International Business Machines Corporation

Andrew P Citron

Kathryn Heninger Britton

James P Gray

Barbara A Maslak

Timothy J Thatcher

Ajamu Akinwunmi Wesley

Chandrasekaran Mohan

Bruce Gilbert Lindsay

John E Drake, Jr

Barron C Housel, Iii

Zvonimir Ordanic

Marsha E Ferree

John E Fetvedt

George M Samaras

Methods, systems, and computer program products are provided for communicating between a source device and a destination device over an external communication link by transmitting a message stored in a source persistent queue at the source device over the external communication link to the destination device. The transmitted message has transmitted with it an associated sequence identifier which identifies the message stored in the source persistent queue. The transmitted message and the associated sequence identifier are received at the destination device and stored in a destination persistent queue at the destination device. Occasionally, a commit message is transmitted to the source device from the destination device which identifies a sequence identifier associated with received message which has been persistently stored in the destination persistent queue. The persistently stored message in the destination persistent queue is made available to users of the destination device independent of whether a commit message identifying the message has been transmitted to the source device.

Methods, systems and computer program products for synchronization of queue-to-queue communications

A computer system and process efficiently provides resource recovery for a failure during a commit procedure. An application is run on a processor and requests a work operation involving a resource such as a protected conversation with another application in a different real machine. A commit procedure is begun for the work request, and if the commit procedure fails before completion, the following steps are taken to optimize the use of one or both of the applications. At some time after the commit procedure fails, a return code is sent to at least the application that initiated the commit indicating the result of the application commit order and that the application can continue to run and does not have to wait for resynchronization (recovery). Then, while the initiating application continues to run and do other useful work, resynchronization is implemented in parallel, asynchronously.

Asynchronous resynchronization of a commit procedure

A transaction network in which, in appropriate cases, a transaction is allowed to complete at each node and new work to commence, before all transaction resources at the node actually complete a syncpoint operation. This desirable result is obtained without the risk of unreported database corruption. At each node in response to a prepare to commit syncpoint command from a parent node, the node in question determines if it or any of its descendant nodes can make a unilateral heuristic decision to commit or backout the transaction irrespective of whether or not the final syncpoint command is to commit or backout. Each node informs its parent node that it is reliable or unreliable. Reliable means that neither this node nor any of its descendant nodes can make a unilateral heuristic decision. Unreliable means that this node or one or more of the descendant nodes may make such a unilateral decision. If a node is reliable, the transaction is released at the node after receiving and propagating to descendant nodes the final commit or backout command and before completion or acknowledgement of completion of the commit or backout command by the node or any of its descendant nodes. If the node is unreliable, then it waits for acknowledgement of completion of the commit or backout syncpoint operation at all unreliable nodes, including itself, before releasing the transaction at the node.

Method and apparatus for improving database reliability and response

A method of managing unit-of-work identifiers in a chained distributed database transaction system. The system has a plurality of processing nodes which are logically connected to form a tree. Normally, each node automatically increments its present identifier at the end of processing each transaction to derive the next transaction identifier. However, in response to a failure condition which results in a severed tree, the distributed database that now reside in the first and second subtrees that result from the severance are forced to consistent states. The transaction identifier is incremented in each of the nodes of the first subtree. Transaction work in the first subtree then proceeds with the incremented identifier. The second subtree is dismantled. In response to a nonfailure condition which results in a severed tree, the distributed database in the first and second subtrees that result from the nonfailure severance is committed to a permanent state. The transaction identifier in each of the nodes of the first subtree is incremented. Transaction work in the first subtree then proceeds with the incremented identifier. A new transaction identifier is generated and propagated to all nodes of the second subtree. Transaction work in the second subtree then proceeds with the new identifier.

System for managing unit-of-work identifiers when a chained,

A method of reducing the number of messages required for sync point (commit or backout) operations by leaving out nodes that have not participated in the corresponding transaction. A two-phase sync point protocol is used in a distributed transaction processing network to commit or backout transactions in the network. In response to the beginning of sync point operations on a transaction x, each node determines if each of its partner nodes stated on the sync point operation for transaction x-1 that the partner could be left out of sync point operations for transaction x-1. If a partner node did so state that it could be left out, the present node determines if the partner node was included by the present node during the present transaction x. If the partner node was not included during the present transaction, the present node excludes the partner node from the present sync point operations.

Method of excluding inactive nodes from two-phase commit operations in a

The links in a data communications network following Systems Network Architecture may be categorized as limited resource links if those links are shared access transport facilities, such as a switched telephone network, X.21, X.25 or token ring local area network facilities. In setting up LU--LU sessions between network users, a limited resource session identifier field is set to a specific value if any of the links in the session data path is defined as a limited resource link. When a conversation between two users ends, the primary logical unit responds by determining whether the session has been identified as a limited resource session. If it has, the primary logical unit initiates action to deactivate the session without waiting for network control operation action. Allowing the primary logical unit to deactivate a limited resources session assures that the limited resource link or links will not remain allocated needlessly to an unused session.

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Raleigh, NC, United States of America

Andrew P Citron