Abstract:
An exemplary embodiment of the invention is a method for providing a path-sensitive branch registry for cyclic distributed transactions. This method requires that a superior node&#39;s transaction manager (TM) identify itself as the root followed by sending the syncpoint cue to at least one subordinate node. Before sending the syncpoint cues to the subordinate the superior links the inbound messages with its specific branch qualifier (BQUAL) as well as a global transaction identifier (GTRID). The TM of each subordinate node receives syncpoint cues and is responsible for knowing who its superior is. In addition, the TM is responsible for recognizing the flow of branch instructions and guarantee that it uses a network-wide unique value for the branch values it generates for a given global transaction. With the recognition of the flow from the superior node the subordinate TM updates the node registry as to the inbound and outbound flow of branch messages by its superior and its subordinates.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates generally to a method for creating a path-sensitive branch registry for use in a processing system and, more specifically, to identifying branch flows as subordinate relative to a path in the distributed transaction tree. 
   2. Description of the Related Art 
   Currently, the method of managing distributed transactions used in computer systems includes a system of tree structures having a plurality of processing nodes which are logically connected. Normally, each node&#39;s transaction manager automatically increments its present identifier at the end of processing each transaction to derive the next transaction identifier. When a distributed transaction is forced into a consistent state its associated superior/subordinate relationship becomes fixed. Typically, a transaction identifier is incremented in each of the nodes of a superior transaction manager. Consequently, transaction tasks in the superior transaction manager then proceed with the incremented identifier to one or more subordinate transaction managers. Similarly, the subordinate nodes assign a static branch qualifier. However, the subordinate transaction manager&#39;s identifier is modified to conform with its superior. As is the case with transactions, superior nodes often times receive instructions from nodes indirectly from the superior&#39;s subordinates. This situation results in cyclic distributed transactions that contain at least one loopback. The current practice is unable to ensure the safe creation of cyclic distributed transactions, without worries of database update failures, or unwanted tightly coupled behavior. 
   In addition, typically, for modem object servers, the two phase commit process is preceded by a phase known as “before-completion.” This process permits the object server to flush updates, cached in the object representation, to backing resource managers prior to the well-known two-phase commit process. 
   For distributed transaction trees that contain cycles, it is sometimes not possible for all updates to be pushed to the backing resource manager prior to that resource manager receiving the first part of the two-phase commit process. This will cause the resource manager to log an error, and commonly mark the global transaction rollback. 
   Therefore, there is a need for a method that unwinds the cyclical distributed transaction tree, while preserving the path for which the tree was allocated, regardless of the depth of the tree which maintains proper ordering of events and preventing unwanted sharing of resources. 
   SUMMARY OF THE INVENTION 
   An exemplary embodiment of the invention is a method for a path-sensitive branch registry for cyclic distributed transactions. This method has a superior node&#39;s transaction manager (TM) identifying itself as the root before sending syncpoint cues to at least one subordinate node. Before sending the syncpoint cues to the subordinate the superior links the cues with its specific branch qualifier (BQUAL) as well as a global transaction identifier (GTRID). The TM of each subordinate node receives syncpoint cues and is responsible for knowing who its superior is. In addition, the TM is responsible for recognizing the flow of branch instructions and guarantee that it uses a network-wide unique value for the branch values it generates for a given global transaction. With the recognition of the flow from the superior node the subordinate TM updates the node registry as to the inbound and outbound flow of branch instructions by its superior and its subordinates. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings, wherein like elements are numbered alike in several FIGURES: 
       FIG. 1  is an exemplary diagram of a superior node and a subordinate node in the distribution transaction tree in one embodiment; 
       FIG. 2  is an exemplary diagram of a simple flow between nodes of the distribution transaction tree in one embodiment; 
       FIG. 3  is an exemplary diagram of a cyclical flow between nodes of the distribution transaction tree in one embodiment; 
       FIG. 4  is an exemplary diagram of a cyclical flow between nodes of the distribution transaction tree with path sensitivity in one embodiment; 
       FIG. 5  is an exemplary diagram of an acyclical flow between nodes of the distribution transaction tree with path sensitivity in one embodiment; and 
       FIG. 6  is an exemplary diagram that illustrates the interrelationship between superior and subordinate transaction managers in one embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As discussed herein, currently cyclic distribution trees cannot ensure the safe creation of cyclic distributed transactions, without worries of database update failures. The current practice requires that when a cycle occurs in a distributed transaction tree that the resultant reentrancy does not cause new work to occur after the resource manager has been directed to prepare for commit by the TM. 
