3  shows a data communications system according to one embodiment.  
         [0027]      FIG. 4  depicts a process performed by the communications system of  FIG. 3  according to one embodiment.  
         [0028]      FIG. 5  depicts a process performed by the multiplier of  FIG. 1  according to one embodiment. 
     
    
       [0029]     The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears.  
       DETAILED DESCRIPTION  
       [0030]     As used herein, the terms “client” and “server” generally refer to an electronic device or mechanism, and the term “message” generally refers to an electronic signal representing a digital message. These terms are used to simplify the description that follows. The clients and servers described herein can be implemented on any standard general-purpose computer, or can be implemented as specialized devices.  
         [0031]     The amount of access to a Web server is often described by the “hit rate” on the server, which reflects the number of requests received and responded to by the Web server in a given amount of time. As described above, the user hit rate for a production Web server is often insufficient to permit prompt identification or diagnosis of a slow resource leak. The inventors have recognized that a slow resource leak would be evident much sooner if the hit rate on the information component causing the leak were higher. In other words, if a resource is leaked at a constant rate per hit, increasing the hit rate will make the leak more evident, and therefore easier to fix.  
         [0032]     One possible approach is to attempt to simulate those user requests, and simply increase the hit rate of the simulation. For example, a tool could be used to repeatedly request a resource from an information component on the server as soon as the server fulfills a request a new request is made. One disadvantage of this approach is that it is necessary to know which information component is causing the leak in order to simulate requests to that information component. This is a significant limitation, since the primary purpose of testing is to discover which information component is leaking! In other words, it&#39;s difficult to accurately simulate the load on a production Web server without knowing which aspects of the load are pertinent to the simulation.  
         [0033]      FIG. 1  shows a data communications system  100  according to one embodiment. Data communications system  100  includes a client  102  such as a Web browser, a Web server  104 , a plug-in  106 , an optional uniform resource locator (URL) filter  108 , and a multiplier  110 . Web server  104 , URL filter  108 , and multiplier  110  are preferably implemented as separate processes executing on one or more computers. Plug-in  106  is preferably implemented as an internet server application program interface (ISAPI) filter, although other implementations are contemplated. Web server  104  hosts one or more information components, such as Web pages and the like, that can be accessed by client  102  by sending an HTTP request.  
         [0034]      FIG. 2  depicts a process  200  performed by communications system  100  according to one embodiment. Client  102  transmits a hyper-text transfer protocol (HTTP) request message to Web server  104  (step  202 ). The HTTP request message can be generated automatically or in response to a user action. The HTTP request message includes an identifier of an information component stored on Web server  104 . Web server  104  receives the HTTP request message. In response to the HTTP request message, Web server  104  generates an HTTP reply message according to conventional methods, and transmits the HTTP reply message to client  102  (step  204 ).  
         [0035]     In embodiments employing optional URL and method filter  108 , plug-in  106  transmits a copy of the HTTP request message to filter  108  (step  206 ). In other embodiments, plug-in  106  transmits a copy of the HTTP request message directly to multiplier  110 . Filter  108  determines whether to forward the HTTP request message to multiplier  110  according to user-selectable filter criteria. In one embodiment, filter  108  applies a regular expression to each HTTP request, and forwards only those HTTP request that match the expression. In another embodiment, filter  108  can forward only those HTTP requests that do not match the expression. In a third embodiment, filter  108  can forward only those HTTP requests that match specified HTTP methods. Other embodiments include various combinations of these and other criteria.  
         [0036]     With this feature, particular portions of a Web site can be amplified, while other portions are not. This feature is particularly useful for isolating resource leaks. For example, if a resource leak is seen, and it&#39;s suspected to be associated with a particular portion of the Web site, URL filter  108  can amplify only that portion of the Web site. If the resource leak is accelerated, the leak is likely associated with that portion of the Web site. Then the reverse test can be performed, to amplify everything except that portion of the Web site. If the leak is not amplified, then it&#39;s very certain that the leak is associated with that portion of the Web site.  
         [0037]     Multiplier  110  receives a forwarded HTTP request message (step  208 ), and generates a predetermined number n of copies of the HTTP request message, where n≧1. Multiplier  110  transmits the copies of the HTTP request message to Web server  110  (step  210 ). In this way, process  200  “amplifies” all user requests for a particular information component, thereby increasing the rate of any resource leak associated with that information component, making that leak easier and faster to identify and diagnose. In some embodiments multiplier  110  includes a reply analysis tool that analyzes the replies returned by Web server  104  (step  212 ) in response to the multiplied requests generated by the multiplier, thereby providing additional test data.  
         [0038]     Embodiments of the invention can be used to test Web servers during manual click testing as well. Rather than multiplying requests from consumers in a production environment, these embodiments multiply requests from testers in a development environment. Each click of the tester is amplified by some large number, simulating many users clicking simultaneously.  
         [0039]      FIG. 3  shows a data communications system  300  according to one embodiment. Data communications system  300  includes a client  302  such as a Web browser, a production Web server  304 , a test Web server  312 , a plug-in  306 , an optional URL filter  308 , and a multiplier  310 . Web servers  304  and  312 , URL filter  308 , and multiplier  310  are preferably implemented as separate processes executing on one or more computers. Plug-in  306  is preferably implemented as an ISAPI filter. Web server  304  hosts one or more information components, such as Web pages and the like, that can be accessed by client  302 . Test Web server  312  hosts one or more of the information components hosted by production Web server  304 .  
