Patent Publication Number: US-7908600-B2

Title: Fault-tolerant patching system

Description:
FIELD OF THE INVENTION 
     The present invention relates to automated software-updating systems. The invention relates more specifically to a fault-tolerant patching system. 
     BACKGROUND OF THE INVENTION 
     The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     After a computer program has been released for sale to the public, and consumers have purchased and installed the program on their computer, updates to the computer program may become available. Such updates may fix errors in the previously released program, or add enhanced features that were not present in the previously released program. Such updates are often supplied to consumers in the form of another customized program that applies changes to the binary code of the previously released program. Often, the changes applied to the binary code do not completely replace the binary code, but only alter portions thereof. The process of applying updates to portions of a previously released program, instead of replacing the program entirely, is called “patching,” and the updates that are applied are called “patches.” 
     Unfortunately, patching programs are sometimes imperfect. Patching programs do not always account for various circumstances that might prevent a patch from being applied completely. Under some circumstances, for various possible reasons, a patching program may fail after beginning to apply a patch, but before finishing. The patching program may be unable to resume. As a result, the target program to which the patch is being applied may be only partially updated. A target program that has been only partially updated might behave erratically, and might stop working altogether. This is clearly an undesirable outcome. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a flow diagram that illustrates a technique for performing a patching operation in an atomic manner, according to an embodiment of the invention; 
         FIG. 2  is a flow diagram that illustrates a technique for performing, atomically, a patching operation that targets files that are distributed among multiple nodes, according to an embodiment of the invention; and 
         FIG. 3  is a block diagram that illustrates a computer system upon which an embodiment of the invention may be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
     Overview 
     A fault-tolerant patching system is described, along with techniques that may be used to implement such a fault-tolerant patching system. According to one such technique, a patching operation is performed in two phases. During the first phase, an attempt is made to backup files, or portions thereof, which are going to be updated by the patching operation. If a failure is detected during the first phase, then the patching operation aborts without proceeding to the second phase. During the second phase, an attempt is made to perform the updates that the patching operation specifies; an attempt is made to update the files, or portions thereof, which were previously backed-up. If a failure is detected during the second phase, then all of the updated files, or portions thereof, are restored; those files or file portions are replaced with their corresponding backed-up copies, which were made during the first phase. Under one variation of the technique, files that are based on the backed-up copies may be regenerated using the backed-up copies. This is advantageous when such files are too large to back up themselves. Such files may be generated after the backed-up copies are restored. For example, the above variation may be employed to perform a “make” operation after the restoration process described herein has been performed. 
     According to one technique, a patching operation that specifies updates to files that reside on separate nodes of a multi-node system is made atomic through a process that is similar to a two-phase commit protocol. During a first phase, each of the nodes on which a prospectively affected file resides is instructed to backup its resident files, or portions thereof, that will be affected by the patching operation. If any of the involved nodes is unable to backup these files or file portions, then all of the involved nodes are instructed to abort the patching operation before any of the files or file portions is modified by the patching operation. Alternatively, if all of the involved nodes are able to backup the prospectively affected files or file portions that reside on those nodes, then all of the involved nodes are instructed to proceed with the patching operation during a second phase. If a patching operation failure is detected while any of the involved nodes is performing the patching operation, then all of the involved nodes are instructed to reverse the effects of the patching operation by replacing the affected files or file portions with their corresponding copies, which were made during the first phase. In one embodiment of the invention, if patching fails on one of the nodes, then the patch tool attempts to recover every node back to the status quo. If the restoration process itself fails on a particular node, then the patch tool still can recover by copying relevant files from a “good” recovered node to the particular node. 
     As a result of the foregoing techniques, patching operations become atomic in nature; either all of the updates specified by a patching operation are applied successfully, or none of the updates specified by the patching operation are applied, in a permanent sense, at all. Thus, the problems that result from a patching operation being applied only partially are avoided. 
     Atomic Patching Operation 
       FIG. 1  is a flow diagram that illustrates a technique for performing a patching operation in an atomic manner, according to an embodiment of the invention. By performing the patching operation in an atomic manner, either the patch is entirely applied to the target files, or the target files are restored to the state in which they were prior to the patch&#39;s application. A patching program that executes on a computer may perform the illustrated technique in an automated way, for example. 
