International Business Machines Corporation

Cherie C Barnes

Robert Bradley Bennett

Thomas J Szczygielski

Michael K Ainsworth

David John Wierbowski

James M Showalter

Barbara A Maslak

Robert C Will

Edmond A Pruul

Amos S Tanner

A shared file computer system has multiple users, and two or more transactions established by the users may contend for the same resource. Such contention may result in a deadlock condition. To search for such deadlocks, the system maintains a lock wait matrix which lists which transactions are waiting on which other transactions. The matrix represents a hierarchical wait tree. A deadlock is present when the top node transaction in the tree also occurs lower in the tree. In such a case, either the top node transaction or any other transaction in the path or branch between the two occurrences of the top node transaction is cancelled to resolve the deadlock represented by this path. However if the intermediary node is cancelled to resolve this deadlock, a similar deadlock can occur in another path and must be resolved also. There can be thousands of paths in the tree to be searched for such a deadlock condition, and to optimize the deadlock search after the intermediary node is cancelled, transactions leading from this intermediary node are not examined. Nevertheless, all deadlock conditions are detected.

System and method for reducing research time through a lock wait matrix

A computer network comprises first and second computers, each having a recovery facility for recovering a two-phase commit procedure and a recovery log. The log comprises a log name log which stores the names of other logs involved in a commit scope and a sync point log which stores sync point phase information. The log names are exchanged prior to a request for sync point. If a failure occurs during sync point, each recovery facility in the commit scope again exchanges log names to verify that there was not a log failure since the prior exchange. Absent a log failure, the logs are used to recover from the sync point failure. Communication facilities are interposed between the first and second computers and include log name exchange tables which record the previous exchanges of log names between the first and second computers. If a protected conversation is initialized from the first computer to the second computer and log names were not previously exchanged, then the communication facilities intercept the conversation and hold it until log names are exchanged.

Log name exchange for recovery of protected resources

In a computer system or process, sync point managers are distributed throughout each real machine for a plurality of execution environments, but all of the execution environments and sync point managers within one real machine share a common recovery facility and recovery log. A common recovery log is used by the recovery facility for all of the execution environments in the system. Different systems are interconnected by a communication facility and each has its own recovery facility and recovery log. A protected conversation can be initiated between the first and second execution environments in the same real machine, and the sync point managers within the respective execution environments coordinate the two-phase commit procedures associated with the protected conversations. A conversation manager within each real machine assists in routing the conversation between the first and second execution environments. Each resource manager, whether residing inside or outside of the real machine, has its own recovery log, but uses the recovery facility of the real machine that accesses the resource.

Coordinated sync point management of protected resources

A Space Management System for a Data Access System of a File Access Processor for servicing requests from a set of Application Support Processors, which can exist in a global network, with each Application Support Processor sharing access to data in files stored by the File access Processor. The File Access Processor manages access to a set of data files and information about files held in file directories, which allow for managing file collections, can relate to each other hierarchically, and may be shared. Each Application Support Processor also maintains therein an internal cache of file information to improve performance by reducing communications required with the File Access Processor for informatin about files. The File Access Processor provides the Application Support Processors with information for updating and maintenance of local caches of directory and file description information through a centralized accumulation and distribution of cache change notifications. The Space Management System manages file space assigned to each Application Support Processor and supports the space management functions of, adding space, deleting space, setting thresholds for limit warnings, querying space, charging space used, warning notifications, crediting space freed, and permitting file spaces to be shared by more than one application suppoort processor.

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Cherie C Barnes