Abstract:
A server processing method for use in a client/server computing system which carries out transactions, includes steps of: receiving a command from a client process to signify the beginning of a transaction; determining whether a local transaction creator exists; and forwarding on the command to another server if a local transaction creator does not exist and for locally creating transaction state data if a local transaction creator does exist.

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of client/server (also known as “distributed”) computing, where one computing device (“the client”) requests another computing device (“the server”) to perform part of the client&#39;s work. The client and server can also be both located on the same physical computing device. 
     BACKGROUND OF THE INVENTION 
     Client/server computing has become more and more important over the past few years in the information technology world. This type of distributed computing allows one machine to delegate some of its work to another machine that might be, for example, better suited to perform that work. For example, the server could be a high-powered computer running a database program managing the storage of a vast amount of data, while the client is simply a desktop personal computer (PC) which requests information from the database to use in one of its local programs. 
     The benefits of client/server computing have been even further enhanced by the use of a well-known computer programming technology called object-oriented programming (OOP), which allows the client and server to be located on different (heterogeneous) “platforms”. A platform is a combination of the specific hardware/software/operating system/communication protocol which a machine uses to do its work. OOP allows the client application program and server application program to operate on their own platforms without worrying how the client application&#39;s work requests will be communicated and accepted by the server application. Likewise, the server application does not have to worry about how the OOP system will receive, translate and send the server application&#39;s processing results back to the requesting client application. 
     Details of how OOP techniques have been integrated with heterogeneous client/server systems are explained in U.S. Pat. No. 5,440,744 and European Patent Published Application No. EP 0 677,943 A2. These latter two publications are hereby incorporated by reference. However, an example of the basic architecture will be given below for contextual understanding of the invention&#39;s environment. 
     As shown in FIG. 1, the client computer  10  (which could, for example, be a personal computer having the IBM OS/2 operating system installed thereon) has an application program  40  running on its operating system (“IBM” and “OS/2” are trademarks of the International Business Machines corporation). The application program  40  will periodically require work to be performed on the server computer  20  and/or data to be returned from the server  20  for subsequent use by the application program  40 . The server computer  20  can be, for example, a high-powered mainframe computer running on IBM&#39;s MVS operating system (“MVS” is also a trademark of the IBM corp.). For the purposes of the present invention it is irrelevant whether the requests for communications services to be carried out by the server are instigated by user interaction with the first application program  40 , or whether the application program  40  operates independently of user interaction and makes the requests automatically during the running of the program. 
     When the client computer  10  wishes to make a request for the server computer  20 &#39;s services, the first application program  40  informs the first logic means  50  of the service required. It may for example do this by sending the first logic means the name of a remote procedure along with a list of input and output parameters. The first logic means  50  then handles the task of establishing the necessary communications with the second computer  20  with reference to definitions of the available communications services stored in the storage device  60 . All the possible services are defined as a cohesive framework of object classes  70 , these classes being derived from a single object class. Defining the services in this way gives rise to a great number of advantages in terms of performance and reusability. 
     To establish the necessary communication with the server  20 , the first logic means  50  determines which object class in the framework needs to be used, and then creates an instance of that object at the server, a message being sent to that object so as to cause that object to invoke one of its methods. This gives rise to the establishment of the connection with the server computer  20  via the connection means  80 , and the subsequent sending of a request to the second logic means  90 . 
     The second logic means  90  then passes the request on to the second application program  100  (hereafter called the service application) running on the server computer  20  so that the service application  100  can perform the specific task required by that request, such as running a data retrieval procedure. Once this task has been completed the service application may need to send results back to the first computer  10 . The server application  100  interacts with the second logic means  90  during the performance of the requested tasks and when results are to be sent back to the first computer  10 . The second logic means  90  establishes instances of objects, and invokes appropriate methods of those objects, as and when required by the server application  100 , the object instances being created from the cohesive framework of object classes stored in the storage device  110 . 
     Using the above technique, the client application program  40  is not exposed to the communications architecture. Further the service application  100  is invoked through the standard mechanism for its environment; it does not know that it is being invoked remotely. 
     The Object Management Group (OMG) is an international consortium of organizations involved in various aspects of client/server computing on heterogeneous platforms with distributed objects as is shown in FIG.  1 . The OMG has set forth published standards by which client computers (e.g.  10 ) communicate (in OOP form) with server machines (e.g.  20 ). As part of these standards, an Object Request Broker (called CORBA—the Common Object Request Broker Architecture) has been defined, which provides the object-oriented bridge between the client and the server machines. The ORB decouples the client and server applications from the object oriented implementation details, performing at least part of the work of the first and second logic means  50  and  90  as well as the connection means  80 . 
     As part of the CORBA software structure, the OMG has set forth standards related to “transactions” and these standards are known as the OTS or Object Transaction Service. See, e.g., CORBA Object Transaction Service Specification 1.0, OMG Document 94.8.4. Computer implemented transaction processing systems are used for critical business tasks in a number of industries. A transaction defines a single unit of work that must either be fully completed or fully purged without action. For example, in the case of a bank automated teller machine from which a customer seeks to withdraw money, the actions of issuing the money, reducing the balance of money on hand in the machine and reducing the customer&#39;s bank balance must all occur or none of them must occur. Failure of one of the subordinate actions would lead to inconsistency between the records and the actual occurrences. 