     In block  102 , the portions of a target program that are going to be updated by a patch are determined. The target program may comprise one or more separate files. The portions may be determined with differing degrees of granularity. According to one embodiment of the invention, each file that is going to be affected by the patch is determined to be a separate portion. According to another embodiment of the invention, each file portion that is going to be affected by the patch is determined to be a separate portion. In such an embodiment, more than one portion may occur within a particular file. 
     Different techniques may be used to determine which portions of the target program are going to be updated by the patch. According to one embodiment of the invention, “static” metadata that identifies files and/or file portions is contained within the patch, and the patching program reads the metadata in order to determine the files and/or file portions that are going to be updated. According to one embodiment of the invention, such metadata is not necessarily contained within the patch, but, instead, is determined “dynamically” by the patching program by comparing the contents of the patch (e.g., updated binary code segments) with the contents of the target program. In one embodiment of the invention, the discovery logic that determines which files and/or file portions to patch is provided externally to the patching code. For example, through pre-script execution, the patch tool can interact with the patch target to determine which files to modify. The files to be modified may vary from system to system. In one embodiment of the invention, both “static” and “dynamic” information is used, as described above, to determine the portions that are going to be updated. 
     In block  104 , for each portion identified in block  102 , a backup copy of that portion is made and stored separately from the original. If the portion comprises a whole file, then a copy of the whole file is made. Alternatively, if the portion comprises only a part of a file, then, in one embodiment of the invention, a copy of that part of the file, without the remainder of the file, may be made. Control passes to block  114 . 
     According to one embodiment of the invention, if a backup copy of any identified portion cannot be made, then the patching operation aborts, and none of the original files are updated as described below. This is shown in blocks  114  and  116 . In block  114 , it is determined whether the backup operation failed. If the backup operation failed, then control passes to block  116 . In block  116 , the patching operation aborts. 
     Alternatively, if the backup operation was successful, then control passes to block  106 . In block  106 , an attempt is made to apply the patch to the target program. For example, the patching program may attempt to update each of the original files or file portions that are affected by the patch. The attempt may complete without the occurrence of a failure, or, because of a failure during the attempt, the attempt might not complete entirely. 
     In block  108 , it is determined whether a failure occurred during the attempt to apply the patch. For example, the patching program may make such a determination by examining the contents of the files that were supposed to be updated, and comparing those contents with the corresponding contents of the patch. If any of the contents do not match, then the patching program may conclude that the patching operation was not entirely successful. If a failure occurred during the attempt to apply the patch, then control passes to block  110 . Otherwise, control passes to block  112 . According to one embodiment of the invention, errors that happen during runtime also can be detected, and the detection of such runtime errors triggers the restoration operation described below with reference to block  110 . 
     In block  110 , the target program is restored to the state in which the target program was prior to the beginning of the patching attempt. This is accomplished by replacing the patch-affected portions with the backup copies of those portions that were made in block  104 . In one embodiment of the invention, this replacement is performed automatically, such as by a patching program, for example. However, in an alternative embodiment of the invention, this replacement may be performed manually. The patching program may alert the user that the patching attempt was unsuccessful. After performing other actions as needed, the user may manually replace the updated portions with their corresponding backup copies. In one embodiment of the invention, files that have not been backed-up or copied, as described above, nevertheless may be regenerated based on the backup copies, if such files are based on the files that were copied. 
     Alternatively, in block  112 , the patching operation was entirely successful, and no portions of the target program need to be restored. The backup copies may be deleted automatically. 
     The technique described above may be contrasted with other possible approaches in which a whole system, or a significant portion thereof, would be backed up. Under these other possible approaches, a large amount of information that was not necessarily related to or affected by a patching operation might be copied. As a result, these other possible approaches would waste storage resources. Additionally, in the event that the backed-up information needed to be restored, these other possible approaches could waste time and I/O resources by restoring lots of information that was not affected by the patching operation. Thus, in one embodiment of the invention, no file that was not updated by the patching operation is restored in the event that a failure occurs during the patching operation. 
     Under other approaches, which back up a whole system, the system may encounter a bad state. For example, under such an approach, preparatory to the application of a patch P 1 , a file “lib.a” might be backed up, after which “lib.a” might be updated with “foo.o.” Subsequently, preparatory to the application of another patch P 2 , “lib.a” might be backed up, after which “lib.a” might be updated with “bar.o.” Subsequently, patch P 1  might be rolled back. During the rollback, the restoration of the copy of “lib.a” that was backed up preparatory to the application of patch P 1  obliterates the “bar.o” update made during the application of patch P 2 . 
