Abstract: A system and method for performing variable speed scanning or browsing, wherein a user controls the playout speed of a movie, which does not require additional disk or network bandwidth resources. In a preferred embodiment, the method provides for scanning operations for an Motion Picture Experts Group (MPEG) video stream. The method satisfies the constraints of the MPEG decoder (in the users set-top box) and require a minimum of additional system resources. The embodiments of the present invention include (a) a storage method, (b1) a segment sampling method, (b2) a segment placement method, and (c) a playout method, where (b1) and (b2) are two alternatives for segment selection. Thus, two sets of solutions are provided to support variable speed scanning in a disk-array-based video server: One using (a), (b1) and (c), and the other using (a), (b2) and (c).

Abstract: In a digital storage disk array system in which parity blocks are created and stored in order to be able to recover lost data blocks in the event of failure of a disk, high-activity parity groups are created for data blocks having high write activity and low-activity parity groups are created for data blocks not having high write activity. High-activity parity blocks formed from the high-activity data blocks are then stored in a buffer memory of a controller rather than on the disks in order to reduce the number of disk accesses during updating.

Abstract: A system and method of supporting pause-resume in a video-on-demand service of a type which can accommodate multiple viewers sharing a common data stream is described. When a video server receives a performance request from one of the viewers for showing a particular video, it identifies and reserves a look-ahead stream. The look-ahead stream is another video stream which is scheduled to become available after a predetermined time period. When the video is commenced, a common data stream for the video is concurrently transmitted from the video server to reception equipment at the viewers' locations. Transmission of the common data stream causes the particular video to be performed on the viewers' reception equipment. When the video server receives a pause request and then a subsequent resume request from one of the viewers, it transmits the video via the look ahead stream instead of the common data stream.

Abstract: An access frequency is determined for each data unit in a data sharing environment employing a hashing scheme, either from an estimate or from a history of data accesses. The data units are then categorized into access frequency classes. Available hash entries are then allocated among the various access frequency classes, with more hash entries being allocated to relatively higher access frequency classes. Once the hash entries are allocated, the data units are allocated to the hash entries in a given access frequency class. In the simplest form, the data units are evenly allocated among the hash entries of a given access frequency class.

Abstract: A task scheduler for use in a multiprocessor, multitasking system in which a plurality of processor complexes, each containing one or more processors, concurrently execute tasks into which jobs such as database queries are divided. A desired level of concurrent task activity, such as the maximum number of tasks that can be executed concurrently without queuing of tasks, is defined for each processor complex. Each job is assigned a weight in accordance with the external priority accorded to the job. For each job there is defined a desired level of concurrent; task activity that is proportional to its share of the total weight assigned to all concurrently executing jobs. The jobs are prioritized for execution of awaiting tasks in accordance with the discrepancy between the desired level of multitasking activity and the actual level of multitasking activity for each job.

Abstract: A plurality of queries (jobs) which consist of sets of tasks with precedence constraints between them are optimally scheduled in two stages of scheduling for processing on a parallel processing system. In a first stage of scheduling, multiple optimum schedules are created for each job, one optimum schedule for each possible number of processors which might be used to execute each job, and an estimated job execution time is determined for each of the optimum schedules created for each job, thereby producing a set of estimated job execution times for each job which are a function of the number of processors used for the job execution. Precedence constraints between tasks in each job are respected in creating all of these optimum schedules. Any known optimum scheduling method for parallel processing tasks that have precedence constraints among tasks may be used but a novel preferred method is also disclosed.

Abstract: A multi-processor computer system in which each processor is under the control of separate system software and access a common database. A two level lock management system is used to prevent data corruption due to unsychronized data access by the multiple processors. By this system, subsets of data in the database are assigned respectively different lock entities. Before a task running on one of the processors access data in the database it first requests permission to access the data in a given mode with reference to the appropriate lock entity. A first level lock manager handles these requests synchronously, using a simplified model of the locking system having shared and exclusive lock modes to either grant or deny the request. All requests are then forwarded to a second level lock manager which grants or denies the request based on a more robust model of the locking system and queues denied requests.

Abstract: A technique for performing joins in parallel on a multiple processor database system effectively deals with data skew. The join operation is performed in three stages with an optional fourth stage. The first stage is a preparatory stage, the detail of which depends on the underlying join algorithm used. This preparatory stage provides pre-processing the results of which are used in the following stage as the basis for defining subtasks for the final join operation. The data provided in the first stage is used in the second stage to both define subtasks and to optimally allocate these subtasks to different processors in such a manner that the processors are close to equally loaded in the final join operation, even in the presence of data skew. This second stage is an assignment stage the details of which depend on the underlying join algorithm.

Abstract: A protocol for a switching system that establishes multiple parallel paths between users through multiple autonomous switching planes by having a user desiring connection to issue connection requests to each of the switching planes. According to the invention, the user monitors the number of connections that have been successfully completed and if only some of the connections have been completed, because of conflicting requests, it follows a conflict protocol to issue retry requests to the planes on which the connection request was unsuccessful. Each switching plane follows the conflict protocol to respond to the retry request by disconnecting existing connections and completing at most one retried connection request.

Abstract: A hybrid scheme for controlling transmission errors in digital data communication systems. Normally, data blocks with a small number of parity digits for error detection are transmitted. When the presence of errors is detected, the retransmissions are not the original data blocks but some properly selected blocks for correcting errors in those erroneously received data blocks which are stored in a buffer at the receiver. The retransmitted blocks are formed based on the original data blocks and error-correcting codes with an invertible property. When such blocks are received, they are used to recover the original data blocks either by an inversion operation or by a decoding process.