     Distributed transaction processing involves a transaction that affects resources at more than one physical or logical location. In the above example, a transaction affects resources managed at the local automated teller device as well as bank balances managed by a bank&#39;s main computer. Such transactions involve one particular client computer (e.g,  10 ) communicating with one particular server computer (e.g.,  20 ) over a series of client requests which are processed by the server. The OMG&#39;s OTS is responsible for coordinating these distributed transactions. 
     Usually, an application running on a client process begins a transaction which may involve calling a plurality of different servers, each of which will initiate a server process to make changes to its local database according to the instructions contained in the transaction. The transaction finishes by either committing the transaction (and thus all servers finalize the changes to their local databases) or aborting the transaction (and thus all servers “rollback” or ignore the changes to their local databases). To communicate with the servers during the transaction (e.g., instructing them to either commit or abort their part in the transaction) one of the processes involved must maintain state data for the transaction. This usually involves the process to set up a series of transaction objects, one of which is a coordinator object which coordinates the transaction with respect to the various servers. 
     A conventional implementation of the OTS, which was developed by the International Business Machines Corporation and included in its Component Broker Series (a trademark of the IBM Corp.) product announced in May of 1997, is shown in FIG. 2. A client process  21  which wants to begin a transaction (e.g., to withdraw money from a bank account) needs to locate a process which is capable of creating and holding the transaction objects that will maintain the state of the transaction. As the modern tendency is to create clients that are “thin” (and thus have only the minimum functionality), the client process  21  will usually not be able to maintain the transaction objects locally and must look for a server process for this purpose. 
     According to this prior art approach, the OTS (or another service, such as the CORBA Lifecycle service) arbitrarily assigns a server process on which to create the transaction objects  221  (which typically include the Coordinator, Control and Terminator objects). The same server process (server A process  22  in FIG. 2) is always chosen according to this prior art. Upon locating the server A process  22 , client process  21  sends (arrow with encircled number  1 ) a message to server A process  22  to instruct server A process  22  to create the transaction objects  221 . Server A process  22  then creates transaction objects  221  and sends a reply (arrow with encircled number  2 ) containing the transaction context to client  21 . Client  21  then sends a debit bank account command (arrow with encircled number  3 ) to server B process  23  (the process containing the bank account object  231  which the client process  21  wishes to withdraw money from). This latter command carries with it the transaction context supplied to the client  21  by the server A process  22 . In this way, the bank account object  231  in process  23  can register itself (arrow with encircled number  4 ) with the transaction objects  221  in process  22  so that the bank account object  231  can be commanded (arrow with encircled number  5 ) to commit or rollback by the transaction objects  221  at the end of the transaction. 
     The system designer may want to maintain the transaction objects on the server where many of the resources likely to be involved in the transaction exists, in order to reduce the number of cross-process calls. Alternatively, in other cases, a designer may want to create and maintain the transaction objects on a server which does not have local resources so as not to load down another server with local resources. However, the prior art implementation does not allow the system designer to select which servers will be used to create and maintain the transaction objects. 
     SUMMARY OF THE INVENTION 
     According to a first aspect, the present invention provides a server processing apparatus for use in a client/server computing system which carries out transactions, the apparatus having: means for receiving a command from a client process to signify the beginning of a transaction; means for determining whether a local transaction creator exists; and means for forwarding on said command to another server if a local transaction creator does not exist and for locally creating transaction state data if a local transaction creator does exist. 
     According to a second aspect, the invention provides a method of carrying out the functionality described above in the first aspect. 
     According to a third aspect, the invention provides a computer program product for, when run on a computer, carrying out the functionality of the first aspect. 
     According to a fourth aspect, the invention provides a server for use in a client/server computing system for executing distributed transactions, the server having a local distributed object transaction service implementation which is incapable of locally creating transaction state data. 
     According to a fifth aspect, the invention provides two servers for use in a client/server computing system for executing distributed transactions, each server having a local distributed object transaction service implementation, one server being capable of locally creating transaction state data, and another server being incapable of locally creating transaction state data. 
     Since the system designer can select which servers are capable of creating and maintaining the state data of a transaction, and which servers are not so capable, a great degree of flexibility in how the transaction is processed is attained due to the present invention. 
     For example, in one case, a server which has local resources can be designated as being capable of creating and maintaining transaction state data, so that the transaction objects and resource objects are located in the same process, thus reducing the number of cross-process calls required to process the transaction. 
     In another case, this same server can be designated as not being capable of creating and maintaining transaction state data, so that this server, which has local resources, can devote all of its processing power to updating and maintaining the local resources without having to be diverted to taking care of the transaction state objects. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by the below description of preferred embodiments thereof to be read while referring to the following figures. 