     In contrast, using a technique described herein, the following operations would take place instead. Preparatory to the application of patch P 1 , the old version of “foo.o” in “lib.a” would be backed up. When patch P 1  was applied, “lib.a” would be updated with the new version of “foo.o.” Then, preparatory to the application of patch P 2 , the old version of “bar.o” would be backed up. When patch P 2  was applied, “lib.a” would be updated with the new version of “bar.o” In the event that patch P 1  is subsequently rolled back, the problems with the other approaches are avoided, because the old version of “foo.o” is restored into “lib.a” instead of the entirety of “lib.a” being restored. The new version of “bar.o” remains in “lib.a” even after the rollback. 
     Distributed Patching Operations 
     In some circumstances, a patch may target files that are distributed among separate nodes of a multi-node system (e.g., an application server system with multi-node mid-tiers and an infrastructure such as a metadata repository). For example, a patch may target a first file that is stored on a first computer, and the same patch may target a second file that is stored on a second computer. Under such circumstances, it is beneficial to have some mechanism for ensuring that the patch will update none of the files unless the patch updates all of the files. 
       FIG. 2  is a flow diagram that illustrates a technique for performing, atomically, a patching operation that targets files that are distributed among multiple nodes, according to an embodiment of the invention. A patching program that executes on a computer may perform the illustrated technique in an automated way, for example. 
     In block  202 , the files and/or file portion that are going to be updated by a patch are identified. The files and/or file portions may reside on separate nodes of a multi-node system. The nodes on which the files and/or file portions reside also are identified. 
     In block  204 , each node on which a file or file portion identified in block  202  resides is instructed to make a backup copy of each of the identified files and/or file portions that resides on that node. For example, a patching program may instruct both a first node and a second node to make backup copies of the previously identified file portions that reside on those nodes. 
     According to one embodiment of the invention, each node responds, to a patching program that instructed that node to make the backup copies, whether that node was able to make the backup copies successfully. Thus, from each node, the patching program may receive a response that indicates whether a failure occurred on that node while that node was attempting to make the backup copies. 
     In block  206 , it is determined whether any of the nodes was unable to make the backup copies whose making was instructed in block  202 . For example, the patching program may determine whether a “backup successful” response was received from each node on which one or more identified files and/or file portions reside. If at least one of the involved nodes did not return such a response in due time, or returned a response indicating a contrary outcome, then the patching program may conclude that a failure occurred on at least one of the involved nodes. If at least one of the involved nodes was unable to make the backup copies, then control passes to block  208 . Otherwise, control passes to block  210 . 
     In block  208 , the patching operation is aborted. None of the files or file portions targeted by the patch is updated as described below. A user may be alerted that the patching operation failed because one or more files or file portions could not be backed up. The user may be given the identities of the files or file portions that could not be backup up. The user may be given the identities of one or more nodes on which those files or file portions reside. 
     Alternatively, in block  210 , each node on which a file or file portion identified in block  202  resides is instructed to apply the patch to the patch-targeted files and/or file portions that reside on that node. For example, a patching program may instruct both a first node and a second node to apply the patch to the previously identified file portions that reside on those nodes. 
     According to one embodiment of the invention, each node responds, to a patching program that instructed that node to apply the patch, whether that node was able to apply the patch to all of that node&#39;s resident patch-targeted files and/or file portions successfully. Thus, from each node, the patching program may receive a response that indicates whether a failure occurred on that node while that node was attempting to apply the patch. 
     In block  212 , it is determined whether any of the nodes was unable to apply the patch whose application was instructed in block  210 . For example, the patching program may determine whether a “patch successful” response was received from each node on which one or more patch-targeted files and/or file portions reside. If at least one of the involved nodes did not return such a response in due time, or returned a response indicating a contrary outcome, then the patching program may conclude that a failure occurred on at least one of the involved nodes. If at least one of the involved nodes was unable to apply the patch completely, then control passes to block  214 . Otherwise, control passes to block  216 . 
