Abstract: In a server system having a predetermined total bandwidth providing data files to a plurality of clients in response to requests received from the clients, a method for providing admission control comprises the steps of allocating a plurality of channel partitions to a plurality of channel groups such that each channel group includes one or more of the channel partitions. The system then obtains a channel group number based on the length of the data file requested by one of the clients and transmits the requested data file when a channel group corresponding to the obtained channel group number contains a vacant channel partition.

Abstract: A dynamic process for improving the performance of a tape-based storage system is disclosed which takes a global view with regard to scheduling and tape selection. All requested data blocks located on multiple tapes within the storage system are analyzed and, taking advantage of the existing replication of some of the requested data blocks on multiple tapes and the location of the data blocks on the tapes, a schedule is formed that results in the reading/downloading of requested data blocks in an efficient manner.

Abstract: A system and method for discovering association rules that display regular cyclic variation over time is disclosed. Such association rules may apply over daily, weekly or monthly (or other) cycles of sales data or the like. A first technique, referred to as the sequential algorithm, treats association rules and cycles relatively independently. Based on the interaction between association rules and time, we employ a new technique called cycle pruning, which reduces the amount of time needed to find cyclic association rules. A second algorithm, the interleaved algorithm, uses cycle pruning and other optimization techniques for discovering cyclic association rules with reduced overhead.

Abstract: A system and method for determining calendric association rules are provided. The method uses calendars to describe the variation of association rules over time, where a specific calendar is defined as a collection of time intervals describing some phenomenon. In accordance with the invention, there is provided a method for identifying calendric association rules in transactional data with time stamped data items. In one exemplary embodiment, the method identifies large itemsets in each time unit, where a large itemset is an itemset that occurs in the transactions more than a given threshold. The method then identifies association rules of the form X—Y from the large itemsets by determining if a requisite support for the itemset XY and a given confidence threshold (ratio of (support of XY)/(support of X)) has been satisfied. Calendric association rules are then generated by examining identified association rules to determine which ones exhibit the temporal patterns specified by given calendars.

Abstract: For use with a primary database residing on a primary computer, the primary computer being couplable to a secondary computer having a secondary database, a system for, and method of, allowing the secondary computer to operate as a hot spare for the primary computer and a database management system employing the system or the method. In one embodiment, the system includes: (1) a transaction logger, associated with the primary database, that maintains log records of transactions involving persistent data in the primary database, (2) a transaction processor, associated with the primary database, that transmits at least a portion of the log records to the secondary computer to allow the secondary computer to commit the at least the portion of the log records to the secondary database and (3) parameters, associated with the primary and secondary databases, that designate a state of the primary and secondary computers and indicate relative synchronization of the primary and secondary databases.

Abstract: A cache management scheme is disclosed for buffering one or more continuous media files being simultaneously accessed from a continuous media server by a plurality of media clients. The continuous media server stores pages of data that will likely be accessed in a cache or buffer. The continuous media server implements a cache management strategy that exploits the sequential page access patterns for continuous media data, in order to determine the buffer pages to be replaced from the cache. The cache management strategy initially identifies unpinned pages as potential victims for replacement. Each unpinned page is evaluated by the continuous media server and assigned a weight. Generally, the assigned weight ensures that a buffer with a larger weight will be accessed by a client later in time than a buffer with a smaller weight. A page associated with a larger weight will be accessed later and hence, is replaced earlier.

Abstract: For use with a database of data records stored in a memory, a system and method for increasing a memory capacity and a memory database employing the system or the method. The system includes: (1) a time stamping controller that assigns a time stamp to transactions to be performed on the database, the time stamp operates to preserve an order of the transactions, (2) a versioning controller that creates multiple versions of ones of the data records affected by the transactions that are update transactions and (3) an aging controller, which is associated with each of the time stamping and versioning controllers, that monitors a measurable characteristic of the memory and deletes ones of the multiple versions of the ones of the data records in response to the time stamp and the measurable characteristic thereby to increase memory capacity.

Abstract: For use with a database of data records organized into components, the database stored in a memory, a processing system for, and method of, physically versioning the database. In one embodiment, the processing system includes: (1) a component copier that creates a physical copy of an original component to be affected by an update transaction to be applied to the database, and that causes pointers in nodes of the physical copy to point to other nodes in the physical copy, (2) a data updater, associated with the component copier, that applies the update transaction to the physical copy to create therefrom a new physical version, the original component remaining unaffected by the update transaction and (3) a pointer updater, associated with the data updated, that employs an atomic word write to revise a component pointer, associated with the database, to cause the pointer to point to the new physical version.

Abstract: A continuous media server that provides support for the storage and retrieval of continuous media data at guaranteed rates using one of two fault-tolerant approaches that rely on admission control in order to meet rate guarantees in the event of a failure of the data storage medium that renders part of the continuous media inaccessible. In the first approach, a declustered parity storage scheme is used to uniformly distribute the additional load caused by a disk failure, uniformly across the disks. Contingency bandwidth for a certain number of clips is reserved on each disk in order to retrieve the additional blocks. In the second approach, data blocks in a parity group are prefetched and thus in the event of a disk failure only one additional parity block is retrieved for every data block to be reconstructed. While the second approach generates less additional load in the event of a failure, it has higher buffer requirements.

Abstract: A method and an apparatus are disclosed for providing enhanced pay per view in a video server. Specifically, the present invention periodically schedules a group of non pre-emptible tasks corresponding to videos in a video server having a predetermined number of processors, wherein each task is defined by a computation time and a period. To schedule the group of tasks, the present invention divides the tasks into two groups according to whether they may be scheduled on less than one processor. The present invention schedules each group separately. For the group of tasks scheduleable on less than one processor, the present invention conducts a first determination of scheduleability. If the first determination of scheduleability deems the group of tasks not scheduleable, then the present invention conducts a second determination of scheduleability.