     FIG. 1 is a block diagram of a conventional heterogeneous client/server architecture using object technology, in the context of which the preferred embodiment of the present invention can be applied; 
     FIG. 2 is a block diagram showing a conventional OTS implementation; 
     FIG. 3 is a block diagram showing a first implementation according to a preferred embodiment of the present invention; 
     FIG. 4 is a block diagram of a server process of the first implementation of FIG. 3; 
     FIG. 5 is a block diagram showing the first implementation of FIG. 3 during transaction execution; 
     FIG. 6 is a block diagram showing a second implementation according to a preferred embodiment of the present invention; 
     FIG. 7 is a block diagram of a server process of the second implementation of FIG. 6; and 
     FIG. 8 is a flowchart showing the operational steps carried out according to the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Common Object Request Broker (CORBA) Object Transaction Service (OTS), implemented in a server, supplies an interface object known as “CosTransactions::Transaction Factory” which can be called upon by client applications in order to create a transaction by creating the transaction state objects in the OTS server. 
     In the preferred embodiment of the present invention, an application running in client process  31  (see FIG. 3) begins a transaction. In this illustrative example, it will be assumed that the transaction being carried out is a withdrawal of money from a bank account, a common transactional operation that is carried out on a daily basis, worldwide, using an Automated Teller Machine (ATM) as the client. 
     A server process  32  is then located by the client process  31  when the client begins a transaction. This is similar to the prior art implementation of FIG.  2 . However, while the server process  32  has an otherwise fully functional OTS implementation  321 , server process  32  does not have a transaction factory object, and is thus incapable of creating the transaction state objects, as will be explained below. 
     When the server process  32  receives the command from the client process  31  to begin the transaction, the server process  32  forwards this command on to another server process, such as server process  33 , since server process  32  does not have the transaction factory object in its OTS  321 . The server process  33 , which does have the transaction factory object  3311  in its OTS  331  then proceeds to locally create (see FIG. 4) the transaction state objects  3312  (which typically include control, coordinator, and terminator objects, referred to as CosTransactions::Control, CosTransactions::Coordinator and CosTransactions::Terminator, respectively). These are analogous to the transaction objects  221  discussed above with respect to the prior art implementation of FIG.  2 . 
     As shown in FIG. 5 the application running in the client process  31  then issues a debit command to bank account object  332  in server process  33 , as the first substantive part of the withdrawal transaction. At this stage, the bank account object  332  communicates with the transaction objects  3312  in the usual way, except that all of such communication takes place within the same process and thus no cross process flows are required for such communication. In the example, the communication that takes place involves the bank account object  332  registering with the transaction objects  3312  and, when the transaction is finished, the transaction objects  3312  send a commit or rollback command to the bank account object  332 . 
     Thus, by configuring server process  32  so that it does not have a transaction factory object within its OTS  321 , a great reduction in cross process flows results as the transaction objects are instead created in server process  33  which contains the bank account object  332  as a local resource. 
     The system designer may, in another case, want to configure the system of servers so that the transaction objects are created in a server process which does not have local resource objects involved in the transaction, and this case will be described now with reference to FIGS. 6 and 7. 
     Client process  61  (FIG. 6) begins a transaction and sends a request to server process  62  to command it to create the transaction objects. As server process  62  has a transaction factory  6211  in its OTS  621 , the server process  62  is capable of creating the transaction objects  6212  and thus creates them as shown in FIG.  7 . Then, the transaction proceeds in a similar fashion to the implementation of FIG. 2 where many cross process calls are involved, as the transaction objects  6212  and the bank account object  632  are located in separate processes. 
     In some architectures, the client process  61  may not always contact the same server when it is making a command to begin a transaction. The client may instead contact a random server. If, for example, it attempts to contact server process  63  first, instead of process  62 , with the present invention, since process  63  does not have a transaction factory object, process  63  will forward the client request on to another process (e.g., process  62 ) that does have a factory. 
     While this latter case shares the disadvantage of FIG. 2 of having many cross process flows, it has the advantage of saving the process  63 , which has local resources, from having to expend its processing power on creating and maintaining the transaction objects. This allows the process  63  more processing power to deal with its local resources. 
     In some situations, it is better to follow the first case and save on cross process flows. In other situations, it is better to follow the second case and save on processing power for the resource-bearing server process. Because of the present invention, the system designer is allowed to design the system depending on which situation is desired. 
     The steps carried out by a server according to the preferred embodiment are shown in FIG.  8 . At step  81 , the server (e.g., server process  62 ) receives a client command to create the transaction objects for a particular transaction that a client has started. The server then checks (step  82 ) to determine whether it has a local transaction factory. If it does, the server creates (step  83 ) the transaction objects locally within the server. However, if the server does not have a local transaction factory, the server forwards (step  84 ) the client command to another server. 
     The system designer uses a systems management interface to designate which server processes will have a factory in its OTS and which will not. Then, upon server startup, only the server processes that have been designated as transaction factory-containing processes will have a transaction factory object instantiated. 
     As stated above, the server that is designated as not capable of creating local transactions (the “no local transactions server”) provides, otherwise, a full OTS implementation. It is able to receive transactional requests and it may contain recoverable OTS data. Thus, any application written to execute in an OTS programming model will also execute with respect to the “no local transactions” server without any modification.