     In block  214 , each node on which a file or file portion identified in block  202  resides is instructed to reverse the effects of the patching operation by replacing all of that node&#39;s resident files and/or file portions that were affected by the patching operation with the corresponding backup copies made earlier. For example, a patching program may instruct both a first node and a second node to restore, from backup copies, the patch-affected file portions that reside on those nodes. In one embodiment of the invention, the restore operation can be controlled from one node, if the system on the other nodes is a copy of that one node. Such a configuration is possible, for example, in a Real Application Cluster. For example, the backup process can be performed on the controlling node, and during the restoration process, the backed-up files can be copied to the other nodes. 
     According to one embodiment of the invention, in response to such an instruction, each node replaces all of that node&#39;s resident files and/or file portions that were affected by the patching operation with the corresponding backup copies made earlier. The patching operation aborts. A user may be alerted that the patching operation failed because one or more files or file portions could not be updated. The user may be given the identities of the files or file portions that could not be updated. The user may be given the identities of one or more nodes on which those files or file portions reside. 
     Alternatively, in block  216 , the patching operation was entirely successful, and no patch-targeted files or file portions need to be restored. The backup copies may be deleted automatically. 
     Hardware Overview 
       FIG. 3  is a block diagram that illustrates a computer system  300  upon which an embodiment of the invention may be implemented. Computer system  300  includes a bus  302  or other communication mechanism for communicating information, and a processor  304  coupled with bus  302  for processing information. Computer system  300  also includes a main memory  306 , such as a random access memory (RAM) or other dynamic storage device, coupled to bus  302  for storing information and instructions to be executed by processor  304 . Main memory  306  also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor  304 . Computer system  300  further includes a read only memory (ROM)  308  or other static storage device coupled to bus  302  for storing static information and instructions for processor  304 . A storage device  310 , such as a magnetic disk or optical disk, is provided and coupled to bus  302  for storing information and instructions. 
     Computer system  300  may be coupled via bus  302  to a display  312 , such as a cathode ray tube (CRT), for displaying information to a computer user. An input device  314 , including alphanumeric and other keys, is coupled to bus  302  for communicating information and command selections to processor  304 . Another type of user input device is cursor control  316 , such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor  304  and for controlling cursor movement on display  312 . This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. 
     The invention is related to the use of computer system  300  for implementing the techniques described herein. According to one embodiment of the invention, those techniques are performed by computer system  300  in response to processor  304  executing one or more sequences of one or more instructions contained in main memory  306 . Such instructions may be read into main memory  306  from another machine-readable medium, such as storage device  310 . Execution of the sequences of instructions contained in main memory  306  causes processor  304  to perform the process steps 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 software. 
     The term “machine-readable medium” as used herein refers to any medium that participates in providing instructions to processor  304  for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as storage device  310 . Volatile media includes dynamic memory, such as main memory  306 . Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise bus  302 . Transmission media can also take the form of acoustic or light waves, such as those generated during radio-wave and infrared data communications. 
     Common forms of machine-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punchcards, papertape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. 
     Various forms of machine-readable media may be involved in carrying one or more sequences of one or more instructions to processor  304  for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system  300  can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector can receive the data carried in the infrared signal and appropriate circuitry can place the data on bus  302 . Bus  302  carries the data to main memory  306 , from which processor  304  retrieves and executes the instructions. The instructions received by main memory  306  may optionally be stored on storage device  310  either before or after execution by processor  304 . 
     Computer system  300  also includes a communication interface  318  coupled to bus  302 . Communication interface  318  provides a two-way data communication coupling to a network link  320  that is connected to a local network  322 . For example, communication interface  318  may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface  318  may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface  318  sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information. 
     Network link  320  typically provides data communication through one or more networks to other data devices. For example, network link  320  may provide a connection through local network  322  to a host computer  324  or to data equipment operated by an Internet Service Provider (ISP)  326 . ISP  326  in turn provides data communication services through the world wide packet data communication network now commonly referred to as the “Internet”  328 . Local network  322  and Internet  328  both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link  320  and through communication interface  318 , which carry the digital data to and from computer system  300 , are exemplary forms of carrier waves transporting the information. 
     Computer system  300  can send messages and receive data, including program code, through the network(s), network link  320  and communication interface  318 . In the Internet example, a server  330  might transmit a requested code for an application program through Internet  328 , ISP  326 , local network  322  and communication interface  318 . 
     The received code may be executed by processor  304  as it is received, and/or stored in storage device  310 , or other non-volatile storage for later execution. In this manner, computer system  300  may obtain application code in the form of a carrier wave. 
     In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.