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    • 3. 发明授权
    • Methods and apparatus for scheduling parallel processors
    • 调度并行处理器的方法和装置
    • US06434590B1
    • 2002-08-13
    • US09053873
    • 1998-04-01
    • Guy E. BlellochPhillip B. GibbonsYossi MatiasGirija J. Narlikar
    • Guy E. BlellochPhillip B. GibbonsYossi MatiasGirija J. Narlikar
    • G06F900
    • G06F9/5066G06F2209/5021
    • A parallel processing method involves the steps of determining a sequential ordering of tasks for processing, assigning priorities to available tasks on the basis of the earliest and then later in the sequential ordering, selecting a number of tasks greater than a total number of available parallel processing elements from all available tasks having the highest priorities, partitioning the selected tasks into a number of groups equal to the available number of parallel processing elements, and executing the tasks in the groups in the parallel processing elements. The determining step establishes an ordering with a specific predetermined sequential schedule that is independent of the parallel execution, and the assigning step assigns priorities for parallel execution on the basis of the sequential schedule that is independent of the parallel execution.
    • 并行处理方法包括以下步骤:确定用于处理的任务的顺序排序,基于顺序排序中的最早然后稍后的顺序为可用任务分配优先级,选择大于总数的可用并行处理 来自具有最高优先级的所有可用任务的元素,将所选择的任务划分成等于可用数量的并行处理元素的多个组,以及在并行处理元素中执行组中的任务。 确定步骤建立具有独立于并行执行的特定预定顺序调度的排序,并且分配步骤基于独立于并行执行的顺序调度分配用于并行执行的优先级。
    • 6. 发明授权
    • Incremental maintenance of an approximate histogram in a database system
    • 在数据库系统中增加一个近似直方图的维护
    • US5870752A
    • 1999-02-09
    • US915804
    • 1997-08-21
    • Phillip B. GibbonsYossi MatiasViswanath PoosalaAndrew Witkowski
    • Phillip B. GibbonsYossi MatiasViswanath PoosalaAndrew Witkowski
    • G06F17/30
    • G06F17/30368Y10S707/99942Y10S707/99943Y10S707/99945
    • Techniques for maintaining an approximate histogram of a relation in a database, in the presence of updates to the relation. The histogram includes a number of subsets, or "buckets," each representing at least one possible value of an attribute of the relation. Each of the subsets has a count associated therewith indicative of the frequency of occurrence of the corresponding value of the attribute. After an update to the relation, the counts associated with the subsets are compared to a threshold. If the count associated with a given subset exceeds the threshold, the given subset is separated at its median into two separate subsets. After the separation operation, the two subsets with the lowest counts are combined such that a constant number of subsets are maintained in the histogram, if the total combined count of the subsets does not exceed the threshold. If no two subsets have a total combined count which does not exceed the threshold, the histogram is recomputed from a random sample of the relation. The invention substantially reduces the number of times the histogram must be recomputed from the random sample, and is particularly well-suited for use with approximate equi-depth and compressed histograms.
    • 在关系更新的情况下维护数据库中关系的近似直方图的技术。 直方图包括多个子集或“桶”,每个子集表示该关系属性的至少一个可能的值。 每个子集具有与其相关联的计数,指示属性的相应值的出现频率。 在更新关系后,将与子集关联的计数与阈值进行比较。 如果与给定子集相关联的计数超过阈值,则给定子集在其中间被分离成两个单独的子集。 在分离操作之后,组合具有最低计数的两个子集,使得如果子集的总组合计数不超过阈值,则在直方图中维持恒定数量的子集。 如果没有两个子集具有不超过阈值的总组合计数,则从该关系的随机样本重新计算直方图。 本发明基本上减少了从随机样本重新计算直方图的次数,并且特别适用于近似等深度和压缩的直方图。
    • 8. 发明授权
    • Maintaining a random sample of a relation in a database in the presence
of updates to the relation
    • 在关系更新的情况下,在数据库中维护关系的随机抽样
    • US6012064A
    • 2000-01-04
    • US915774
    • 1997-08-21
    • Phillip B. GibbonsYossi MatiasViswanath Poosala
    • Phillip B. GibbonsYossi MatiasViswanath Poosala
    • G06F17/30
    • G06F17/30595Y10S707/954Y10S707/99933Y10S707/99934Y10S707/99942Y10S707/99943Y10S707/99944
    • Techniques for maintaining a random sample of a relation in a database in the presence of updates to the relation. The random sample of the relation is referred to as a "backing sample," and it is maintained in the presence of insert, modify and delete operations involving the relation. When a new tuple is inserted into the relation, a sample of the given tuple is added to the backing sample if the size of the backing sample is below an upper bound. Otherwise, a randomly-selected tuple of the backing sample is replaced with the new tuple if a sample of the new tuple must be inserted into the backing sample to maintain randomness or another characteristic. When a tuple in the relation is the subject of a modify operation, the backing sample is left unchanged if the modify operation does not affect an attribute of interest to an application which uses the backing sample. Otherwise, a value field in a sample of the tuple in the backing sample is updated. When a tuple is deleted from the relation, any sample of that tuple in the backing sample is removed. A new backing sample may be computed if this removal causes the size of the backing sample to fall below a prespecified lower bound. The backing sample can be of a size which is negligible in comparison to the relation, and need only be modified very infrequently. As a result, its overhead in terms of computation time and storage space is minimal.
    • 在存在关系更新的情况下,在数据库中维护关系随机抽样的技术。 该关系的随机样本被称为“后备样本”,并且在存在涉及该关系的插入,修改和删除操作的情况下保持该样本。 当一个新元组被插入关系中时,如果背景样本的大小低于上限,则将给定元组的样本添加到背景样本中。 否则,如果必须将新元组的样本插入到背景样本中以保持随机性或其他特征,则将随机选择的背衬样本的元组替换为新的元组。 当关系中的元组是修改操作的主题时,如果修改操作不影响使用后备样本的应用程序感兴趣的属性,则后备样本将保持不变。 否则,将更新背景样本中的元组样本中的值字段。 当从该关系中删除元组时,将删除该背景样本中该元组的任何样本。 如果这种去除导致背衬样品的尺寸低于预先指定的下限,则可以计算新的背衬样品。 背衬样本的尺寸可以与关系相比可以忽略不计,并且只需要非常频繁地修改。 因此,其在计算时间和存储空间方面的开销是最小的。