     FIG. 1  is an exemplary diagram depicting a typical flow from a superior or root node to a subordinate node. Specifically, a root node  12  is sending syncpoint cues (outbound messages) of the distributed transaction tree to subordinate nodes represented as  14 ,  18  and  22 . The subordinate nodes  14 ,  18  and  22  each have a specific global transaction identifier (GTRID) which is the same in each node of the tree, and unique in the network for each distributed transaction tree. The GTRID is assigned by a root coordinator, and is propagated as the transaction flows from node to node.  FIG. 1  demonstrates GTRID naming with BQUALs  16 ,  20  and  24 . In addition, each node of a distributed transaction can be referred to as a branch, and also, within each node resides a transaction manager (TM). The TM manages a branch registry, recording inbound and outbound participants. Inbound flows represent flows from a superior node in the distributed transaction tree. Further, each transaction has a unique identifier that represents a singleton instance of a given node in the distributed transaction tree. These unique identifiers are received by the subordinate node&#39;s TM and are generally statically bound. Next, the incremented identifier is sent to another subordinate node that is able to coordinate and process the particular syncpoint cues. All node transactions utilize registries that are managed by the node&#39;s TM. With this registry the TM is able to track the responsibilities of the superior node. 
     FIG. 2  is a diagram depicting a directed acyclic distributed transaction tree. A distributed WS node  52  usually has a well-known name that it uses as its branch qualifier (BQUAL)  56 ,  60 . The distributed WS node  52  sends syncpoint cues in the form of outbound flow  62  to a subordinate node  54 . The outbound flow is received as inbound flow  62  by the subordinate node  54 . The TM of the subordinate node  54  examines its registry for the inbound flow&#39;s GTRID before proceeding. If the TM of the subordinate node  54  has not seen the incoming flow&#39;s  62  GTRID it will create a new branch in the registry for this transaction, and add the BQUAL to the inbound branch registry. If the TM of subordinate node  54  has seen the incoming flow  62 , it uses the transaction that was created previously to coordinate updates to protected resources. Thus, the TM considers this reentry as a direct synchronous inbound flow because the distributed WS node  52  may flow to subordinate node  54  and to subordinate node  58  repeatedly with no update to BQUAL  60  prior to committing. 
     FIG. 3  is a diagram depicting a distributed transaction tree containing a cycle. Node  104  receives two inbound flows  116 ,  118 ; one from the WS node  102 , and one from node  114 . When node  104  receives the flow there is the possibility that it will erroneously assume that this is the same branch in the distributed tree that was noted before. If this branch is assumed to be the same as the one previously sent there will be a likelihood that there will be an unwanted sharing of protected resource locks. Further, node  104  may become confused with its syncpoint responsibilities. To correct this confusion, node  104  will receive a prepare flow from the WS node  102  and node  114  during the commit processing phase. Consequently, node  104  will be directed to prepare, for which it will drive pre-prepare instructions for all local resource managers, and after preparing will flow a prepare signal to node  110 . In sending the prepare signal node  104  also sends its non-incremented BQUAL  106 . Similarly, node  110  issues pre-prepare instructions and prepares local resources. Next, node  110  directs the flow to node  114  along with its non-incremented BQUAL  108 . During the preparing of resources for node  114 , it is possible that updates may flow to node  104 . Consequently, the pre-prepare instruction of node  114  causes updates on node  104  and its non-incremented BQUAL  106 , which has been previously prepared. Unfortunately, allowing updates on node  104  without incrementing the BQUAL  112  will invariably result in an error. 