         [0040]      FIG. 4  depicts a process  400  performed by communications system  300  according to one embodiment. Client  302  transmits a HTTP request message to production Web server  304  (step  402 ). The HTTP request message can be generated automatically or in response to a user action. The HTTP request message includes an identifier of an information component stored on production Web server  304 . Production Web server  304  receives the HTTP request message. In response to the HTTP request message, production Web server  304  generates an HTTP reply message according to conventional methods, and transmits the HTTP reply message to client  302  (step  404 ).  
         [0041]     In embodiments employing optional URL filter  308 , plug-in  306  transmits a copy of the HTTP request message to URL filter  308  (step  406 ). In other embodiments, plug-in  306  transmits a copy of the HTTP request message to multiplier  310 . URL filter  308  determines whether to forward the HTTP request message to multiplier  310  according to user-selectable filter criteria (step  412 ). In one embodiment, URL filter  308  applies a regular expression to each HTTP request, and forwards only those HTTP request that match the expression. In another embodiment, URL filter  308  can forward only those HTTP requests that do not match the expression. Other embodiments include various combinations of these and other criteria.  
         [0042]     Multiplier  310  receives a forwarded HTTP request message (step  408 ), and generates a predetermined number n of copies of the HTTP request message, where n≧1. Multiplier  310  transmits the copies of the HTTP request message to test Web server  312  (step  410 ). In some embodiments multiplier  310  includes a reply analysis tool that analyzes the replies returned by test Web server  302  (step  412 ) in response to the multiplied requests generated by the multiplier, thereby providing additional test data.  
         [0043]     In this way, process  400  “amplifies” all user requests for a particular production Web server information component to a test Web server, thereby increasing the rate of any leakage associated with that information component, making that leak easier and faster to detect and diagnose without disturbing the production environment. In addition, custom or off-the-shelf debugging tools can be used on the test Web server without disturbing the production environment.  
         [0044]     Some embodiments include a Web session mapping feature. When a client connects to a Web server, it&#39;s common to track the state of the session for that client using a session cookie. The contents of the session cookie are determined by the Web server and sent to the client, which includes the session cookie in subsequent requests to the Web server. But when a request is forwarded from a production Web server to a test Web server, the session cookie is not forwarded, because the test Web server will not understand it. Instead, the multiplier maintains a mapping between corresponding session cookies generated by the development and production Web servers, and performs appropriate session cookie substitutions. When a session is first established, there is no session cookie. In this case, the multiplier recognizes that no session cookie mapping has been established for that session, and so waits for the production Web server to set up a session cookie. Once the session cookie is established, the multiplier forwards the request to the test Web server, and maps the session cookie provided by the development server to the session cookie provided by the production Web server. When the multiplier receives subsequent requests in the session, it substitutes the session cookie according to the mapping before forwarding the request to the test Web server.  
         [0045]      FIG. 5  depicts a process  500  performed by multiplier  310  according to one embodiment. Multiplier  310  receives a request directed to the production Web server (PWS—step  502 ), and determines whether the request contains a session cookie (step  504 ).  
         [0046]     If the request does not contain a session cookie, multiplier  310  generates one or more copies of the request (step  506 ) and transmits the copy or copies to the test Web server (TWS—step  520 ). When multiplier  310  receives the reply or replies to the request from the test Web server (step  522 ), it parses the replies to obtain the session cookies provided by the test Web server (step  524 ). Multiplier  310  also passes the original request to the production Web server (step  508 ). When multiplier  310  receives the reply to the original request from the production Web server (step  510 ), it parses the reply to obtain the session cookie provided by the production Web server (step  512 ). Multiplier  310  then records a cookie mapping between the session cookie obtained from the production Web server in step  512  and the session cookies obtained from the test Web server in step  524  (step  514 ). Then process  500  ends (step  516 ).  
         [0047]     But if at step  504  the request contains a session cookie, multiplier  310  determines whether the session cookie has been mapped (step  526 ).  
         [0048]     If the request contains a session cookie, and the cookie has been mapped, multiplier  310  generates a copy or copies of the request (step  544 ), replaces the production Web server session cookie in the copy with the corresponding test Web server cookies from the map ( 546 ), and transmits the modified copy or copies to the test Web server (step  548 ). Then process  500  ends (step  550 ).  
         [0049]     But if at step  526  the session cookie exists in the request but has not been mapped, then multiplier  310  generates a copy or copies of the request from the production Web server (step  528 ) and transmits the copies to the test Web server (step  538 ). When multiplier  310  receives the replies to the request from the test Web server (step  540 ), it parses the replies to obtain the session cookies provided by the test Web server (step  542 ). Multiplier  310  also parses the original request to obtain the session cookie in the request (step  530 ) and passes the original request to the production Web server (step  532 ). Multiplier  310  then records a cookie mapping between the session cookie obtained from the production Web server in step  532  and the session cookies obtained from the test Web server in step  542  (step  534 ). Then process  500  ends (step  536 ). In one embodiment, multiplier  310  uses a single test Web server session cookie in all of the copies of a single request. In another embodiment, it uses a different test Web server session cookie in each copy of a single request.  
         [0050]     The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Apparatus of the invention can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the invention can be performed by a programmable processor executing a program of instructions to perform functions of the invention by operating on input data and generating output. The invention can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).  
         [0051]     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.