Abstract: The invention provides protocols for managing transactions operating on replicated data items at multiple physical sites in a distributed database system. The protocols make use of dynamically changing sets of data items referred to as "virtual sites" and a replication graph or other suitable globally consistent representation of the relationships between the transactions and the virtual sites. Illustrative embodiments of the invention include a static global serializability (SGS) protocol, a commit-oriented protocol (COP) and a multiversion optimistic protocol (MOP). The SGS protocol broadcasts the data access set of a given transaction to all physical sites, and applies the Thomas Write Rule (TWR) to write-write conflicts on secondary copies of data items. The COP protocol defers testing of the replication graph until a transaction is ready to commit, and each transaction is allowed to proceed at its origination site independently of other transactions that are executing at other sites.

Abstract: A new scheduling method and policy for shared (server) resources, such as the CPU or disk memory of a multiprogrammed data processor. The scheduling is referred to as Move-To-Rear List Scheduling and it provides a cumulative service guarantee and well as more traditional guarantees such as fairness (proportional sharing) and bounded delay. In typical operation, a list is maintained for a server of processes seeking service from the server. Processes are admitted to the list only when maximum capacity constraints are not violated, and once on the list, are served in a front-to-back order. After receiving service, or upon the occurrence of other events, the position of the process on the list may be changed.

Abstract: A method for recovering spin locks in a system having one or more processes capable of accessing a shared resource, the system providing a lock indicating exclusive access to the shared resource by a single process and enabling one or more processes to repeatedly attempt to gain access to the lock when ownership of the shared resource is desired. The method includes generating a linked list queue structure containing a first process currently having exclusive access to the lock and one or more processes added to the queue structure to spin on the lock, each process capable of modifying the queue structure by obtaining exclusive access of the lock from a process having exclusive access of the lock and releasing the lock to another process in the linked list queue structure; detecting when one or more processes having exclusive access to the lock terminates, and upon detection, removing the terminated process from the queue structure, and restoring consistency to said linked list queue structure.

Abstract: A method and apparatus are disclosed for providing enhanced pay per view in a video server. Specifically, the present invention periodically schedules a group of non pre-emptible tasks corresponding to videos in a video server having a predetermined number of processors, wherein each task begins at predetermined periods and has a set of sub-tasks separated by predetermined intervals. To schedule the group of tasks, the present invention divides the tasks into two groups according to whether they may be scheduled on a single processor. The present invention schedules each group separately. For the group of tasks not scheduleable on a single processor, the present invention determines a number of processors required to schedule such group and schedules such tasks to start at a predetermined time. For the group of tasks scheduleable on a single processor, the present invention determines whether such tasks are scheduleable on the available processors using an array of time slots.

Abstract: Two methods are disclosed for storing multimedia data that reduces the amount of disk I/O required by the system and cache misses experienced by the system. The first method determines the future access of each data buffer in a cache memory. Once the future of the data buffer is determined, the data buffer with the maximum future is allocated to store new blocks of data. The method approximates an optimal method of data buffer allocation, by calculating the future of a data buffer, relative to clients that will access the data buffers. The second method orders the clients based on the increasing distance of each client from the previous client; clients release the buffers in this order into a LIFO queue; if a buffer is selected to load a new block of data, the buffer at the head of the LIFO queue is selected.

Abstract: For use with an active database stored in volatile memory for direct revision thereof, the active database having multiple checkpoints and a stable log, having a tail stored in the volatile memory, for tracking revisions to the active database to allow corresponding revisions to be made to the multiple checkpoints, the active database subject to corruption, a system for, and method of, restoring the active database and a computer system containing the same. The system includes: (1) a checkpoint determination controller that determines which of the multiple checkpoints is a most recently completed checkpoint and copies the most recently completed checkpoint to the volatile memory to serve as an unrevised database for reconstructing the active database and (2) a revision application controller that retrieves selected ones of the revisions from the stable log and the tail and applies the revisions to the unrevised database thereby to restore the active database.

Abstract: For use with a central database associated with a server of a network, the central database having distributed counterparts stored in volatile memories of clients of the network to allow operations to be performed locally thereon, the central database further having multiple checkpoints and a stable log stored in the server for tracking operations on the central database to allow corresponding operations to be made to the multiple checkpoints, the stable log having tails stored in the volatile memories to track operations on corresponding ones of the distributed counterparts, the distributed counterparts to corruption, a system for, and method of, restoring a distributed counterpart stored in one of the volatile memories.

Abstract: A system for scheduling read-requests for a serpentine data tape. The transit time between arbitrarily selected locations in the tape is not a linear function of distance between the locations. Despite this non-linearity, a model has been developed which accurately predicts such transit times. Using the model, a list of read-requests is re-organized into a sequence requiring a minimal, or at least smaller, total time to execute.

Abstract: Various systems and methods of scheduling media segments of varying display rate, length and/or periodicity on at least one clustered, vertically-striped or horizontally-striped continuous media database volume. With respect to the at least one horizontally-striped database volume, one method includes the steps of: (1) associating a display value with each of the media segments, (2) sorting the media segments in a non-increasing order of value density to obtain an ordered list thereof and (3) building a scheduling tree of the media segments, the scheduling tree having a structure that increases a total display value of the media segments.

Abstract: An apparatus and method provide an interrupt-based add-on service for use in a service subscription system having a central service provider and at least one subscriber unit. The interrupt-based system includes a database for storing subscriber information specific to at least one subscriber, where the subscriber information includes at least one subscriber selectable condition. The system further includes a computer for interrupting a service request when the service request satisfies at least one subscriber selectable condition and for making a service connection when the service request does not match the subscriber selectable condition.