     FIG. 4  is a diagram depicting a solution to the problem introduced by cyclic distribution transaction trees by introducing a path-sensitive branch registry. Here, node  154  receives an inbound flow  166  from node WS  152 . Node  154  does not find the inbound flow  166  from node WS  152  in its inbound registry. Next, node  154  will associate an indexed, transaction-unique BQUAL  156  (A 1 ) with the inbound flow, where the index ( 1 ) indicates the number of times that the transaction has looped through the node  154 . Subsequently, node  154  will send a flow  168  and its BQUAL  156  (A 1 ) to node  160 . Next, node  160  will receive the inbound flow  168 , and associate its own indexed BQUAL  158  (B 1 ) with the inbound indexed BQUAL  156  (A 1 ). Likewise, node  160  sends a flow  170  with its indexed BQUAL  158  (B 1 ) to node  164 . The cycle completes when node  164  sends a flow  172  with its indexed BQUAL  162  (C 1 ) to node  154 , where node  154  will consult its inbound registry to see that it has not received an inbound flow from node  164  for this transaction, and will create a new BQUAL (A 2 ) with an incremented index ( 2 ) that is different for any other index in the registry for that node for that transaction. Therefore, the cyclic flow, WS→A→B→C→A has become the acyclic flow WS→A 1 →B 1 →C 1 →A 2 . 
     FIG. 5  is a diagram depicting a creation of a path-sensitive registry. Node  202  is a subordinate of node  214  and other nodes based on the inbound flows  218 . Node  202  is a superior to node  210 . As in  FIG. 3 , WS will deliver a prepare instruction to node  202 , in turn node  202  will issue pre-prepare instructions to the local resources. Node  202  will then prepare local resources, and flow prepare to node  210 . Next, node  210  flows prepare to node  214 . Consequently, after preparing local resources node  214  flows prepare to node  202 . Following the prepare of the local resources node  202  then pre-prepares local resources associated with this subordinate transaction. Therefore, the path-sensitive registry prevents the unwanted sharing of database and/or protected resource locks and correctly delivers pre-prepare to objects and prepare to resources. The unwanted sharing of database and/or protected resource locks and correct delivery of pre-prepare objects is achieved by incrementing BQUALs  204 ,  206 ,  208  and  212  before they are sent to another node. 
     FIG. 6  is a diagram depicting the relationship between transaction managers and their subordinates. As in  FIG. 3 , WS  252  represents a root transaction. The TM  254  of node  260  receives inbound flow  278  from the transaction root  252  and evaluated against the inbound registry of the node. Specifically, an inbound registry contains the node&#39;s BQUAL  258  and its GTRID  256 . The TM  254  compares incoming syncpoint cues with those stored in the memory. When the TM  254  does not find a matching syncpoint cue it adds the incoming syncpoint cue to its registry and increments its BQUAL and links it to the syncpoint cue prior to sending it to its subordinate(s). In addition, the registry contains the node&#39;s BQUAL  258 . For example, node  260  sends outbound flow to node  276  and node  274 . The TM of a subordinate node  254  searches its registry to see if the inbound flow&#39;s GTRID matches any previously recorded GTRID. If there is no match the TM  254  directs the recording of the new GTRID. If there is a match the TM  254  renames the transaction and sends the newly named flow  282  to its subordinate(s), and so on. Next, the subordinate nodes  274  receives the outbound flow  282  and reports back to the superior node  260 , confirming its subordinate status. 
   The embodiment described above solves the problems by introducing a method that unwinds the pretzel-like situations created by cyclic flows. This method ensures that transaction managers are able to properly drive the syncpoint cues with the proper superior or root TM in the transaction. In addition, the exemplary embodiment described above enables the safe creation of cyclic distributed transactions, free from database update failures. 
   The preferred embodiment uses a optimization that fully prepares the nodes at the same depth in the synchronization tree, and at completion of the prepare phase if there are distributed subordinate registrations for the related transactions. In addition, the superior nodes receive a prepare signal to initiate node registration. During the start of the prepare phase, the subordinate will drive locally registered synchronization objects before completion methods are run, and so on. Consequently, this optimization can cause the object server to attempt to drive “work after prepare” to the resource managers in the case of a cyclic tree. This application preserves the performance optimization while properly delivering the “work before prepare” instructions. 
   This invention ensures that loopbacks do not cause unwanted database back sharing. If sharing is attempted from the loopback node, a deadlock will occur to protect the resource manager from corruption. 
   While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention not be limited to the particular embodiments disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.